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Published on: 20/09/2019
Chemistry in Everyday Life
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1.
Calculate the boiling point of a 1M aqueous solution (density 1.04 g mL-1) of potassium chloride (Kb for water = 0.52 K kg mol-1, Atomic masses : K = 39 u, CI = 35.5 u). Assume, potassium chloride is completely dissociated in solution.
2.
How can you remove the hard calcium carbonate layer of the egg without damaging its semi-permeable membrane? Can this egg be inserted into a bottle with a narrow neck without distorting its shape? Explain the process involved.
3.
An aqueous solution of 3.12 g of BaCl2 in 250 g of water is found to boil at 100.0832oC. Calculate the degree of dissociation of BaCl2. [K b (H2O) = 0.52 K/m.]
4.
A solution of sucrose (Mol. Wt. 342) is prepared by dissolving 68.4 g of it per litre of solution. What is osmotic pressure at 300 K? (R = 0.0821 L atm K-1 mol-1)
5.
A mongst the following compounds, identify which are insoluble, partially soluble in water?
(i) phenol , (ii) toluene,
(iii) formic acid, (iv) ethylene glycol,
(v) chloroform, (vi) pentanol.
6.
An aqueous solution of 2% non-volatile solute exerts a pressure of 1.004 bar at the normal boiling point of the solvent. What is the molecular mass of the solute?
7.
The vapour pressure of water is 12.3 kPa at 300 K. Calculate vapour pressure of 1 molal solution of a non-volatile solute in it.
8.
A 0.1539 molal aqueous solution of cane sugar (mol. mass = 342 g mol -1) has a freezing point of 271 K while the freezing point of pure water is 273.15 K. what will be the freezing point of an aqueous solution containing 5 g of glucose (mol. mass = 180 g mol-1) per 100 g of solution?
9.
0.1 mole of acetic acid was dissolved in 1 kg of benzene. Depression in freezing point of benzene was determined to be 0.256 K. what conclusion can you draw about the state of the solute in solution? [Given: Kf for benzene = 5.12 K/m]
10.
A solution of urea in water has a boiling point of 373.128 K. Calculate the freezing point of the same solution. [Given: For water, K f = 1.86 Km-1, Kb = 0.52 Km-1]
11.
100 g of liquid A (molar mass 140 g mol -1) was dissolved in 1000 g of liquid B (molar mass 180 g mol-1). The vapour pressure of pure liquid B was found to be 500 torr. Calculate the vapour pressure of pure liquid A and its vapour pressure in the solution if the total vapour pressure of the solution is 475 torr.
12.
What role does the molecular interaction play in solution of alcohol and water?
1.
Molar mass of KCI = 39 + 35.5 = 74.35 g mol-1
A KCI dissociates completely, number of ions produced are 2.There, Van't Hoff factor, i = 2
Mass of KCI solution = 1000 \(\times\)1.04 = 1040 g
Mass of solvent = 1040 - 74.5 = 965.5 g = 0.9655 kg1/2
Molality of the solution :
\(\\ \frac { No.\quad of\quad moles\quad of\quad solute }{ Mass\quad of\quad solvent\quad in\quad kg } =\frac { 1\quad mol }{ 0.9655\quad kg } =1.0357\quad m\)
Tb = i \(\times\)Kb \(\times\)m
= 2 \(\times\) 0.52 \(\times\)1.0357 = 1.078 \(°\) C
Therefore, boiling point of solution
= 100 = 1.078 = 101.078\(°\)C
2.
1. Place the egg in dil. HCl or dil. H2SO4 solution.
2. After sometime , outer shell of egg dissolves.
3. Egg with only semi-permeable membrane is now removed and placed in hypertonic solution.
4. After sometime. the size of the egg gets reduced due to osmosis.
5. Egg is now placed in bottle with narrow neck
6. Add hypotonic solution in the bottle containing egg.
7. Egg regains its shape due to osmosis.
3.
ΔTb = 100.0832 - 100.0 = 0.0832°C,
Kb = 0.52 K kg mol-1,
WA = 250 g, WB = 3.12 g,
MB = 137 + 71 = 208 9 mol-1
Now \(ΔT_b=iK_b\times{W_B\over M_B}\times{1000\over W_A}\)
⇒ \(0.0832 = i \times 0.52 \times{3.12\over4 6.489}\times{1000\over 250}\)
\(⇒ i={0.0832\times208\over 4\times3.12\times0.52}={17.30\over 6.489}=2.66\)
\(\alpha={i-1\over n-1}={2.66-1\over 3-1}={1.66\over 2}=0.83\)
Degree of dissociation (α) = 83%
4.
\(\pi V\)= nRT = \(\frac{{W}^{B}}{{M}^{B}}\times R \times T\)
\(\Rightarrow \) \(\pi \times1 = \frac{68.4}{342}\times0.0821 \times 300 K \)
\(\Rightarrow \) \(\pi =\frac{24.63}{5} = 4.92 \ atm\)
5.
