2.1 Classifying Matter Objectives – 9/18/2015 Law of Conservation of Mass Classify pure substances as elements or compounds. Describe the characteristics

2.1 Classifying Matter

Objectives – 04/21/23• Law of Conservation of Mass• Classify pure substances as elements or

compounds.• Describe the characteristics of an element and

the symbols used to identify elements.• Describe the characteristics of a compound.• Distinguish pure substances from mixtures.• Classify mixtures as heterogeneous or

homogeneous.• Classify mixtures as solutions, suspensions, or

colloids.


M atte r E n erg y

E veryth in g inth e U n ive rse


Law of Conservation of Mass

• Mass is never destroyed– a relation stating that in a chemical reaction,

the mass of the products equals the mass of the reactants.

• When we burn something it isn’t destroyed, it just changes into other compounds



MatterClassification of Matter

E lem en ts C om p ou n d s

P u re S u b s tan ces

H om og en eou sM ixtu res

H eterog en eou sM ixtu res

M ixtu res

M atte r


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.



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


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


Identify the following as an element or a compound

• Sucrose (table sugar)• The helium in a balloon• Baking soda• A diamond• Aluminum foil• Calcium Chloride pellets used

to melt ice.

• Compound• Element• Compound• Element• Element• Compound


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



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


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.

Solutions, Suspensions, and Colloids


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.



homogeneous or heterogeneous mixture

• 70% isopropyl alcohol• A pile of rusty iron

filings• Concrete• Saltwater• Gasoline• Bread

• Homogeneous• Heterogeneous• Heterogeneous• Homogeneous• Homogeneous• Heterogeneous


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


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 Objectives – 9/18/2015 Law of Conservation of Mass Classify pure substances as elements or compounds. Describe the characteristics