If a hot, saturated solution of copper sulfate is cooled rapidly in ice-cold water, smaller and less well-formed crystals will form than if it is cooled slowly at room temperature. How would you design and perform an experiment to test this hypothesis?
To test the hypothesis, I will prepare a hot saturated solution of copper sulfate. I will take 1 g of copper sulfate in a 100 mL beaker, add 25 mL of water, and a drop of dilute sulfuric acid. I will heat it in a water bath while stirring, adding more copper sulfate until the solution becomes saturated.
Next, I will filter the hot solution to remove insoluble impurities and collect it in a clean beaker. I will then divide this filtered hot saturated solution into two equal parts in separate clean beakers.
For the first part, I will cool it rapidly by placing the beaker in ice-cold water. This rapid cooling will not give particles enough time to come together, resulting in smaller and less well-formed crystals.
For the second part, I will allow the solution to cool slowly at room temperature without disturbing it. Slow cooling gives enough time to the particles to come together, resulting in the formation of larger, shiny, well-shaped blue-coloured crystals.
Finally, I will filter, rinse with cold water, and dry the crystals from both beakers on a watch glass. Comparing the size and shape of the crystals from both setups will test the hypothesis.
Explanation
The textbook provides a step-by-step procedure for creating a saturated copper sulfate solution (Activity 5.3) and explicitly suggests dividing the hot saturated solution into two equal parts to test the cooling rate hypothesis (Think as a Scientist). It explains that slow cooling allows particles enough time to come together to form larger, well-shaped crystals, whereas rapid cooling does not, leading to smaller, less well-formed crystals. The experiment design directly applies these provided steps and scientific principles.
Solution Steps
Step 1: Prepare a hot saturated solution of copper sulfate by heating 1 g copper sulfate and 25 mL water with a drop of dilute sulfuric acid, adding more solid until saturated.
Step 2: Filter the hot solution to remove insoluble impurities and divide the filtrate into two equal parts.
Step 3: Cool the first part rapidly by placing it in ice-cold water.
Step 4: Cool the second part slowly at room temperature without disturbing it.
Step 5: Filter, rinse, and dry the crystals from both parts, then compare their size and shape to verify the hypothesis.