unit 4 solubility & solvents

7/29/2019 Unit 4 Solubility & Solvents

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Starting solutions Can you think of any examples of solutions that you

use everyday? How do you know they are solutions?

Now, what is a solution? Asolution is a homogeneous mixture of two or more

substances

Homogeneous refers to the fact that the composition of

the solution is the same throughout think onecomposition This means that any sample or aliquot, of any amount, taken

from anywhere the solution will have the same composition


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Parts of a solution Lets consider of a salt water solution and identify the parts

of the solution: The solvent in the substance present in the greatest amount

in the solution we often refer to it as the substance intowhich something else is dissolved When the solvent of a solution is water, we refer to the solution as an

aqueous solution (think aqueous, aqua which is Latin for water) In the case of the salt water solution, water is the solvent

The solute is the substance that is dissolved in the solution

In the case of the salt water solution, salt is the solute Think back to the examples of solutions you came up with

for the last slide Identify the solute and solvent of each solution


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Types of solutionsState of Solute Solvent Examples

Gas

Liquid

Solid


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Solubility In Unit 2 we talked about various compounds being soluble in water or in other

solutions What do we mean when we say something is soluble?

Solubilityis maximum amount of a solute that can dissolve in a given quantity ofsolvent at a particular temperature We usually use 100mL of water at 20C We can think of it as the ability of a solute to dissolve in a certain amount of solvent

at a particular temperature We call two substances that can mix together or can be dissolved, miscible

Conversely, when two substances cannot be mixed, we refer to them as immiscible Can you think of examples of miscible substances? Can you think of examples of immiscible

substances?

We tend to classify solutes based on based on how much will dissolve in 100mL ofwater

If more than 1g of solute can dissolve in 100mL of water, the solute is consideredsoluble If between 0.1g and 1g of solute can dissolve in 100mL of water, the solute is

considered slightly soluble If less than 0.1g of solute will dissolve in 100mL of water, the solute is considered

insoluble Keep in mind that nothing is reallyinsoluble most anything will dissolve to some extent, but

we call things insoluble if very little is able to dissolve


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Stuff in solution We can also classify solutions based on how much solute

they contain An unsaturated solution is one that can dissolve more of the

same solute think of a sponge that can take up more water Asaturated solution is one that cannot dissolve more of the

same solute think of a sponge that cannot take up any morewater

Asupersaturated solution is one that contains more solute

than a saturated solution at the temperature think of asaturated sponge that is cooled

In groups of 4 you will act out 1 of each of theabovementioned types of solutions


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Homework Pg. 358 #1-7, 10-15


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Why do things dissolve? Consider salt dissolving in water:

What is happening, at the molecular level The solute (salt) particles are breaking apart, and are becoming

attracted to solvent (water) particles What can we say about the attractive forces between the solute and

solvent particles, since we know that salt does indeed dissolve in water?

As you can imagine, substances have a range of solubilities, thatis, abilities to dissolve Why? On what does the solubility of a solute depend?

We need to think about the particles within a solution: the particles ofsolvent and solute

How can they interact to affect solubility? Solubility depends on the relative strength of the following factors:

Forces that attract particles of solute to each other Forces that attract particles of the solute to particles of the solvent Forces that attract particles of the solvent to each other


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The universal solvent Water is sometimes called the universal solvent

Because of waters polarity, it can dissolve a wide variety ofsolutes

Where are the poles in a water molecule?

The O-H bond of water is highly polar, with the O being thenegative pole and H being the positive pole

What type of bond is an O-H bond?

The O-H bond is an H (hydrogen) bond, which is very strong

Life as we know it would not exist, or continue, if water

were not such a good solvent!


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Solubility the nitty gritty

Weve talked about what solubility is and how ithappens, in a general sense, but now we are going

to look at the solubility of the following types ofcompounds at the molecular level:

Ionic compounds

Molecular compoundsPolar compounds


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Solubility of ionic compounds Knowing what you know about the polarity of water, how might we explain

how ionic compounds dissolve? The positive and negative poles of the water molecule attract the oppositely

charged ions of an ionic solute, and cause them to move away from eachother and thus dissolve

The water molecules surround each ion, with each pole facing the

oppositely charge ion of the solute, and surround the ion in a process calledhydration Sometimes ionic compounds do not dissolve in water

How might we explain this, thinking about attractive forces between ionsand the ions and water molecules? If the attractive forces between the ions in an ionic compound are stronger than those

between the ions and the poles of the water molecules, the ionic compound will notdissolve

In a chemical equation, how do we represent an ionic compound that isdissolved? We use the subscript (aq), meaning aqueous or dissolved in water this

indicates that ions are separated, but distributed evenly, in solution


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Hydration Notice how the positive

and negative ends of thewater attract theoppositely charged endsof the ionic compoundmolecules

This is how dissolving or hydration - happens!


