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?

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Answer 1 · 2018-08-13T23:29:08

5 mL

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:

$C_1V_1 = C_2V_2$

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

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