Elevation in Boiling Point

Q.

Define ebullioscopic constant?

Q. Consider a first order decomposition process $A_3\to \frac{3}{2}{A}_2$
A plot of the concentration of $A_3$ and $A_2$ versus time is shown below. At time , the percentage of the reaction decomposed is

1. 40%
2. 30%
3. 75%
4. 50%

Q.

K_f of 1, 4-dioxane is 4.9 mol^-1 for 1000 g. The depression in freezing point for a 0.001 m solution in dioxane is:

1. 0.0049

2. 4.9

3. 0.49

4. 0.049

Q.

The boiling point of a solution of 0.105 gm of a substance in 15.84 gram of ether was found to be 100°C higher than that of pure ether. What is the molecular weight of the substance [Molecular elevation constant of ether per 100 g = 21.6]

1. 144.50

2. 143.18

3. 140.28

4. 146.66

Q. On dissolving $10.8g$ glucose (molar weight = $180g/mol$) in $240g$ of water, its boiling point increases by ${0.13}^{\circ }C$. Calculate the molal elevation constant of water.

1. ${0.45}^{\circ }Ckgmo{l}^{-1}$
2. ${0.52}^{\circ }Ckgmo{l}^{-1}$
3. ${0.75}^{\circ }Ckgmo{l}^{-1}$
4. $1^{\circ }Ckgmo{l}^{-1}$

Q.

A 0.2 molal aqueous solution of a weak acid (HX) is 20% ionised. The freezing point of this solution is (Given for water)

1. - 0.31° C

2. - 0.45°C

3. - 0.53°C

4. - 0.90°C

Q.

The molal elevation constant is the ratio of the elevation in B.P. to

1. Molarity

2. Molality

3. Mole fraction of solute

4. Mole fraction of solvent

Q. If $30g$ of a solute of molecular weight $154gmo{l}^{-1}$is dissolved in $250g$ of benzene, what will be the boiling point of the resulting solution under atmospheric pressure?
The molal boiling-point elevation constant for benzene is $2.61Kkgmo{l}^{-1}$ and the boiling point of pure benzene is ${80.1}^{o}C.$

Q. When a non-volatile solute of $10g$ is added to $150g$ of carbon disulphide, the boiling point of the solution raised to ${0.55}^{\circ }C$ above that of pure solvent. The boiling point of pure carbon disulphide is ${46.30}^{\circ }C$ and its heat of vapourisation is $84cal/g$. Determine the molar mass of the solute.

Q. $18g$ of glucose, $C_6{H}_{12}{O}_6$ is dissolved in $1kg$ of water in a saucepan. At what temperature will the water boil
under atmospheric pressure? $K_b$ for water is $0.52Kkgmo{l}^{-1}$

Q.

Pressure cooker reduces cooking time for food because:

1. Heat is more evenly distributed in the cooking space
2. Boiling point of water involved in cooking is increased
3. The higher pressure inside the cooker crushes the food material
4. Cooking involves chemical changes helped by a rise in temperature

Q.

The boiling point of water (100°C) becomes 100.52°C, if 3 grams of a non-volatile solute is dissolved in 200ml of water. The molecular weight of

solute is

1. 

2. 15.4 g mol

3. 17.3 g mol^-1

4. 20.4 g mol

Q.

The molal elevation constant of water = 0.52⁰C. The boiling point of 1.0 molal aqueous KCl solution (assuming complete dissociation of KCl), therefore, should be

1. ${100.52}^{\circ }C$

2. ${101.04}^{\circ }C$

3. ${99.48}^{\circ }C$

4. ${98.96}^{\circ }C$

Q. The enthalpy of vapourisation of water is $9700calmo{l}^{-1}$. Given that pure water boils at ${100}^{\circ }C$, then calculate the value of ebullioscopic constant of water :

Q. A solution of $2.5g$ of a non - volatile solid in $100g$ benzene is boiled at $0.42K$ higher than the boiling point of pure benzene. Calculate the molar mass of the substance. Molal elevation constant of benzene is $2.67Kkgmo{l}^{-1}$

Q.

When 30 g of urea are dissolved in 9.0 g of water, the relative lowering of vapour pressure is:

1. 30/90
2. 30/39
3. 39/30
4. 1/2

Q.