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Solubility of molecular compounds Recall that molecular compounds can have dipoles due to EN Since water is polar, the more polar a molecular compound is, the easier

it is for it to dissolve in water Depending on the magnitude (amount) of the EN (which dictates polarity

in a molecule), the attractive forces between the particles in the compoundmay be weaker or stronger than the attractive forces between the particlesand the water molecules Molecular compounds that are polar can dissolve in water if the attractive forces

between the particles and water are stronger than those between the particles ofthe compound itself What are some examples of molecular compounds that will dissolve in water? What

are some examples of molecular compounds that will not dissolve in water?

As you may remember, some molecular compounds do not dissolve in

water How might you explain this?

The atoms of slightly polar covalent, and non-polar covalent compounds shareelectrons in order to complete their individual octets

They have no poles, and as such nothing with which to attract the oppositelycharged ends of a water molecule This means that the particles will stay together, and away from water


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Molecular compounds in water

Notice how the attractiveforces the particles of themolecular compound areholding the compound

together The attractive forces between

the water molecule and theparticles of the molecularcompound are not as strong,and as such it will not breakapart

Note that whether or not amolecular compound willdissolve will depend on howpolar the compound is


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Solubility of polar compoundsAgain, knowing what you know about the polarity of

water, what can you say about the solubility of polarcompounds in water?

Recall that dipole-dipole forces are weaker than H-bonding forces

This means that the attractive forces between the watermolecules and the particles of the polar compound will be

stronger that the attraction between the particles of thecompound


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Seeing solubility


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So, ionic or molecular?What is the best way to determine if a compound is

ionic or molecular? (Think back to the labs we didabout molecular and ionic compounds)

Conductivity is the best way to determine if a compoundis molecular or ionic

Which type of compound is conductive, and which is not?

Ionic compounds dissociate in water, and are able to carry

electrical charge passing through the solution Molecular compounds do not dissociate, remain neutral in

charge and as such cannot carry charge


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Predicting solubility So, we know how to distinguish ionic and molecular

compounds from each other But how do we predict solubility of ionic compounds?

Factor Description Affect on Solubility Example

Ion Charge Charges on each ion in anionic compound affectwhether or not thecompound is soluble

The greater the charge ofan ion, the stronger theionic bond and the lesssoluble the compound willbe

F1- and O2-: since Ohas twice the charge ofF, an oxide has astronger bond than anfluoride with the samecation

Ion Size Solubility increases withincreasing ion size

Compounds with largerions are usually moresoluble than those withsmaller ions. The largerthe ion, the greater thedistance between charges,the easier it is to pull the

ion out of its compound

AgCl vs. AgI: AgI ismore soluble thanAgCl because I- is alarger than Cl-


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Solubility rules revisitedWeve already talked about solubility rules for ionic

compounds (ie. solubility table)

But now that we know how to predict solubility of ioniccompounds, we can explain how the solubility rules werecreated

The solubility rules take into account ion size and ion charge,and list the solubilities of various anion and cation

combinations


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More predicting solubility

Molecule size is the significant factor in predicting solubilityof molecular compounds

The greater the size, the less soluble the compound is

Think of walking through a crowded mall with your friends

Imagine you are walking with your arms linked: the larger your groupis, the more difficult it will be for you to pass through the crowds

If you were walking through the mall by yourself, or with a smallergroup, it is easier to move through the crowds

Presence of polar groups will also increase solubility of a

molecular compound We need to remember, though, that even with a polar group, a large

molecular size will result in a reduced solubility of the compound

Refer to Table 8.4 on Pg. 364 for an chart illustrating the affect of

molecular size on solubility


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When and how?We now know how to predict solubility of types of

compounds, and how to determine if a compound isionic or molecular

We can also determine when something is soluble ifwe:

Know the solvent and solute

Know the conditions in which two things are beingmixed:

Temperature

Pressure


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Like dissolves like You may have heard the phrase like dissolves like before, but

what does it actually mean? Solutes with a certain polarity (ie. polar, non-polar) will dissolve in

solvents of the same polarity

For example: NaCl(s)will dissolve in H2O(); I2(g)will dissolve in Br2()

Like dissolves like also explains why some gases dissolve in water, and

why some compounds with polar and non-polar components can dissolvein polar and in non-polar solvents

So, can you fill out the following table in terms of usually solubleor usually insoluble?

Solute

Polar or Ionic Non-polar

Solvent

Polar

Non-polar


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Temperature and solubility Which is easier: dissolving sugar into warm water, or into

cold water? Thinking back to our sugar in water example

If you increase the temperature of the solvent (water), how does itaffect the solubility of the solute (sugar)?

