📋 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

You plot mass of sodium carbonate (x-axis) against volume of CO₂ produced (y-axis), ignore anomalies, and draw a line or curve of best fit. Then you pick a sensible point on the line — say, 0.35 g gives 79.0 cm³ — and work through the maths:

Application: Finding an Unknown Metal

This is the classic exam twist: instead of finding the molar gas volume, you're given it (usually 24 dm³ at room temperature and pressure) and asked to identify an unknown Group 2 metal carbonate, MCO₃.

2️⃣ Core Practical 2: Determining Enthalpy Change of Reaction

What Is Calorimetry?

Calorimetry is just a fancy word for "measuring heat changes." A calorimeter can be as simple as a polystyrene cup (great insulator, cheap, easy to use) or as sophisticated as a vacuum flask or metal can. The polystyrene cup is the classic school-lab version because polystyrene barely conducts heat, so very little energy escapes to the surroundings while you're taking readings.

Sample Method — Zinc + Copper Sulfate Displacement

1. Pipette 25 cm³ of 1.0 mol dm⁻³ copper(II) sulfate solution into the polystyrene cup.
2. Weigh out roughly 6 g of zinc powder — it's in excess, so an exact mass isn't crucial.
3. Record the initial temperature, then temperature every half-minute for 2.5 minutes (this establishes a stable "before" baseline).
4. At exactly 3 minutes, tip in the zinc powder (don't record a reading at that exact moment — you're mid-action).
5. Keep stirring and recording temperature every half-minute for a further 6 minutes.

Temperature Correction Graphs — Why We Need Them

Here's the problem: many reactions aren't instant. While the reaction is still happening, the mixture is also losing heat to the surroundings the whole time. So by the time the reaction actually finishes, the measured "peak" temperature is already lower than the true maximum would have been if no heat had escaped. It's like trying to catch the exact top of a bouncing ball's trajectory while gravity is already pulling it down — you need to work backward.

The fix: plot temperature vs. time. You get a flat baseline before the reactant is added, then a rising/falling section, then a steady cooling section that slopes gently downward as heat leaks out. You draw a best-fit line through that cooling section and extrapolate it backwards until it crosses the exact time the second reactant was added. That intersection point gives you the "true" peak temperature (T₂), as if no heat had been lost at all.

3️⃣ Core Practical 3: Determining Concentrations (Titration)

The Apparatus

A titration is essentially a very precise "add-a-little-at-a-time" experiment. You know the exact volume and concentration of one solution (in the conical flask, measured by volumetric pipette), and you slowly add a second solution (from the burette) until an indicator shows the reaction has just finished — the end point (equivalence point).

Step-by-Step Method

1. Pipette a known volume (usually 20 or 25 cm³) of one solution into a conical flask.
2. Fill the burette with the other solution, usually starting at 0.00 cm³.
3. Add a few drops of indicator to the flask.
4. Open the burette tap and add solution portion by portion, swirling constantly.
5. As you approach the end point (the colour starts to change more persistently), slow right down and add dropwise — ideally you can stop after just one drop causes the permanent colour change.
6. Repeat until you get concordant results — titres within 0.1 cm³ of each other.

Recording Results Properly

All burette readings are recorded to 2 decimal places (e.g. 23.15 not 23.1), and — because burettes are marked in 0.10 cm³ intervals — the second decimal digit should always be a 0 or a 5 (like 23.15 or 23.10, never 23.13). The first "rough" titration is done quickly to find the approximate end point, then discarded from the final average since it's usually too high (you weren't being precise near the end point yet).

4️⃣ Core Practical 4: Preparing a Standard Solution

What Is Volumetric Analysis?

Volumetric analysis uses the volume and concentration of one solution (a "volumetric" or "standard" solution) to find the concentration of an unknown one. Before you can titrate anything, though, you first need to make that known solution — precisely and accurately. That's what this practical is about.

The 5-Step Method

1. Weigh a precise mass of the solid on a 3-decimal-place balance.
2. Dissolve it in a small volume of water in a beaker, stirring with a glass rod until fully dissolved.
3. Transfer the solution to a volumetric flask using a funnel — don't lose any solid on the way!
4. Rinse the beaker and glass rod with distilled water, adding all the rinsings to the flask (this ensures no solute is left behind — every last bit must end up in the flask).
5. Make up to the mark: add more water carefully until the bottom of the meniscus sits exactly on the graduation (scratch) mark, then stopper and invert/mix thoroughly.

The Core Concentration Formula

🧠 What to Memorise

✅ Concepts Checklist

• I can describe both methods for collecting gas (gas syringe & displacement of water)
• I can list the assumptions made in the molar volume of gas experiment
• I can calculate molar gas volume from mass and volume data
• I can identify an unknown Group 2 metal carbonate from experimental data
• I understand and can apply q = mcΔT
• I can explain why a temperature correction graph is needed and how to extrapolate it
• I can calculate ΔH using ΔH = q ÷ n, including identifying the limiting reagent
• I know the correct sign convention for exothermic vs endothermic reactions
• I can describe the full titration method step-by-step, including safety/precision details
• I understand burette uncertainty (±0.05 cm³ per reading, ±0.10 cm³ per titre)
• I can identify and average concordant titration results correctly
• I can calculate an unknown concentration from titration data using mole ratios
• I can describe the 5-step method for preparing a standard solution
• I can calculate the mass of solute needed for a target concentration and volume
• I know the three ways concentration can be expressed (mol dm⁻³, g dm⁻³, ppm)

🎯 Exam Tips & Common Mistakes