Chung Cheng High School (Main)

Chung Cheng High School (Main) Pure Chemistry ANSWERS (Acids, Bases & Salts) 25

Duration: 45 minutes

Name: ______Class: ______Index No.: ____ Date: ______

Section A (MCQ – 8 marks)

1 The pH scale below shows the position of five aqueous solutions P, Q, R and S of equal concentrations. P Q R S 1 7 14 pH scale What could the aqueous solutions be?

Ethanoic acid Sulfuric acid Ammonia Sodium Chloride A P Q S R B Q P R S C R S P Q D Q P S R ( D )

2 A solution of sodium hydroxide containing universal indicator was bubbled with carbon monoxide. What will be the colour of the indicator after a long period of time? A Blue B Green C Purple D Red ( C )

3 Which one of the following lists consists of an acid, a base and a salt?

A H2SO4, NaOH, ZnO B HCl, HNO3, BaSO4 C HCl, MgO, Na2CO3

D K2SO4, H2O, NH4Cl ( C )

4 Which of the following oxides reacts with aqueous sodium hydroxide to give a salt? A Zinc oxide B Iron(II) oxide C Copper(II) oxide D Calcium oxide ( A )

5 Which of the following should not be used with hydrochloric acid to prepare zinc chloride? A Zinc carbonate B Zinc hydroxide C Zinc metal D Zinc nitrate ( D )

1 6 An experiment was conducted using the apparatus as shown below. Liquid X is an aqueous solution which has the ability to conduct electricity.

Bulb

Platinum Platinum

Liquid X

Which substance, when added into Liquid X, would cause the bulb to light up the brightest? A Ammonia B Ethanoic acid C Sulfuric acid D Sugar ( C )

7 There are two unlabelled test-tubes. One contains sodium carbonate solution and the other contains sodium chloride solution. Which test would you use to identify the solutions? A Add sodium hydroxide solution B Add dilute hydrochloric acid C Add aqueous ammonia D Add lead(II) nitrate solution ( B )

8 What gas is produced when magnesium reacts with dilute hydrochloric acid? A A gas that extinguish a lighted splint with a “pop” sound. B A gas that forms white precipitate in limewater. C A gas that turns moist blue litmus red. D A gas that turns moist red litmus blue. ( A )

2 Section B (Structured Questions – 17 marks)

9 Answer the questions (a) to (d) using the list of substances below.

Ammonium chloride Ammonia Carbon monoxide Carbon dioxide Chlorine Dilute hydrochloric acid Dilute nitric acid Water Dilute sulfuric acid Copper(II) sulfate Silver chloride Hydrogen

[A substance may be used once, more than once or not at all]

(a) An acid which reacts with lead(II) carbonate to give a gas and a soluble salt. Dilute nitric acid

(b) A salt that can be prepared by precipitation. Silver chloride

(d) A gas that is produced when ammonium sulfate crystals is warmed gently with aqueous sodium hydroxide. Ammonia [4]

10 Hydrochloric acid is a strong acid while ethanoic acid is a weak acid. (a) Describe a simple test to show which is the strong acid and which is the weak acid. Test the acids using pH meter/pH paper; a strong acid will give a lower pH than a weak acid. OR Add a few drops of universal indicator into each acid. A strong acid will turn indicator red while a weak acid will turn indicator orange/yellow [2] Note: Acid don’t change colour

(b) Describe the difference between strong and weak acids. [2] A strong acid is a compound that ionises completely in water to form hydrogen ions while a weak acid is one that ionises partially to form hydrogen ions. Note: ions don’t ionize!

(c) Explain why hydrochloric acid should not be used for removing limescale from steel pipes. [1] Being a strong acid, hydrochloric acid is more likely to react with iron in the pipe.

3 11 Two investigations were made between Reaction A and B.

Reaction A: dilute sulfuric acid + magnesium ribbon Reaction B: dilute sulfuric acid + platinum

(a) (i) Based on your knowledge in Chemistry, which reaction(s) will take place? Give a reason for your choice. [1] Reaction A Magnesium is a reactive metal but not platinum.

(ii) Describe your observation, if any, for Reaction A. [2] Effervescence, magnesium ribbon dissolves

(b) State one use of sulfuric acid. [1] Any one of the following - Manufacture of fertilizers - Manufacture of detergents - As electrolyte inside car batteries

12 Describe how you will prepare and obtain pure dry sample of the following salts: (Name the reagents used and describe the procedure)

(a) Lead(II) sulfate [2] Mix aqueous lead(II) nitrate with aqueous sodium sulfate Filter the mixture Wash the residue with distilled water Dry the salt between filter papers

(b) Copper(II) sulfate [2] Add excess copper(II) oxide to sulfuric acid Filter to remove excess copper(II) oxide Heat filtrate till saturated. Allow the solution to cool Filter to obtain crystals formed and dry between filter papers