Answer:
a)0.67 molal
b) 5.67 molal
c) 2.82 molal
d) 0.0268 molal
Explanation:
Step 1: Data given
Molality = moles solute / mass solvent
(a) 0.710 kg of sodium carbonate (washing soda), Na2CO3, in 10.0 kg of water—a saturated solution at 0°C
Calculate moles of Na2CO3 = 710 grams / 105.99 g/mol = 6.70 moles
Molality = 6.70 moles / 10 kg = 0.67 molal
(b) 125 g of NH4NO3 in 275 g of water—a mixture used to make an instant ice pack
Calculate moles of NH4NO3 = 125 grams / 80.04 g/mol = 1.56 moles
molality = 1.56 moles / 0.275 kg = 5.67 molal
(c) 25 g of Cl2 in 125 g of dichloromethane, CH2Cl2
Calculate moles Cl2 = 25 grams / 70.9 g/mol= 0.353 moles
Molality = 0.353 moles / 0.125 kg = 2.82 molal
0.372 g of histamine, C5H9N, in 125 g of chloroform, CHCl3
Calculate moles histamine = 0.372 grams / 111.15 g/moles = 0.00335 moles
Calculate molality = 0.00335 moles / 0.125 kg = 0.0268 molal
NOTE: histamine is C5H9N3 not C5H9N
The molality of a solution is the ratio of the number of moles to the mass of the solvent in kilograms.
a) Number of moles of sodium carbonate = 0.710 × 10^3g/106 g/mol = 6.698 moles
Molality = Number of moles/ mass of solvent in Kg = 6.698 moles/10.0 kg = 0.67 m
b) Number of moles of ammonium nitrate = 125 g/80.043 g/mol = 1.56 moles
Molality = 1.56 moles/ 275 × 10^-3 Kg = 5.67 m
c) Number of moles of chlorine = 25 g/71 g/mol = 0.35 moles
Molality = 0.35 moles/125 × 10^-3 = 2.8 m
d) Number of moles of histamine = 0.372 g/111.15 g/mol = 0.0033 moles
Molality = 0.0033 moles/125 × 10^-3 = 0.0264 m
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