Question

chemistry unit 1b practice ws#3
section 3.3 mixtures of matter
t/f (if false, correct to make the statement true)

1. matter can be combined both physically and chemically.
2. pure substances have changing composition.
3. elements can be chemically broken down into simpler substances.
4. compounds can be physically separated into simpler substances.
5. compounds are pure substances that are a physical combination of elements.
6. compounds have physical and chemical properties that are different from the individual element properties in their composition.
7. mixtures are a chemical combination of substances and can only be separated by breaking chemical bonds.
8. pure water is a homogeneous mixture.
9. tap water is a homogeneous mixture. t
10. the salt in a saltwater mixture retains its individual physical and chemical properties.
11. oil and water is a homogeneous mixture.
12. you can see individual elements in a homogeneous mixture.
13. a solution is a heterogeneous mixture.
14. sugar dissolved in coffee is an example of a solution.
15. classify the following as either element (e), compound (c) or mixture (m):

a. iron
b. oxygen
c. air
d. milk
e. baking soda (nahco₃)
f. vinegar (acetic acid and water)
g. carbon dioxide (co₂)
h. water (h₂o)
i. rust (fe₂o₃)
j. table sugar (c₁₂h)
k. soil
l. penny (pennies coated in copp)
m. helium

Explanation:

1. Matter can be combined physically and chemically. True.
2. Pure substances have fixed composition. So the statement "Pure substances have changing composition" is False.
3. Elements cannot be chemically broken - down into simpler substances. False.
4. Compounds can only be separated into simpler substances chemically, not physically. False.
5. Compounds are pure substances formed by chemical combination of elements and have different physical and chemical properties from individual elements. True.
6. Compounds have distinct physical and chemical properties due to their chemical - bonding and composition. True.
7. Mixtures are physical combinations of substances and can be separated by physical means. False.
8. Pure water is a compound, not a mixture. False.
9. Tap water contains dissolved minerals and gases, so it is a homogeneous mixture. True.
10. In a salt - water mixture, salt retains its individual properties. True.
11. Oil and water do not mix uniformly, it is a heterogeneous mixture. False.
12. In a homogeneous mixture, individual elements are not visible. False.
13. A solution is a homogeneous mixture. False.
14. Sugar dissolved in coffee is a solution (homogeneous mixture). True.

For classification:

• a. Iron is an element (E) as it is a pure substance made of one type of atom.
• b. Oxygen is an element (E) for the same reason.
• c. Air is a mixture (M) of various gases like nitrogen, oxygen, carbon - dioxide etc.
• d. Milk is a mixture (M) containing water, fats, proteins etc.
• e. Baking soda ($NaHCO_3$) is a compound (C) as it is made of different elements chemically bonded.
• f. Vinegar (acetic acid and water) is a mixture (M).
• g. Carbon dioxide ($CO_2$) is a compound (C).
• h. Water ($H_2O$) is a compound (C).
• i. Rust ($Fe_2O_3$) is a compound (C).
• j. Table sugar ($C_{12}H_{22}O_{11}$) is a compound (C).
• k. Soil is a mixture (M) containing minerals, organic matter etc.
• l. Penny (coated in copper) is a mixture (M) if considering the coating and the base material, or can be considered an alloy (mixture) if made of multiple metals.
• m. Helium is an element (E).

Answer:

1.

• 1. T
• 2. F (Pure substances have fixed composition.)
• 3. F (Elements cannot be chemically broken down into simpler substances.)
• 4. F (Compounds can only be separated into simpler substances chemically.)
• 5. T
• 6. T
• 7. F (Mixtures are physical combinations of substances.)
• 8. F (Pure water is a compound.)
• 9. T
• 10. T
• 11. F (Oil and water is a heterogeneous mixture.)
• 12. F (You cannot see individual elements in a homogeneous mixture.)
• 13. F (A solution is a homogeneous mixture.)
• 14. T

2.

• a. E. Iron
• b. E. Oxygen
• c. M. Air
• d. M. Milk
• e. C. Baking soda ($NaHCO_3$)
• f. M. Vinegar
• g. C. Carbon dioxide ($CO_2$)
• h. C. Water ($H_2O$)
• i. C. Rust ($Fe_2O_3$)
• j. C. Table sugar ($C_{12}H_{22}O_{11}$)
• k. M. Soil
• l. M. Penny
• m. E. Helium