UNIT TEST 3 (24-25)
CLASS -XI CHEMISTRY MARKS : 40
Note: There are 21 questions in this question paper.
Q.No.1-7consist of multiple-choice questions carrying 1 markeach.
Q.No.8-10 consist of Assertion and Reason questions carrying 1 mark each.
Q.No.11-15 consist of very short answer questions carrying 2 marks each.
Q.No.16-20 consists of short answer questions carrying 3 marks each.
Q.No.21 consists of case-based questions carrying 5 marks.
S.No. | Questions | Marks |
1. | What is the approximate pH of a 5 × 10–3 M NaOH solution? (a)2.3 (b) 11.7 (c) 3.2 (d) 11 × 10–11 | 1 |
2. | Which of the following can act as both Bronsted acid and Bronsted base? (a) H2SO4 (b) H2O (c) HCO3– (d) NH3
| 1 |
3. | For the reaction C(s) + O2(g) → CO2(g) (a) △H >△U (b) △H < △U (c) △H = △U (d) None of these | 1 |
4. | The pKa of a weak acid, HA, is 4.80. The pKb of a weak base, BOH, is 4.78. The pH of an aqueous solution of the correspondng salt, BA, will be (a) 9.58 (b) 4.79 (c) 7.01 (d) 9.22 | 1 |
5. | The least random state of the water system is: (a) ice (b) liquid water (c) steam (d) randomness is same | 1 |
6 | What is the entropy change (in JK-1 mol-1) when 1 mole of ice is converted into water at 0℃? (The enthalpy change for the conversion of ice to liquid water is 6.0 kJ mol-1 at 0℃) (a) 20.13 (b) 2.013 (c) 2.198 (d) 21.98 | 1 |
7 | The Solubility of A2X3 is y mol/dm3.Its Solubility product is (a) 6y 4 (b) 64y 4(c) 36 y 5 (d) 108y5 | 1 |
8 | Assertion : The heat absorbed during the isothermal expansion of an ideal gas against vaccum is zero. Reason : The volume occupied by the molecules of an ideal gas is zero. | 1 |
9 | Assertion (A): For any chemical reaction at a particular temperature, the equilibrium constant is fixed and is a characteristic property. Reason (R) : Equilibrium constant is independent of temperature.
| 1 |
10. | Assertion : Kp can be less than, greater than or equal to Kc. Reason : Relation between Kp and Kc depends on difference between number of moles of gaseous productss and reactants (∆n). | 1 |
11. | In a process, 701J heat is absorbed and 394J work is done by system. What is change in Internal energy for process? | 2 |
12. | For the following equilibrium, K =6.3 x 1014 at 1000 K. NO (g)+O3—–>NO2(g) + O2(g) Both the forward and reverse reactions in the equilibrium are elementary bimolecular reactions. What is Kc’ for the reverse reaction?
| 2 |
13. | For the equilibrium, 2NOCl(g) ⇌ 2NO(g) + Cl2(g) the value of the equilibrium constant, Kc is 4×10–6 at 1000 K. Calculate the Kp for the reaction at this temperature? ( R= 0.0831) | 2 |
14 | Define Bronsted and Lowry’s definition of Acids and bases. Write the conjugate acid of NH3 and H2O | 2 |
15. | Explain homogeneous and heterogeneous equilibrium giving examples OR The concentration of hydrogen ion in a sample of soft drink is 2 X 10-3 M. What is its pH? | 2 |
16. | For a water gas reaction at 1000k, the standard Gibb’s free energy change is -8.1kJ/mol. Calculate the Value of equilibrium constant Kc, for the reaction.
| 3 |
17. | Enthalpies of formation of CO (g), CO2 (g), N2O (g) and N2O4 (g) are –110, – 393, 81 and 9.7 kJ mol–1, respectively. Find the value of ∆rH for the reaction:
N2O4(g) + 3CO(g) → N2O(g) + 3 CO2(g)
| 3 |
18. | For the reaction at 298K, 2A(g) + B(g) → C (g) ΔH = 400 kJmol−1 ΔS= 0.2 kJmol−1K−1 At what temperature will the reaction become spontaneous considering ΔS and ΔH to be constant over the temperature range? | 3 |
19 | . On the basis of Le Chatelier principle explain how temperature and pressure can be adjusted to increase the yield of ammonia in the following reaction. N2 (g) + 3H2(g) ⇌ 2NH3(g), ∆H = – 92.38 kJ mol–1
| 3 |
20. | The concentration of hydrogen ion in a sample of soft drink is 3.0 × 10–8 M. what is its pH? | 3 |
21 | CASE BASED QUESTION According to Arrhenius theory, acids are substances that dissociate in water to give hydrogen ions H+ (aq) and bases are substances that produce hydroxyl ions OH–(aq). The ionization of an acid HX (aq) can be represented by the following equations: HX (aq) → H+ (aq) + X – (aq) or HX(aq) + H2O(l) → H3O + (aq) + X – (aq) Similarly, a base molecule like MOH ionizes in aqueous solution according to the equation: MOH(aq) → M+ (aq) + OH–(aq) Bronsted acids are proton donors whereas Bronsted bases are proton acceptors. Acids on donating proton form conjugate bases whereas bases form conjugate acids after accepting proton. Buffer solution is a solution whose pH does not change. By adding small amount of H+ or OH- .The decrease in concentration of the ion by adding other ion as common ion is called common ion effect. Ksp (solubility product) is product of molar concentrations of ions raised to power no. of ions per formula of ions per formula of the compound in sparingly soluble salt. Precipitation occurs only if ionic product exceeds solubility product. Solubility of salt decreases in presence of common ion. Kw the ionic product of water is 1x10-14 at 298 k. Kw increases with increase in temperature. pH is –log[H3O + ] where [H3O + ]=cα in monoprotic acid, is molar conc., α is degree of ionisation.
(a) What will be the conjugate base of (i)H2SO4 (ii) HCO3-?
(b) What will be the conjugate acid of (i)NH2 - (ii)NH3
(c) The conc. of H3O+ is 4x 10-4 .Find its pH.
(d) Kb forNH3 is1.80 x 10-5 , what will be Ka? [Kw is 1 x10-14]
| 5 |
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