In general, the solubility of a solid will increase with increasingtemperature

Why? Heat is just a form of energy, and something that is hot has more

energy that something that is cold

So, how can we explain the fact that the sugar dissolves more easilyin warm water?

Because the warm water has more energy, there are moreenergetic collisions with the sugar particles


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Solubility curvesWe know that solubility increases with increasing

temperature From this we can deduce that at different temperatures

the same solute will have different solubililities We can graph the solubility of various ionic compounds

at different temperatures on a solubility curve Recalling our definition of solubility, solubility is reported in

g/100mL

Using solubility curves we can determine the solubility of anionic compound at different temperatures Solubility curves show us the concentration of a saturated

solution at a specific temperature


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Reading solubilities Looking at the solubility

curve to the right,determine the followingsolubilities: NaNO3 at 30C:

KClO3 at 95C:

Cesium sulfate at 15C:

Consider the solubilitiesyou just determined: Classify each compound as

unsaturated, saturated, orsupersaturated


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So, how much is saturated?

Lets determine the concentration, in mol/L of asaturated solution of NaNO3 at 30C

According to the solubility curve, the solubility is

We need to convert the g/100mL to mol/L First, convert 100mL to 1L (remember 1L = 1000mL)

Now we can convert g to mol, using M (molar mass)

So, a saturated solution of NaNO3 at 30 C has a concentration of


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Back to temperature and solubility Weve just looked at the solubility of solids, but what about

liquids and gases? Two liquids of the same temperature usually exchange little to no

energy when combined in solution So, temperature does not affect the solubility of liquids into each other

In the same way, the solubility of one gas into another is not

influenced by temperature What about gases and liquids combined?

Gas particles have a higher kinetic energy that the particles of aliquid, so you can imagine that in order for a gas to dissolve in aliquid the gas must lose, or experience a decrease in, kinetic energy

Knowing this, what can we say about temperature and the solubility of agas in a liquid? The solubility of a gas in a liquid solvent will decrease with increasing

temperature

So, can you explain, in terms of energy and particles, what happens ifyou leave a carbonated drink out to sit at room temperature?


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Pressure and solubility What is pressure?

Pressure is defined as the force per unit area

The solubility of liquids and gases is not influenced by

pressure

The solubility of gases is greatly influenced by pressure

The solubility of a gas in a liquid is directly proportional to thepressure of the gas above the liquid

That is, the greater the pressure (force per unit area) of a gas above aliquid, the greater that gas solubility in that liquid

The pressure of other gases will not influence the dissolving gassolubility


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Solubility in societyYou will be split into 2 large groups

Each group will read about 1 of 2 topics concerningsolubility and pressure or temperature in real-world

situations Heat pollution

Scuba diving

In your groups you will prepare a short presentation on

your topic to deliver to the other group Be sure to explain the chemistry in each of the cases, as well

as why solubility is so important in each cases

Present one articlefrom a reputable source about your topic


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Rate of dissolving Weve talked about things being soluble or insoluble, but

what about how fast things dissolve? We refer to the measure of how quickly a solute dissolves in a

solvent as the rate of dissolving There are certain factors that affect how quickly a solute dissolves

Can you think of any factors that can increase the rate ofdissolving of a solute?

You will be split up into 3 groups In your groups, you will rotate around the stations set up

around the room and determine how the rate of solubility isaffected by each of the following factors: Temperature Agitation Surface area

You will have 8min at each station, in which time you are tocomplete the tasks and fill out your table as a group


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Homework Pg. 370 #1-6, 8-15


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Solutes, many and few Now that we know that things can, or cannot, dissolve,

we also need to consider the how much of something isdissolved into a solvent

Check out the following article to see how the amountof solute dissolved in a solvent, not just the fact that itdissolved, can impact our health:

http://www.scientificamerican.com/article.cfm?id=ski-wax-chemicals-buildup-blood
http://www.scientificamerican.com/article.cfm?id=ski-wax-chemicals-buildup-bloodhttp://www.scientificamerican.com/article.cfm?id=ski-wax-chemicals-buildup-bloodhttp://www.scientificamerican.com/article.cfm?id=ski-wax-chemicals-buildup-bloodhttp://www.scientificamerican.com/article.cfm?id=ski-wax-chemicals-buildup-bloodhttp://www.scientificamerican.com/article.cfm?id=ski-wax-chemicals-buildup-bloodhttp://www.scientificamerican.com/article.cfm?id=ski-wax-chemicals-buildup-bloodhttp://www.scientificamerican.com/article.cfm?id=ski-wax-chemicals-buildup-bloodhttp://www.scientificamerican.com/article.cfm?id=ski-wax-chemicals-buildup-bloodhttp://www.scientificamerican.com/article.cfm?id=ski-wax-chemicals-buildup-bloodhttp://www.scientificamerican.com/article.cfm?id=ski-wax-chemicals-buildup-bloodhttp://www.scientificamerican.com/article.cfm?id=ski-wax-chemicals-buildup-blood


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How much?Youve probably all heard the word concentration

before

What does it mean?

