Matter Unit Review

1. Which material is a pure substance?

• alloy

• compound

• mixture

• solution

Answer explanation

A compound is a pure substance made of two or more elements chemically combined in fixed proportions. In contrast, alloys, mixtures, and solutions contain multiple components and are not pure substances.

2. Which is an example of a heterogenous mixture?

• gasoline

• diet soda

• flour and water

• grape juice

Answer explanation

Flour and water form a heterogeneous mixture because the flour does not completely dissolve in water, creating distinct layers. In contrast, gasoline, diet soda, and grape juice are homogeneous mixtures.

3. The chemical formula for glucose is C6H12O6, so it is classified as a(n)

• pure substance

• element

• mixture

• solution

Answer explanation

Glucose, with the formula C6H12O6, is a pure substance because it consists of a specific arrangement of atoms in a fixed ratio. It is not an element, mixture, or solution, which involve different compositions.

4. During physical changes, matter always retains its __________________________

• size

• identity

• state

• texture

Answer explanation

During physical changes, matter undergoes alterations in form or appearance but retains its identity, meaning the substance remains the same at a molecular level. Therefore, the correct answer is 'identity'.

5. One difference between mixtures and pure substances is that ____________

• pure substances have no chemical bonds

• pure substances can be physically seperated

• mixtures can be physically seperated

• mixtures are made of one type of atom

Answer explanation

Mixtures consist of two or more substances that can be physically separated, while pure substances have a uniform composition and cannot be separated by physical means. Thus, the correct choice is that mixtures can be physically separated.

6. In the classification of matter, how would you classify air?

• Pure mixture

• Pure substance

• Homogeneous mixture

• Heterogeneous mixture

Answer explanation

Air is classified as a homogeneous mixture because it consists of various gases (like nitrogen and oxygen) that are uniformly distributed, making it appear consistent throughout. It does not have distinct layers or phases.

7. Which of the four containers represents a compound?

• Sodium

• Water

• Nitrogen

• Chlorine

Answer explanation

Water is a compound made of two hydrogen atoms and one oxygen atom (H2O), while sodium, nitrogen, and chlorine are elements. Therefore, water is the correct choice representing a compound.

8. Which image(s) would be considered pure substances?

• V

• I and II

• II and IV

• III and V

Answer explanation

Pure substances consist of only one type of particle. Images III and V represent pure substances, while I, II, and IV contain mixtures or compounds. Therefore, the correct answer is III and V.

9. A student has a sample of an insoluble solid and a liquid. The task is to separate the mixture into its pure components. What question is best asked in the design of the experiment to determine how to separate the components?

• Is the solid/liquid mixture toxic in its combined form?

• Is the solid large enough to be caught by the pores of a filter

• Is the melting temperature of the solid lower than that of the liquid?

• Can the solid be crushed into smaller particles to allow for distillation?

Answer explanation

The best question to ask is whether the solid is large enough to be caught by the pores of a filter. This directly relates to the feasibility of using filtration to separate the solid from the liquid in the mixture.

10. When elements form mixtures, the elements ____________________

• keep their original properties

• react to form new substances with new properties

• combine in a specific mass ration

• always change their physical state

Answer explanation

When elements form mixtures, they retain their original properties. This means that the individual characteristics of each element remain unchanged, unlike in chemical reactions where new substances with different properties are formed.