name ______ class ______ date ______ concept review continued 16. when is a sample of matter considered a pure substance? ______ ______ 17. what is the difference between a mixture and a compound? ______ ______ ______ 18. briefly explain why a beaker containing sand and water is a mixture although sand itself is a pure substance. ______ ______ ______ 19. briefly explain why a compound has characteristic properties. ______ ______ label whether each material below is a pure substance, a homogeneous mixture, or a heterogeneous mixture. 20. c₂h₂ ______ 21. au ______ 22. hg ______ 23. ch₃cooh ______ 24. carbonated beverage ______ 25. raisin bran cereal ______ 26. stainless steel ______ 27. h₂o₂ ______ 28. orange juice ______ 29. sugar ______ 30. gasoline ______

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Accepted Answer

### Question 16
# Brief Explanations:
A sample of matter is a pure substance when it has a fixed composition and distinct properties, meaning it consists of only one type of element or compound (e.g., pure water, pure gold).
# Answer:
A sample of matter is a pure substance when it consists of only one type of element or compound (has a fixed composition and distinct properties).

### Question 17
# Brief Explanations:
A mixture is a physical combination of two or more substances (elements or compounds) where each retains its properties, and the composition can vary (e.g., salt - water). A compound is a chemical combination of two or more elements in a fixed ratio, with properties different from its constituent elements (e.g., water, $H_2O$).
# Answer:
A mixture is a physical combination of substances (composition variable, substances retain properties). A compound is a chemical combination of elements (fixed ratio, new properties).

### Question 18
# Brief Explanations:
A mixture is a combination of two or more substances. Sand (a pure substance) and water are physically mixed. They retain their own properties, and the composition (amount of sand and water) can vary. So the beaker with sand and water is a mixture.
# Answer:
Sand and water are physically mixed (retain properties, variable composition), so it's a mixture.

### Question 19
# Brief Explanations:
A compound has a fixed ratio of elements chemically bonded. The chemical bonds and the arrangement of atoms give it a unique set of properties (e.g., water's properties come from $H$ and $O$ in a 2:1 ratio bonded as $H_2O$).
# Answer:
A compound has a fixed element ratio (chemical bonds), giving it unique properties.

### Question 20
# Brief Explanations:
$C_2H_2$ (acetylene) has a fixed composition (2 C and 2 H atoms per molecule) and is a single compound. So it's a pure substance.
# Answer:
Pure substance

### Question 21
# Brief Explanations:
Au (gold) is an element, which has a fixed composition (only gold atoms). So it's a pure substance.
# Answer:
Pure substance

### Question 22
# Brief Explanations:
Hg (mercury) is an element, with a fixed composition (only mercury atoms). So it's a pure substance.
# Answer:
Pure substance

### Question 23
# Brief Explanations:
$CH_3COOH$ (acetic acid) has a fixed composition (2 C, 4 H, 2 O atoms per molecule) and is a single compound. So it's a pure substance.
# Answer:
Pure substance

### Question 24
# Brief Explanations:
A carbonated beverage has water, dissolved $CO_2$, sweeteners, etc. The composition is uniform throughout (you can't see the individual components), so it's a homogeneous mixture.
# Answer:
Homogeneous mixture

### Question 25
# Brief Explanations:
Raisin bran cereal has raisins, bran, and other components that are not uniformly distributed (you can see the raisins and bran separately). So it's a heterogeneous mixture.
# Answer:
Heterogeneous mixture

### Question 26
# Brief Explanations:
Stainless steel is an alloy (mixture of iron, chromium, nickel, etc.). The components are not uniformly visible, but it has a uniform composition at the microscopic level? No, actually, stainless steel is a homogeneous mixture (alloy) as the components are uniformly distributed at the atomic level. Wait, no, some sources consider alloys as homogeneous mixtures. But actually, stainless steel has a uniform composition throughout (the metals are mixed at the atomic level), so it's a homogeneous mixture.
Wait, correction: Stainless steel is a homogeneous mixture (alloy) because the components (iron, chromium, nickel) are uniformly distributed.
# Answer:
Homogeneous mixture (alloy, uniform composition)

### Question 27
# Brief Explanations:
$H_2O_2$ (hydrogen peroxide) has a fixed composition (2 H and 2 O atoms per molecule) and is a single compound. So it's a pure substance.
# Answer:
Pure substance

### Question 28
# Brief Explanations:
Orange juice (with pulp) has pulp, water, sugars, etc. The pulp is not uniformly distributed (you can see the pulp), so it's a heterogeneous mixture. If it's pulp - free, it could be homogeneous, but typically, orange juice with pulp is heterogeneous.
# Answer:
Heterogeneous mixture (if with pulp; homogeneous if pulp - free, but typical is heterogeneous)

### Question 29
# Brief Explanations:
Sugar (e.g., sucrose, $C_{12}H_{22}O_{11}$) has a fixed composition and is a single compound. So it's a pure substance.
# Answer:
Pure substance

### Question 30
# Brief Explanations:
Gasoline is a mixture of various hydrocarbons. The composition is uniform throughout (you can't see the individual hydrocarbons), so it's a homogeneous mixture.
# Answer:
Homogeneous mixture

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