Friday, 23 September 2011 @08:58
Sorry, i tried to change the font. But it keep changing. I tried to make to more normal. Anyway, sorry.
@08:34
Q5 Excess zinc carbonate is added to hydrochloric acid in the preparation of zinc chloride salt.
(i) Write an ionic equation for the reaction.
Answer: ZnCO3(s) + 2HCl (aq) à ZnCl2(aq) + H20 (l) + CO2(g)
(ii) Why excess zinc carbonate is used?
Answer: Excess zinc carbonate solid can ensure that all the hydrcoholoric acid has react completely with the zinc carbonate. So only aqueous zinc chloride and water is in the solution. To make sure that hydrochloric acid has completely react with calcium carbonate to form zinc chloride.
(iii) Briefly explain how the zinc chloride crystals can be obtained.
Answer:
Step 1: Add excess zinc carbonate solid to a beaker of dilute hydrochloric acid until there is excess zinc carbonate left behind.
Step 2: Filter to remove the excess unreacted zinc carbonate solid.
Step 3: Evaporate the zinc chloride solution to remove the water and make a saturated salt solution.
Step 4: The hot saturated solution form zinc chloride crystals when it is cooled.
- Take From Chemistry Notes-
@08:25
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.
Answer: Titration method is used when the salt is double and is a Group (I) soluble salt. The reactants should be acid and alkali. Hence, titration method is recommended.
(ii) Write an ionic equation for the reaction.
Answer: H+ (aq) + OH- (aq) --> H2O (l)
@06:54
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.
Answer: Ammonia Gas
(ii) This is a confirmatory test for an anion. Name this anion.
Answer: Nitrate ( NO2+)
(iii) Give a possible cation which gives the green solution.
Answer: Iron(II) ( Fe2+).
@06:43
Q2 Ammonium sulfate is heated with sodium hydroxide. (i) Write a chemical equation (include state symbols) for the reaction.
Answer : (NH4)2SO4 (aq) + 2 NaOH (aq) --> Na2SO4 (aq)
+ 2 H2O (l) + 2 NH3 (g)
(ii) Describe a test for the gas.
Answer: The ammonia gas will turn damp red litmus paper to blue. Pungent smell will be detected.
Thursday, 22 September 2011 @23:24
Q1 Zinc nitrate reacts with aqueous ammonia (NH4OH) to form a salt and a base.
(i) Name the salt and the base.
Answer: The salt is ammonium nitrate and the base is zinc hydroxide.
(ii) Describe the observations for the reaction.
Answer: 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).
Answer:
Zn(NO3)2(aq) + 2NH4OH (aq) --> Zn(OH)2 (s) + 2NH4NO3 (aq)
(iv) Write an ionic equation for the reaction.
Answer:
Zn2+ (aq) + 2OH- (aq) --> Zn(OH)2 (S)