Concentration is the quantity (ie. a number) of solute

per unit of solution or of quantity of solvent There are several ways of reporting how much of a solute

is dissolved in a solvent:

Qualitatively (degree of concentration)

Percent concentration (, v/v, m/m, m/v)

Small concentrations (ppb)

Molar concentration (mol/L)


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Qualitative concentrations How would you describe how concentrated a solution

is, without using numbers?

We generally use the words concentrated or dilute

When we say concentrated in this sense, we mean that there isa lot of solute for the amount of solvent

We can also say that the solute:solvent particle ratio is high

When we say diluted in this sense, we mean that there is very

little solute for the amount of solvent We can also say that the solute:solvent particle ratio is low


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Percent concentrationsAs mentioned earlier, we can also report

concentrations in terms of percent concentrations:

Percent mass of solute in volume of solution (m/v)

Percent mass of solute in mass of solution (m/m)

Percent volume of solute in volume of solution (v/v)

For each of the percentage concentrations, work withyour elbow partner to create the formulas

You know that these quantities are percents, and youknow what they are percentages of

Once you determine the formulas, determine the unitsfor each percent concentration


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Percent concentrations contd Percent mass of solute in volume of solution

Percent m/v = msolute(g) x 100

vsolvent(ml)

- Percent mass of solute in mass of solution

Percent m/m = msolute(g) x 100

msolution(g)

- Percent volume of solute in volume of solution

% v/v = vsolute(ml) x 100

vsolution(ml)


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Lets try it out

An intravenous solution for a patient was prepared bydissolving 17.5g of glucose in distilled water to make350mL of solution. Find the % m/v concentration ofthe solution.


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Lets try it outAn intravenous solution for a patient was prepared by dissolving 17.5g of

glucose in distilled water to make 350mL of solution. Find the % m/vconcentration of the solution.

Given:

Required:

Analysis:

Solve:

Statement:


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Lets practice Try Practice Problems:

#1, 8 on Pg. 373

#11, 13 on Pg. 375

#21, 23 on Pg. 376


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Verysmall concentrations Sometimes concentrations are very small, less than 1%, but

it is still important that we know them An example of such a concentration is the maximum

permitted concentration of mercury in fish, or the maximumpermitted concentration of certain chemicals in soil

We report such small concentrations in parts per million(ppm) or parts per billion (ppb) For ppm the concentration is reported as mass of solute to

solution x 106

For ppb the concentration is reported as mass of solute tosolution x 109 For ppm and ppb, work with your elbow partner to determine the

formulas


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Verysmall concentrations contd

Parts per millon:

Parts per billion

Notice how in both cases the units of mass cancel out becausewe use the mass of both the solute and of the solution, withunits of grams for both quantities


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Lets try this outHealth Canadas guideline for the

maximum mercury content in

commercial fish is 0.5ppm. When a1.6kg salmon was tested, it wouldfound to contain 0.6mg of mercury.

Would this salmon be safe to eat?

h


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Lets try this outHealth Canadas guideline for the maximum mercury content in commercial fishis 0.5ppm. When a 1.6kg salmon was tested, it would found to contain 0.6mg of

mercury. Would this salmon be safe to eat?

Given:

Required:

Analysis:

Solve:

Statement:


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Lets practice Try Practice Problems #31 and 32 on Pg. 378


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Molar concentration

Another way we can express concentrations is inmolarity, or molar concentration What word do you see in molarity or molar?

Yes, this has to do with moles

Molarity, or molar concentration, is the amount ofsolute, in moles, per litre of solution Given this, what are the units of molarity?

Chemists tend to like to speak in molar

concentrations because it gives clear informationabout the number of solute particles in 1L of solution From the number of moles of a solute in a solution we

can easily determine the mass of solute


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Molar concentrations of ions Just like we can determine the molar concentration of a compound in

a solute, we can also determine the molarity of ions in a solution,using molar ratios The only time we can talk about ions floating around is when an ionic

compound is dissolved, and the ions become separated in solution

Remember, though, that they are balanced by oppositely charged ions, sothey are not really floating around Looking at the formula of an ionic compound, and understanding how it

separates into its constituent ions, we can determine the molar concentrationof each ion, For example: Ca(NO3)2(aq) Ca

2+(aq) + 2NO3-(aq)

How many moles of Ca2+ ions are there for every mole of Ca(NO3)2? How

many moles of NO3- ions are there for every mole of Ca(NO3)2 ? How do youknow? This is the same idea as knowing that for 1 car there are 4 wheels and 1

steering wheel With a known mass of the ionic compound, you can determine the exact

molar amounts of each ion.


