Variables & Solubility
Understanding independent and dependent variables — and seeing them in action through a real experiment.
Variable
Variable
Quick memory trick: The Dependent variable is the one that Depends on what you do. The Independent variable is what I (the researcher) control. Ask: "What am I changing?" = Independent. "What am I watching change?" = Dependent.
affects
Type or amount of fertilizer given to the plants
Growth of the plants (height, number of leaves)
Amount of time spent studying (hours per day)
Students' test scores (measured after studying)
Temperature at which the ice cream is kept (°F or °C)
Time it takes for the ice cream to melt (minutes)
(wood, metal,
plastic)
Variable
experiment
Conditions
required
(Newton-meters)
Variable
Key Points to Remember
The independent variable is what the researcher changes or controls at the start.
The dependent variable is what the researcher measures or observes as a result.
The dependent variable depends on the independent variable — one causes, one responds.
A well-designed experiment changes only one independent variable at a time so results are clear.
What is Solubility?
Solubility means how much of a substance (like sugar or salt) can dissolve in a liquid. A scientist heated water to different temperatures and measured how much sugar dissolved at each temperature. Let's break down the experiment step by step.
The independent variable is what the scientist changed on purpose. In this experiment, the scientist set the water to different temperatures while keeping everything else the same.
Independent Variable = Water Temperature (°C)
The dependent variable is what the scientist measured — the result that changed because of the temperature. As the temperature changed, the amount of sugar that dissolved also changed.
Dependent Variable = Amount of Sugar Dissolved (grams)
Notice that the amount of water stays at 100 g every row — that means water is a controlled variable, not the one being tested.
| 🌡️ Water Temp (°C) | 💧 Water (g) | 🍬 Sugar Dissolved (g) |
|---|---|---|
| 5°C | 100 | 180 g |
| 15°C | 100 | 200 g |
| 25°C | 100 | 215 g |
| 60°C | 100 | 290 g |
| 80°C | 100 | 365 g |
Look at how the sugar amount grows as temperature rises. The bars below show this visually:
Rule: Hotter water dissolves more sugar. Temperature ↑ → Sugar dissolved ↑
When both variables go up together, it is called a direct relationship. When one goes up and the other goes down, it is called an inverse relationship.
Common mistake: Don't confuse the amount of water with the dependent variable. The water stayed at 100 g every time — it never changed. That makes it a controlled variable, not the one being measured.
✅ Lesson Summary
The scientist changed temperature → that's the independent variable.
The scientist measured sugar dissolved → that's the dependent variable.
Water amount stayed at 100 g every trial → that's the controlled variable.
Higher temperature → more sugar dissolves → this is a direct relationship.