(i) Phenol is partially soluble in water
(ii) Toluene is insoluble in water
(iii) Formic acid is soluble in water
(iv) Ethylene glycol is soluble in water
(v) Chloroform is insoluble in water
(vi) Pentanol is partially soluble in water.
6.
According to Raoult’s Law,
\(\frac{\mathrm{P}_{\mathrm{A}}^{\circ}-\mathrm{P}_{\mathrm{S}}}{\mathrm{P}_{\mathrm{S}}}=\frac{n_{\mathrm{B}}}{n_{\mathrm{A}}}=\frac{\mathrm{W}_{\mathrm{B}}}{\mathrm{M}_{\mathrm{B}}} \times \frac{\mathrm{M}_{\mathrm{A}}}{\mathrm{W}_{\mathrm{A}}}\)
\(\mathrm{P}_{\mathrm{A}}^{\circ} \text { (for water) }=1 \cdot 013 \mathrm{bar} ; \mathrm{P}_{\mathrm{S}}=1 \cdot 004 \mathrm{bar} ; \mathrm{W}_{\mathrm{B}}=2 \mathrm{~g} ; \mathrm{W}_{\mathrm{A}}=100-2=98 \mathrm{~g}\)
\(\mathrm{M}_{\mathrm{A}}=18 \mathrm{~g} \mathrm{~mol}^{-1}\)
\(\frac{(1 \cdot 013-1 \cdot 004) \text { bar }}{(1 \cdot 004 \text { bar })}=\frac{(2 \mathrm{~g}) \times\left(18 \mathrm{~g} \mathrm{~mol}^{-1}\right)}{\mathrm{M}_{\mathrm{B}} \times(98 \mathrm{~g})}\)
\(\therefore M_{B}=\frac{(2 g) \times\left(18 g m o l^{-1}\right) \times(1 \cdot 004 \text { bar })}{(0.009 \text { bar }) \times(98 g)}=41 \cdot 0 \mathrm{~g} \mathrm{~mol}^{-1}\)
7.
1 molal solution of solute means 1 mole of solute in 1000g of the solvent.
\(\text { Molar mass of water (solvent) }=18 \mathrm{~g} \mathrm{~mol}^{-1}\)
\(\therefore \text { Moles of water }=\frac{1000}{18}=55.5 \text { moles. }\)
\(\therefore \text { Mole fraction of solute }=\frac{1}{1+55 \cdot 5}=0 \cdot 0177\)
\(\text { Now, } \frac{P^{\circ}-P_{s}}{P^{\circ}}=x_{2}\)
\( \frac{12 \cdot 3-P_{s}}{12 \cdot 3}=0 \cdot 0177 \\ \Rightarrow P_{s}= 12 \cdot 08 \mathrm{kPa} \)
8.
269.27 K
9.
\(\triangle { T }_{ f }={ K }_{ f }\times m\)
\(\\ \Rightarrow \ \triangle { T }_{ f }=5.12 \ K \ \times 0.1\)
\(\\ \Rightarrow \ \triangle { T }_{ f }=0.512 \ K\)
\(\\ i=\frac { Observed\triangle { T }_{ f } }{ Normal\triangle { T }_{ f } } =\frac { 0.256 }{ 0.512 } =\frac { 1 }{ 2 } \)
It shows that acetic acid exists as dimer in benzene.
10.
\(\triangle { T }_{ b }=373.128 \ K-373.0 \ K=0.128 \ K\)
\(\\ \triangle { T }_{ b }={ K }_{ b } \ \times \ m\)
\( \Rightarrow m=\frac { 0.128 }{ 0.52 } =0.246 \ mol/kg\)
\( Now,\triangle { T }_{ f }={ K }_{ f } \ \times \ m=1.86\times0.246=0.457\)
Freezing point = \(273-0.457=272.543 \ K\)
11.
\(\text { No. of moles of solute, } n_{2}=\frac{100}{140}=\frac{5}{7} \text { mole }\)
\(\text { No. of moles of solvent, } n_{1}=\frac{1000}{180}=\frac{50}{9} \text { mole }\)
Mole fraction of solute
\(x_{2}=\frac{n_{2}}{n_{1}+n_{2}}=\frac{5 / 7}{5 / 7+50 / 9}=0.114\)
\(\text {Mole fraction of solvent, } x_{1}=\left(1-x_{2}\right)=(1-0 \cdot 114)\)
= 0.886
According to Raoult's law
\( P_{A}=x_{A} P_{A}^{0}=0.114 \times P_{A}^{0} \)
\(P_{B}=x_{B} P_{B}^{\circ}=0.886 \times 500=443 \text { torr } \)
\(P_{\text {Total }}=P_{A}+P_{B}\)
\(475=0.114 P_{A}^{\circ}+443\)
\( P_{A}^{\circ}=\frac{475-443}{0 \cdot 114}=280 \cdot 7 \text { torr } \)
\(\therefore P_{A}=0 \cdot 114 \times 280 \cdot 7=32 \text { torr. }\)
12.
Alcohol is polar compound. It can form H-0bound with water molecule. That is why alcohols are miscible with water in all proportion. They also have dipole-dipole interactions due to which there is the force of attraction between alcohol and water molecules.
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