Unit 5- Solutions, Acids, and

Bases

Terms to KnowSolvent= liquid that dissolves

the chemical compound (usually water)

Solute= substance that dissolves into the water

Dissolution= process of dissolving

Aqueous (aq) = water based solutionsex: NaCl(aq) = salt water

Soluble- ability of a solvent to dissolve a solute.

solute + solvent = solution

Ex: Solute & Solvent

• Your blood is a

solution:

• Solvent= plasma

(which is mostly water)

• Solute= white blood

cells, red blood cells,

etc.

Why Water is a Great Solvent

• Water is POLAR!!

– It is unevenly charged

– The highly

electronegative

oxygen hogs the

electrons.

• Polar & ionic solutes

will dissolve in water

because of the

charges.

“Like Dissolves Like”

Rule of Thumb for Solubility:

• Charged things dissolve in

charged things :

– Polar/ Ionic solutes will

dissolve in polar solvents.

• Nonpolar solutes will

dissolve in nonpolar

solvents.

“Like Dissolves Like”Polar/Ionic compounds

dissolve in polar solvents.Non polar compounds dissolve in non polar solvents.

Sugar (polar) mixes with water (polar) for easy cleaning.

Grease, oil and gasoline (non polar) will dissolve one another.

Not all solutes are water soluble

• Nonpolar substances

do NOT dissolve in

water

– Ex: Oil & Water

• Nonpolar substances

will only dissolve in

nonpolar solvents!

Substances that are soluble in H2O: “Like Dissolves Like”

Ionic Compounds (ex: salts) – made up of + cations and -

anions.

– charged ions attracted to the polar ends of water

Polar Substances (ex: Sugar)

– Covalently bonded

– Both sugar and water are polar.

Dissolving of Ionic Substances-ex: NaCl (salt)

•charged (Na+ & Cl-) are more attracted to several polar water molecules and are pulled apart.

•They dissociate (break apart)

Dissolving of Polar Substances-ex: C6H12O6 (Glucose)

• Polar water surrounds the glucose molecules and pulls them away from each other

• Molecules themselves remain intact

Weak hydrogen bond between glucose is broken and glucose is surrounded by

water

FYI-Why does soap dissolve both polar & nonpolar things?

-Alcohol, soap, & acetone will dissolve most substances because contain polar and non-polar regions.

How soap can dissolve a lot of substances

FYI-Cell Membranes- have both

polar & nonpolar ends

Properties of Solutions & The

Dissolving Process

Electrolytes• Electrolyte= a substance containing free ions

(charged particles) that will conduct electricity.

• acids, bases or salts

All these substances disassociate/

break apart in water:

NaCl Na+ + Cl- (in water)

HCl H+ + Cl – (in water)

NaOH Na + + OH – (in water)

Non Electrolytes• Some solutions do not

conduct electricity.

They are called non-electrolytes.

Examples include:

sugar

ethanol (alcohol)

ethylene glycol

FYI:Sports Drinks & Electrolytes

• Electrolytes are important in your body because they are what your cells use to carry electrical impulses (nerve impulses, muscle contractions) across themselves and to other cells.

• As for your body, the major electrolytes are as follows:

– sodium (Na+)

– potassium (K+)

– chloride (Cl-)

– calcium (Ca2+)

– magnesium (Mg2+)

– bicarbonate (HCO3-)

– phosphate (PO42-)

– sulfate (SO42-)

Source: Howstuffworks "What are electrolytes?“. Created 3/19/2008. HowStuffWorks.com.

3/19/2008. http://health.howstuffworks.com/question565.htm

• When you exercise, you lose

electrolytes through your sweat.

• Many sports drinks now contain

electrolytes to replenish what you

have lost.

FYI: Tasers- you conduct

electricity

1) Increase Temperature-makes molecules move faster

2) Increase Surface area-more surfaces to interact with

3) Stirring/ Shaking

4) Increasing Pressure-only works for gases

Factors that Speed up Dissolving Process

-Need to make the solute & solvent come into contact more frequently

Solubility Curves-Show much solvent you can put in H2O @ certain Temp.

• Solubility usually increases as temperature increases

• EX:

• At 20°C, 200 g of sugar will dissolve in 100g (= 100 mL) of H2O.

• If the temp. is increased to 60°C, 300g of the sugar will dissolve in 100g (or 100mL) H2O.

Solubility Practice Problems

1

.

KNO3at

70°C

2

.

NaCl at

100°C

3

.

NH4Cl at

90°C

.

What mass of solute will dissolve in

100mL of water at the following

temperatures. :

Answers:

140g / 100mL

40g / 100mL

72g / 100mL

Saturated

solution

Supersaturated

solution

Unsaturated

solution

Concentration of a Solution

• Amount of solute is dissolved in a given amount of solution.

