ONE-EIGHTH STAGE 2025
Opoku Ware School: 67 points
Amenfiman SHS: 36 points
Fijai SHS: 30 points
QUESTION
Calculate the mass of Fe(NO₃)₃ in 1.10 dm³ of a 0.420 mol/dm³ solution.
(Fe = 56.0)
ANSWER: 112 g
SOLUTION:
$\text{Moles} = 1.10\times0.420$
$\text{Moles} = 11\times10^{-1} \times 42\times10^{-2}$
$\text{Moles} = 11 \times 42 \times10^{-3}$
$\text{Moles} = 0.462\ \text{mol}$
Molar mass of
$Fe(NO_3)_3 = 56.0+3(14.0+3\times16.0)$
$Fe(NO_3)_3 = 242\ \text{g/mol}$
$\text{Mass} = 0.462\times242$
$\text{Mass} \approx 112\ \text{g}$
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PRACTICE QUESTIONS
1. QUESTION: Calculate the mass of sodium chloride in 2.00 dm³ of a 0.100 mol/dm³ solution. (Na = 23.0, Cl = 35.5)
ANSWER: 11.7 g or $1.17\times10^{1}$ g
SOLUTION:
$n = 0.100\times2.00$
$n = 10^{-1} \times 2$
$n = 0.200\text{ mol}$
$M(NaCl) = 58.5\text{ g/mol}$
$m = 0.200\times58.5$
$m = 2\times10^{-1} \times 585\times10^{-1}$
$m = 2 \times 585 \times10^{-2}$
$m = 11.7\text{ g}$
2. QUESTION: Calculate the mass of potassium chloride in 0.400 dm³ of a 0.250 mol/dm³ solution. (K = 39.0, Cl = 35.5)
ANSWER: 7.45 g
SOLUTION:
$n = 0.250\times0.400$
$n = 25\times10^{-2} \times 4\times10^{-1}$
$n = 25 \times 4 \times10^{-3}$
$n = 0.100\text{ mol}$
$M(KCl) = 74.5\text{ g/mol}$
$m = 0.100\times74.5$
$m = 10^{-1} \times 745\times10^{-1}$
$m = 745 \times10^{-2}$
$m = 7.45\text{ g}$
3. QUESTION: Calculate the mass of calcium chloride in 1.50 dm³ of a 0.200 mol/dm³ solution. (Ca = 40.0, Cl = 35.5)
ANSWER: 33.3 g or $3.33\times10^{1}$ g
SOLUTION:
$n = 0.200\times1.50$
$n = 2\times10^{-1} \times 15\times10^{-1}$
$n = 2 \times 15 \times10^{-2}$
$n = 0.300\text{ mol}$
$M(CaCl_2) = 111\text{ g/mol}$
$m = 0.300\times111$
$m = 3\times10^{-1} \times 111$
$m = 33.3\text{ g}$
4. QUESTION: Calculate the mass of sodium hydroxide in 0.500 dm³ of a 0.400 mol/dm³ solution. (Na = 23.0, O = 16.0, H = 1.00)
ANSWER: 8.00 g
SOLUTION:
$n = 0.400\times0.500$
$n = 4\times10^{-1} \times 5\times10^{-1}$
$n = 4 \times 5 \times10^{-2}$
$n = 0.200\text{ mol}$
$M(NaOH) = 40\text{ g/mol}$
$m = 0.200\times40$
$m = 2\times10^{-1} \times 40$
$m = 8.00\text{ g}$
5. QUESTION: Calculate the mass of potassium nitrate in 2.00 dm³ of a 0.0500 mol/dm³ solution. (K = 39.0, N = 14.0, O = 16.0)
ANSWER: 10.1 g or $1.01\times10^{1}$ g
SOLUTION:
$n = 0.0500\times2.00$
$n = 5\times10^{-2} \times 2$
$n = 0.100\text{ mol}$
$M(KNO_3) = 101\text{ g/mol}$
$m = 0.100\times101$
$m = 10^{-1} \times 101$
$m = 10.1\text{ g}$
6. QUESTION: Calculate the mass of magnesium sulfate in 0.250 dm³ of a 0.400 mol/dm³ solution. (Mg = 24.0, S = 32.0, O = 16.0)
ANSWER: 12.0 g or $1.20\times10^{1}$ g
SOLUTION:
$n = 0.400\times0.250$
$n = 4\times10^{-1} \times 25\times10^{-2}$
$n = 4 \times 25 \times10^{-3}$
$n = 0.100\text{ mol}$
$M(MgSO_4) = 120\text{ g/mol}$
$m = 0.100\times120$
$m = 10^{-1} \times 120$
$m = 12.0\text{ g}$