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Lets try this out 2.0L of 0.60M FeCl3 solution are mixed with 1.0L of

0.9M solution. Will a reaction occur? What are thefinal molar concentrations of each ion?

Given:


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Required:

Analysis:

Solve:

Statement:

Ion n (mol) C (mol/L)

Dissociation

EquationsFe3+

Ba2+

Cl-


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Lets practice

Try Practice Problems #41, 42, and 46 on Pg. 381


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Homework Pg. 382 #1, 3, 4-8, 10-12, 14


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Did you know . . .? Knowing concentrations of solutions, and being able

to make a solution of a particular concentration, areboth very important in chemistry

Think about the liquid medications we use in everydaylife:

What would happen if we didnt know the concentrations ofthose liquids, or if we could not make these liquids in a

particular concentration? Check out the following article about standard solutions

and solutions of known concentrations:


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The standard solution

A solution of an accurate, and known, concentration is astandard solution We have several ways of making standard solutions:

We can dissolve a specific mass of a solute in a particularvolume of solvent

We can dilute a certain volume of a solution of a known highconcentration, called a stock solution, with a particular volumeof the same solvent

We use what is called a volumetric flask to make standardsolutions Just looking at the name, what is a volumetric flask? (break up

the word, what words to do you see?) Avolumetric flask is a glass container with a round bottom and a

long, thin neck with a gradation on the neck indicating the exactamount (in L) that it can hold


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Preparing solutions from solids Recall that molar concentration is the amount of solute, in moles,

per litre of solvent Knowing this, how could you make a solution of known concentration

from a solid? We can get moles of solute from mass of solute, so we need to use a certain

mass of solute We do not always make solutions of 1L, but we can use specific volumes that

would be equivalent to thex/L concentration we want With an elbow partner, and without looking at your textbook, come

up with a series of steps for making a solution from a solid thatincludes glassware: Your list of steps might look like:

A: Determine the required mass of solute and volume of solvent 1. Carefully measure out the required mass of solute into a clean, dry beaker 2. Dissolve the solute with some of the solvent in a volumetric flask 3. Add more solute until the desired volume is reached 4. Invert volumetric flask to mix solution thoroughly 5. Clearly label flask with the chemical formula, and concentration, of the

solution


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Preparing solutions from solids

contd Thats all great, but how do wedetermine the required massof solute and volume ofsolvent?

We use the concentration withwhich we want to end up todetermine these amounts Molar concentration is reported

asx/L, and so from this we knowthe n of solute we need per 1L

If we are not working with 1L,we can use the moles and thevolume we want to determinethe n for our particular

volume We can determine the m of

solute we need

Lets try this out: We want tomake 250mL of 0.6M NaOH.What mass of NaOH do we need,and would we make the solution?

nNaOH =

mNaOH =

Preparing solutions from stock


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epa g so ut o s o stoc

solutions Often times we dilute a concentrated solution in order to make the

same solution with a reduced concentration We often do this qualitatively at home, like when we dilute

concentrated juice with water

In the lab we are a little bit more quantitative, using theconcentration of solution with which we want to end up, and the

concentration with which we are starting Consider diluting your juice at home: describe what is happening, at

the molecular level, in terms of amounts of particles of solute and ofparticles of solvent We are not changing the number of particles when we dilute a solution, we

are changing the concentration, and the nsolute

:vsolvent

by changing the volume

With your elbow partner, and without referring to your textbook,come up with a series of steps to prepare a diluted solution from astock solution Once you are finished, compare your list with the steps in the text

book



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solutions contd The units of concentration are mol/L, Knowing the units of molar concentration, and what they tell us, we know: C= N V

If we rearrange for n we get: n=cv We know the concentration of the stock solution, as well as that of the

solution we want to end up with Since number particles, n, of solute does not change, we can write:

n1=n2C1V1= C2V2

1 refers to our starting solution, and 2 refers to our diluted solution

We have all the information for solution 1, but we have only have C forsolution 2 Using this equality, we can determine the V2, the volume of the diluted

solution Once we have V2, we can use the difference between V2 and V1 to calculate how

much solvent we need to add to reach the desired concentration


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Lets try this out

You are asked to make a0.1M NaCl solution from

500mL of 0.4M NaClsolution. How muchwater would you need toadd?

