Question

Investigations were carried out in a science lab to explore the topic of chemical and physical changes. Investigation A Step 1. Add 5 tsp. salt to 100 ml warm water.and stir until most or all of the salt is no longer visible. Step 2. Heat the salt solution on a burner until only a white solid remains. Investigation B Step 1. Mix 10 tsp. white sugar into 100 ml water and stir until most or all of the sugar is no longer visible. Step 2. Heat the sugar solution on a burner until the solution thickens and turns brown.In which step(s) did a chemical change most likely occur?

Answer 1

Answer:

Investigation B, Step 2

Explanation:

The colour change is a good indication of a chemical change. The sugar molecules were most likely changing into something else.

Investigation A, Step 1. Wrong. The dissolving of salt is a physical process.

Investigation A, Step 2. Wrong. You simply boiled off the water (a physical process) and recovered the salt.

Investigation B, Step 1. Wrong. The dissolving of sugar is a physical process.

Answer 2

Answer:

Answer is: B step 2,  Heat the sugar solution on a burner until the solution thickens and turns brown.

This is chemical change (chemical reaction), because new substance (caramel) is formed, the atoms are rearranged and the reaction is followed by an energy change.

In other examples physical change is occured.

The same substance is present before and after the psysical change, just with different form or state of matter. Making mixture is physical change (physical change is reversible).

Explanation: