1 S – Block Elements
Chemical A is used for water softening to remove temporary hardness. A reacts with sodium carbonate to generate caustic soda. When CO2 is bubbled through it turns cloudy. What is the chemical formula of A?
1) Ca(HCO3)2
2) Ca(OH)2
3) CaO
4) CaCO3
The chemical A is calcium hydroxide Ca(OH)2?. It reacts with sodium carbonate to produce sodium hydroxide (caustic soda). Ca(OH)2?+Na2?CO3?→CaCO3?+2NaOH Calcium hydroxide reacts with carbon dioxide to form calcium carbonate. Hence, it turns milky. Ca(OH)2?+CO2→CaCO3?↓+H2?O
2 Ionic Equilibrium
0.1 mole of CH3NH2 (Kb = 5 × 10-4) is mixed with 0.08 mole of HCl and diluted to 1L. What will be the H+ concentration in the solution ?
1) 8 × 10-2 M 2) 8 × 10-11 M 3) 1.6 × 10-11 M 4) 8 × 10-5 M
SOLUTIONS
3 Surface Chemistry
Calculate the surface area in (sq m) of a catalyst that adsorbs 103cm3 of nitrogen reduced to STP per gram in order to form the monolayer. The effective area (in m2) occupied by N2? molecule on the surface is: ( surface area of N2?=1.62×10−15cm2)
1) 4115 m2 2) 2355 m2 3) 4355 m2 4) 435.5 m2
According to the given data,
Number of N2? molecules = Volume(ml) × NA / Volume at STP(in ml)
= (103×6.023×1023) / 22400 = 2.69×1022
Total area covered by N2? = 2.69×1022 × 1.62×10−15 = 435×105 cm2 = 4355 m2.
4 Chemical Equilibrium
The equilibrium constant for the decomposition of water H2O(g) -> H2(g) + 1/2 O2(g) is given by : (α = degree of dissociation of H2O (g) ; p = Total equilibrium pressure )
SOLUTION
5 Surface Chemistry
If the half-life of an isotope X is 10 yr, its decay constant is
1) 6.932 yr -1 2) 0.6932 yr -1 3) 0.06932 yr -1 4) 0.006932 yr -1
6 Surface Chemistry
The dispersed phase in colloidal iron (III) hydroxide and coltoidal gold is positively and negatively charged, respectively. Which of the following statements is not correct?:
1) Sodium sulphate solution causes coagulation in both sols 2) Magnesium chloride solution coagulates, the gold sol more readily than the iron (III) hydroxide sol. 3) the processes of electrophoresis provide charge on both the sols 4) Colloidal iron is coagulated by Mg+2 and coltoidal gold is coagulated by Cl−
Since, dispersed phase of colloidal iron (III) hydroxide is positively charged, colloidal iron can't be coagulated by positive ion Mg+2 because positively charged iron hydroxide colloidals repel Mg2+ ion. In the same way, negatively charged gold colloids can't be coagulated by anion Cl-.
7 P – Block Elements
When nitric acid reacts with nitric oxide, a gas is released, which converts H2S into
When nitric acid (HNO3) reacts with nitric oxide (NO), NO2 gas is released which oxidises H2S into sulphur. The reactions are as follows
8
When Reactivity of Halogen atom is minimum in 1. propyl oxide 2. propyl chloride 3. isopropyl chloride 4. isopropyl bromide
9 Polymers
The monomer of the polymer;
10 Ionic Equilibrium
At 298K a 0.1 M CH3COOHsolution is 1.34% ionized. The ionization constant Ka for acetic acid will be
1) 0.182×10−5 2) 18.2×10−5 3) 1.82×10−5 4) none
Solution:
K = cα2 = 0.1 × (1.34 / 100)2 = 1.82×10−5
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