Question

a student used an experiment to determine the effect of salt on the boiling point of water. she measured the boiling points of 100 ml of water with salt added in 5 g increments. as a control, she measured the temperature of water with no salt added. what is the purpose of this control? options (paraphrased from ocr): 1. ensure no additional tool issue at experiment start. 2. provide a reference for comparison (variable changed). 3. provide an overview of results/data. 4. determine starting temp for thermometer calculations.

Explanation:

To solve this, we analyze the experiment: the control is water with no salt (measured boiling point), and the experimental group is water with salt. In scientific experiments, a control group is used to provide a baseline (standard) to compare the experimental group against. Let's analyze each option:

• Option A: The control isn’t about showing an initial state (the experiment is about boiling point change, not initial state display). Eliminate A.
• Option B: The control (pure water) is not a “substitute” for the experimental group (salt water); it’s a baseline. Eliminate B.
• Option C: The control (pure water’s boiling point) provides a standard (baseline) to compare the experimental group (salt water’s boiling point) against. This matches the purpose of a control group in an experiment (to establish a reference for comparison).
• Option D: The control isn’t about “collecting data from the thermometer” differently; it’s about having a baseline for comparison. Eliminate D.

Answer:

C. The control provides a standard (baseline) for comparison to see how salt affects the boiling point.