Question

A stock solution contains 5 g per 100 ml of sucrose. How many ml of this stock solution would you use to prepare 1 litre of sucrose solution at a concentration of 0.25 g per litre?

Answer 1

5 mL

Explanation:

It's a dilution problem since it starts with a concentrated stock solution and a lower concentration solution is prepared from it.

First of all, we'll need to do is calculate the 2 concentrations that are given:

We can do that using 2 ways:

• `Molarity = "mol" / "volume in L"`
  Using this formula will require additional calculation, converting from grams to mol using molar mass of sucrose.

• `%(m/v)=("g of solute")/("mL of solution")xx 100%`
  I'll proceed using this concentration. Take note on the unit required for mass (g) and volume (mL).

`"Concentration of stock solution" =C_1 = ("5g")/(100 mL)xx100%=5%`

`"Concentration of diluted solution" =C_2 = ("0.25g")/(1000 mL)xx100%=0.025%`

We also know from the question, that the final volume of solution `V_2`) is 1 L = 1000 mL.

Since we need to find out the volume of stock solution used (`V_1`) to prepare the diluted solution, we'll use the dilution formula:

`C_1V_1 = C_2V_2`

`5% xx V_1 = 0.025% xx 1000 mL`

`V_1=(0.025 xx 1000)/5="5 mL"`