Given:

C2=0.1M V1=0.5LC1=0.1M

Required:

V = V2-V1 Analysis:

C1V1=C2V2 -Solve:

Statement:


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Lets practice Try Practice Problems #51-53, 56 on Pg. 386


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Add acid

Acids can be extremely dangerous if not handled carefully What precautions do we usually take when handling acids? We alwayswear gloves and goggles when handling acids

Acids can be highly corrosive (that is, they can burn skin)

Acids should always be diluted in fume hoods

Dilutions of strong acids are very exothermic (they give offheat energy) They also give off noxious fumes

Given how exothermic the dilution of acids is, it is alwayssafest to add acid, that is, add acid to water NOT water toacid If you add water, the solution could very easily boil and

splatter The heat of the dilution may also crack, or shatter, the glassware

Add acid


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Homework Pg. 390 #1-9, 11, 12

Chapter Review Pg. 400 #18-20, 22-25, 27-30, 32


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Double displacements - revisited When we looked at double displacement reactions, we

noticed a few key things: There were two aqueous solutions of ionic compounds

This means that the ionic compound is dissolved in water, that is,the ions are separated by the water

Water is not a reactant, simply the medium in which the ioniccompound is dissolved

In some cases a precipitate, an insoluble solid, was formed This happened because certain combinations of ions are insoluble,

while some are

When certain ion combinations are soluble, this simplymeans that they remain dissolved in solution They do not participate in the reaction, and as a result are called

non-reacting ions or spectator ions


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The players and the spectators Imagine a chemical reaction, and specifically a double

displacement reaction, as a sporting event

At a sporting event there are the players who participate, andthe spectators, those who do not participate in the game

As was previously mentioned, some combinations ofanions and cations in a double displacement are soluble

These do not participate in the reaction, and as a result arecall non-reacting ions or spectator ions

We can think of these as the spectators to a sports game

We also have anion-cation combinations that are insoluble

These do participate in the reaction

These are the players in the game


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Net ionic equations Up to now, how have we written the chemical equation for a double

displacement reaction in which there is a soluble (aqueous) product andinsoluble (solid) product? Lets use the reaction of silver nitrate and sodium chromate as an example

We have always written both these types of products as compounds, and indicated theirstates

In fact, because the aqueous compounds are just that aqueous or dissolved we can write them as their separate ions, and indicate their states

Note that the ions are notjust floating around, they are balanced by appropriatenumbers of oppositely charged ions

When we do this, the spectator ions will cancel out, leaving only the insolubleproducts

The equation that is left after we cancel out the spectator ions is called the netionic equation, which shows only the ions that combine to produce aninsoluble produce

This of this like net income, income after taxes and other costs have been deducted


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Lets practice Try Practice Problems #1-6 on Pg. 410


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Qualitative Analysis You and your group are a group of chemists looking to be hired

by a chemical company to identify a stock room full substancesthat were not labelled You are proposing your own unique technique to identify the anion

and cation of each substance, and thus identify the substance

In 3 groups, you will read, and prepare a short presentation, on 1

of each type of qualitative test Flame tests Colours of ions in solution Precipitation reactions

In your presentation be sure to identify the benefits, shortfalls,and unique characteristics of your groups qualitative test Remember, you are looking to get hired, so make your presentation

as polished, professional, and factually correct as possible


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Stoich revisitedWe already looked at stoichiometry in Unit 3 when we

talked about proportions in reactions

We are still talking about proportions, but we are

looking at, specifically, how known volumes andconcentrations of certain species in a reaction can berelated to volumes, concentrations, and mass of otherspecies (reactants or products) in the reaction we refer

to this as solutions stoichiometry Because we are determining numerical values for quantities of

reaction species, this is a quantitative analysis (think quantity,number)


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A few tips In order to successfully complete a quantitative analysis insolutions stoichiometry, there are a few things you need toconsider: Always work with a correct and correctly balanced chemical

equation Your quantities will be incorrect otherwise

As chemists, we always speak in moles, so use the coefficients ofyour correct and correctly balanced chemical equation to determinemolar ratios, and number of moles, of various species in thechemical reaction Use molar ratios as a springboard to the quantities you are looking for

Remember to use the units of the quantities you have, and thoseyou need, to determine how you will arrive at your answer


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Lets try this outWhen excess lead (II) nitrate was added to 125mL of a

solution of sodium iodide, a bright yellow precipitateof lead (II) iodide was formed. The dry precipitate had

a mass of 4.13g. What was the concentration of iodideions in the solution of sodium iodide?

