SOME BASIC CONCEPTS OF CHEMISTRY Quiz-24

 

SOME BASIC CONCEPTS OF CHEMISTRY Quiz-24

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IIT JEE exam which consists of JEE Main and JEE Advanced is one of the most important entrance exams for engineering aspirants. The exam is held for candidates who are aspiring to pursue a career in the field of engineering and technical studies. Chemistry is important because everything you do is chemistry! Even your body is made of chemicals. Chemical reactions occur when you breathe, eat, or just sit there reading. All matter is made of chemicals, so the importance of chemistry is that it's the study of everything..

Q1.Ammonium salts can be decomposed by:

•  aq Na_2 O
•  aq CaO
•  Both (a) and (b)
•  None of these

Solution
(c) NH_4^++OH^-⟶NH_3+H_2 O

Q2.In a titration H_2 O_2 is oxidized to O_2by MnO_4^-.24 mL of 0.1 M H_2 O_2 of require 16 mL of 0.1 M MnO_4^- solution. Hence, MnO_4^-changes to

•  MnO_4^(2-)
•  MnO_2
•  MnO_4^(2-)
•  Mn_2 O_7

Solution
(b) H_2 O_2→2H^++O_2+2e^- 0.1 M=0.2 N MnO_4^-→Mn^(x+) 0.1 M=0.1(7-x)N N_1 V_2=N_2 V_2 0.2×24=0.1(7-x)16 (7-x)=3 x=4 Thus, change in oxidation number of MnO_4^- is 3. Thus, MnO_4^- changes to MnO_2

Q3.On adding KNO_2 and CH_3 COOH solution to the neutral solution of CoCl_2, there is formation of yellowish orange precipitate of  

•  K_3 [Co(NO_2 )_6 ]
•  K_4 [Co(NO_2 )_6 ]
•  K_3 [Co(NO_2 )_4 (CH_3 COO)_2 ]
•  K_2 [Co(NO_2 )_4]

Solution
(b) CH_3 COOH+KNO_2⟶CH_3 COOK+HNO_2 CoCl_2+2KNO_2⟶Co(NO_2 )_2 3KNO_2+Co^II (NO_2 )_2+2HNO_2⟶ K_3 [Co^III (NO_2 )_6 ]+H_2 O+NO↑ potassium cobaltinitrite (yellowish orange pH)

Q4.M (molarity) and M^'(molality) are related to each other by equation (m= molecular weight of solute, x= density g/mL)  

•  M(m/1000+1/M^' )=d
•  M^'=((1000 M)/(1000 d-Mm))
•  Both (a) and (b)
•  DNone of the above

Solution
(c)

Q5.On repeated sparking, 10 mL of a mixture of carbon monoxide and nitrogen required 7 mL of oxygen for combustion. What was the volume of nitrogen? (All volumes are measured under identical conditions)

•  7/2 mL
•  4 mL
•  7 mL
•  17/2 mL

Solution
 (b) CO=x mL,N_2=(10-x)mL CO_2+1/2 O_2→ CO_2, N_2+ O_2→2NO O_2 required=x/2 mL,O_2 required=(10 –x)mL x/2+ (10-x)=7,x=6 mL N_2=10-6=4 mL

Q6.The molar mass of a compound if 0.372 mole of it has a mass of 186 g, is

•  200 g
•  372 g
• 500 g
•  186 g

Solution
(c) 0.372 mol=186 g 1 mol=186/0.372=500 g

Q7.If 5.0 g of Al react with 4.45 g of O_2, empirical formula of aluminum oxide is

•  Al_2 O_3
•  AlO_2
•  Al_2 O
•  AlO_3

Solution
(a) Mol Al 5 g 0.185 1.0 O_2 4.45 g 0.278 1.5 Thus, Al_2 O_3

Q8.1 mole of ferric oxalate is oxidized by x moles of MnO_4^-.Thus, x is

•  1.2
•  2.1
•  3.1
•  1.3

Solution
(a) Fe_2 (C_2 O_4 )_3⇌2Fe^(3+)+3C_2 O_4^(2-) 1 mol 3 mol Only C_2 O_4^(2-) oxidised 2MnO_4^-+5C_2 O_4^(2-)→10CO_2+2Mn^(2+) 5 mol C_2 O_4^(2-)≡2 mol MnO_4^- ∴3 mol C_2 O_4^(2-)=1.2 mol MnO_4^-

Q9. NH_4 SCN can be used to test one or more out of Fe^(3+),Co^(2+),Cu^(2+)

•  Fe^(3+) only
•  Co^(2+),Cu^(2+) S
•  Fe^(3+),Cu^(2+)
•  All of these

Solution
(d) Cu^(2+)+2SCN^-→Cu(SCN)_2↓ □(→┴( ∆ ) ) CuSCN↓+(SCN)_2 black white Fe^(3+)+SCN^-→[Fe(SCN)]^(2+) red Co^(2+)+SCN^-→[Co(SCN)_4 ]^(2-) blue

Q10. To increase significantly the concentration of free Zn^(2+) ion is a solution of the complex ion [Zn(NH_3 )_4 ]^(2+),Zn^(2+) (aq)+4NH_3 (aq)⇌[ZN(NH_3 )_4 ]^(2+) (aq) add to the solution some  

•  H_2 O
•  HCl(aq)
•  NH_3 (aq)
• NH_4 Cl(aq)

Solution
(b) [Zn(NH_3 )_4 ]^(2+)+4H^+→Zn^(2+)+4NH_4^+ Addition of H^+ shifts equilibrium in backward side releasing Zn^(2+) ions

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