• Unsaturated Solution (dilute)– more solute can be dissolved

• Saturated Solution (full)–no more solute can be dissolved under @ that temp • Saturation Point

• Supersaturated Solution–the solution has a higher solute concentration than can be reached under normal conditions.

Crystallization

occurring when

solution cools

Calculating Concentrations in

Solutions

Concentration=

Can be expressed in:

– %composition

– Parts per million (ppm)

– Grams/ Liter

– Molarity (M)2 Fish

1 L

10 Fish

1 L

Amount of solute (part)

Amount of solvent (whole)

Conversion factors to know:

1 g H2O = 1 mL

1 L = 1000 mL

% Composition

• 1 mL water = 1 gram of water

– These solutions are so dilute, we can assume that 1

mL solution = 1 gram of solution

Example 1: 13.0 grams of NaOH is dissolved in

enough water to make 850 mL of solution.

– Given: 13.0 g NaOH

850 mL solution = 850 g solution

– Find: percent composition

13.0 g NaOHX 100 = 1.53 % NaOH

850 g solution

grams of soluteX 100

grams of solution

Back of Toothpaste

Parts per million (ppm)- Used to describe

the concentration of very dilute solutions

Example 1: 13.0 grams of NaOH is dissolved in enough water to make 850 mL of solution.

• Given: -13.0 g NaOH (solute)

–850 mL solution = 850 g* (solution)

*(1 mL water = 1 gram of water… so dilute we can assume this 1 mL = 1 gram)*

• Find: ppm

13.0 g NaOHX 1,000,000 = 15294 ppm NaOH

850 g solution

grams of soluteX 106

grams of solution

What’s in your drinking water?National Primary Drinking Water Standards as of 10/03

Contaminant Parts per

Million (ppm)

Potential Health Effects from

Ingestion of Water

Arsenic 0.010 Skin damage or problems with circulatory

systems, and may have increased

risk of getting cancer

Asbestos (fibers >10

micrometers)

7 (million

fibers per

Liter)

Increased risk of developing benign

intestinal polyps

Carbon

tetrachloride

0.005 Liver problems; increased risk of cancer

Lead 0.015 Infants and children: Delays in physical

or mental development; children could

show slight deficits in attention span

and learning abilities; Adults: Kidney

problems; high blood pressure

Mercury (inorganic) 0.002 Kidney damage

Source: US EPA. Water On Tap: What You Need To Know. Modified 12/14/2004. EPA. 3/13/2008.

http://www.epa.gov/safewater/wot/pdfs/book_waterontap_full.pdf

Grams per liter

• Used to discuss the solubility of a solid in solution.

• Example: 13.0 grams of NaOH is dissolved in enough water to make 850 mL of solution.

– Given: 13.0 g NaOH

850 mL solution = 0.850 L solution

– Find: g/L

– Solve:

grams of solute

Liters of solution

13.0 g NaOH= 15.3 g/L

0.850 L

Expressing Concentrations of Solutions

Molarity (M) = moles soluteliters of solution

Step 1: Molarity = moles

Liters

Step 2: Convert grams to Moles

24.5 g NaCN x 1 mole NaCN = 0.500 mol

49.01 g

Step 3: Convert mL to L

250.0 mL x 1 L = .2500 L

1000mL

Step 4: Plug into equation

M = 0.500 mol = 2.00 M NaCN

0 .2500

PROBLEM: What is the molarity of a solution prepared by dissolving 24.5 g of NaCN in water to a final volume of 250.O mL?

Ex #1 (no calculator needed)

How many moles of HNO3 are needed to prepare 5.0L of 2.0 M solution of HNO3?

Solution: Molarity= moles

Liter

2.0 M = moles = 10 moles5.0 L

Labeling on solutions in chemistry

Kool- Aid Lab- a little history

Over 900 people died in a

“mass suicide” by drinking

punch laced with poisons

Chemistry of Acids and Bases

pH Scale- a way of expressing the strength of acids

and bases

Common Acids

HC2H3O2 Acetic Acid Vinegar

HCl Hydrochloric Acid Stomach acid

H3C6H5O7 Citric Acid Citrus Fruit

HNO3 Nitric Acid

H2SO4 Sulfuric Acid Battery Acid

Some Common Bases

NaOH sodium hydroxide lye/ Drano

KOH potassium hydroxide liquid soap

Ba(OH)2 barium hydroxide stabilizer for plastics

Mg(OH)2 magnesium hydroxide Milk of magnesia

Al(OH)3 aluminum hydroxide Maalox (antacid)

NH3 Ammonia Windex & cleaners

What Are Acids & Bases?(Arrhenius theory)

