Page 30 - ACE YR IGCSE A TOP APPROACH TO CHEM

Part 2: Structured Questions (c)
K + Cl – K +
1 (a) V [1] – + –
V has 2 electrons in the outer shell. It is a member Cl K Cl
of Group II. It is a metal. K + Cl – K +
(b) 2,8,8,2 [1] Regular arrangement [1]
+
–
(c) Covalent bond [1] of alternating K and Cl [1]
Y and Z are both non-metals. Covalent bonds form
between non-metals. (d) Ionic bond is strong. [1]
(d) (i) A regular arrangement [1] Require a lot of energy to overcome. [1]
Potassium chloride is an ionic compound. Ionic
of alternating positive and negative ions. bond is formed between ions of opposite charge.
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[1]
Lattice = regular arrangement (e) Ions cannot move in solid. [1]
Ionic = alternating positive and negative ions Ions can move in molten. [1]
(ii) CaO [1] – Solid +
Calcium loses 2 electrons to form Ca . Oxygen
2+
gains 2 electrons to form O . + – + – + – + – + – + –
2–
1 atom of Ca is enough to cancel out the – + – + – + – + – + – +
2+
+ – + – + – + – + – + –
charge of 1 atom of O . In the formation of
2–
calcium oxide, the ratio of calcium to oxygen Ions are fixed in the lattice and cannot move
is 1 : 1.
(iii) 2+ 2– – Molten or aqueous solution +
Ca O – + + + – – – – + – –
+ – – + – + – –
+ + + + + + –
+ + + – – – – + – –
Ca has 8 electrons in the outer shell. [1]
2+
O has 6 electrons in the outer shell and Ions can now move and conduct electricity
2–
gains 2 electrons from Ca. [1] (f) (i) Potassium loses 1 electron to form K . [1]
+
Correct charge [1] Oxygen gains 2 electrons to form O . [1]
2–
+
(e) Y and X [1] 2 moles of K is needed to cancel out the
2–
Carbon dioxide [1] charge of 1 mole of O . [1]
In a complete combustion, carbon dioxide is (ii) Dissolve potassium oxide in water and add
formed. Y has the electronic configuration of 2,4. universal indicator / litmus paper / methyl
It is a carbon. X has the electronic configuration of orange / phenolphthalein / pH meter [1]
2,6. It is an oxygen. Turn blue / purple / yellow / pink / > pH 7
W is not the answer because W is carbon-14, which [1]
is radioactive.
Physical test (a qualitative or quantitative test
(f) W and Y [1] that determines the properties of a substance
They have the same number of protons [1] at macroscopic level.)
but different number of neutrons. [1] Universal indicator has a wide range of colour
Both W and Y have the same number of protons, 6, changes giving more accurate pH.
but different number of neutrons, 8 and 6 Litmus paper: acid ➞ red; base ➞ blue / purple
respectively. Methyl orange: acid ➞ red; neutral ➞ orange;
base ➞ yellow
(g) Any one from: Phenolphthalein: acid ➞ colourless; neutral ➞
Cancer treatment / Sterilise medical instrument colourless; base ➞ pink
/ Trace blockage in blood [1] pH meter: gives accurate pH in digit.
Any one from: 3 (a) Its boiling point is below room temperature. [1]
Fuel in nuclear power plant / Trace pipe leakage (b) (i) Covalent bond [1]
[1]
(ii)
2 (a) KCl [1]
O C O
(b) K loses 1 electron to form K . [1]
+
Cl gains 1 electron from the potassium to form
Cl . [1] The correct ratio of carbon to oxygen is
–
1 : 2. [1]
4 sharing electrons at each intersection.
There are 2 intersections. [1]
2 lone pairs on each oxygen. [1]

Cambridge IGCSE TM
142 Ace Your Chemistry

Answers.indd 142 3/4/22 3:54 PM