Chapter 3, Problem 18QAP

Classify each of the following as aphysical or chemicalchange or property.

1. A fireplace poker glows red when you heat it in the fire.

A marshmallow turns black when toasted Loo long in a campfire.

Hydrogen peroxide dental strips will make your teeth whiter.

If you wash your jeans with chlorine bleach, they will fade.

If you spill some nail polish remover on your skin, it will evaporate quickly.

When making ice cream at home, salt is added Lo lower the temperature of the ice being used to freeze the mixture.

A hair clog in your bathroom sink drain can be cleared with drain cleaner.

The perfume your boyfriend gave you for your birthday smells like flowers.

Mothballs pass directly into the gaseous state in your closet without first melting.

A log of wood is chopped up with an axe into smaller pieces of wood.

A log of wood is burned in a fireplace.

Interpretation Introduction

(a)

Interpretation:

The following change should be classified as a physical or chemical change or property:

A fireplace poker glows red when you heat it in the fire.

Concept Introduction:

Chemical change occurs in a chemical reaction where there is a change in the composition of the reactants to form new products. On the other hand physical change occurs when there is a difference in the appearance, odor of the substance without a change in its chemical composition.

Answer to Problem 18QAP

Physical change.

Explanation of Solution

A fireplace poker is metal iron. At high temperature the iron metal glows red hot in the heat of the fire. This a physical change as there is change in the appearance of fire iron but no change in its chemical composition.

Interpretation Introduction

(b)

Interpretation:

The following change should be classified as a physical or chemical change or property:

A marshmallow turns black when toasted too long in a campfire.

Concept Introduction:

Chemical change occurs in a chemical reaction where there is a change in the composition of the reactants to form new products. On the other hand physical change occurs when there is a difference in the appearance, odor of the substance without a change in its chemical composition.

Answer to Problem 18QAP

Chemical change.

Explanation of Solution

A marshmallow is made up of water and gelatine. When marshmallow is toasted too long in the campfire, the sugar which is made up of carbon, hydrogen and oxygen undergoes an oxidation reaction. Sugar is finally converted into char which is simply carbon. Marshmallow appears black due to the conversion of sugar to carbon by a chemical reaction. So this is a chemical change.

Interpretation Introduction

(c)

Interpretation:

The following change should be classified as a physical or chemical change or property:

Hydrogen peroxide dental strips will make your teeth whiter.

Concept Introduction:

Chemical change occurs in a chemical reaction where there is a change in the composition of the reactants to form new products. On the other hand physical change occurs when there is a difference in the appearance, odor of the substance without a change in its chemical composition.

Answer to Problem 18QAP

Chemical change.

Explanation of Solution

Hydrogen peroxide is a bleaching agent. Hydrogen peroxide in dental strips can help in whitening teeth by bleaching it. Thus bleaching or whitening of teeth by hydrogen peroxide is a chemical change.

Interpretation Introduction

(d)

Interpretation:

The following change should be classified as a physical or chemical change or property:

If you wash your jeans with chlorine bleach, they will fade.

Concept Introduction:

Chemical change occurs in a chemical reaction where there is a change in the composition of the reactants to form new products. On the other hand physical change occurs when there is a difference in the appearance, odor of the substance without a change in its chemical composition.

Answer to Problem 18QAP

Chemical change.

Explanation of Solution

The chlorine in the bleach will oxidize the dye in the jeans, thus causing the color of the jeans to fade. Here chlorine is carrying out an oxidation reaction; hence the fading of jeans on treatment with chlorine bleach is a chemical change.

Interpretation Introduction

(e)

Interpretation:

The following change should be classified as a physical or chemical change or property:

If you spill some nail polish remover on your skin, it will evaporate quickly.

Concept Introduction:

Chemical change occurs in a chemical reaction where there is a change in the composition of the reactants to form new products. On the other hand physical change occurs when there is a difference in the appearance, odor of the substance without a change in its chemical composition.

Answer to Problem 18QAP

Physical change.

Explanation of Solution

Nail polish remover has volatile liquids such as acetone, or ethyl acetate. Both these solvents in nail polish remover easily evaporate at room temperature. Here the volatile liquids are undergoing a phase change from liquid to gas. So this is a physical change from the liquid phase to gaseous phase.

