Question

reviewing content
choose the letter that best answers the question or completes the statement.

1. which of these substances is not an element?

a. water b. hydrogen
c. aluminum d. iron

1. tap water is

a. an element. b. a compound.
c. a substance. d. a mixture.

1. when a homemade oil - and - vinegar salad dressing is left standing, it separates into layers. the salad dressing is a

a. solution. b. suspension.
c. colloid. d. compound.

1. which of the following is not an example of a physical property?

a. density b. flammability
c. hardness d. melting point

1. which material is a poor conductor of heat?

a. iron b. silver
c. wood d. copper

1. a material that can be hit without shattering is

a. viscous. b. flammable.
c. malleable. d. hard.

1. at room temperature, a substance with a melting point of 40°c is a

a. solid. b. liquid.
c. gas. d. mixture.

1. which action involves a chemical change?

a. making ice cubes
b. adding sugar to tea
c. cutting wrapping paper
d. baking a cake

1. a substance that has little tendency to change into other substances is said to have low

a. reactivity. b. density.
c. viscosity. d. conductivity.

1. formation of a precipitate is usually evidence of

a. the separation of a mixture.
b. a chemical change.
c. the formation of a mixture.
d. a physical change.
understanding concepts

1. explain why the properties of a pure substance do not vary from sample to sample.
2. what is the difference between an element and a compound?
3. how does the composition of a mixture of hydrogen and oxygen differ from the composition of a compound containing hydrogen and oxygen?
4. suppose all the grains in a sample of sand were exactly the same size. could the sample still be a heterogeneous mixture? explain your answer.
5. what allows a mixture to be separated by filtration?
6. explain why viscosity is classified as a physical property.
7. based on these pieces of pottery found in grand canyon national park, would you describe pottery as a malleable or brittle material?
8. a sample of copper can be drawn into a thin wire. is this property of copper a physical property or a chemical property? explain.
9. name one physical property and one chemical property of wood.
10. why is breaking down a compound into its elements considered a chemical change?
11. list one physical change and one chemical change that occur when a candle burns.
12. suppose you need to identify the material in an object without changing the object in any way. should you use physical or chemical properties to identify the material? explain your choice.

Explanation:

Step1: Recall element definition

An element is a pure - substance made of only one type of atom. Water ($H_2O$) is a compound made of hydrogen and oxygen atoms, while hydrogen, aluminum, and iron are elements. So for question 1, the answer is a.

Step2: Identify tap - water composition

Tap water contains water along with various dissolved substances like minerals, etc. So it is a mixture. For question 2, the answer is d.

Step3: Analyze salad - dressing separation

A suspension is a heterogeneous mixture where the particles settle out over time. Oil - and - vinegar salad dressing separates into layers over time, so it is a suspension. For question 3, the answer is b.

Step4: Distinguish physical properties

Physical properties can be observed or measured without changing the substance's chemical identity. Flammability involves a chemical change (burning), while density, hardness, and melting point are physical properties. For question 4, the answer is b.

Step5: Consider heat - conduction materials

Wood is a poor conductor of heat compared to metals like iron, silver, and copper. For question 5, the answer is c.

Step6: Define malleability

Malleability is the ability of a material to be shaped by hammering or rolling without shattering. For question 6, the answer is c.

Step7: Compare melting point and room temperature

Room temperature is approximately 20 - 25°C. A substance with a melting point of 40°C is a solid at room temperature. For question 7, the answer is a.

Step8: Identify chemical change

Making ice cubes is a phase change (physical), adding sugar to tea is a dissolution (physical), cutting wrapping paper is a physical change. Baking a cake involves chemical reactions between ingredients like flour, eggs, and baking powder. For question 8, the answer is d.

Step9: Understand reactivity concept

Reactivity is the tendency of a substance to undergo a chemical reaction to form other substances. A substance with low reactivity has little tendency to change into other substances. For question 9, the answer is a.

Step10: Recognize precipitate formation

The formation of a precipitate is usually evidence of a chemical change as new substances are formed. For question 10, the answer is b.

Step11: Explain pure - substance properties

A pure substance has a fixed composition. Its properties are determined by its chemical structure, which is the same in all samples. So the properties of a pure substance do not vary from sample to sample.

Step12: Differentiate element and compound

An element is a pure substance made of only one type of atom. A compound is a pure substance made of two or more different types of atoms chemically combined in a fixed ratio.

Step13: Compare mixture and compound composition

In a mixture of hydrogen and oxygen, they are just physically combined in varying proportions. In a compound like water ($H_2O$), hydrogen and oxygen are chemically combined in a fixed 2:1 ratio by atoms.

Step14: Analyze sand - sample heterogeneity

Even if all grains in a sample of sand are the same size, a sample of sand can still be a heterogeneous mixture because it may contain different minerals or impurities that are not uniformly distributed.

Step15: Understand filtration principle

Filtration separates a mixture based on particle size. The solid particles in a mixture must be large enough to be retained by the filter while the liquid or gas passes through.

Step16: Classify viscosity as physical property

Viscosity is a measure of a fluid's resistance to flow. It can be measured without changing the chemical identity of the fluid, so it is a physical property.

Step17: Determine pottery property

Pottery is brittle because it breaks easily when subjected to stress.

Step18: Classify copper property

Drawing copper into a thin wire is a physical change as the chemical composition of copper does not change. So it is a physical property.

Step19: List wood properties

A physical property of wood is density. A chemical property of wood is flammability.

Step20: Explain compound - breakdown as chemical change

Breaking down a compound into its elements involves breaking chemical bonds and forming new substances, which is a chemical change.

Step21: List candle - burning changes

A physical change when a candle burns is the melting of the wax. A chemical change is the burning of the wax in the presence of oxygen to produce carbon dioxide and water.

Step22: Choose property for material identification

To identify the material in an object without changing the object, physical properties should be used. Physical properties can be observed or measured without altering the object's chemical nature.

Answer:

1. a. water
2. d. a mixture
3. b. suspension
4. b. flammability
5. c. wood
6. c. malleable
7. a. solid
8. d. baking a cake
9. a. reactivity
10. b. a chemical change
11. A pure substance has a fixed composition, and its properties are determined by its chemical structure which is the same in all samples.
12. An element is a pure substance made of only one type of atom, while a compound is a pure substance made of two or more different types of atoms chemically combined in a fixed ratio.
13. In a mixture of hydrogen and oxygen, they are physically combined in varying proportions, while in a compound like water, hydrogen and oxygen are chemically combined in a fixed 2:1 ratio by atoms.
14. Yes, even if all grains are the same size, a sample of sand can still be a heterogeneous mixture because it may contain different minerals or impurities that are not uniformly distributed.
15. Filtration separates a mixture based on particle size, where the solid particles in a mixture must be large enough to be retained by the filter while the liquid or gas passes through.
16. Viscosity is a measure of a fluid's resistance to flow and can be measured without changing the chemical identity of the fluid, so it is a physical property.
17. Brittle, because pottery breaks easily when subjected to stress.
18. Physical property, because drawing copper into a thin wire is a physical change as the chemical composition of copper does not change.
19. Physical property: density; Chemical property: flammability.
20. Breaking down a compound into its elements involves breaking chemical bonds and forming new substances, which is a chemical change.
21. Physical change: melting of the wax; Chemical change: burning of the wax in the presence of oxygen to produce carbon dioxide and water.
22. Physical properties should be used. Physical properties can be observed or measured without altering the object's chemical nature.