2.1 classifying matter objectives: the student will be able to: describe properties in order to...

2.1 Classifying Matter

Objectives: The student will be able to:

• Describe properties in order to describe materials.

• Classify pure substances as elements or compounds.

• Distinguish pure substances from mixtures.

• Classify mixtures.


Inquiry Activity

• P.37 in book

Mixtures, elements, Mixtures, elements, compoundscompounds

Scientists like to classify things.Scientists like to classify things. One way that scientists classify One way that scientists classify

matter is by its composition.matter is by its composition. Ultimately, all matter can be Ultimately, all matter can be

classified as mixtures, elements and classified as mixtures, elements and compounds.compounds.

Why isnWhy isn’’t it a good idea to t it a good idea to classify matter by its classify matter by its

phases?phases?

Because one kind of substance can exist in Because one kind of substance can exist in more than one phase – such as Hmore than one phase – such as H220. And 0. And matter changes phases rather easily.matter changes phases rather easily.

Why isnWhy isn’’t matter classified t matter classified according to its physical according to its physical

characteristics, such as color?characteristics, such as color?

Scientists wouldnScientists wouldn’’t find it very useful to t find it very useful to group gold, sunflowers, and the sun group gold, sunflowers, and the sun together.together.

Scientists ask themselves these Scientists ask themselves these questions?questions? Is the matter uniform throughout?Is the matter uniform throughout? Can it be separated by physical means?Can it be separated by physical means? Can it be separated by chemical means?Can it be separated by chemical means?

By asking these questions scientists can By asking these questions scientists can classify matter into:classify matter into:

MixturesMixtures – two or more substances that are – two or more substances that are not chemically combined with each other and not chemically combined with each other and can be separated by physical means. The can be separated by physical means. The substances in a mixture retain their substances in a mixture retain their individual properties.individual properties. Solutions – a special kind of mixture where one Solutions – a special kind of mixture where one

substance dissolves in another.substance dissolves in another. ElementsElements – simplest form of pure substance. – simplest form of pure substance.

They cannot be broken into anything else by They cannot be broken into anything else by physical or chemical means.physical or chemical means.

CompoundsCompounds – pure substances that are the – pure substances that are the unions of two or more elements. They can be unions of two or more elements. They can be broken into simpler substances by chemical broken into simpler substances by chemical means.means.


Each piece of your clothing has a label that recommends cleaning methods. A 100%-cotton shirt may need to be ironed after washing. A cotton and polyester blend fabric may come out of the dryer wrinkle free. There is no cleaning process that works for all materials.


Why are elements and compounds classified as pure substances?

Pure Substances


A pure substance is matter that always has exactly the same composition.

• Table salt and table sugar are two examples of pure substances.

• Substances can be classified into two categories—elements and compounds.

Pure Substances


Every sample of a given substance has the same properties because a substance has a fixed, uniform composition.

Pure Substances


How do mixtures differ from pure substances?

An element is a substance that cannot be broken down into simpler substances.

Elements

An element has a fixed composition because it contains only one type of atom.

No two elements contain the same type of atom.

ElementsElements

All elements are All elements are made of atoms.made of atoms.

Atoms of the Atoms of the same element same element are alike.are alike.

Atoms of different Atoms of different elements are elements are different.different.

ElementsElements

In 1813, a system In 1813, a system of representing of representing elements with elements with symbols was symbols was introduced.introduced. Each symbol consists of one Each symbol consists of one

or two letters.or two letters. Two letters are needed for a Two letters are needed for a

chemical symbol when the chemical symbol when the first letter of that elementfirst letter of that element ’’s s name has already been name has already been used.used.

Common ElementsCommon Elements

AluminumAluminum AlAl

BromineBromine BrBr

CalciumCalcium CaCa

CarbonCarbon CC

GoldGold AuAu

HeliumHelium HeHe

HydrogenHydrogen HH

NitrogenNitrogen NN


Examples of Elements•Some elements are solids at room temperature. Most soft drink cans are made from aluminum. Carbon is the main element in the marks you make with a pencil.

•The elements oxygen and nitrogen are the main gases in the air you breathe.

•Two elements are liquids at room temperature–bromine and mercury.

Elements


Symbols for Elements

Chemists use symbols of one or two letters to represent elements. The first letter is always capitalized. If there is a second letter, it is not capitalized.

• C represents carbon.• Al represents aluminum.• Au represents gold. (The Latin name for

gold is aurum.)

