Question

a. multiple - choice questions: encircle the letter of the best answer.

1. which statement best describes a mixture?

a. a pure substance made of one type of atom
b. a substance formed by chemical bonding
c. a combination of substances not chemically combined
d. a substance that cannot be separated

1. which of the following is a homogeneous mixture?

a. oil and water
b. cereal and milk
c. air
d. sand and gravel

1. which characteristic is true for compounds but not mixtures?

a. components keep their properties
b. composition is variable
c. elements are chemically bonded in fixed ratios
d. they can be separated physically

1. which of the following is an example of a heterogeneous mixture?

a. saltwater
b. brass (copper + zinc)
c. soda
d. soil

1. which method can be used to separate a mixture but not a compound?

a. filtration
b. electrolysis
c. chemical reaction
d. decomposition
b. identification: identify the following substances as an element, compound, or mixture.

1. carbon dioxide
2. air
3. iron
4. saltwater
5. water
6. soil
7. oxygen gas
8. salad

Explanation:

• Question 1: A mixture is a combination of substances not chemically combined.
• Question 2: Air is a homogeneous mixture as its components are uniformly distributed.
• Question 3: Compounds have elements chemically bonded in fixed ratios, which is not true for mixtures.
• Question 4: Soil is a heterogeneous mixture as its components are not uniformly distributed.
• Question 5: Filtration can be used to separate a mixture but not a compound.
• Part B:
• Carbon dioxide is a compound as it is made of two elements (carbon and oxygen) chemically bonded.
• Air is a mixture as it contains various gases like nitrogen, oxygen, etc.
• Iron is an element as it is made of only one type of atom.
• Saltwater is a mixture as it contains salt and water.
• Water is a compound as it is made of hydrogen and oxygen chemically bonded.
• Soil is a mixture as it contains various components like minerals, organic matter, etc.
• Oxygen gas is an element as it is made of only oxygen atoms.
• Salad is a mixture as it contains various ingredients like vegetables, fruits, etc.

Answer:

1. C. A combination of substances not chemically combined
2. C. Air
3. C. Elements are chemically bonded in fixed ratios
4. D. Soil
5. A. Filtration

B.

1. Compound
2. Mixture
3. Element
4. Mixture
5. Compound
6. Mixture
7. Element
8. Mixture