If 0.15g of a solute dissolved in 15g of solvent is boiled at a temperature higher by 0.216⁰C than that of the pure solvent, then the molecular weight of the

substance is (molal elevation constant for the solvent is 2.16):

1. 1.01

2. 10

3. 10.1

4. 100

Q. An 8% aqueous solution of urea (by mass of solvent) has an elevation in boiling point of $x_1$. 20% aqueous solution of glucose (by mass of solvent) has an elevation in boiling point of $x_2$. If these two solutions are mixed, then the elevation in boiling point is $x_3$.
Then,

1. $x_1+x_2=2x_3$
2. $3x_1+x_2=x_3$
3. $x_1<x_2<x_3$
4. $x_1=x_2=x_3$

Q. If the boiling point elevation constant and the boiling point of benzene are $2.16{\text{K kg mol}}^{-1}$ and ${81.0}^{\circ }\text{C}$ respectively, calculate the boiling point of a solution formed when $5\text{g}$ of $C_{14}{H}_{12}$ is dissolved in $15\text{g}$ of benzene.

1. ${90}^{\circ }\text{C}$
2. ${75}^{\circ }\text{C}$
3. ${81}^{\circ }\text{C}$
4. ${85}^{\circ }\text{C}$

Q. The decomposition of $N_2{O}_5$ according to the equation $2N_2{O}_5\left(g\right)\to 4N{O}_2\left(g\right)+O_2\left(g\right)$
is a first order reaction. After 2 minutes from the start of decomposition in a closed vessel, the total pressure developed is found to be 500 mm Hg. On complete decomposition, the total pressure is 800 mm Hg. If the rate constant of the reaction is $ymi{n}^{-1}$ then, what is the value of y? (given log 2 = 0.3, log 3 = 0.5)

Q. The vapour pressure of an aqueous solution is found to be $750\text{torr}$ at certain temperature ${}^{\prime }{T}^{\prime }$. If ${}^{\prime }{T}^{\prime }$ is the temperature at which pure water boils under atmospheric pressure and same solution show elevation in boiling point $\Delta T_b=1.04\text{K}$, find the atmospheric pressure $(K_b=0.52{\text{k kg mol}}^{-1})$

Q. If the boiling point elevation constant and the boiling point of benzene are $2.16{\text{K kg mol}}^{-1}$ and ${81.0}^{\circ }\text{C}$ respectively, calculate the boiling point of a solution formed when $5\text{g}$ of $C_{14}{H}_{12}$ is dissolved in $15\text{g}$ of benzene.

1. ${90}^{\circ }\text{C}$
2. ${75}^{\circ }\text{C}$
3. ${81}^{\circ }\text{C}$
4. ${85}^{\circ }\text{C}$

Q.

The molal boiling point constant for water is . When 0.1 mole of sugar is dissolved in 200 ml of water, the solution boils under a pressure of one atmosphere at

1. 

2. 

3. 

4. 

Q.

Boiling point of chloroform was raised by 0.323 K, when 0.5143 g of anthracene was dissolved in 35 g of chloroform. Molecular mass of anthracene is(= 3.9 kg mol^-1)

1. 79.42 g/mol

2. 132.32 g/mol

3. 177.42 g/mol

4. 242.32 g/mol

Q.

The latent heat of vapourisation of water is 9700 Cal/mole and if the b.p. is 100⁰C, ebullioscopic constant of water is

1. ${0.513}^{\circ }C$

2. ${1.026}^{\circ }C$

3. ${10.26}^{\circ }C$

4. ${1.832}^{\circ }C$

Q.

Two compounds A and B forms non-volatile compounds having molecular formulae $A{B}_2$ and $A{B}_4$. when 1 g of $A{B}_2$ and 1g of $A{B}_4$ are separately dissolved in 20 g of Benzene, the B.P. was lowered by ${2.3}^{\circ }C$ and ${1.3}^{\circ }C$ respectively. Find the molar mass of A and B. $k_b$ of Benzene is S.1 k kg/mol

1. $M_A=32g,B_B=26.4g$

2. $M_A=25.60g,M_B=42.65g$

3. $M_A=14.6g,M_B=22.4g$

4. $M_A=8.4g,M_B=15g$

Q.

What is the effect of the addition of impurities on the freezing and boiling point of a substance?

Q.

Which of the following aqueous solutions, containing 10 gm of solute in each case, has highest boiling point?

1. NaCl solution

2. KCl solution

3. Sugar solution

4. Glucose solution

Q. The freezing point depression constant for water is ${1.86}^{\circ }C{m}^{-1}$. If 5.00 g $N{a}_{2}S{O}_4$ is dissolved in 45.0 g $H_{2}O$, the freezing point is changed by $-{3.82}^{\circ }C$. Calculate the Van't Hoff factor for $N{a}_{2}S{O}_4$.

[AIMPT 2011]

Q.

The temperature, at which the vapour pressure of a liquid becomes equal to the atmospheric pressure is known as

1. Freezing point

2. Boiling point

3. Absolute temperature

4. None of these