Question

Pure ice is heated to obtain pure water. The water is heated to convert it into steam. The following graph shows the pattern of the heating curves of ice and water combined.


Then, select the correct statement(s) from the following.

• A. The pressure in the range QR $>1\text{atm}$
• B. The MP of ice is $-5{}^{\circ }\text{C}$.
• C. The BP of water is $75{}^{\circ }\text{C}$.
• D. The pressure in the range PQ $>1\text{atm}$

Answer 1

Answer: (B), (C), (D)

The pressure in the range PQ $>1\text{atm}$


From the given heating curve,

• In the range PQ, the ice melts gradually at a temperature of $-5{}^{\circ }\text{C}$, i.e. the slope of the graph is constant. So, the melting point of the ice is $-5{}^{\circ }\text{C}$.
• After R, the water gradually turns into steam at a temperature of $75{}^{\circ }\text{C}$, i.e. the slope of the graph is constant. So, the boiling point of the water is $75{}^{\circ }\text{C}$.

For substances like ice that contract on melting, the melting point (MP) decreases with increase in pressure. Pure ice melts at $0{}^{\circ }\text{C}$ at $1\text{atm}$ pressure. Since ice melted at $-5{}^{\circ }\text{C}$, the pressure in the range PQ $>1\text{atm}$.
The boiling point (BP) of a liquid increases with increase in pressure, and decreases with decrease in pressure. Pure water boils at $100{}^{\circ }\text{C}$ at 1 atm pressure. Since water boiled at $75{}^{\circ }\text{C}$, the pressure in the range QR $<1\text{atm}$.