Year 8 Science · Unit 3 · Lesson 11
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Learning Goals
Identify the variable type
Each row describes a factor in a different investigation. Write the variable type in the "Variable Type" column: IV (independent), DV (dependent), or CV (controlled).
| Investigation | Factor | Variable Type |
|---|---|---|
| 1. Does acid concentration affect how fast chalk dissolves? | Acid concentration (5%, 10%, 20%) | |
| Time taken for chalk to fully dissolve | ||
| Mass of chalk used (kept at 2 g each trial) | ||
| 2. Does surface area affect the rate of rusting? | Mass of iron gained (rust formation) | |
| Surface area of iron pieces (whole, halved, powdered) | ||
| Amount of water surrounding each piece (kept equal) | ||
| 3. Does temperature affect how much gas vinegar + bicarb produces? | Volume of CO₂ gas produced | |
| Temperature of the mixture (10°C, 25°C, 40°C) |
Order the steps
A student is designing a fair test for: "Does concentration of vinegar affect how fast it reacts with bicarbonate of soda?" Number the steps from 1 to 8 to show the correct order.
| Order | Step |
|---|---|
| Record the time taken for fizzing to stop in a results table. | |
| Repeat each concentration level three times to improve reliability. | |
| State your hypothesis: "I predict that as vinegar concentration increases, the reaction time will decrease because…" | |
| Identify your independent variable (vinegar concentration) and write a list of all controlled variables. | |
| Add 5 g of bicarbonate of soda to the vinegar and start a stopwatch. | |
| Write a conclusion that references your data and whether it supports your hypothesis. | |
| Prepare three different vinegar solutions: 5%, 10%, and 20% concentration. | |
| Measure and calculate the average time for each concentration. |
1. A student measures the mass of a product in a chemical reaction but forgets to keep the temperature the same between trials. Explain which aspect of their investigation is affected — reliability or validity — and why.
2. What is a confounding variable? Describe one confounding variable that might affect an investigation into whether sunlight speeds up the rusting of iron.
Wrap Up
In one sentence, what was the main idea of this lesson?