Chapter 3, Problem 19CR

Which of the following represent physical properties or changes, and which represent chemical properties or changes?

1. You curl your hair with a curling iron.

You curl your hair by getting a “permanent wave” at the hair salon.

Ice on your sidewalk melts when you put salt on it.

A glass of water evaporates overnight when it is left on the bedside table.

Your steak chars if the skillet is too hot.

Alcohol feels cool when it is spilled on the skin.

Alcohol ignites when a flame is brought near it.

Baking powder causes biscuits to rise.

Interpretation Introduction

(a)

Interpretation:

It should be discussed, that whether the given statement is a physical property or a change or chemical property or a change.

Concept Introduction:

Physical properties can be observed or measured without changing the composition of matter. Physical properties include: appearance, texture, color, odor, melting point, boiling point, density, solubility, polarity etc. a physical change involves a change in one or more physical properties but no change in the fundamental components that make up the substance. The most common physical changes are changes of state: solid, liquid or gas.

A chemical change involves a change in the fundamental components of the substance; a given substance changes into a different substance or substances. Chemical changes are called reactions.

Answer to Problem 19CR

Curling hair with a curling iron is a physical change.

Explanation of Solution

Curling iron with a curling iron does not make any change in fundamental components that make up hair. It just changes the appearance of hair which is a physical property. So curling up hair is a physical change.

Interpretation Introduction

(b)

Interpretation:

It should be discussed, that whether the given statement is a physical property or a change or chemical property or a change.

Concept Introduction:

Physical properties can be observed or measured without changing the composition of matter. Physical properties include: appearance, texture, color, odor, melting point, boiling point, density, solubility, polarity etc. a physical change involves a change in one or more physical properties but no change in the fundamental components that make up the substance. The most common physical changes are changes of state: solid, liquid or gas.

A chemical change involves a change in the fundamental components of the substance; a given substance changes into a different substance or substances. Chemical changes are called reactions.

Answer to Problem 19CR

Curling hair by getting a “permanent wave” is a chemical change.

Explanation of Solution

A permanent wave, involves the use of heat and chemicals to break and reform the cross-linking bonds of the hair structure. A chemical solution is applied on hair and this solution reacts chemically softening the inner structure of the hair by breaking some of the cross links within and between the protein chains of the hair. So getting permanent wave is a chemical change.

Interpretation Introduction

(c)

Interpretation:

It should be discussed, that whether the given statement is a physical property or a change or chemical property or a change.

Concept Introduction:

Physical properties can be observed or measured without changing the composition of matter. Physical properties include: appearance, texture, color, odor, melting point, boiling point, density, solubility, polarity etc. a physical change involves a change in one or more physical properties but no change in the fundamental components that make up the substance. The most common physical changes are changes of state: solid, liquid or gas.

A chemical change involves a change in the fundamental components of the substance; a given substance changes into a different substance or substances. Chemical changes are called reactions.

Answer to Problem 19CR

Melting of ice when salt is put on it is a physical change.

Explanation of Solution

Salt causes “freezing point depression”, i.e. salt helps in lowering the freezing point and, consequently, the melting point of water. Water freezes at 0°C or 32°F. By using salt, that freezing point can be lowered which causes the ice to melt.

Interpretation Introduction

(d)

Interpretation:

It should be discussed, that whether the given statement is a physical property or a change or chemical property or a change.

Concept Introduction:

Physical properties can be observed or measured without changing the composition of matter. Physical properties include: appearance, texture, color, odor, melting point, boiling point, density, solubility, polarity etc. a physical change involves a change in one or more physical properties but no change in the fundamental components that make up the substance. The most common physical changes are changes of state: solid, liquid or gas.

A chemical change involves a change in the fundamental components of the substance; a given substance changes into a different substance or substances. Chemical changes are called reactions.

Answer to Problem 19CR

Evaporating glass of water overnight is a physical change.

Explanation of Solution

When water evaporates, it changes its physical state from liquid state to the gaseous state. Evaporation of water does not make any change to the fundamental components of water, which is H₂ O. So evaporation of water is a physical change.

Interpretation Introduction

(e)

Interpretation:

It should be discussed, that whether the given statement is a physical property or a change or chemical property or a change.

Concept Introduction:

Physical properties can be observed or measured without changing the composition of matter. Physical properties include: appearance, texture, color, odor, melting point, boiling point, density, solubility, polarity etc. a physical change involves a change in one or more physical properties but no change in the fundamental components that make up the substance. The most common physical changes are changes of state: solid, liquid or gas.

A chemical change involves a change in the fundamental components of the substance; a given substance changes into a different substance or substances. Chemical changes are called reactions.

Answer to Problem 19CR

Charring of steak, when the skillet gets too hot is a chemical change.

Explanation of Solution

When the skillet gets too hot, because of the high temperature, components of steak like proteins, carbohydrates are chemically changed. So the steak is no longer in its original form. So this is a chemical change.

Interpretation Introduction

(f)

Interpretation:

It should be discussed, that whether the given statement is a physical property or a change or chemical property or a change.

Concept Introduction:

Physical properties can be observed or measured without changing the composition of matter. Physical properties include: appearance, texture, color, odor, melting point, boiling point, density, solubility, polarity etc. a physical change involves a change in one or more physical properties but no change in the fundamental components that make up the substance. The most common physical changes are changes of state: solid, liquid or gas.

A chemical change involves a change in the fundamental components of the substance; a given substance changes into a different substance or substances. Chemical changes are called reactions.

Answer to Problem 19CR

Alcohol feels cool when it splits on skin due to a physical change.

Explanation of Solution

When alcohol splits on the skin, it evaporates quickly using the body temperature. Due to the sudden decrease of body temperature we feel cool. And because alcohol changes its physical state from liquid state to gaseous state, this is a physical change.

Interpretation Introduction

(g)

Interpretation:

It should be discussed, that whether the given statement is a physical property or a change or chemical property or a change.

Concept Introduction:

Physical properties can be observed or measured without changing the composition of matter. Physical properties include: appearance, texture, color, odor, melting point, boiling point, density, solubility, polarity etc. a physical change involves a change in one or more physical properties but no change in the fundamental components that make up the substance. The most common physical changes are changes of state: solid, liquid or gas.

A chemical change involves a change in the fundamental components of the substance; a given substance changes into a different substance or substances. Chemical changes are called reactions.

Answer to Problem 19CR

Ignition of alcohol is a chemical change.

Explanation of Solution

When alcohol ignites, it reacts with oxygen in the air and converted into carbon dioxide and water. So the components of alcohol are changed. So this is a chemical change.

Interpretation Introduction

(h)

Interpretation:

It should be discussed, that whether the given statement is a physical property or a change or chemical property or a change.

Concept Introduction:

Physical properties can be observed or measured without changing the composition of matter. Physical properties include: appearance, texture, color, odor, melting point, boiling point, density, solubility, polarity etc. a physical change involves a change in one or more physical properties but no change in the fundamental components that make up the substance. The most common physical changes are changes of state: solid, liquid or gas.

A chemical change involves a change in the fundamental components of the substance; a given substance changes into a different substance or substances. Chemical changes are called reactions.

Answer to Problem 19CR

Baking powder causes the biscuits to rise due to a chemical change.

Explanation of Solution

Baking powder’s chemical name is sodium bicarbonate. When sodium carbonate and other materials are heated a chemical reaction undergoes and converts sodium bicarbonate into sodium carbonate, carbon dioxide and water. This carbon dioxide causes the biscuits to rise. So this is a chemical change.