Uses and reactions of acids5

ZZZ

2014-08-08 9:21 pm

extracted from long question part:
1. Why does it mention that NaOH is a ACTIVE INGREDIENT OF drain cleanser instead of just saying that it can be used to manufacture drain cleanser?

2. State whether CO2 gas will be liberated and write a chemical equation involved for each of the following:
(a) Heating sodium carbonate
(b) Adding calcium to water
(c) Heating zinc oxide with carbon
(d) Mixing CaO with dilute HNO3

3. Why is H2SO4 used in the treatment of metal surfaces in the elctroplating industry?

回答 (1)

andrew

2014-08-08 10:08 pm

✔ 最佳答案

1.
Drain cleanser contains sodium hydroxide. The cleansing effect is due to the sodium hydrogen in the cleanser. It is because sodium hydrogen can hydrolyze grease into soap and glycerol, and they are soluble in water and thus can be removed by rinsing with water. Besides, the soap formed can also remove the unreacted grease by emulsification.

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2.
(a)
No CO2 gas is liberated.
There is no reaction, and thus there is no chemical equation.

(b)
No CO2 gas is liberated.
Ca + 2H2O → Ca(OH)2 + H2

(c)
CO2 gas is liberated.
2ZnO + C → Zn + CO2

(d)
No CO2 gas is liberated.
CaO + 2HNO3 → Ca(NO3)2 + H2O

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3.
A layer of metal oxide is formed on the surface of metal. H2SO4 can react with the metal oxide to form soluble metal sulphate and water. The soluble metal sulphate can be removed by rinsing with water.

2014-08-08 16:16:06 補充：
手民之誤，第一題的 sodium hydrogen 應是 sodium hydroxide 之誤。

參考: andrew, andrew

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