Question

-You wish to make a 0.203 M hydrochloric acid solution from a stock solution of 6.00 M hydrochloric acid. How much concentrated acid must you add to obtain a total volume of 175 mL of the dilute solution?

mL

-In the laboratory, a student dilutes 20.3 mL of a 8.20 M hydrochloric acid solution to a total volume of 200.0 mL. What is the concentration of the diluted solution?

Concentration =
M
-How many milliliters of 9.36 M perchloric acid solution should be used to prepare 1.50 L of 0.700 M ?

mL

Answer 1

For all three questions, we will use the fact that

• molarity = (moles of solute)/(liters of solution)

1) For 175 mL of solution at 0.203 M, this means that:

• 0.203 = (moles of solute)/0.175
• moles of solute = 0.035523 mol

Considering the hydrochloric acid solution, if we have 0.035523 mol, then:

• 6.00 = 0.035523/(liters of solution)
• liters of solution = 0.035523/6.00 = 0.0059205 = 5.92 mL (to 3 sf)

2) If there is 20.3 mL = 0.0203 L, then:

• 8.20 = (moles of solute)/0.0203
• moles of solute = 0.16646 mol

This means that the molarity of the diluted solution is:

• 0.16646/(0.200) = 0.832 M (to 3 sf)

3) If we need 1.50 L of 0.700 M solution, then:

• 0.700 = (moles of solute)/1.50
• moles of solute = 1.05 mol

Considering the 9.36 M acid solution, from which we need 1.05 mol of perchloric acid from,

• 9.36 = 1.05/(liters of solution)
• liters of solution = 1.05/9.36, which is 0.11217948717949 L, or 112 mL (to 3 sf)