Elements


Symbols for Elements

Symbols allow scientists who speak different languages to communicate without confusion. For example, nitrogen is azote in France, stickstoff in Germany, and nitrógeno in Mexico. But all scientists use N as the symbol for the element nitrogen.

Elements


Aluminum, carbon, and gold are elements that you can see in common objects, such as cans, pencils, and rings. Mixtures containing iodine are used to prevent and treat infections.

Elements

Aluminum Carbon Gold Iodine



Compounds


A compound always contains two or more elements joined in a fixed proportion.

Compounds

A compound is a substance that is made from two or more simpler substances and can be broken down into those simpler substances.


The properties of a compound differ from those of the substances from which it is made.

• Water is composed of the elements hydrogen and oxygen. Oxygen and hydrogen are gases at room temperature, but water is a liquid.

• Hydrogen can fuel a fire, and oxygen can keep a fire burning, but water does not burn or help other substances to burn.

Compounds

CompoundsCompounds

Compounds are also Compounds are also pure substances.pure substances.

But compounds are But compounds are made from more made from more than one element.than one element.

Water is a Water is a compound.compound.

Water can be broken Water can be broken down into simpler down into simpler substances – substances – hydrogen and hydrogen and oxygen.oxygen.


Silicon dioxide is a compound found in most light-colored grains of sand and in crystals of quartz. It is a colorless, transparent solid. Yet, silicon dioxide is made from a colorless gas (oxygen) and a gray solid (silicon). In silicon dioxide, there are always two oxygen atoms for each silicon atom.

Compounds

Silicon

Oxygen

Silicon dioxide



Mixtures


If you make salsa, a recipe can guide you. You can use exactly the amounts in the recipe, or you can adjust the ingredients to your own taste. Salsa is a mixture. Each batch may be slightly different.

Mixtures


The properties of a mixture can vary because the composition of a mixture is not fixed.• Mixtures can retain some of the properties of their

individual substances. • The properties of a mixture are less constant than the

properties of a substance.

Mixtures


Mixtures can be classified by how well the parts of the mixture are distributed throughout the mixture.

Heterogeneous Mixtures

In a heterogeneous mixture, the parts of the mixture are noticeably different from one another.

Homogeneous Mixtures

In a homogeneous mixture, the substances are so evenly distributed that it is difficult to distinguish one substance in the mixture from another.

Mixtures

Is it uniform throughout?Is it uniform throughout?

If the answer is no, the matter is a If the answer is no, the matter is a heterogeneous mixture.heterogeneous mixture. Considered the Considered the ““least mixed.least mixed.”” Does not appear to be the same Does not appear to be the same

throughout.throughout. Particles are large enough to be seen Particles are large enough to be seen

and to be separated from the mixture.and to be separated from the mixture.

Examples of heterogeneous Examples of heterogeneous mixturesmixtures

Sand and pebblesSand and pebbles Oil and waterOil and water Powdered iron and powdered sulfurPowdered iron and powdered sulfur

Granite is a heterogeneous mixture.

Is it uniform throughout?Is it uniform throughout?

If the answer is yes, the matter is If the answer is yes, the matter is homogeneous (looks the same homogeneous (looks the same throughout).throughout).

That leads us to another question.That leads us to another question.

Can it be separated by Can it be separated by physical means?physical means?

If the answer is yes, the matter is a If the answer is yes, the matter is a homogeneous mixture or solution.homogeneous mixture or solution.

Homogeneous MixturesHomogeneous Mixtures

A mixture that appears to be the A mixture that appears to be the same throughout.same throughout.

It is It is ““well mixed.well mixed.”” The particles that make up the The particles that make up the

mixture are very small and not easily mixture are very small and not easily recognizable.recognizable.

Examples of homogeneous Examples of homogeneous mixturesmixtures

Milk, toothpaste, and mayonnaise are homogeneousmixtures. They are also colloids.


The sand is a heterogeneous mixture of different kinds of grains. The spoon is stainless steel, a homogeneous mixture of iron, chromium, and nickel.

Mixtures


Do the Contents of Two Cans of Mixed Nuts Meet FDA Regulations?

According to Food and Drug Administration (FDA) regulations, a can labeled mixed nuts must contain at least four types of shelled nuts other than peanuts. The mass of each type of nut must be not less than 2 percent of the total mass and not more than 80 percent of the total mass.

