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Prepare for EYE : 5 Questions on Ionic Equations, Colours of Cations & Anions, Acids, Bases, Alkalis, Salts
Friday 23 September 2011

Q1 Zinc nitrate reacts with aqueous ammonia (NH4OH) to form a salt and a base. 
(i) Name the salt and the base.
The name of the salt is ammonia nitrate and the base is zinc hydroxide.

(ii) Describe the observations for the reaction.
White precipitate of zinc hydroxide will be form with ammonium hydroxide. This precipitate will dissolve in excess aqueous ammonia to form complex zinc ion, which give you a colourless solution.

(iii) Write a chemical equation for the reaction (include state symbols).
ZnNO3 (aq) + NH4OH (aq) -> ZnOH (s )+ NH4NO3 (aq)

  (iv) Write an ionic equation for the reaction. 
  Zn 2+ (aq) + 2OH - (aq) -> Zn(OH)2 (s)


Q2 Ammonium sulfate is heated with sodium hydroxide.

(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 over the cloud of gas released. If it turns blue, it is ammonia gasQ3 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.
Ammonia gas

 (ii) This is a confirmatory test for an anion.  Name this anion. 
Nitrate ion  (NO3-).

 (iii) Give a possible cation which gives the green solution.
Iron(III) ion
Q4 Sulfuric acid is titrated with potassium hydroxide in the preparation of potassium sulfate salt. 

(i) Explain why this method is recommended for the preparation for this salt. 
 (ii) Write an ionic equation for the reaction.

Q5 Excess zinc carbonate is added to hydrochloric acid in the preparation of zinc chloride salt.

 (i) Write an ionic equation for the reaction.
ZnCO3 (s) + H+ (aq) > Zn+ (aq) + H2O(L) + CO2(g)

 (ii)  Why excess zinc carbonate is used?
To ensure that zinc carbonzte has fully reacted with hydrocloric acid.

 (iii) Briefly explain how the zinc chloride crystals can be obtained.Filter out the excess Zinc carbonate with the filter paper first from the solution so that zinc chloride solution will be left. to obtain the crystals, heat the solution gently to evaporate the water leaving us a saturated solution. When there is only little water left, take the saturated solution away from the fire, allowing it to cool down to form the zinc chloride crystals.
H+ (aq) + OH- (aq) > H2O (L)

 It is soluble Group I salt and hence by using titration method, we will be able to get the salt.