Question 1

Why is bromine ($$\mathrm{Br_2$}) $$dissolved in cyclohexane and not in water during hydrocarbon testing?

Accepted Answer

Because both cyclohexane and bromine are nonpolar, allowing bromine to dissolve.

Question 2

Which type of hydrocarbon reacts immediately with bromine solution, resulting in decolorization?

Accepted Answer

Alkenes

Question 3

Write the balanced equation for the reaction between hexane ($$\mathrm{CH_3CH_2CH_2CH_2CH_2CH_3}) $$and bromine ($$\mathrm{Br_2$}) $$under UV light.

Accepted Answer

$$\mathrm{CH_3CH_2CH_2CH_2CH_2CH_3 + Br_2$ \rightarrow CH_3CH_2CH_2CH_2CH_2CH_2Br + HBr}$$

Question 4

What is the role of ultraviolet (UV) light in the bromine substitution reaction with alkanes?

Accepted Answer

It acts as a catalyst to initiate the substitution reaction.

Question 5

During the potassium permanganate ($$\mathrm{$$KMnO_4$$}) $$test, which type of hydrocarbon reacts and causes the purple color to disappear?

Accepted Answer

Alkenes

Question 6

What is the main chemical difference between saturated and unsaturated hydrocarbons as detected by the potassium permanganate test?

Accepted Answer

Unsaturated hydrocarbons contain double or triple bonds, which react with $$\mathrm{$$KMnO_4$$}.$$

Question 7

A student adds $$\mathrm{$$KMnO_4$$} to $$two test tubes: one with hexane and one with cyclohexene. What observation should they expect?

Accepted Answer

Hexane remains purple, cyclohexene turns brown as the purple color disappears.

Question 8

Which gas is produced when calcium carbide ($$\mathrm{$$CaC_2$$}) $$reacts with water?

Accepted Answer

Acetylene ($$\mathrm{C_2H_2})$$

Question 9

Write the balanced equation for the reaction between calcium carbide ($$\mathrm{$$CaC_2$$}) $$and water.

Accepted Answer

$$\mathrm{$$CaC_2$$ + 2H_2O \rightarrow Ca(OH)_2 + C_2H_2}$$

Question 10

A hydrocarbon sample is tested with bromine water and potassium permanganate. The sample decolorizes both solutions. What type of hydrocarbon is most likely present?

Accepted Answer

Alkyne

Question 11

During the ignition test, which property is most commonly observed for alkanes?

Accepted Answer

They burn with a clean, non-sooty flame.

Question 12

Which observation indicates the presence of an aromatic hydrocarbon during the bromine test?

Accepted Answer

No change in bromine color.

Question 13

A student observes that a hydrocarbon is insoluble in water but dissolves in cyclohexane. What does this suggest about the hydrocarbon's polarity?

Accepted Answer

The hydrocarbon is nonpolar.

Question 14

Which test can be used to distinguish between an alkene and an alkane?

Accepted Answer

Potassium permanganate test

Question 15

If a hydrocarbon sample does not react with bromine in the dark but reacts under UV light, what type of reaction is occurring?

Accepted Answer

Substitution reaction

Question 16

Which of the following is a correct statement about the flammability of ethyne (acetylene)?

Accepted Answer

Ethyne burns with a very sooty flame.

Question 17

A student tests an unknown hydrocarbon and observes that it does not react with bromine or potassium permanganate. What is the most likely identity of the hydrocarbon?

Accepted Answer

Alkane

Question 18

Which of the following best explains why potassium permanganate is used to test for unsaturation in hydrocarbons?

Accepted Answer

It oxidizes double or triple bonds, causing the purple color to disappear.

Question 19

A mixture of calcium carbide and water produces a gas that is used in welding. What is the chemical formula of this gas?

Accepted Answer

$$\mathrm{C_2H_2}$$

Question 20

Which of the following reactions is an example of a substitution reaction?

Accepted Answer

$$\mathrm{CH_3CH_2CH_2CH_3 + Br_2$ \rightarrow CH_3CH_2CH_2CH_2Br + HBr}$$

Properties and Reactions of Hydrocarbons: Laboratory Study Notes

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