Question

1. What is the molarity of 6.4g of methanol dissolved in 50 moles of water2. If the density of the above solution at 25C is 1.03kg/L what is the molarity methanol solution at 25°C

Answer 1

Answer:

1. 0.22 mol/dm³

2. 0.23 mol/dm³

Explanation:

Molarity: This can be defined as the concentration of a substance  in mol per dm³

1.

M = n/v ...................... Equation 1

M = molarity of methanol, n = number of mole of methanol, v = volume of the solvent/water/solution.

n = g/m.m

Where g = mass of methanol, m.m = molar mass of methanol.

g = 6.4 g, m.m = 32 g /mole.

n = 6.4/32 = 0.2 mole

and ,

v = m/d

Where m = mass of water, d = density of water

m = mass of 50 moles of water = 18×50 = 900 g.

d = 1000 g/dm³.

v = 900/1000 = 0.9 dm³

Substituting the value of v and n into equation 1

M = 0.2/0.9

M = 0.22 mol/dm³

2.

M = n/v

v = volume of the solution

v = (mass of methanol + mass of water in the solution)/density of the solution

v = [(900+6.4)/1000]/1.03

v = 0.9064/1.03

v = 0.88 dm³

n = 0.2 mole

Therefore,

M = 0.2/0.88

M = 0.23 mol/dm³