Friday 23 September 2011
Q5. Excess zinc carbonate is added to hydrochloric acid in the preparation of zinc chloride salt.
(i) Write an ionic equation for the reaction.
Ans: ZnCO3(S)+2H+(aq) = Zn2+(aq)+CO2(G)+H2O(L)
(ii) Why excess zinc carbonate is used?
Ans: It is to ensure that the excess zinc carbonate has completely reacted with hydrochloric acid to form calcium chloride.
(iii) Briefly explains how the zinc chloride crystals can be obtained.
Ans:
First, add the excess zinc carbonate solid to the dilute hydrochloric acid until excess zinc carbonate is formed.
Second, filter to remove the excess unreacted zinc carbonate solid.
Third, evaporate the remaining solution to remove water and make a saturated salt solution.
Last, leave the hot saturated solution to cool down and zinc chloride crystals will be form.
(i) Write an ionic equation for the reaction.
Ans: ZnCO3(S)+2H+(aq) = Zn2+(aq)+CO2(G)+H2O(L)
(ii) Why excess zinc carbonate is used?
Ans: It is to ensure that the excess zinc carbonate has completely reacted with hydrochloric acid to form calcium chloride.
(iii) Briefly explains how the zinc chloride crystals can be obtained.
Ans:
First, add the excess zinc carbonate solid to the dilute hydrochloric acid until excess zinc carbonate is formed.
Second, filter to remove the excess unreacted zinc carbonate solid.
Third, evaporate the remaining solution to remove water and make a saturated salt solution.
Last, leave the hot saturated solution to cool down and zinc chloride crystals will be form.
what we could have been, 06:22.
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.
Ans: Potassium sulfate is soluble salt, so it cannot be prepared by precipitation method. For group (I) and ammonium salt, titration method is used. Potassium sulfate is a group (I) salt, hence it can be prepared using titration method.
(ii) Write an ionic equation for the reaction.
Ans: H+ (aq) + OH- (aq) = H2O (L)
(i) Explain why this method is recommended for the preparation for this salt.
Ans: Potassium sulfate is soluble salt, so it cannot be prepared by precipitation method. For group (I) and ammonium salt, titration method is used. Potassium sulfate is a group (I) salt, hence it can be prepared using titration method.
(ii) Write an ionic equation for the reaction.
Ans: H+ (aq) + OH- (aq) = H2O (L)
what we could have been, 06:18.
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.
Ans: The gas evolved is ammonia gas.
ii) This is a confirmatory test for an anion. Name this anion.
Ans: The ion is nitrate.
iii) Give a possible cation which gives the green solution.
Ans: Iron (II), Fe2+
Sodium hydroxide solution.
i) The gas produced turns damp red litmus paper blue. Name the gas evolved.
Ans: The gas evolved is ammonia gas.
ii) This is a confirmatory test for an anion. Name this anion.
Ans: The ion is nitrate.
iii) Give a possible cation which gives the green solution.
Ans: Iron (II), Fe2+
what we could have been, 06:13.
Sunday 18 September 2011
Q2. Ammonium Sulfate is heated with Sodium hydroxide.
(i) Write a chemical equation for the reaction (include state symbols).
Ans: (NH4)2SO4 (s) + NaOH (aq) = Na2SO4(s) + 2NH3(g) + H2O(l)
(ii) Describe a test for the gas.
Ans: ( Ammonia gas) Turn damp red litmus paper blue.
(i) Write a chemical equation for the reaction (include state symbols).
Ans: (NH4)2SO4 (s) + NaOH (aq) = Na2SO4(s) + 2NH3(g) + H2O(l)
(ii) Describe a test for the gas.
Ans: ( Ammonia gas) Turn damp red litmus paper blue.
what we could have been, 01:22.
Q1. Zinc nitrate reacts with aqueous ammonia(NH4OH) to form a salt and a base.
(i) Name the salt and the base.
Ans: The salt formed is Ammonium nitrate (NH4NO3), the base formed is Zinc hydroxide(Zn(OH)2).
(ii)Describe the observation for the reaction.
Ans: A white precipitation is formed when zinc nitrate reacts with aqueous ammonia.
(iii)Write a chemical equation for the reaction. ( include state symbols)
Ans: NH4OH (aq) + 2Zn(NO3)2 (aq)= Zn(OH)2 (s) + NH4NO3(aq)=
(iv) Write an ionic equation for the reaction.
Ans: Zn2+ (aq) + 2OH-(aq)= Zn(OH)2 (s)
(i) Name the salt and the base.
Ans: The salt formed is Ammonium nitrate (NH4NO3), the base formed is Zinc hydroxide(Zn(OH)2).
(ii)Describe the observation for the reaction.
Ans: A white precipitation is formed when zinc nitrate reacts with aqueous ammonia.
(iii)Write a chemical equation for the reaction. ( include state symbols)
Ans: NH4OH (aq) + 2Zn(NO3)2 (aq)= Zn(OH)2 (s) + NH4NO3(aq)=
(iv) Write an ionic equation for the reaction.
Ans: Zn2+ (aq) + 2OH-(aq)= Zn(OH)2 (s)
what we could have been, 00:57.
Friday 8 July 2011
Comments:
1) Junwei- He explained his answers clearly, & he included the diagrams of sodium atom and sodium ions, this can help others who don't know to differentiate between atom and ions.
2) Kaiqi- She explained it clearly and i like her answers for question three, it is detailed and easy to understand. The diagrams are clear and helps me to understand better.
3) Xueting- She explained her answers in details and it is informative. She included diagrams and even her own drawing to explain her answers. Her drawings are neat and tidy, which make it easy to understand.
1) Junwei- He explained his answers clearly, & he included the diagrams of sodium atom and sodium ions, this can help others who don't know to differentiate between atom and ions.
2) Kaiqi- She explained it clearly and i like her answers for question three, it is detailed and easy to understand. The diagrams are clear and helps me to understand better.
3) Xueting- She explained her answers in details and it is informative. She included diagrams and even her own drawing to explain her answers. Her drawings are neat and tidy, which make it easy to understand.
what we could have been, 01:22.
what we could have been, 01:07.