• Acids - Increase the concentration of hydrogen ions (H+) in aqueous solution.– Examples: HCl, H2SO4,

HNO3

• Bases - Increase the concentration of hydroxide ions (OH-) in aqueous solution.– Examples: NaOH,

Mg(OH)2, KOH,

Characteristic Ions of AcidsHydrogen Ion (H+)• Many acids contain H+

• Acids dissociate in H2O, # of H+ ions increases in the solution

Hydronium Ion (H3O+)• As H+ interact with water

molecules, they combine to form H3O+

HCl + H2O H3O+ + Cl-

Acid donates to

H2O

H3O+ = hydronium

ion

gives solution the

acidic properties

Hydronium Ion (detailed FYI)H2O with extra proton (H+)

H & Cl form a polar covalent bond, but H is very attracted to water.

Some Properties of Acids• Produce H+ ions (+ H2O) H3O+, hydronium ion

• 0-7 on pH scale

• Taste sour

• Acids are Electrolytes

• Acids are neutralized with a base (forms salt + water)

• Turns blue litmus paper to “Red”

• Reacts with metals to form H2 gas

HCl + Mg MgCl2 + H2 gas(Acid) + (metal)

Why we use Drano (a base) in our drain pipes vs. acids

Capsaicin- Acid found in chilis

• All sorts of interesting applications:

– Pain relief for topical application on arthritic limbs

– Animal deterrent

– Drug abuse deterrent

– Diet functionPepper spray

Characteristic Ion of Bases

• Hydroxide Ion (OH-)

• Many bases contain OH-

• As bases dissociate in water, the concentration of OH- ions increases in the solution

2 ways to explain Bases:

1) Donators of OH- ions

2) Acceptor of H+ ions

water

NaOH Na+ (aq) + OH- (aq)

Some Properties of Bases Produce OH- ions in water (hydroxide) / Accept H+

ions

pH greater than 7-14

Taste bitter, chalky

Are electrolytes

Feel soapy, slippery

Are neutralized by acids (form salt + water)

Turns red litmus paper to blue “Basic Blue”

Strong vs. Weak Acids & Bases

• Strength of an acid or base is determined by the amount of ionization (how often it dissociates in water)

• Examples:

– Strong acid: hydrochloric acid (HCl)

– Weak acid: Acetic acid (vinegar)

– Strong Base: sodium

hydroxide (NaOH)

– Weak Base: Ammonia (NH3)

Strong- break apart easily

Weak – Do NOT ionize as much

Ex: Strong vs. Weak Acids/Bases

HCl= strong acid that completely

breaks apart in water.

Acetic Acid= weak acid that does

not completely break apart in water

Strong acids/ bases = strong

electrolytes• Strong acids (dissociate 100% in water)=

HNO3, HCl, H2SO4 and HClO4

• Weak acid = acetic acid (aka vinegar) -CH3CO2H

• Strong base (dissociate 100% in water) =

NaOH (aq) ---> Na+ (aq) + OH- (aq)

• Weak base = Ammonia (NH3)

NH3 (aq) + H2O (l) NH4+ (aq) + OH- (aq)

pH Scale- a way of expressing the strength of acids

and bases

pH & the Environment

pH testing- Lots of ways!

pH meter

Phenolphthalein (PPT)

responds to bases only

pH- paper

Some chemicals respond

to acids &/or bases by

changing colors

pH indicator: Cabbage JuiceBy boiling purple

cabbage, the

natural pigments

can serve as an

indicator.

Some other pH chemical indicators

Some indicators work only in a specific pH range.

Neutralization Reactions

Neutralization- a special type

of double replacement reaction

Tums neutralizes the acid in

your stomach.

Neutralization Reactions Cont.

• Acids React with Carbonates

You may have made a volcano :

2HC2H3O2 + Na2CO3 2 NaC2H3O2 + H2O + CO2

Vinegar + Baking Soda Sodium acetate (salt)

Effects of Acid rain on marble

H2SO4 + CaCO3 CaSO4 + H2O + CO2

Titration- way of determining the

molarity of an unknown solution.

acid of unknown strengthW/ indicator in it

drop base of known Molarity into acid until it’s neutralized

By knowing how much base it took to neutralize

acid (& a little math) you can find the strength.

Formula: MV = MV (see problem on next slide)

Use formula:

(Molarity acid) (*Volume acid) = (Molarity base) (*Volume base)

*Volume must be in Liters (1 L = 1000 mL)*

Titration Problem:35 mL of NaOH is neutralized

with 25 mL of 0.1 M HCl by titration to an

equivalence point. What is the concentration of the

NaOH?

Solution: Plug & Chug …(0.1 M ) (0.025 L) = (?M) (0.035 L)

M= 0.07 M NaOH

Buffers