CHEM MC - Ans.fyi 參考答案

CHEM MC

Kyy010203

2010-11-20 5:33 am

Question 1:
When ethanol vapour is allowed to pass over heated porcelain, it is converted into
A. ethane
B. ethene
C. ethanoic acid
D. ethyl ethanoate
Question 2:
Bromine in tetrachloromethane reacts with an organic compound X to form a
single product Y. From the information alone, which of the following conclusions
can you draw?
A. Compound X is alkene.
B. Compound X is an unsaturated compound.
C. Compound Y is a saturated compound.
D. Compound Y is an unsaturated compound.
Question 3:
The boiling points of some hydrocarbons are given in the table below:
Hydrocarbon Boiling Point (oC)
Ethane -89
Ethene -104
Propene -48
If a mixture of these three hydrocarbons at -115oC is allowed to warm up gradually
to -70oC,
A. ethene will remain in liquid state.
B. propene will remain in liquid state.
C. ethane and ethene will remain in liquid state.
D. ethene, ethane and propene will remain in gaseous state.
Question 4:
The hydrocarbons ethene, propene and but-1-ene
(1) have the same general formula.
(2) are unsaturated and form compounds by addition.
(3) are gases at room temperature.
A. (1) and (2) only
B. (1) and (3) only
C. (2) and (3) only
D. All of them
2
Question 5:
Which of the following descriptions is not true for ethene?
A. It burns with a luminous flame.
B. It can be polymerized.
C. It is a liquid at room temperature and pressure.
D. It decolourizes bromine water.
Question 6:
Ethene burns with a more luminous and smoky flame than ethane does because
ethene
A. has a higher boiling point than ethane.
B. has a lower boiling point than ethane.
C. contains a higher percentage of carbon than ethane.
D. contains a lower percentage of carbon than ethane.
Question 7:
Ethene can be distinguished from ethane by
(1) bubbling the gas through bromine in tetrachloromethane.
(2) bubbling the gas through acidified potassium permanganate solution.
(3) burning the gas in air.
A. (1) and (2) only
B. (1) and (3) only
C. (2) and (3) only
D. All of them

回答 (1)

用戶26240

2010-11-20 6:33 am

✔ 最佳答案

Question 1:
The answer is: B. ethene

On the hot surface of porcelain, ethanol is dehydrated to give ethene.
CH3CH2OH → CH2=CH2 + H2O

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Question 2:
The answer is: B. Compound X is an unsaturated compound.

A is incorrect.
X may be an alkene or an alkyne.

B is correct.
Either an alkene or an alkyne is an unsaturated compound.

C and D are incorrect.
The product Y is saturated if all the multiple bonds are reacted, but is unsaturated if some of the multiple bonds have not yet reacted (e.g. Y contains benzene ring which is unsaturated but does not react with bromine).

=====
Question 3:
The answer is: B. propene will remain in liquid state.

A hydrocarbon is a liquid at a temperature lower than its boiling point, but is a gas at a temperature higher than its boiling point.
At -115°C, all of the three hydrocarbons are in liquid state.
At -70°C, Ethane and ethene are in gaseous state, while propene is in liquid state.

=====
Question 4:

The answer is: D. All of them

(1) is correct.
The general formula of ethene (CH2=CH2), propene (CH2=CHCH3) and but-1-ene (CH3=CHCH2CH4) is CnH2n.

(2) is correct.
They all contain C=C double bond, and thus can undergo addition reaction.

(3) is correct.
They are gases at room temperature and pressure.

=====
Question 5:

The answer is: C. It is a liquid at room temperature and pressure.

Ethene is a gas at room temperature and pressure.

=====
Question 6:

The answer is: C. contains a higher percentage of carbon than ethane.

In an ethane (C2H6) molecule, there are 2 C atoms out of the 8 atoms.
In an ethene (C2H4) molecule, there are 2 C atoms out of the 6 atoms.

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Question 7:

The answer is: D. All of them

(1) is correct.
Ethene can decolorize the bromine solution, but ethane cannot.

(2) is correct.
Ethene can decolorize the acidified potassium permanganate solution.

(3) is correct.
Ethene burns with a sootier flame.

參考: 土扁

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