Hwa Chong Institution
Acids, Bases and Salts (Worksheet 3)
Name: __________________ (
)
Date: ___________________
Class: ___________________
Section A:
Answer all the questions in this section in the brackets provided
1. Which of the following salts cannot be prepared with a dilute acid and a metal?
A.
B.
C.
D.
Copper(II) sulfate
Zinc chloride
Magnesium sulfate
Calcium nitrate
( A )
2. Which of the following pairs reacts to give a precipitate when their aqueous solutions are
mixed?
A. Sodium hydroxide and sulphuric acid
B. Silver nitrate and potassium iodide
C. Calcium chloride and barium nitrate
D. Magnesium nitrate and ammonium chloride
( B )
3. Which of the following is best used for preparing calcium sulfate?
A. Adding calcium oxide to dilute sulfuric acid.
B. Adding calcium oxide to carbonic acid followed by ammonium sulfate.
C. Adding calcium oxide to nitric acid followed by sulfuric acid.
D. Adding calcium chloride to barium sulfate.
( C
)
4. Which of the following gases will not turn moist blue litmus paper red at all?
A. Nitrogen monoxide
B. Chlorine
C. Carbon dioxide
D. Sulfur trioxide
( A )
5. Two unknown solutions, containing lead(II) ions and zinc ions respectively are to be
distinguished. Which methods will not be appropriate?
A. Adding sulfuric acid.
B. Adding potassium iodide.
C. Adding hydrochloric acid.
D. Adding sodium hydroxide.
( D )
6. Metal X reacts with dilute nitric acid and dissolves to give a colourless solution. Upon
addition of potassium hydroxide, a white precipitate is formed, which dissolves in excess
potassium hydroxide. What could X be?
A. Aluminium
B. Sodium
C. Calcium
D. Barium
( A )
7. When a solid Y was heated strongly for some time in a test tube, a brown and pungent
gas was evolved. At the same time, when a glowing splint was inserted in the test tube, it
rekindled. Which of the following is most likely Y?
A.
B.
C.
D.
Aluminium sulfate
Sodium carbonate
Zinc nitrate
Potassium chloride
(
C
)
8. The following table shows some properties of four chlorides. Which of the following
could be zinc chloride?
Chloride
A.
B.
C.
D.
Colour
White
Blue
Green
White
Solubility in water
Soluble
Soluble
Soluble
Insoluble
Method of preparation
Metal and acid
Insoluble base and acid
Metal and acid
Precipitation
( A )
9. The following observations were made when an aqueous solution of R was tested.
Reagent added
Colour of precipitate
Acidified aqueous silver nitrate
Yellow
Aqueous potassium hydroxide
Blue
Which of the following could be R?
A. Copper(II) chloride
B. Iron(II) iodide
C. Iron(II) chloride
D. Copper(II) iodide
(
D )
10. When a solution M was added to aqueous ammonium chloride and the mixture was
heated, a gas which turned red litmus paper blue was produced. What ion is present in M?
A.
B.
C.
D.
H+
OHCO32SO32( B )
Section B:
Answer all the questions in this section in the spaces provided
1. Describe what is observed in the following reactions:
a. Aqueous sodium hydroxide is added to zinc chloride dropwise until in excess.
A white precipitate was formed which dissolved in excess sodium hydroxide.
b. Aqueous lead(II) nitrate is added to aqueous barium chloride.
A white precipitate of lead(II) chloride was formed.
c. Aqueous copper(II) sulphate is heated strongly until dry.
Blue crystals of hydrated copper(II) sulfate were obtained which turned into a white solid
on prolonged heating.
2. When orange crystals of ammonium dichromate(VI), (NH4)2Cr2O7, are heated in a test
tube, the products are green chromium(III) oxide, nitrogen and water. Name the reagents
that you would use to test the following and give the corresponding observations:
a) To determine that the orange crystals contain ammonium ions.
