Molality

Q.

QUESTION 2.8

An antifreeze solution is prepared from 222.6 g of ethylene glycol $\left(C_2{H}_6{O}_2\right)$ and 200 g of water. Calculate the molality of the solution. If the density of the solution is $1.072gm{L}^{-1}$, then what shall be the molarity of the solution?

Q.

If the density of some lake water is $1.25gm{L}^{-1}$ and contains 92 g of $N{a}^{+}$ ions per kg of water, calculate the molarity of $N{a}^{+}$ ions in the lake.

Q.

Calculate the amount of benzoic acid (${\mathrm{C}}_6{\mathrm{H}}_5\mathrm{COOH}$) required for preparing 250 ml of 0.15 M solution in methanol.

Q.

Lowering of vapour pressure due to solute in 1 molal aqueous solution at 100°C is

BOOK ANSWER - 13.44 Torr

MY SOLUTION

Since molality is 1 mole kg^{​​​​​-1}

That's mean 1 mole of solute is present in 1 kg of solvent (H_{​​​​​​2}​​​​​O)

No. Of moles of Water = 1000g/18 = 55.55

No. Of moles of solute = 1

Mole Fraction of solute = 1/1+55.55 = 0.0176 .... (I)

Pressure of solvent (assuming ideal behaviour)

PV = nRT

P = 55.55 x 0.0821 x 373 / 1 (d of water = 1)

P = 1701.2774 atm

1 atm = 760 Torr

p_{​​​​​​solvent} = 1292970.8 Torr

We know from Raoult Law

∆p = X_{​​​​​​solute} . P(solvent)

∆p = 0.0176 x 1292970.8

∆p = 22756.286

So, According to my answer ∆p amount of vapour pressure will be low. But my answer and book answer is not same.

I don't want solution of this question.

You just tell me the place where I am going in wrong direction in my solution.

Q. mole fraction of ethanol water mixture 0.25 .hence percentage concentration by weight of mixture is 1.25% 2.75% 3.46% 4.54%

Q.

The vapour pressure of benzene at a certain temperature is 640mm of Hg. A non volatile and non electrolyte solid weighing 2.175 g is added to 39.08 g of benzene. The vapour pressure of the solution is 600mm of Hg. What is the molecular mass of the solid substance?

Q.

O2 is bubbled through water at 293K. How many moles of O2 will dissolve in 1L of water, if partial pressure of 02 is 2 kilobar and Kh is 34.86 kilobar?

Q. The boiling point elevation constant $\left(K_b\right)$ of water is $0.52{\text{K kg mol}}^{-1}$. The boiling point of $0.1maq.$ solution of urea is:

1. ${105.2}^{\circ }C$
2. ${1002.5}^{\circ }C$
3. ${100.52}^{\circ }C$
4. ${100.052}^{\circ }C$

Q.

Molarity of H2SO4 solution is 0.8M and its density is 1.06g/cm-3 What will be the concentration of the solution in terms of molality and determine the mole fraction of the solution

Q. Calculate the molality of a 20% $CaC{O}_3$ solution (by mass). The density of the solution is 1.2 g/mL.

1. 1.25 m
2. 2.50 m
3. 1.52 m
4. 2.08 m

Q. Dissolving 120 g of urea (mol. wt. 60) in 1000 g of water gave a solution of density 1.15 g/mL. The molarity of the solution is

1. 2.05 M
2. 2.22 M
3. 1.78 M
4. 2.00 M

Q.

What is molality and molarity?

Q.

Question 2.29

Nalorphene $\left(C_{19}{H}_{21}N{O}_3\right)$, similar to morphine, is used combat withdrawal symptoms in narcotic users. Does of nalorphene generally given is 1.5 mg. Calculate the mass of $1.5\times {10}^{-3}m$ aqueous solution required for the above dose.

Q. A solution of sodium sulfate contains 92 g of $N{a}^{+}$ ions per kilogram of water. The molality of $N{a}^{+}$ ions in that solution in $molk{g}^{-1}$ is:

1. 16
2. 8
3. 4
4. 12

Q.

Assuming complete ionization, calculate freezing point of solution prepared by adding 6g Glauber's salt ${Na}_{2}S{O}_4.10H_{2}O$ in 0.1 kg of water ?(Given $K_f$ = 1.86 K kg/mol , Atomic masses, $Na=23,O=16,S=32,H=1$ )

Q.

Find out the mole fraction of solute in an aqueous solution of $30\%\mathrm{NaOH}$.

Q.

4L of 0.02M aqueous solution of NaCl was diluted by adding 1L of water. The molality of the sol. Is

Q. Calculate the molality of 58.5 g of NaCl (Molar mass of NaCl= 58.5 $gmo{l}^{-1})$ dissolved in 500 g of water.

1. 1 m
2. 2 m
3. 0.5 m
4. 1.5 m

Q. Calculate the molality of an aqueous glucose solution in which mole fraction of glucose is 0.25.

1. 20.64 m
2. 18.26 m
3. 13..88 m
4. 18.52 m

Q.

36.5% HCl has density 1.20g/ml. The molarity and molality are..

Q. An aqueous solution ethanol has density $1.025gm{L}^{-1}$ and $2M$. What is the molality of this solution?

1. $2.143m$
2. None of these
3. $1.79m$
4. $1.951m$

Q.

$2\mathrm{molal}$ solution of a weak acid $\mathrm{HA}$ has a freezing point of $3.885{}^{\mathrm{o}}\mathrm{C}$. The degree of dissociation of this acid is $\mathrm{\_\_\_\_\_\_\_\_\_}\times {10}^{–3}$. (Round off to the Nearest Integer). [Given: Molal depression constant of water $=1.85\mathrm{K}\mathrm{kg}{\mathrm{mol}}^{–1}$, Freezing point of pure water $=0{}^{\mathrm{o}}\mathrm{C}$]

Q. The density of a solution prepared by dissolving $120g$ of urea (Mol. Mass $=60u$) in $1000g$ of water is $1.15g/mol$. The molarity of this solution is
(AIEEE 2012)

1. $1.02M$
2. $0.50M$
3. $1.78M$
4. $2.05M$

Q. Calculate the molality of a 1 L solution of 80% $H_{2}S{O}_4$$\left(\frac{w}{v}\right)$, given that the density of the solution is 1.80 g $m{L}^{-1}$.

1. 8.16 m
2. 8.60 m
3. 1.02 m
4. 10.8 m

Q. The molality of a sulphuric acid solution is 0.2 mol/kg. Calculate the total weight of the solution having 1000 g, of solvent:-

1. 1000 g
2. 1098.6 g
3. 980.4 g
4. 1019.6 g

Q. Find the molality of 1 M HCl solution having a density of 1.5365 g/mL:

1. 0.22 m
2. 0.44 m
3. 0.33 m
4. 0.67 m

Q. Two liquid having vapour pressure P1 note and P2 note in pure state in the ratio of 2:1 are mixed in the molar ratio of 1:2.The ratio of their moles in the vapour state would be

Q.

According to the Raoult's law the relative decrease in the solvent vapour pressure over the solution containing a nonvolatile solute is equal to the

1. the mole fraction of the solute.

2. the viscosity of solution.

3. the number of moles of the solute.

4. the mole fraction of the solvent

Q. 10L of urea solution contains 240g of urea. The active mass of Urea will be

1. 0.04
2. 0.02
3. 0.2
4. 0.4

Q. if mole fraction of urea in aqueous solution is 0.1 , then mass percentage of urea in the solution will be(molar mass of the urea 60g /mol