Introduction to Laboratory Chemistry Practice Questions & Answers

A volumetric flask is calibrated to contain a precise volume of liquid when filled to the mark, making it the standard apparatus for preparing solutions of known concentration. Beakers and Erlenmeyer flasks are for mixing/holding, and graduated cylinders are less precise.

A buret is a long, graduated glass tube with a stopcock at the bottom, specifically designed to dispense variable precise volumes of liquid (titrant) during a titration.

The conical shape (narrow neck and sloped sides) of an Erlenmeyer flask allows the user to swirl the solution vigorously to ensure mixing without splashing the liquid out, which is a risk with the wide mouth of a beaker.

A volumetric pipette is calibrated to deliver a single, fixed volume with very high precision (often to $\pm 0.01\ \text{mL}$±0.01 mL or better), superior to graduated cylinders or beakers.

A crucible is made of heat-resistant ceramic or metal and is designed to withstand the very high temperatures of direct flame heating, unlike watch glasses or volumetric glassware.

For concave menisci (like water in glass), the correct technique is to position the eye level with the liquid surface and read the volume at the bottom of the meniscus.

When recording a measurement, you estimate one digit beyond the smallest marking. Since the buret is marked every $0.1\ \text{mL}$0.1 mL, the reading should be estimated to the hundredths place ($0.01\ \text{mL}$0.01 mL), making $20.15\ \text{mL}$20.15 mL the correct format.

Using the molarity formula $M = \frac{\text{moles}}{\text{liters}}$M=litersmoles​:
$\text{moles} = M \times V = 2.0\ \text{mol/L} \times 0.250\ \text{L} = 0.50\ \text{moles}$moles=M×V=2.0 mol/L×0.250 L=0.50 moles

Add Acid to Water (AA). Adding water to concentrated acid can cause the water to boil instantly due to the high heat of hydration, potentially splashing acid out. Adding acid slowly to a larger volume of water dissipates the heat safely.

Rinsing with the titrant solution ensures that any remaining water droplets inside the buret do not dilute the concentration of the titrant being used for the experiment.