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) + 2H+ (aq) --> Zn 2+ (aq) + H2O (l) + CO2 (g)

ii) Why excess zinc carbonate is used?

 

Is to ensure that all the hydrochloric acid is completely reacted, before filtering the excess unreacted zinc carbonate from the zinc chloride solution.

iii) Briefly explain how the zinc chloride crystals can be obtained.

Step 1: Add the excess zinc carbonate to a beaker of hydrochloric acid until there is excess zinc carbonate seen.

Step 2: Filter to remove the excess unreacted zinc carbonate.

Step 3: Evaporate the zinc chloride solution to remove the water and to obtain a saturated salt solution (heat slowly to prevent salt to jump out)

Step 4: Leave the hot saturated solution to cool down. When the hot saturated salt solution cools down, zinc chloride crystals is obtained.

 

 

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.

Potassium sulfate is a group (I) salt, colourless and soluble. Titration method is for group (I) and ammonium salt. Therefore, the salt can be prepared using titration method

ii)Write an ionic equation for the reaction.

2H+ (aq) + OH- (aq) à H2O

Q3 An unknown green solution is heated with a piece of aluminum foil and sodium hydroxide solution.

(i) The gas produced turns damp red litmus paper blue.  Name the gas evolved


Its ammonia gas


(ii) This is a confirmatory test for an anion.  Name this anion.


The anion is nitrate ion (NO3 -)


(iii) Give a possible cation which gives the green solution.

Q2 Ammonium sulfate is heated with sodium hydroxide.

(ii)  Describe a test for the gas

Hold a piece of damp red litmus paper over the mouth of the test tube. When the damp red litmus paper turns blue, it mean that ammonia gas is produce.

Q2 Ammonium sulfate is heated with sodium hydroxide

(i) Write a chemical equation (include state symbols) for the reaction.
 

•(NH4)2 SO4 (aq) + 2NaOH (aq) --> Na2 SO4 (aq) + 2H2O (l) + 2NH3 (g)

1. Zinc nitrate reacts with aqueous ammonia (NH4OH) to form a salt and a base.

(iv) Write an ionic equation for the reaction.  

 Zn 2+ (aq) + 2OH - (aq) -> Zn(OH)2 (s)

Q1 Zinc nitrate reacts with aqueous ammonia (NH4OH) to form a salt and a base.

(iii) Write a chemical equation for the reaction (include state symbols).

 Zn(NO3)2 (aq) + 2NH4OH (aq) --> 2NH4NO3 (aq) + Zn(OH)2 (s)