Physical Chemistry Core Practicals

📋 Summary — What This Chapter Covers

• Core Practical 1 — Molar Volume of a Gas: React a solid (e.g. a metal carbonate) with excess acid, collect the CO₂ gas produced, and use the mass–volume data to calculate the molar volume of the gas or identify an unknown metal.
• Core Practical 2 — Enthalpy Change of Reaction: Use a simple polystyrene-cup calorimeter to measure a temperature change, then calculate the heat released/absorbed and the molar enthalpy change, correcting for heat loss with a temperature-correction graph.
• Core Practical 3 — Determining Concentrations (Titration): Use a burette and pipette to titrate an acid against a base of known concentration, recording concordant titres, then calculate the unknown concentration using mole ratios.
• Core Practical 4 — Preparing a Standard Solution: Accurately weigh a solid, dissolve it, and make it up to a precise volume in a volumetric flask to create a solution of known concentration (a "standard solution") — the starting point for any titration.
• All four practicals share the same underlying skill: convert a measurement (mass, volume, temperature, titre) into moles, then use mole ratios from a balanced equation to find what you actually want.

1️⃣ Core Practical 1: Molar Volume of a Gas

The Setup — Two Ways to Collect Gas

Imagine you're reacting a metal carbonate with acid and CO₂ gas bubbles off. You need to trap and measure that gas somehow. There are two classic methods:

• Gas syringe method: the flask is sealed with a bung connected directly to a gas syringe. As gas is produced, it pushes the plunger out, and you read the volume straight off the syringe scale.
• Displacement of water method: gas is piped through a delivery tube into an upturned, water-filled measuring cylinder standing in a trough of water. As gas enters, it pushes water out of the cylinder, and the volume of water displaced equals the volume of gas collected.

Think of it like blowing into a plastic bag versus blowing bubbles underwater into an upside-down glass — both trap the same gas, just with different apparatus.

The Method (Sodium Carbonate + HCl Example)

The reaction used as the standard example is:

1. Measure a fixed volume of HCl (e.g. 25.0 cm³) into a conical flask.
2. Add a known, small mass of sodium carbonate (e.g. 0.05 g) to the flask.
3. Immediately connect the gas syringe delivery tube (speed matters — you don't want gas escaping before you seal it!).
4. Let the reaction go to completion.
5. Record the volume of CO₂ produced.
6. Repeat with increasing masses of sodium carbonate (0.10 g, 0.15 g … up to 0.50 g) to build a dataset.

Turning Results Into a Molar Volume

2️⃣ Core Practical 2: Determining Enthalpy Change of Reaction

What Is Calorimetry?

Calorimetry calorimeter

🧠 What to Memorise