CH 7 Physical Properties & 8 Separation Techniques

Question 1

Which of the following represents a chemical change?
A. Boiling water
B. Dissolving salt in water
C. Melting ice
D. Rusting of iron

Answer 1

D. Rusting of iron

Question 2

What happens to a liquid’s viscosity and surface tension as temperature increases?
A. Viscosity decreases, surface tension increases
B. Viscosity increases, surface tension increases
C. Viscosity increases, surface tension decreases
D. Viscosity decreases, surface tension decreases

Answer 2

D. Viscosity decreases, surface tension decreases

Question 3

Which compound below has the highest boiling point?
A. H₂
B. HBr
C. HI
D. HF

Answer 3

D. HF
HF forms hydrogen bonds, the strongest IMF among these, resulting in the highest boiling point.

Question 4

Which of the following would have the lowest boiling point?
A. Hexane
B. Butane
C. Isobutane
D. Pentane

Answer 4

C. Isobutane
More branching → lower surface area → lower boiling point.

Question 5

Which method is best for separating a solid like salt from a saltwater solution?
A. Decanting
B. Filtration
C. Evaporation
D. Chromatography

Answer 5

Evaporation
Explanation: Heat off the water and recover the salt (solute). Ideal for soluble solids.

Question 6

You are separating ethanol (BP 78°C) from water (BP 100°C). Which technique is most appropriate?
A. Chromatography
B. Simple distillation
C. Decanting
D. Extraction

Answer 6

B. Simple distillation
Use when BP difference is ≥25°C.

use fractional distillation when BP are close to eachother

Question 7

Which method is best to separate benzoic acid from an organic mixture using acid/base properties?
A. Chromatography
B. Simple distillation
C. Extraction
D. Evaporation

Answer 7

C. Extraction
Acid/base extraction allows you to isolate compounds by changing their solubility.

Question 8

Which technique is best to isolate colored dyes from ink based on polarity and solubility?
A. Fractional distillation
B. Filtration
C. Chromatography (TLC)
D. Extraction

Answer 8

C. Chromatography (TLC)
TLC separates compounds by polarity (Rf values) on a silica plate.

Question 9

How many atoms are in a simple cubic unit cell?
A. 1
B. 2
C. 4
D. 8

Answer 9

A. 1
in a Body centered - 2
in a Face centered - 4

Question 10

Which of the following would have the highest boiling point?
A. CH₄
B. CH₃CH₂OH
C. CH₃CH₃
D. CH₃OCH₃

Answer 10

B. CH₃CH₂OH
Ethanol (CH₃CH₂OH) can hydrogen bond, significantly increasing its boiling point.

Question 11

Which of the following will decrease the boiling point of a molecule?
A. More hydrogen bonding
B. Larger surface area
C. Branching of the carbon chain
D. Higher molecular weight

Answer 11

C. Branching of the carbon chain

Question 12

Which of the following has the lowest boiling point?
A. H₂O
B. HF
C. NH₃
D. HCl

Answer 12

D. HCl
HCl only has dipole-dipole interactions, not hydrogen bonding like the others.

Question 13

Which of the following will have a higher boiling point than water?
A. CO₂
B. CH₃CH₂OH
C. CH₄
D. NH₄⁺

Answer 13

B. CH₃CH₂OH

Question 14

Which of the following is an example of a physical change?
A. Iron rusting
B. Burning wood
C. Ice melting
D. Digestion of food

Answer 14

C. Ice melting

Question 15

Which best describes a chemical change?
A. Water boiling
B. Paper being shredded
C. Baking a cake
D. Salt dissolving in water

Answer 15

C. Baking a cake

Question 16

Which of the following does not involve a chemical change?
A. Decomposition of hydrogen peroxide
B. Condensation of steam
C. Combustion of methane
D. Oxidation of copper

Answer 16

B. Condensation of steam

Question 17

Which process is both irreversible and involves a chemical change?
A. Freezing water
B. Burning gasoline
C. Boiling alcohol
D. Breaking glass

Answer 17

B. Burning gasoline

Question 18

Which change would increase a liquid’s boiling point?
A. Decrease in atmospheric pressure
B. Hydrogen bonding between molecules
C. Increased vapor pressure
D. Molecular symmetry

Answer 18

B. Hydrogen bonding between molecules