Singapore-Cambridge O-Level Chemistry

## Measuring apparatus Time is measured with a stopwatch or stop clock, temperature with a thermometer, and mass with a balance. Volume is measured with different pieces of apparatus depending on how precise the measurement has to be. | Apparatus | Used for | |---|---| | Measuring cylinder | Approximate volumes of liquid, such as $\pu{25 cm3}$ of an acid that is in excess | | Pipette | One fixed, accurate volume of liquid, usually $\pu{25.0 cm3}$ | | Burette | A variable and accurate volume of liquid delivered drop by drop, as in a titration | | Gas syringe | The volume of a gas produced in a reaction, read as the plunger is pushed out | A burette is read at the bottom of the meniscus with the eye level with it, and the volume delivered is the difference between the final and initial readings. ## Collecting and drying gases The way a gas is collected depends on how it behaves. A gas that is not very soluble in water, such as hydrogen or oxygen, can be collected over water by displacement, which also shows how fast it is being made. A gas syringe collects any gas and measures it at the same time. A gas that is denser than air, such as carbon dioxide or chlorine, is collected in a gas jar by downward delivery (upward displacement of air). A gas that is less dense than air and very soluble in water, such as ammonia, is collected by upward delivery (downward displacement of air), with the jar held upside down. A gas made in solution is usually damp. It is dried by passing it…