Answer:
- Part A: m = 0.02356 mol/kg = 0.02356 m
- Part B: Xsolute = 4.243×10⁻⁴
Explanation:
<u>1. Data:</u>
a) M = 2.350×10⁻² M
b) V sol = 1.000 L
c) V H₂O = 994.4 mL = 0.9944 L
d) d H₂O = 0.9982 g/mL
<u>2. Formulae</u>
- M = n solute / V sol (L)
- m = n solute / Kg solvent
- X solute = n solute / N total
- % m/m = (mass of solute / mass of solution) × 100
- ppm = (mass of solute / mass of solution) × 1,000,000
- density = mass in grams / volume in mL
<u>3. Solution</u>
<u>Part A: Calculate the molality of the salt solution. </u>
<u />
m = n solute / Kg solvent
i) M = n solute / V sol (L) ⇒ n solute = M × V sol (L)
⇒ n solute = M = 2.350×10⁻² M × 1.000 L = M = 2.350×10⁻² mol
ii) density H₂O = mass H₂O / volume H₂O
⇒ mass H₂O = density H₂O × volume H₂O
⇒ mass H₂O = 0.9982 g/mL × 999.4 mL = 997.6 g
iii) kg H₂O = 997.6 g / (1,000 g/Kg) = 0.9976 kg
iv) m = 2.350×10⁻² mol / 0.9976 kg = 0.02356 mol/kg = 0.02356 m
<u>Part B: Calculate the mole fraction of salt in this solution</u>.
X solute = n solute / N total
i) n solute = 2.350×10⁻² mol
ii) n solvent = n H₂O = mass H₂O in grams/ molar mass H₂O
⇒ 997.6 g / 18.015 g/mol = 55.38 mol
iii) X solute = 2.350×10⁻² mol / 55.38 mol = 4.243×10⁻⁴
<u>Part C: Calculate the concentration of the salt solution in percent by mass</u>.
% m/m = (mass of solute / mass of solution) × 100
i) molar mass = mass in grams / molar mass
⇒ mass of solute = mass of NaCl = n solute × molar mass NaCl
⇒ mass of solute = 2.350×10⁻² mol × 58.44 g/mol = 1.373 g
ii) % m/m = (1.373 g / 997.6 g) × 100 = 0.1376%
Part D: Calculate the concentration of the salt solution in parts per million.
ppm = (mass of solute / mass of solution) × 1,000,000
i) ppm = ( (1.373 g / 997.6 g) × 1,000,000 = 1,376 ppm