Sodium hydroxide is added to the solution of ammonium dichromate(VI). Upon gentle
heating, if a pungent colourless gas (ammonia) was evolved which turned red litmus
paper blue, then the orange crystals contain ammonium ions.
b) To determine that the reaction products contain water.
Heat the compound gently. If a colourless odourless gas was obtained which turns blue
cobalt(II) chloride paper pink, water is present. A colourless liquid is also observed to
condense on the cooler parts of the test tube.
3. Describe how you would prepare pure ammonium chloride, stating reagents used clearly.
Titration of aqueous ammonia and hydrochloric acid using methyl orange as an indictor.
Steps to titration can be found in your notes/textbook.
4. The instructions below show the steps to preparing magnesium sulphate. There are 2
major errors in the set of instructions. Identify the errors and correct them accordingly:
1. Add one spatula of magnesium chloride to 50 cm3 of dilute sulfuric acid.
2. When it has reacted, add further amounts until no more dissolves.
3. Filter the mixture.
4. Heat the filtrate using a Bunsen flame until it is completely dry.
5. Collect the crystals.
Error 1: In step 1, both magnesium chloride and magnesium sulfate are soluble in water,
so we cannot use magnesium chloride. Instead, magnesium carbonate or magnesium
ribbons can be used.
Error 2: In step 4, heating the filtrate until it is completely dry will give the anhydrous
magnesium sulfate and might cause the compound to decompose. Instead heat to
saturation and perform crystallization.
5. Barium sulfate can be prepared from the reaction between aqueous barium nitrate and
dilute sulfuric acid.
a) Write the equation for this reaction.
Ba(NO3)2(aq) + H2SO4(aq)  BaSO4(s) + 2HNO3(aq)
b) Describe how you will prepare barium sulfate using this method.
By precipitation. The steps to precipitation can be found in your notes/textbook.
c) A sample of barium sulfate was contaminated with some barium carbonate. Suggest a
test to confirm that it is indeed contaminated by a carbonate.
Add dilute nitric acid to the solid. If there is effervescence, and a colourless odourless gas
was produced which gives a white precipitate with limewater, it shows the presence of a
carbonate.
6. You are given sulfuric acid and hydrochloric acid of the same concentration. Describe
briefly how you will determine that sulfuric acid is dibasic whereas hydrochloric acid is
monobasic.
Titration using sodium hydroxide and methyl orange as an indicator. Sulfuric acid will
require two times the volume of sodium hydroxide as compared to hydrochloric acid to
completely neutralise. Hence, the acid which requires more sodium hydroxide to produce
a colour change in the indicator is dibasic.
7. Compound X reacts with nitric acid to give a colourless gas that gave a white precipitate
Y with limewater. Aqueous ammonia was added dropwise to the colourless solution that
remained. A white precipitate was formed which dissolved in excess ammonia.
a) Deduce the identity of X and explain how you got to the conclusion.
Zinc carbonate. The colourless gas produced which gave a white precipitate with
limewater must indicate presence of carbonate ions. The only cation that will give a white
precipitate with aqueous ammonia that dissolves in excess ammonia is Zn2+. Hence X
must be ZnCO3.
b) What is Y?
Y is calcium carbonate.
c) What will you observe if aqueous sodium hydroxide is added to X?
A white precipitate is formed which dissolves in excess sodium hydroxide.
8. Suggest and describe how you would prepare lead(II) sulfate from lead(II) carbonate.
(Hint: It might take more than one step.)
1. Add excess lead(II) carbonate to nitric acid until no more dissolves.
2. Filter the solution and collect the filtrate.
3. The filtrate now contains only lead(II) nitrate. Add sulfuric acid to lead(II) nitrate
solution. A white precipitate of lead(II) sulfate will be formed.
4. Filter the solution and collect the residue. Wash with cold distilled water and dry to
obtain pure crystals of lead(II) sulfate