Question

a chemistry student must write down in his lab notebook the concentration of a solution of sodium hydroxide. the concentration of a solution equals the mass of what’s dissolved divided by the total volume of the solution. here’s how the student prepared the solution: - the label on the graduated cylinder says: empty weight: 3.500 g - he put some solid sodium hydroxide into the graduated cylinder and weighed it. with the sodium hydroxide added, the cylinder weighed 15.55 g. - he added water to the graduated cylinder and dissolved the sodium hydroxide completely. then he read the total volume of the solution from the markings on the graduated cylinder. the total volume of the solution was 97.73 ml. what concentration should the student write down in his lab notebook? be sure your answer has the correct number of significant digits. g·ml⁻¹

Explanation:

Step1: Calculate the mass of sodium hydroxide

The mass of sodium hydroxide ($m$) is the difference between the mass of the cylinder with sodium hydroxide ($15.55\ g$) and the mass of the empty cylinder ($3.500\ g$).
$$m = 15.55 - 3.500=12.05\ g$$

Step2: Calculate the concentration

Concentration ($C$) is defined as mass per unit volume. The volume ($V$) of the solution is $97.73\ mL$.
$$C=\frac{m}{V}=\frac{12.05}{97.73}\ g\cdot mL^{-1}\approx0.1233\ g\cdot mL^{-1}$$

Answer:

$0.1233\ g\cdot mL^{-1}$