Chapter 2, Problem 65A

Interpretation Introduction

Interpretation: The substance which is solid at ${\text{7 }}^{\text{o}}\text{C}$ needs to be determined.

Concept Introduction: The 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.

Answer to Problem 65A

Sulphur.

Explanation of Solution

The substance whose boiling point and melting point is above ${\text{7 }}^{\text{o}}\text{C}$ will be solid at ${\text{7 }}^{\text{o}}\text{C}$ .

From the given substance, bromine, ethanol, mercury, and water are liquid at room temperature. On the other hand, chlorine, and neon is gas at room temperature. Since the boiling point and melting point of sulphur is very high, it is solid at room temperature.

On checking the temperature ranges, bromine will be liquid in the temperature range $-{\text{7 }}^{\text{o}}{\text{C to 59 }}^{\text{o}}\text{C }$ , chlorine will be gas above ${\text{-34 }}^{\text{o}}\text{C}$ , ethanol is liquid in the temperature range $-11{\text{7 }}^{\text{o}}{\text{C to 78 }}^{\text{o}}\text{C }$ , mercury is liquid in the temperature range $-39{}^{\text{o}}{\text{C to 357 }}^{\text{o}}\text{C }$ , neon is gas above $-{\text{246 }}^{\text{o}}\text{C}$ and water is liquid in the range $0{}^{\text{o}}\text{C}-100{}^{\text{o}}\text{C}$ . Thus, these substances cannot be solid at ${\text{7 }}^{\text{o}}\text{C}$ .

Now, the melting point of sulphur is ${\text{115 }}^{\text{o}}\text{C}$ and boiling point is even higher; thus, it is solid at ${\text{7 }}^{\text{o}}\text{C}$ .

Therefore, the correct answer is sulphur.

Conclusion

Thus, sulphur is solid at ${\text{7 }}^{\text{o}}\text{C}$ .