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
