Question

(a) Calculate the molarity of a solution made by dissolving 0.0715 mol Na2SO4 in enough water to form 550 mL of solution. Give the answer again with the correct amount of significant figures. (b) How many moles of KMnO4 are present in 50.0 mL of a 0.0850 M solution? Give the answer again with the correct amount of significant figures. (c) How many milliliters of 11.6 M HCl solution are needed to obtain 0.205 mol of HCl? Give the answer again with the correct amount of significant figures.

Answer 1

a) we know that

molarity = moles / volume (L)

so

molarity = 0.0715 / 550 x 10-3

molarity = 0.13

so

the molarity of the solution is 0.13

b)

we know that

moles = molarity x volume (L)

so

moles of KMnO4 = 0.0850 x 50 x 10-3

moles of KMnO4 = 4.25 x 10-3

so

there are 4.25 x 10-3 moles of KMnO4

c)

we know that

volume (L) = moles / molarity

so

volume of HCl solution = 0.205 / 11.6

volume of HCl solution = 0.01767 L

now

1 L = 1000 ml

so

volume = 0.01767 x 1000

volume = 17.67

so

17.67 milliliters of HCl solution is needed