Lets try this out


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Let s try this out Given:

Required:

Analysis:

Solve:

Statement:


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Homework Pg. 421 #1-9


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Youre the experts You will be split into 2 experts groups and 2 panel groups

In your expert groups you will split the reading of Section 9.3 and 9.4 I suggest the following split:

9.3: Introduction Harmful substances from natural sources (2 people) Harmful water pollutant from human activities (2 people)

Drinking water standards 9.4:

Introduction Treating water hardness Desalination (2 people) Water supply treatment Waste-water treatment

Once you have finished reading and making notes, you will confer withthe rest of your expert group about the topics you have read You will then move to your panel group, brief them about what you have read:

Learning Check Pg. 424 #13-18 (Panel 2 will ask Panel 1) Learning Check Pg. 434 #19-24 (Panel 1 will ask Panel 2)


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Homework Pg. 436 #1-3, 5-11 Chapter Review Pg. 448 #17-21, 23,24, 26-28


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Properties of acids and basesAs a class, let us brainstorm some properties of acidsand bases that we know from everyday experience:

Acids

Bases

So what are acids and bases?


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So, what are acids and bases? Knowing the properties of acids and bases, how would you

define an acid? How would you define a base? In fact, there are several theories about how acids and bases can

be defined and categorized The theory we tend to subscribe to is the Arrehenius theory of acids

and bases, named after Swedish chemist and physicists! - SvantArrhenius, a significant part of whose doctoral thesis in 1884 wasthis theory TheArrhenius theory of acids and bases states that:

An acid is a species that produces a hydrogen ion (H+) in solution This obviously means that an acid must contain an H that can separate

when the acid is in aqueous solution A base is a species that produces a hydroxide (OH-) ion in solution

This means that a base must contain a hydroxide that can separate

when the base is in aqueous solution Take a look at the following equations paying special attention to what

happens when each species dissolves: H2SO4(aq)2H

+(aq) + SO4

2-(aq)

Ca(OH)2(aq) Ca2+

(aq) + 2OH-(aq)

l k l l l


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Lets look a little closer

What is actually happening, on the molecular level, whenacids and bases dissolve in water? Consider some examples of acids (eg. HCl, HCN, H2SO4)

What kinds of compounds are these? (think EN gradient)

In fact, acids are molecular compounds, held together by covalentbonds

When an acid dissolved in water, the two resulting species areions, and as such acids undergo ionization (the formation of ions)in water

Consider some examples of bases (eg. NaOH, Ca(OH)2,Mg(OH)2) Again, what kinds of compounds are these? Bases are ionic compounds, held together by ionic bonds

When a base is dissolved in water, the ions separate or dissociatein water


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Properties revisited Now that you know a little bit more about what exactlyacids and bases are, look at Table 10.1 and compare it tothe properties we came up with as a class

How do our mind-maps compare?


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The pH scale We have probably all know of products that have pH control, or of

products that we know qualitatively are acidic or basic Can you think of any examples?

How do we actually tell if something is acidic or basic? We use what is called the pH scale, a scale which rates the acidity or

basicity of a solution from 1-14 pH is, in fact, a measure of the concentration of hydronim ions ([H3O

+]) orof hydrogen ions [H+]

Which end of the scale is more acidic? Which is more basic?

How canwe explain the fact that smaller number indicatesomething is acidic, and larger numbers indicate somethingthat is basic? The pH scale a negative logarithmic (base 10) scale, so the smaller the

number , the greater the [H3O+]

So acidic or basic?


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So, acidic or basic? As previously mentioned, acids produce H+(aq) ions when

dissolved in water As a result, we measure the acidity of an acid based on how many

H+(aq) ions the acid produces As you can imagine [H+] (concentration of H+(aq) ions) is greater than

[OH-] (concentration of OH-(aq)) The pH of acids is less than 7

Again, bases produce OH-(aq) ions when dissolved in water We still measure pH based on [H+] even in the substance we are

measuring is a base So measuring the acidity of a base we find that [OH-]>[H+] The pH of bases is greater than 7

We have just established that the pH of acids and bases isrelated to the [H+] relative to [OH-] When [H+]>[OH-] we have an acid, and when [H+]


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Indicating pH We can also determine whether or not something is acidicor basic, and its pH range, using indicators Just like they sound, acid-base indicators change colour in the

presence of an acid or base An indicator will turn a characteristic colour with a particular pH or

pH range

For example, phenolphthalein turns pink in a pH of about 9-10and bromocresol green turns yellow to blue in a pH of about 4-5

While most indicators turn a specific colour with a specific pH or

pH range, universal indicator turns a range of colours for pHvalues throughout the pH scale (0-14)

See Table 10.2 on Pg. 457 for pH ranges and colour ranges forspecific indicators

Powerful acids and bases


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Powerful acids and bases We can talk about acids and bases in an absolute sense that is,

whether something is acidic or basic We can also talk about how acidic or basic something is

We refer to this as the strength of an acid or of base Astrong acid is one that completely ionizes in water

