Chapter 2, Problem 90A

Solution

(a)

Interpretation: The substances which are liquid at $125{}^{\text{o}}\text{C}$ needs to be determined.

Concept Introduction: There are generally three states of matter that is solid, liquid and gas. Substances which are solid at room temperature have high melting and boiling points. Melting point is defined as temperature at which a solid substance starts melting. The boiling point is defined as the temperature of a liquid when its vapor pressure is equal to the atmospheric pressure. This is the temperature when liquid starts boiling and converts into vapor.

Mercury and sulphur.

Any substance is said to be liquid at $125{}^{\text{o}}\text{C}$ if its melting point is less than $125{}^{\text{o}}\text{C}$ and boiling point is more than $125{}^{\text{o}}\text{C}$ . Substances that fulfill these requirements are mercury and sulphur. The melting and boiling point of mercury is $-39{}^{\text{o}}\text{C}$ and $357{}^{\text{o}}\text{C}$ respectively; thus, mercury is liquid in this range. Similarly, the melting and boiling points of sulphur are $115{}^{\text{o}}\text{C}$ and $445{}^{\text{o}}\text{C}$ respectively; thus, it will be liquid in this range.

Therefore, substances liquid at $125{}^{\text{o}}\text{C}$ are mercury and sulphur.

(b)

Interpretation: The physical properties of one of the substances which are liquid at $125{}^{\text{o}}\text{C}$ need to be determined.

Concept Introduction: There are generally three states of matter that is solid, liquid and gas. Substances that are solid at room temperature have high melting and boiling points. Melting point is defined as the temperature at which a solid substance starts melting. The boiling point is defined as the temperature of a liquid when its vapor pressure is equal to the atmospheric pressure. This is the temperature when liquid starts boiling and converts into vapor.

As per the table, two substances that are liquid at $125{}^{\text{o}}\text{C}$ are mercury and sulphur. The physical properties of mercury are as follows:

1. It is the only metal that is liquid at room temperature.
2. The melting and boiling point of mercury is $-39{}^{\text{o}}\text{C}$ and $357{}^{\text{o}}\text{C}$ respectively.
3. The color of mercury is silver-white.
4. It has very high surface tension.
5. It is a good conductor of electricity.

Similarly, the physical properties of sulphur are as follows:

1. The melting and boiling point of sulphur are $115{}^{\text{o}}\text{C}$ and $445{}^{\text{o}}\text{C}$ respectively.
2. Sulphur has no taste or odor.
3. It is pale yellow.
4. It is a poor conductor of electricity.
5. Pure sulphur is a brittle solid.

(c)

Interpretation: The substances given in the table need to be arranged other than the increasing order of melting point.

Concept Introduction: There are generally three states of matter that is solid, liquid and gas. Substances that are solid at room temperature have high melting and boiling points. Melting point is defined as the temperature at which a solid substance starts melting. The boiling point is defined as the temperature of a liquid when its vapor pressure is equal to the atmospheric pressure. This is the temperature when liquid starts boiling and converts into vapor.

The given data can also be arranged in increasing order of boiling point as follows:

Substance	State	Colour	Melting point	Boiling point
Neon	Gas	Colorless	$-249{}^{\text{o}}\text{C}$	$-246{}^{\text{o}}\text{C}$
Oxygen	Gas	Colorless	$-218{}^{\text{o}}\text{C}$	$-183{}^{\text{o}}\text{C}$
Chlorine	Gas	Greenish-yellow	$-101{}^{\text{o}}\text{C}$	$-34{}^{\text{o}}\text{C}$
Bromine	Liquid	Reddish-brown	$-7{}^{\text{o}}\text{C}$	${\text{59 }}^{\text{o}}\text{C}$
Ethanol	Liquid	Colorless	$-117{}^{\text{o}}\text{C}$	${\text{78 }}^{\text{o}}\text{C}$
Water	Liquid	Colorless	${\text{0 }}^{\text{o}}\text{C}$	${\text{100 }}^{\text{o}}\text{C}$
Mercury	Liquid	Silvery-white	$-{\text{39 }}^{\text{o}}\text{C}$	${\text{357 }}^{\text{o}}\text{C}$
Sulfur	Solid	Yellow	${\text{115 }}^{\text{o}}\text{C}$	${\text{445 }}^{\text{o}}\text{C}$
Sulfur	Solid	White	${\text{801 }}^{\text{o}}\text{C}$	${\text{1413 }}^{\text{o}}\text{C}$
Aluminum	Solid	Silver	${\text{660 }}^{\text{o}}\text{C}$	${\text{2519 }}^{\text{o}}\text{C}$
Copper	Solid	Reddish-yellow	${\text{1084 }}^{\text{o}}\text{C}$	${\text{2562 }}^{\text{o}}\text{C}$
Gold	Solid	Yellow	${\text{1064 }}^{\text{o}}\text{C}$	${\text{2856 }}^{\text{o}}\text{C}$