15.00 mL of a NaCl solution that has a mass of 15.78 grams is placed in an evaporating dish and heated to
dryness. The remaining solid has a mass of 3.26 grams. Calculate the following concentrations for the
solution: % by mass, % mass/volume, and molarity.

Question

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Neetoo Neetoo · Answer 1 · 2019-10-14T15:48:28+02:00

Answer:

a = % (mass/mass) = 20.66 g

b = % (mass/volume) = 21.7 g/mL

c = Molarity = 3.7 M

Explanation:

Given data:

Volume of NaCl solution = 15.00 mL

Mass of NaCl solution= 15.78 g

After drying mass of remaining solid = 3.26 g

Concentration % (mass/mass) = ?

Concentration % (mass/volume) = ?

Concentration (molarity) = ?

Solution:

a = Concentration % (mass/mass)

% (mass/mass) = 3.26 g/ 15.78 g×100

% (mass/mass) = 20.66 g

b= Concentration % (mass/volume)

% (mass/volume) = 3.26/15 ×100

% (mass/volume) = 21.7 g/mL

c = Concentration (molarity)

We will find the number of miles first.

Number moles = mass/molar mass

Number moles = 3.26 g/58.4428 g/mol

Number moles = 0.056 mol

Now we will convert the volume in litter which is in milliliter.

15/ 1000 = 0.015 L

Molarity = number of moles/ volume in litter

Molarity= 0.056 mol / 0.015 L

Molarity = 3.7 M