Mixtures


1. Comparing and Contrasting How are the two brands of mixed nuts alike? How are they different?

Answer:

Mixtures


1. Comparing and Contrasting How are the two brands of mixed nuts alike? How are they different?

Answer: Both brands contain the same types of nuts but the amount of each type differs.

Mixtures


2. Calculating What is the percent by mass of each type of nut in each can?

Answer:

Mixtures


2. Calculating What is the percent by mass of each type of nut in each can?

Answer:Brand A: 44.2% peanuts, 13.64% almonds, 16.79% Brazil nuts, 13.4% cashews, 5.77% hazelnuts, and 6.21% pecans

Brand B: 54.8% peanuts, 8.90% almonds, 5.59% Brazil nuts, 21.06% cashews, 4.82% hazelnuts, and 4.82% pecans

Mixtures


3. Drawing Conclusions Do the contents of each can meet the FDA regulations? Explain.

Answer:

Mixtures


3. Drawing Conclusions Do the contents of each can meet the FDA regulations? Explain.

Answer:Yes. Both brands contain more than four types of nuts other than peanuts. The masses are within the 2% to 80% range.

Mixtures


4. Inferring On the Brand A label, the nuts are listed in this order: peanuts, Brazil nuts, almonds, cashews, pecans, and hazelnuts. What do you think determines the order?

Answer:

Mixtures


4. Inferring On the Brand A label, the nuts are listed in this order: peanuts, Brazil nuts, almonds, cashews, pecans, and hazelnuts. What do you think determines the order?

Answer: The ingredients are listed in order by total mass. The ingredient with the largest mass is listed first.

Mixtures


What is the main difference among solutions, suspensions, and colloids?

Solutions, Suspensions, and Colloids

The size of the particles in a mixture has an effect on the properties of the mixture.

Based on the size of its largest particles, a mixture can be classified as a solution, a suspension, or a colloid.


Solutions

When substances dissolve and form a homogeneous mixture, the mixture that forms is called a solution.

Suspensions

A suspension is a heterogeneous mixture that separates into layers over time.


SolutionsSolutions

A solution is a type of homogeneous A solution is a type of homogeneous mixture formed when one substance mixture formed when one substance dissolves in another.dissolves in another.

It is the best mixed of all mixtures.It is the best mixed of all mixtures. A solution always has a substance that is A solution always has a substance that is

dissolved and a substance that does the dissolved and a substance that does the dissolving.dissolving.

The substance that is dissolved is the The substance that is dissolved is the solute and the substance that does the solute and the substance that does the dissolving is the solvent.dissolving is the solvent.

Ocean water is a solutionOcean water is a solution

The universal solvent: WaterThe universal solvent: Water


Colloids

A colloid contains some particles that are intermediate in size between the small particles in a solution and the larger particles in a suspension.

• Like solutions, colloids do not separate into layers.

• You cannot use a filter to separate the parts of a colloid.


ColloidsColloids

A colloid will not A colloid will not separate upon separate upon standing.standing.

The particles are The particles are constantly colliding, constantly colliding, and this allows a and this allows a colloid to scatter colloid to scatter light – thus colloids light – thus colloids often seem cloudy.often seem cloudy.

Water as a solventWater as a solvent

Many liquid solutions contain water Many liquid solutions contain water as the solvent.as the solvent.

Ocean water is basically a water Ocean water is basically a water solution that contains many salts.solution that contains many salts.

Body fluids are also water solutions.Body fluids are also water solutions.

Types of solutionsTypes of solutions

GasGas GasGas Air (oxygen in nitrogen)Air (oxygen in nitrogen)

GasGas LiquidLiquid Soda water (carbon dioxide Soda water (carbon dioxide in water)in water)

SolidSolid LiquidLiquid Ocean water (salt in water)Ocean water (salt in water)

Solute Solvent Example

SolidSolid SolidSolid Gold jewelry Gold jewelry (copper in gold)(copper in gold)

Metals dissolved in metals are called

alloys.

Air is a solution of oxygen and Air is a solution of oxygen and other gases dissolved in other gases dissolved in

nitrogennitrogen

AlloysAlloys

Brass is an alloy of copperand zinc.

Stainless steel is a mixtureof iron and chromium.


These liquids represent three categories of mixtures.

• Windshield wiper fluid is a solution. • Muddy water collected from a swamp is a

suspension. • Milk is a colloid.


