Quick questions on Measurement and apparatus explained: O-Level Chemistry

A balance measures mass in grams. An electronic balance reads to $0.01\ \text{g}$ or $0.001\ \text{g}$ and is used for weighing solids when preparing a solution of known concentration. To find the mass of a solid accurately, weigh the container, add the solid, and weigh again; the difference is the mass of solid. This method by difference avoids the error of solid sticking to the weighing boat.

The choice depends on how exact the volume must be:

A gas syringe collects a gas and reads its volume directly, typically to $\pm 1\ \text{cm}^3$. It is the standard apparatus for following the rate of a reaction that gives off a gas. An inverted measuring cylinder over water can also collect a gas that is not very soluble.

State the most suitable apparatus to deliver exactly $25.0\ \text{cm}^3$ of a solution into a flask. [1 mark]

Explain why a student weighs a solid by difference rather than directly on the balance pan. [2 marks]

A thermometer reads $21\ ^\circ\text{C}$ at the start and $34\ ^\circ\text{C}$ at the end of a reaction. State the temperature change and the precision to which a school thermometer is usually read. [2 marks]