This means that all the H+(aq) have ionized, and there is a large [H+] in the

solution

In Unit 2 we looked at binary (made up of 2) acids, and oxoacids the samething applies : these acids will ionize in water, losing their H+(aq) We call the oxoacids that have 2 or 3 Hs (such as H2SO4 and H3PO4) as diprotic and

triprotic (protic protons, H+s), respectively The first H is lost fairly easily, but the second, and in some cases the third, are not lost

as easily, and the resulting ions are weak acids

Often the [H+] of a strong acid is equal to the [acid] See Table 10.3 on Pg. 458 for examples of strong acids

Astrong base, then, is one that completely dissociated in water All the OH-(aq) have dissociated from the cation to which they were bonded, and

there is a large [OH-] Again, the [OH-] of a strong base is equal to the [base]

See Table 10.4 on Pg. 460 for examples of strong bases


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The weak

If a strong acid is one that completely ionizes in water,what is a weak acid? Aweak acid is one that does not completely ionize in

water Most of the acid molecules will stay bonded when in solution

Ionization can occur, but the extent to which it does dependson temperature and concentration of the solution

Again, if a strong base is one that completelydissociates in water, what is a weak base?

Aweak base is one that does not completely dissociatein water A weak base will produce relatively few OH-(aq) ions

Strong and weak


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Strong and weak

Also see Figure 10.6 on Pg. 459 for a comparisonof strong and weak acids


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Strong vs concentrated What is the difference between saying an acid or base is

strong vs saying an acid or base is concentrated? Strength of an acid or a base refers to the extent of ionization

or dissociation, respectively

Concentration of an acid or a base, on the other hand, refersto the amount of acid or base molecules per L of solution A strong acid can be diluted and is still a strong acid

A weak base can be concentrated and is still a weak base

Concentration refers to particles of solute per amount ofsolvent, and strength refers to extent of ionization anddissociation DO NOT get the two confused!!


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Homework Pg. 463 #1-6, 8-13, 15, 16


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Neutralization


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Neutralization From the word neutralization, you see neutral, meaning not

taking either side, or (in the chemical sense) neither acid norbase Thus, a neutralization reaction is one between an acid and a base

that produces a species that is neither acidic nor basic Neutralization does not necessarily mean [OH-]=[H+], but that the acid

and the base are neutralized

A neutralization reaction produces water and a salt

Based on what we now know about acids and bases, on the molecularlevel, work with your elbow partner to determine how the water and thesalt are produced

The H+(aq) ions of the acid combine with the OH-(aq) ions of the base to

form water

The other ions from the acid and the base combine to form the salt


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The numbers of neutralization Neutralizations can be used to determine the

concentration of the acid or base if the concentrationof one of them is known

How can we do this? Neutralization is when the acidity and basicity of an acid and

base, respectively, have been neutralized or balanced

That is, when [H+]=[OH-], or as close to this equality as we canget

So, if we know one, we can easily determine the other


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Lets try it out Ms. Vandaiyar made up a solution of Ba(OH)2, but

forgot to write the concentration of the solution on thebottle. Danielle suggested we react the Ba(OH)2 with

a 0.1250M solution of HCl that Ms. Vandaiyar haspreviously made to determine the concentration.When Kristal performed the reaction, she used32.86mL of the HCl to neutralize 25.00mL of the

Ba(OH)2. What is the concentration of the Ba(OH)2?

Lets try it out


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Let s try it out Given:

Analysis:

Required:

Solve:

Statement:


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Titrations


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Titrations In terms of reactions of acids with bases, we have simply called them

neutralizations or reactions of The procedure in which a neutralization reaction between an acid and a base is

performed is called a titration In a titration, you add a known volume of a solution (acid or base) whose concentration you

know to a known volume of the other solution(acid or base) whose concentration you donot know We call the solution whose concentration is known the titrant We use a burette, a long tube with gradations, and open top, and a valve or tap on the

bottom, to carefully and incrementally add the titrant to the solution we are titrating(which has indicator in it) We do this until we reach what is called an end-point, which is the point at which the

indicator changes colour What we are looking for in a titration is the equivalence point (equivalence,

equivalent, equal), which is the point at which the all of the titrant has reacted with allof the reactance

While we work under the assumption that the equivalent point is equal to the end point, thisis not always the case, and often the eqivalence point is just before the end point

Check out this video on how to properly perform titrations: As you watch the video, record the steps for a successful titration

http://www.youtube.com/watch?v=sFpFCPTDv2w&feature=related Once you are finished, read the Procedure for an Acid-base Titration on Pg. 468 and

compare it with the one you produced
http://www.youtube.com/watch?v=sFpFCPTDv2w&feature=relatedhttp://www.youtube.com/watch?v=sFpFCPTDv2w&feature=related


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Homework Pg. 470 #1-3, 7, 8-14, 16

Chapter Review: Pg. 480 #18-24, 26-28, 30, 32, 35

unit 4 solubility & solvents

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