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

A chemical change likely occurred in Investigation B Step 2 during the caramelization of sugar, whereas in Investigation A, the changes were physical. Chemical changes are indicated by new substances being created, often accompanied by color changes, temperature changes, light emission, bubble formation or the creation of a precipitate.

Step-by-step explanation:

In the provided scenarios, chemical changes most likely occurred in Investigation A Step 2 and Investigation B Step 2. In Investigation A Step 2, heating the salt solution until only a white solid remains involves the process of evaporation, which is a physical change, but the salt remains chemically unchanged. In Investigation B Step 2, the heating of the sugar solution until it thickens and turns brown is indicative of caramelization, a chemical change where sugar molecules break down and form new compounds.

Indicators of chemical change include a color change not attributable to simple dilution or concentration, a change in temperature that isn't caused by external heating or cooling, the emission of light or the formation of gas bubbles when the substance is not boiling, and formation of a precipitate.

In summary, melting, dissolving, and evaporation are typically physical changes because they do not change the substance's molecular composition. However, rusting, burning, caramelization and reactions that result in color change, bubbles or precipitates are all signs of chemical reactions and chemical changes.

Answer 2

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).