Question

What is the molarity of an aqueous solution that is 6.16 % NaCl by mass? (Assume a density of 1.02 g/mL for the solution.) (Hint: 6.16 % NaCl by mass means 6.16 g NaCl/100.0 g solution.)

Answer 1

Answer -

Given,

aqueous solution is 6.16% NaCl by mass

Density = 1.02 g/ml

Molarity = ?

Let the Volume of solution = 1 L

We know that,

Density = Mass /Volume

Mass = density * Volume

So, mass of 6.16% NaCl by mass = Density of solution * Volume

mass of 6.16% NaCl by mass in 1 L (1000 ml)= 1.02 g/ml * 1000 ml

mass of 6.16% NaCl by mass in 1 L (1000 ml)= 1020 g

Also,

percentage concentration by mass of NaCl Solution = 6.16%

i.e. 6.16 g per 100.0 g of solution

So, mass of NaCl in the sample = percentage concentration * Total mass of solution

mass of NaCl in the sample = 6.16 g NaCl /100 g * 1020 g

mass of NaCl in the sample = 62.8 g

Now,

Molarity = Moles / Volume in L

Also,

Moles = Mass / Molar Mass

So,

Molarity = Mass / (Molar Mass * Volume in L)

Put the values,

Molarity = 62.8 g / (58.5 * 1L)

Molarity = 1.07 M [Answer]