Question

a chemistry student needs 15.0 g of 2-ethyltoluene for an experiment. she has available 0.20 kg of a 12.8% w/w solution of 2-ethyltoluene in benzene.
calculate the mass of solution the student should use. if theres not enough solution, press the
o solution\ button.
round your answer to 3 significant digits.
$square$ g

Explanation:

Step1: Define mass percent formula

Mass percent: $\text{w/w} \% = \frac{\text{mass of solute}}{\text{mass of solution}} \times 100\%$
Rearrange to solve for solution mass: $\text{mass of solution} = \frac{\text{mass of solute} \times 100\%}{\text{w/w} \%}$

Step2: Convert units (if needed)

The available solution mass is 0.20 kg = 200 g, but we first calculate required solution mass.
Given: $\text{mass of solute} = 15.0\ \text{g}$, $\text{w/w} \% = 12.8\%$

Step3: Calculate required solution mass

$\text{mass of solution} = \frac{15.0\ \text{g} \times 100}{12.8} = 117.1875\ \text{g}$

Step4: Check solution availability

Available solution is 200 g, which is more than 117.1875 g, so we can use this amount. Round to 3 significant digits.

Answer:

117 g