chem question(practice paper)

👨🏻‍🏫 學術台化學

[匿名]

2012-01-20 11:42 pm

a. suugest one wat to show that a saturated solution has been obtained (in the step of heating the filtrate until it becomes satureated)?

b.explain why a little amount of cold distilled water is used to wash the crystals. (2 marks)

c.state the principle behind the use of argon in preserving wine.

d. Helium gas is also chemically unreactive. suggest why helium is not used for preserving wine in an opened bottle.

e. another way of wine preservation involves pumping air out from an opened bottle of wine and then stoppering the bottle. suggest one possible drawback of preserving wine in this way.

更新1:

a. until no more solute is dissolved in the solution b. since some impurities may adhere to the surface of the crystal, a little amount of cold distilled water is used to remove the soluble impurities c.驅除紅酒入面的空氣? d.helium的density低過O2 in the air,所以helium不會sink下去,所以repel唔到酒瓶入面的air? e. 有d細菌入去酒瓶?

回答 (3)

知識就是力量

2012-01-21 5:03 am

✔ 最佳答案

Have you done it yet?

2012-01-20 21:03:38 補充：
a. Dip a glass rod into the solution and take it out, observe whether there are any small crystals formed on the surface of glass rod.
b. There are two main points: 1. Little amount ; 2. Distilled water (for 2 marks)
Little amount is used to prevent the crystal from dissolving into the water again
Remove the impurities of solution attached on the surface of crystal
c. Argon is denser than air. When argon is injected into the jar, the argon sinks, prevent the wine from being contacted with air (containing oxygen). So the wine is prevented from being oxidized.
d. Yes, as you have mentioned. There will be contact between the air and the wine.
e. Guess: The atmospheric pressure is greater than the pressure inside the glass bottle of wine, as a result the glass bottle may leak.

參考: Knowledge is power.

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己式庚辛

2012-01-21 3:59 am

Post up yours so that we can discuss on them.

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[匿名]

2012-01-21 3:21 am

yes,,but i don't sure the answer of these questions

2012-01-20 20:45:09 補充：
已加個人答案,不知對不對

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