06-07 Formulae, Equations and the Mole, Set A Answer Key To print: Ctrl + P, paper A4, margins Default.
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06-07

Formulae, Equations and the Mole

Set AAnswer key
A

Multiple choice

9 marks
1

D16[1]

The formula has two units of CH3CNOH: 4 carbon, 8 hydrogen, 2 nitrogen and 2 oxygen atoms, 16 atoms in total.

2

DIr(ClO)3[1]

Ir2(SO4)3 shows the ions are Ir3+ and SO42−. Zn(ClO)2 shows the ions are Zn2+ and ClO−. So Ir3+ and ClO− give Ir(ClO)3.

3

A2Zn + O2 → 2ZnO[1]

Oxygen is diatomic, O2, and zinc oxide is ZnO (Zn2+ and O2−).

4

AC6H12O6 + 3O2 → 6CO2 + 6H2O[1]

In A there are 12 oxygen atoms on the left (6 + 6) but 18 on the right (12 + 6). It needs 6O2.

5

Cw = 3, x = 2, y = 1, z = 6[1]

There are 3 Hg on the right, so w = 3 and y = 1. The values in D fit for Hg, P and y, but z is wrong, as H and O are not balanced.

6

CNO[1]

Al(NO3)3: 19.7%. Mg3N2: 28%. NO: 1430 × 100 = 46.7%. NO2: 30.4%.

7

B63.67[1]

Ar = 68.54100 × 63 + 29.51100 × 65 + 1.95100 × 67 = 63.67

8

BCH2[1]

Moles: C = 4.812 = 0.4, H = 0.81 = 0.8. The ratio is 1 : 2, so CH2.

9

DN2O5[1]

Mass of oxygen = 19.30 − 5.00 = 14.30 g. Moles: N = 5.0014 = 0.357, O = 14.3016 = 0.894. The ratio is 1 : 2.5 = 2 : 5.

B

Structured questions

18 marks
10
(a)

(1), 12, 8 [1]

(b)

(1), 5, 3, 4 [1]

(c)

2, 3, 6, (1) [1]

11
(a)

2Na + 2H2O → H2 + 2NaOH [1]

(b)

2HNO3 + CaO → Ca(NO3)2 + H2O [1]

(c)

2C3H6 + 9O2 → 6CO2 + 6H2O [1]

12
(a)

Ba(NO3)2 + K2SO4 → BaSO4 + 2KNO3 [1]

(b)

Ba2+ + SO42− → BaSO4 [1]

13

Masses in 100 g: B = 78.6 g and C = 21.4 g. [1]

Moles: B = 78.611 = 7.15 and C = 21.412 = 1.78. [1]

Ratio 7.15 ÷ 1.78 = 4.01, about 4 : 1. The empirical formula is B4C. [1]

14
(a)

Moles of sulfuric acid = 0.025 × 0.40 = 0.01 mol [1]

Moles of NaOH = 2 × 0.01 = 0.02 mol, so concentration = 0.020.035 = 0.571 mol/dm3 [1]

(b)

H+(aq) + OH−(aq) → H2O(l) [1]

15

Moles of Ca3(PO4)2 = 100310 = 0.32258 mol [1]

Ca3(PO4)2 : CaSiO3 = 2 : 6 = 1 : 3, so moles of CaSiO3 = 0.96774 mol [1]

Theoretical mass of CaSiO3 = 0.96774 × 116 = 112.26 g [1]

Percentage yield = 87112.26 × 100% = 77.5% [1]

A common mistake is to include the number in front of a formula when working out its Mr.