Practical Skills: Apparatus, Measurement and Graphs
Chemistry has a separate practical paper, and it rewards a distinct set of skills. The good news is that the same handful of ideas — variables, accurate readings, graphs and improvements — come up every year.
1. Choosing apparatus
| Apparatus | Use | Why |
|---|---|---|
| Burette | variable volumes, precisely | reads to ±0.05 cm³ |
| Pipette | a fixed volume | most accurate for one volume |
| Measuring cylinder | approximate volumes | less accurate |
| Balance | mass | to the stated decimal places |
| Thermometer | temperature | read to the nearest 0.5 °C |
| Gas syringe | volume of gas | |
| Stopwatch | time |
Use a BURETTE rather than a measuring cylinder when accuracy matters — tutors flagged this directly. If a question asks how to improve accuracy, upgrading the measuring apparatus is often the answer.
Name apparatus specifically. “A container” earns nothing; “a conical flask” does. Using the correct names for common laboratory equipment was flagged as a source of marks.
2. Variables
INDEPENDENT — what you change DEPENDENT — what you measure CONTROL — what you keep the same for a fair test
Naming all three, plus giving QUANTIFIABLE values, is crucial for the practical paper — tutors flagged this explicitly. Say “the concentration of acid, from 0.5 to 2.0 mol/dm³”, not just “the acid”.
Use EQUAL VOLUMES and equal amounts in comparative experiments. Not understanding the need for this was recorded — if you are comparing two conditions, everything else must match.
Not every investigation has independent and dependent variables — an observation-based test (identifying an unknown) may not. Tutors noted this; read the task before forcing the framework onto it.
3. Recording readings
Record to the precision of the instrument, and consistently:
- Burette: 2 decimal places, ending in .00 or .05 — read the bottom of the meniscus at eye level
- Thermometer: to the nearest 0.5 °C
- Balance: to the decimal places shown
- Time: in seconds
Misread burette readings were recorded, as were inconsistent temperature readings. Take your time and read at eye level to avoid parallax error.
Tables:
Head every column with quantity / unit — e.g. volume / cm³, temperature / °C Keep consistent significant figures down each column Include columns for repeats and a mean
Always include units — recorded as a specific loss.
4. Graphs
Graph work is worth a lot of marks, and each element is marked separately.
Axes: independent variable on the x-axis, dependent on the y-axis, both labelled with units Scale: sensible steps (1, 2, 5 or 10 per square) that use at least half the grid Points: small, neat CROSSES Line: a best-fit line or smooth curve — not dot-to-dot
Use crosses rather than dots for plotted points — tutors flagged this, as small dots are easily lost.
Choosing a scale that uses the space is itself a mark. Struggling with scale selection was recorded twice. Check your largest value against the number of squares before plotting.
Don’t mix up the axes. Mixing up x and y was recorded — the thing you changed goes across the bottom.
Plot what the question asks for. A recorded error plotted temperature where temperature CHANGE was required. Read the axis label you have been given.
Reading values off a graph:
SHOW your construction lines on the graph — draw across from the y-axis and down to the x-axis. Tutors flagged twice that you must show how a value was obtained to get full marks.
Deciding between a line and a curve: look at the pattern of the points. If they lie on a straight trend, use a ruled line; if they curve, draw a smooth curve. Don’t force a straight line through curved data.
Error carried forward is usually allowed — so if an earlier value was wrong, you can still gain marks for correct plotting and interpretation afterwards. Never leave the graph blank because you doubt your table.
5. Common chemistry practicals
Titration — burette, pipette, conical flask, white tile; swirl; concordant titres within 0.10 cm³.
Rate of reaction — measure gas volume (gas syringe) or mass loss (balance) against time; ensure the apparatus is sealed so no gas escapes.
Preventing gas escape was a recorded difficulty — check the bung fits and the syringe is connected before starting.
Energy changes — polystyrene cup with a lid and insulation to reduce heat loss; stir; record initial and highest/lowest temperature.
Salt preparation — add base in excess, filter, then crystallise — do not evaporate to dryness.
Drying a product — leave in a warm oven or a desiccator, or press between filter papers.
A desiccator dries by absorbing moisture; an oven dries by warming. Confusion between them was recorded — a desiccator is used where heat would decompose the product.
Identifying an unknown — carry out the standard ion and gas tests, recording reagent, observation and conclusion each time.
Identify an excess reactant by looking for UNREACTED SOLID remaining after the reaction has stopped.
6. Sources of error and improvements
Be SPECIFIC. “Human error” earns nothing.
| Instead of… | Write |
|---|---|
| ”human error” | misreading the burette / parallax error |
| ”heat was lost” | heat lost to the surroundings, especially from the top |
| ”gas escaped” | gas escaped before the bung was inserted |
| ”the equipment was inaccurate” | the measuring cylinder is only accurate to ±1 cm³ |
Standard improvements — these earn marks repeatedly:
REPEAT and take a MEAN — the most-cited improvement of all Use more accurate apparatus (burette instead of measuring cylinder) Insulate and use a lid in thermal experiments Stir for even mixing Take more readings over a wider range
“Repeat the experiment to increase reliability” and “calculate a mean” were flagged repeatedly — if in doubt, this is the safe improvement to offer.
7. Comparing results
Include the actual VALUES when comparing — tutors flagged this twice.
“Experiment 2 produced 45 cm³ of gas compared with 28 cm³ in experiment 1, so the reaction was faster at the higher concentration.”
A comparison without numbers is a description, not an analysis — quantitative comparison is what earns the mark.
8. Mistakes that cost marks
Vague apparatus names.
Not naming all three variable types, or giving no values.
Unequal volumes in a comparative test.
Burette read to 1 decimal place or from the top of the meniscus.
Missing units in table headings or answers.
Awkward graph scales, or a graph using less than half the grid.
Dots instead of crosses; joining points dot-to-dot.
Plotting the wrong quantity (temperature vs temperature change).
No construction lines when reading off a graph.
“Human error” as a source of error.
Inconsistent significant figures.
Frequently asked questions
Which apparatus is most accurate for a variable volume? A burette.
What are the three types of variable? Independent (changed), dependent (measured), control (kept the same).
How should I record burette readings? To 2 decimal places, ending in .00 or .05, at the bottom of the meniscus.
How should graph axes be labelled? Quantity / unit, with the independent variable on the x-axis.
What should I use to plot points? Small, neat crosses.
How do I show a value read from a graph? Draw construction lines across and down.
Why is “human error” not accepted? It is too vague — name the specific mechanism.
What is the standard way to improve reliability? Repeat and calculate a mean.
How do I compare two results? Quote the actual values and state the conclusion.
What if my earlier answer was wrong? Error carried forward usually applies — still plot and interpret.
Quick revision checklist
- I can name apparatus specifically and choose the most accurate
- I state all three variable types with values
- I keep volumes and amounts equal in comparisons
- I record readings to the right precision with units
- I head table columns quantity / unit
- I choose a scale filling half the grid
- I plot crosses and draw a best-fit line or smooth curve
- I plot the quantity actually asked for
- I show construction lines when reading off
- I give specific sources of error
- I know the standard improvements
- I make quantitative comparisons
This page covers practical skills for the Cambridge IGCSE Chemistry (0620) practical paper and is written for Grade 9–11 / Year 10–11 students. It is based on teaching patterns observed across a large set of one-to-one IGCSE Chemistry lessons, with particular attention to the errors students make most often and the wording examiners reward. Always check the current syllabus and the practical paper requirements for your own exam series.
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