Homogeneus Mixtures (Solutions)• Homogeneous mixture:

– a mixture in which the components are evenly distributed among each other.

– You cannot see the component parts.

• Homogeneous means the samethroughout.

• It has a constant composition throughout.

Examples: Salt dissolved in water, sugar dissolved in water, apple juice, tea, copper (II) sulfate solution in water, alloys....

Solutions

• Well-mixed (uniform) – single phase

• homogeneous

• transparent (if liquid)

• cannot be separated by filter

• do not separate on standing

States of Matter in Solution Examples of Solutions

gas in gas air ( N2, O2 , Ar, CO2 , other

gases)gas in liquid soda pop (CO2 in water)

liquid in liquid gasoline (a mixture of hydrocarbon compounds)

solid in liquid Salt water

gas in solid H2 in platinum or palladium

liquid in solid dental amalgams (mercury in silver)

solid in solid alloys ( brass, (Cu/Zn), sol-der (Sn/Pb), Steel (Fe/C ))

Q: Can a solution be separated by filtration?

A. Yes

B. No

Heterogeneous MixturesHeterogeneous Mixture (Suspension or Colloid): •the components are not evenly distributed among each other•has two or more distinct phases that are usually visible •does NOT have uniform properties.•Heterogeneous mixtures that look like solutions can be distinguished because they scatter light (Tyndall Effect).

Ex: muddy water, oil and water, milk, sulfur and iron, granite, blood...

Suspensions

• A suspension is a mixture where the particles are dispersed but are big enough to settle out or be filtered out.

• A mixture that needs to be shaken before use is probably a suspension.

• Ex.– Mud or muddy water, where soil, clay, or silt

particles are suspended in water. – Paint (needs to be mixed before use)– Snow globe (eventually settles)– Orange Juice (needs to be shaken before use)

http://en.wikipedia.org/wiki/Mud

http://en.wikipedia.org/wiki/Soil

http://en.wikipedia.org/wiki/Clay

http://en.wikipedia.org/wiki/Silt

http://en.wikipedia.org/wiki/Paint

•Suspensions like coffee are easily filtered to take out the tiny solid clumps floating in the liquid.

• Solutions are mixtures that have particles that are so small they pass through most filters.

Colloids

Non-transparent, uniform, large particles, cloudy (milky)but stable system

Colloids

ColloidsTyndall Effect

• You can see the light beam as it passes through a colloid or suspension.

• particles scatter light


• Mixtures and Solutions


Kahoot


Assessment Questions

1. Which of these substances is a compound? a. copper

b. water

c. oxygen

d. carbon



1. Which of these substances is a compound? a. copper

b. water

c. oxygen

d. carbon

ANS: B



2. Which of these groups of letters could be used as a symbol for an element? a. HF

b. Cm

c. Car

d. fe



2. Which of these groups of letters could be used as a symbol for an element? a. HF

b. Cm

c. Car

d. fe

ANS: B



3. Which of the following statements does not apply to a compound? a. It is made of two or more elements.

b. It has components that are joined in fixed proportions.

c. It can be separated into components by physical methods.

d. It can be broken down into elements or other compounds.



3. Which of the following statements does not apply to a compound? a. It is made of two or more elements.

b. It has components that are joined in fixed proportions.

c. It can be separated into components by physical methods.

d. It can be broken down into elements or other compounds.

ANS: C



4. How does a compound differ from a mixture? a. A compound cannot be broken down into simpler

substances.

b. Compounds can be separated by physical processes and mixtures cannot.

c. The composition of a mixture cannot vary.

d. A compound is made of two or more elements in fixed proportion.



4. How does a compound differ from a mixture? a. A compound cannot be broken down into simpler

substances.

b. Compounds can be separated by physical processes and mixtures cannot.

c. The composition of a mixture cannot vary.

d. A compound is made of two or more elements in fixed proportion.

ANS: D



5. Which of these materials is a heterogeneous mixture? a. air

b. seawater

c. sand

d. steel



5. Which of these materials is a heterogeneous mixture? a. air

b. seawater

c. sand

d. steel

ANS: C



6. Which of the following can be separated with a filter? a. colloids

b. compounds

c. solutions

d. suspensions



6. Which of the following can be separated with a filter? a. colloids

b. compounds

c. solutions

d. suspensions

ANS: D

2.1 classifying matter objectives: the student will be able to: describe properties in order to...

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