Chemistry 5070/11 — October/November 2020

Walkthrough

The question asks which piece of equipment should be used to measure exactly $17.60\text{ cm}^3$ of hydrochloric acid. The key is that the volume is not a standard fixed volume, so the apparatus must be able to measure a range of volumes accurately.

A burette is a long, graduated tube that can deliver any volume up to about $50\text{ cm}^3$ and can be read to $\pm 0.05\text{ cm}^3$. This makes it suitable for measuring $17.60\text{ cm}^3$ accurately.

A pipette is also accurate, but it only measures one fixed volume, such as $10.0\text{ cm}^3$, $20.0\text{ cm}^3$ or $25.0\text{ cm}^3$. It cannot be used to measure $17.60\text{ cm}^3$.

A measuring cylinder can measure a range of volumes, but it is much less precise and would not be suitable when a volume is quoted to two decimal places.

A gas syringe is designed to measure gas volumes, not liquids, so it is not appropriate here.

Therefore the correct choice is A.

Key Takeaways

• A burette is used when a precise, variable volume of liquid is needed.
• A pipette measures one fixed volume only.
• A measuring cylinder is used for approximate volumes.
• A gas syringe is used for measuring gases.
• Volumes written to two decimal places, such as $17.60\text{ cm}^3$, suggest a need for accurate measurement.

Common Mistakes

• Choosing the pipette because it is accurate, without remembering that it only measures a fixed volume.
• Choosing the measuring cylinder because it can measure any volume, without considering that it is not precise enough for $17.60\text{ cm}^3$.
• Choosing the gas syringe because it has graduations, without recognising that it is for gases, not liquids.

Things to Be Careful About

• Burette readings are usually recorded to two decimal places, with the last digit being 0 or 5, such as $17.60\text{ cm}^3$.
• In titration experiments, the acid is often placed in the burette and the alkali in the conical flask, but the key here is simply that the burette can measure the required volume accurately.