Question

(a) Calculate the molarity of a solution made by dissolving 0.0715 mol Na₂SO₄ in enough water to form 650 mL of solution.
   
Answer-

Answer with correct sig figs-

(b) How many moles of KMnO₄ are present in 25.0 mL of a 0.0950 M solution?

Answer-

Answer with correct sig figs-

(c) How many milliliters of 12.6 M HCl solution are needed to obtain 0.205 mol of HCl?

Answer-

Answer with correct sig figs-

Answer 1

(a)

We know the formula of Molarity

Molarity = Number of Moles / Liter of Solution

And 1 L = 1000 mL then 650 mL = 0.65 L

So

Molarity = 0.0715 moles / 0.65 L

= 0.11 M

(b)

25.0 mL = 0.025 L

So

Molarity = Number of Moles(n) / Liter of Solution

0.0950 M = n / 0.025 L

So

Number of Moles = 0.0950 x 0.025

= 0.002375 Moles = 2.37 x 10^-3 Moles

(c)

We know that

Molarity = Number of Moles(n) / Liter of Solution(V)

So

12.6 M = 0.205 mol / V

So

Volume V = 0.205 /12.6

= 0.01626 L

= 16.26 mL