Chem 高手請答!

2008-03-13 9:17 am

1. Magnesium oxide 同 hydrogen heat 時會唔會有reaction?

2. Which statement about acids is correct?

A. All electrolytes that give out H+ in water are acids
B.Compounds that contain ionizable hydrogen ion are acids.
C.Electrolysis of the aqueous solution of acids always gives hydrogen gas
at the cathode .
D.All acids are formed from non-metal oxides.

Ans:C

我想問點解C 會岩?? Electrolysis唔係仲要睇埋佢用咩electrode ga 咩??
例如用copper electrode ge 話,就唔會有H2 gas release ,會係
copper deposited on cathode

3. Which is the most common ingredient of anti-acids?
A.Magnesium hydroxide
B.Potassium hydroxide
C.Calcium oxide
D.Sodium carbonate

Ans :A

我想問點解 C and D 都唔得?
anti-acids係唔係一定要包含Magnesium至得??

更新1:

我都係唔多明第2題如果用copper electrode ,,點解仲會有H2 gas discharge at cathode 仲有我想問多少少野 1.CuO + 2HCl ----> CuCl2 + H2O 呢個係neutralization 點解?? Copper(II) oxide 係base 黎咩??

更新2:

2.我想問點解 50cm3 of 1M HCL react with 50 cm3 of 1 M NaOH 同 200cm3 of 1M HCL react with 200 cm3 of 1 M NaOH rise ge temperature 係一樣?? 如果acid 同 alkali 都用2M 會唔會唔同個result? thz!

回答 (1)

Uncle Michael

2008-03-13 8:45 pm

✔ 最佳答案

1.
There is no reaction between magnesium oxide and hydrogen.
This is because the reducing power of hydrogen is not strong enough to reduce magnesium oxide.

2.
In C, the electrolyte is an acid solution. The acid is ionized to give H+(aq) and the corresponding anions, and water is slightly ionized to give H+(aq) and OH- (aq) ions. H+(aq) ions are the only cations in the solution. Therefore, only H+(aq) ions migrate to the cathode, and discharge at the cathode to give H2(g).
When copper is used as the anode, it may dissolved (be oxidized) to give Cu2+(aq) ions. When copper is used as the cathode, the copper would never change.
I think you have made confusion that copper is deposited at the cathode in electrolysis of a solution containing Cu2+(aq) ions.

3.
Anti-acid is mild base which can neutralized excess acid in gastric juice, and should not cause bad side effect to human. Anti-acid may contain magnesium or may not.
C is incorrect, because CaO is a strong base which gives off a large amount of heat when neutralization with an acid.
D is incorrect, because Na2CO3 would give off CO2 gas when neutralization with an acid. Too much CO2 gas formed in stomach will cause an uncomfortable feeling. Besides, It is not advisable for human to have too much sodium salt.

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