set-up: http://www.flickr.com/photos/83350318@N07/7636062666/in/photostream
1.The set-up above is used to collect dry ammonia gas.
a)Give the equation for the reaction in A. (1)
b)Explain two necessary modifications that should be made to the set-up, such that ammonia gas can be collected successfully. (4)
c)Assume that the modifications in b) have been made, state the function of B.(1)
d)Explain if calcium hydroxide solution can be used in place of sodium hydroxide. (3)
2.The same set-up is used to collect dry carbon dioxide gas.
a)State a change that should be made in A. (1)
b)Hence, give the equation for the reaction in A. (1)
c)If there is no change in C, a change in pH of the water occurs. Explain this change. (3)
d)Suppose carbon dioxide gas is collected successfully, suggest a chemical test to confirm its identity. (2)
please try to ans the questions; you may also point out any mistakes. thanks loads.
自製 Chem LQ (Acids and Alkalis)
2012-07-25 2:21 am
回答 (2)
2012-07-25 2:55 am
✔ 最佳答案
1.a)
(NH4)2CO3(s) + 2NaOH(aq) → Na2CO3(aq)+ 2H2O(l) + 2NH3(g)
b)
In B, a drying tube of calcium oxide should be used instead of concentrated H2SO4. This is because acidic concentration H2SO4absorbs basic NH3.
In C, the gas should be collected by using upward delivery (downward displacementof air) or using a syringe. This isbecause NH3 is very soluble in water.
c)
B is used to dry NH3 gas.
d)
Yes, (NH4)2CO3 can also react with Ca(OH)2solution to give NH3 gas.
However, the yield is very low. This isbecause the solubility of Ca(OH)2 is low and thus the Ca(OH)2solution is dilute. Besides, if a largevolume of calcium hydroxide is used, the NH3 gas would dissolve muchin the aqueous solution.
(You may answer "No" with the above reasons.)
2.
a)
Hydrochloric acid (HCl(aq)) should be used instead of NaOH(aq).
b)
(NH4)2CO3(s) + 2HCl(aq) → 2NaCl(aq) + H2O(l)+ CO2(g)
c)
Carbon dioxide dissolves in water to give a slightly acidic solution.
d)
Carbon dioxide gas turns lime water milky.
2012-07-25 23:55:15 補充：
The answer 2 d) should be changed as :
No.
This is because an insoluble layer of calcium carbonate solid is formed coating on the surface of the lumps of ammonium carbonate, and thus reaction stops as the reactants are separated by the calcium carbonate layer.
2012-07-26 22:35:53 補充：
2b) should be :
(NH4)2CO3(s) + 2HCl(aq) → 2NH4Cl(aq) + H2O(l)+ CO2(g)
參考: 賣女孩的火柴, 賣女孩的火柴, 賣女孩的火柴
2012-07-25 8:45 am
2b) Note the product
(NH4)2CO3 + HCl --> NH4Cl + ...
not NaCl
(NH4)2CO3 + HCl --> NH4Cl + ...
not NaCl
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