2.1 Classifying Matter - Acadia Parish School Boardacadia.k12.la.us/view/12892.pdf · 2.1 Classifying Matter A pure substance is matter that always has exactly the same composition

2.1 Classifying Matter

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.


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



substances?

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


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



substances?

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


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.



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.



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.



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

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2.1 Classifying Matter - Acadia Parish School Boardacadia.k12.la.us/view/12892.pdf · 2.1 Classifying Matter A pure substance is matter that always has exactly the same composition