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Friday 23 September 2011
Qs and As on Ionic Equations, Colours of Cations & Anions, Acids, Bases, Alkalis, Salts @ 05:53
Q1) Zinc nitrate reacts with aqueous ammonia (NH4OH) to form a salt and a base.
Zinc nitrate + aqueous ammonia ---> Ammonium nitrate + Zinc hydroxide
(i) Name the salt and the base.
The salt is Ammonium nitrate, NH4NO3
The base is Zinc hydroxide, Zn(OH)2
(ii) Describe the observations for the reaction.
A white precipitate (Zinc hydroxide) is formed when Zinc nitrate solution is added to aqueous Ammonia solution.
(iii) Write a chemical equation for the reaction (include state symbols).
Zn(NO3)2 (aq) + NH3 (aq) --> NH4NO3 (aq) + Zn(OH)2 (s)
(iv) Write an ionic equation for the reaction.
Ionic Equation: Zn2+
(aq) + 2OH- (aq) --> Zn(OH)2 (s)
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Q2. Ammonium sulfate is heated with sodium hydroxide.
Ammonium sulfate + Sodium hydroxide --> Sodium sulphate + water + ammonia
(i) Write a chemical equation (include state symbols) for the reaction.
(NH4)2SO4 (aq) + 2NaOH
(aq) --> Na2SO4 (aq) + 2H2O (l) + 2NH3
(g)
(ii) Describe a test for the gas.
Use a damp red litmus paper. If it turns blue, it's ammonia gas.
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Q3. An unknown green solution is heated with a piece of aluminium foil and sodium hydroxide solution.
(i) The gas produced turns damp red litmus paper blue. Name the gas evolved.
The gas evolved is Ammonia gas.
(ii) This is a confirmatory test for an anion. Name this anion.
This anion is nitrate, NO−
3
3
(iii) Give a possible cation which gives the green solution.
Iron (III) ion.
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Q4. Sulfuric acid is titrated with potassium hydroxide in the preparation of potassium sulfate salt.
Sulfuric acid + Potassium hydroxide --> Potassium sulfate + water
(i) Explain why this method is recommended for the preparation for this salt.
Firstly, Potassium Sulfate is a Group(1) salt. Group(1) salts are all colourless soluble solutions, and thus, titration is require to determine the end-point of the neutralization between the acid and the alkali in preparation for this salt.
(ii) Write an ionic equation for the reaction.
H+2 (aq) + 2OH- (aq) --> 2H2O (l)
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Q5. Excess zinc carbonate is added to hydrochloric acid in the preparation of zinc chloride salt.
Zinc carbonate + Hydrochloric acid --> Zinc chloride + water + carbon dioxide
(i) Write an ionic equation for the reaction.
ZnCO3 (s) + 2H+ (aq) --> Zn2+ (aq) +
H2O (l) + CO2 (g)
(ii) Why excess zinc carbonate is used?
This is to ensure that all the Zinc Carbonate is completely reacted with the Hydrochloric acid to form Zinc Chloride. When there is excess black copper (II) oxide seen, I know that the reaction has stopped.
(iii) Briefly explain how the zinc chloride crystals can be obtained.
The
Zinc Chloride formed is dissolved in water to obtain the
solid crystals. Heat the Zinc Chloride solution until a saturated solution is achieved. By allowing the solution to
cool down, we can obtain the Zinc Chloride crystals.
............................The End :) ...............................
