# Chemistry Experiment Design and Variables
Research Summary passages on the ACT describe multi-experiment studies. You need to identify variables, understand controls, and evaluate experimental design in chemistry contexts.
1. Types of Variables
| Variable | Definition | Example |
|---|---|---|
| Independent | What the scientist changes | Temperature, concentration |
| Dependent | What is measured | Reaction time, mass of product |
| Controlled | Kept the same | Volume, type of acid, catalyst |
2. Controls
- Control group: baseline experiment with no treatment
- Controlled variables: factors kept constant so only the independent variable changes
- Without controls, you can't determine cause and effect
3. Common Chemistry Experiments on ACT
| Experiment Type | IV | DV |
|---|---|---|
| Rate study | Temperature or concentration | Time to react or volume of gas |
| Acid-base titration | Volume of titrant | pH |
| Solubility | Temperature or solvent | Mass dissolved |
| Electrochemistry | Metal type or concentration | Voltage |
| Calorimetry | Mass or type of fuel | Temperature change |
4. Evaluating Design
Ask yourself:
- Was only ONE variable changed between experiments?
- Were other variables controlled?
- Were enough trials done for reliability?
- Is there a control experiment?
- Could any other factor explain the results?
5. Practice Questions
- In an experiment testing 3 temperatures, identify the IV, DV, and controlled variables.
- A student changes both temperature AND concentration. Why is this a flaw?
- What control would you include in an experiment testing catalysts?
- How would you modify an experiment to test if surface area affects rate?
- Two experiments give different results. Identify the variable that was changed.
Want to check your answers and get step-by-step solutions?
6. ACT Tips
- Quickly identify the IV and DV in each experiment
- Compare experiments to see what changed
- The question often asks: "what was the purpose of Experiment 2?" — answer by identifying what new variable was tested
- If an experiment has a flaw, it's usually because multiple variables changed