Interpretation Introduction

(f)

Interpretation:

The following change should be classified as a physical or chemical change or property:

When making ice cream at home, salt is added to lower the temperature of the ice being used to freeze the mixture.

Concept Introduction:

Chemical change occurs in a chemical reaction where there is a change in the composition of the reactants to form new products. On the other hand physical change occurs when there is a difference in the appearance, odor of the substance without a change in its chemical composition.

Answer to Problem 18QAP

Physical change.

Explanation of Solution

Freezing point of a substance is its physical property. When adding salt reduces the freezing point of ice then the ice goes through a physical change. There is no change in the chemical composition of ice.

Interpretation Introduction

(g)

Interpretation:

The following change should be classified as a physical or chemical change or property:

A hair clog in your bathroom sink can be cleared with drain cleaner.

Concept Introduction:

Chemical change occurs in a chemical reaction where there is a change in the composition of the reactants to form new products. On the other hand physical change occurs when there is a difference in the appearance, odor of the substance without a change in its chemical composition.

Answer to Problem 18QAP

Chemical change.

Explanation of Solution

Liquid drain clog remover is a great substitute for baking soda and vinegar. Many commercially available drain cleaners contain high concentration of sulphuric acid. Concentrated sulphuric acid is highly effective in removing hair and grease from the bathroom sink. There is a chemical reaction between sulphuric acid and the grease. So cleaning a hair clog in the bathroom sink with a drain cleaner is a chemical change.

Interpretation Introduction

(h)

Interpretation:

The following change should be classified as a physical or chemical change or property:

The perfume your boyfriend gave you for your first birthday smells like flowers.

Concept Introduction:

Chemical change occurs in a chemical reaction where there is a change in the composition of the reactants to form new products. On the other hand physical change occurs when there is a difference in the appearance, odor of the substance without a change in its chemical composition.

Answer to Problem 18QAP

Physical change.

Explanation of Solution

Perfume is made up of different substances which include flowers, wood, resins, fruits, alcohol and more. The liquid perfume is volatile at room temperature. Perfume in the gaseous state smells like perfume. This is a physical change as the liquid perfume changes to gaseous perfume.

Interpretation Introduction

(i)

Interpretation:

The following change should be classified as a physical or chemical change or property:

Mothballs pass directly into the gaseous state in your closet without first melting.

Concept Introduction:

Chemical change occurs in a chemical reaction where there is a change in the composition of the reactants to form new products. On the other hand physical change occurs when there is a difference in the appearance, odor of the substance without a change in its chemical composition.

Answer to Problem 18QAP

Chemical change.

Explanation of Solution

Mothballs are made of naphthalene or paradichlorobenzene both of which volatilize into the air. Mothball is solid in appearance. Sublimation involves the direct conversion of solid mothball to gaseous state. Here only the appearance of mothball is changing from solid to gas. Hence it is a physical change.

Interpretation Introduction

(j)

Interpretation:

The following change should be classified as a physical or chemical change or property:

A log of wood is chopped up with an axe into smaller pieces of wood.

Concept Introduction:

Chemical change occurs in a chemical reaction where there is a change in the composition of the reactants to form new products. On the other hand physical change occurs when there is a difference in the appearance, odor of the substance without a change in its chemical composition.

Answer to Problem 18QAP

Physical change.

Explanation of Solution

This is a physical change as the original wood is chopped into small pieces. So there is only a change in the appearance of wood but no change in the chemical composition of the wood.

Interpretation Introduction

(k)

Interpretation:

The following change should be classified as a physical or chemical change or property:

A log of wood is burned in a fireplace.

Concept Introduction:

Chemical change occurs in a chemical reaction where there is a change in the composition of the reactants to form new products. On the other hand physical change occurs when there is a difference in the appearance, odor of the substance without a change in its chemical composition.

Answer to Problem 18QAP

Chemical change.

Explanation of Solution

Wood is made up of cellulose, hemicelluloses and lignin, which are mostly hydrocarbon. So when wood is burned in oxygen heat is released along with the release of carbon dioxide and water vapour. So this is a physical change as after burning the original wood is converted into ash, carbon dioxide and water vapour.