Page 38 - ACE YR IGCSE A TOP APPROACH TO CHEM

(b) 2H ➞ 4H + 4e [1] • Paints
+
2
O + 4H + 4e ➞ 2H O [1] • Bleaches
+
2 2
(c) 2H + O ➞ 2H O [1] • Hydrochloric acid
2
2
2
(d) Energy gained to break the bonds = 1362 kJ/mol Sodium hydroxide
[1] Any one from: [1]
Energy lost to form the bonds = 1852 kJ/mol • Soaps
[1] • Detergents
Enthalpy change = –490 kJ/mol [1] • Textiles
(432 × 2) + 498 = 1362 kJ/mol • Paper
(463 × 4) = 1852 kJ/mol • Ceramics
Enthalpy change = energy gained to break the • Dyes
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bonds – energy lost to form the bonds • Medical drugs
= 1362 – 1852 8 (a) Oxygen [1]
= – 490 kJ/mol
Glowing splint [1]
(e) Advantage relight [1]
Any one from: [1] OH will lose electrons.
–
• No pollutant / Only water is formed 4OH ➞ O + 2H O + 4e
–
2
2
• Give out plenty of energy Oxygen is needed in burning. The glowing splint will
• Renewable resources relight when exposed to oxygen.
Disadvantage (b) Copper(II) sulfate contains ions [1]
Any one from: [1] In liquids, ions are moving. [1]
• Can cause explosion with a spark In solids, ions are not moving. [1]
• Hard to store (c) Cathode: Cu + 2e ➞ Cu [1]
2+
• Costly Anode: Cu ➞ Cu + 2e [1]
2+
• Hydrogen filling stations are not yet widely
available 9 (a) Silver [1]
+
7 (a) Na , H , Cl , OH [4] (b) Ag ➞ Ag + e [1]
–
+
+
–
Ag + e ➞ Ag [1]
+
(b) Hydrogen [1]
+
2H + 2e ➞ H [1] (c) The spoon is not totally covered by the solution.
2
[1]
(c) 2Cl (aq) ➞ Cl (g) + 2e If the spoon is not totally soaked in the solution, part
–
2
Correct balanced equation [1] of the spoon will not be plated. The appearance of
Correct state symbols [1] the final product will be less attractive.
(d) Damp litmus paper [1] (d) Any two from: [2]
bleached [1] • Shiny
• Attractive
(e) Titanium cannot react with chlorine gas. [1]
• Prevent rusting
(f) To keep the gases apart [1]
10 (a) Chlorine, [1]
(g) Change from green to purple [1] hydrogen [1]
NaOH is alkaline. [1] and sodium hydroxide [1]
Chlorine gas is produced at the anode. Hydrogen
+
gas is produced at the cathode. (b) Cathode: 2H + 2e ➞ H [1]
2
–
–
Na and OH remain in the electrolyte, forming Anode: 2Cl ➞ Cl + 2e [1]
+
2
–
+
NaOH. Na and OH remain in the solution, forming
NaOH. [1]
(h) Hydrogen Note: Students are encouraged to put both words
Any one from: [1] and equations to describe how the products are
• Make nylon obtained.
• Make hydrogen peroxide
• Make margarine (c) Only hydrogen gas. Chlorine gas and sodium
• As fuel hydroxide are not produced. [1]
At the anode, oxygen will be produced. [1]
Chlorine Na and Cl remain in the solution, forming
–
+
Any one from: [1] NaCl. [1]
• Plastic PVC Water is being removed. [1]
• As a solvent At the cathode, H is less reactive than Na . H gains
+
+
+
• Medical drugs electrons to form hydrogen gas.
• Pesticides
Cambridge IGCSE TM
150 Ace Your Chemistry
Answers.indd 150 3/4/22 3:54 PM