ADVANCED CHEMISTRY QUESTIONS & ANSWERS – SOLVED PROBLEMS

ANSWERS:

1.   11.  (a) (i) Partition law:

               “When a solute is dissolved in a mixture of two immiscible solvents, it distributes itself in a constant ratio of concentration”.

         (ii)   Conditions

1.The two solvents must be completely immiscible.
2.  Temperature should be constant.
3.  There should be no change in molecular state of the solute i.e. should not dissociate or associate in any of the solvents.

     (b)   (i)  Standard molar enthalpy of formation:

       Is the heat change when 1 mole of a substance is formed from its elements in their standard states?

               _(g) +  _(g)   N _(g)

             Heat of solution of a substance:

   Is the enthalpy change when 1 mole of a substance is added to so much water that further addition of water produces no farther change.

   Ionization energy:
Is the energy required to remove the most loosely held electron from the shell of an atom or ion.

(c)    (i)  Hess’s law:

The enthalpy change for a particular reaction is same whether the reaction takes place in one step or in a series of steps.

         (ii)     Solution:

  Applying Hess’s law

   H_C   = -393 KJ mol^-1

      H_C   = +285 KJ mol^-1

 K.D  =

 0.0243a = 10^{-4   -a}

1.0243a = 10^-4

 a = 9.76×10^-5  moles

     Fraction of Iodine extracted by C will be
= 9.76 x 10^-5

1 x 10^{-4
=   0.976}

(iii)   Solution:

12.(a)  (i)  Nucleophilic addition reaction is the reaction in which nucleophile is added

         First followed by electrophile.

 Elimination reaction is the reaction whereby an atom or group of atoms are removed from a compound

   e.g:   C C Cl  +  NaOH   C  +  NaCl  +  O

   C   C and C CC OH

  By Lucas Test

Propanol will not form cloudness when it undergoes Lucas test but propan -2-ol will form cloudness after 5 minutes upon Lucas test.

(ii)  C   CH – C and C C C Cl
Using KOH followed by AgN in the presence of HN, yellow ppt will be observed for C C CCl while there is

                                 Cl

No reaction for C CH C

(iii)  C C CHO and C C – C C
C C CHO will react with Tollen’s reagent [Ag (N]OH to form a white ppt of silver at the bottom of the test-tube while
CC C   – C C will not react.

(c) (i)  Propanoic acid from ethane

C CN  +  O ⁴
  C C   –  N CH3 C– OH

Propanoic acid

(ii)  Propan-2-ol from propan-1-ol

CC C OH  +  S   C  CH  =  C

(iii) Propyne from Ethyne

λ m  = 

  = 133 S cm³ mol

 = 6.4×10^-3 g cm-1

C = 5 X 10 ^-2 M

 =  

1 dm³ = 10 ³ cm³

x =1cm³

             = 10^-3

=              =

=   = 

  = 128 S cm^-2 mol^-1

∝  = O.96  

13. Salt hydrolysis is the reaction between salt and water to form an acidic or alkaline solution:

Order of reaction:                                                                        Molecularity:

–   It cannot be determined                                                – Can be determined from the equation

From equation (determined experimentally).

–   It can be a whole number or fraction .                        – It can only be a whole number

–   It is the sum of concentrations terms on                     – It is the number of ions atoms or

Which the rate of reaction actually depends                molecules that must collide so as to

(It is sum of exponents of the concentrations              results in a chemical reaction.

in the rate law).

–   It cannot be obtained from the stoichiometry             – It can be obtained from the

Of an unbalanced equation.                                           Stoichiometry of the equation.

 = 30 x 60 = 1800s at 27

 = 10×60 = 600s at  47

Log   = 

n log   =   

log  =  – 1.088 x 10^-5 Ea

=       Ea  = 4.3833

K =
K = 

K = 3.85×10^-4

Tollen’s reagent (silver mirror test)

Acyl halides (Acid halide)

Derivatives of carboxylic acids upon hydrolysis go back to carboxylic acids

Transesterification is the reaction between ester and alcohol to form another ester

Conditions for a chemical reaction to take place

i.  The collision of the molecules must be energetic enough to break the bonds between the molecule

ii. The colliding molecule must have right orientation (geometry)

Log K₁ =     log A –
Log K₂ =     log A –

Log K₁ –log K₂ = –

Log =

In = Kt           =

– = Kt         =

Homolytic bond cleavage.

Is the type of bond cleavage in which the covalent bond breaks symmetrically so that are electron moves to each end.

Heterolytic bond cleavage.

Here the covalent bond breaks unsymmetrical and all bonding electrons are taken by the more electronegative atom

 _{(g) +}     →      2N  Slow

R=  [] [] this slow step will determine rate law

 =  [NO] [NO]

= [NO

= []

At equilibrium =

 [NO] ² =  []

[NO] ² = []

R=   [NO]² []

R= K [NO]² []

The slow step will determine the rate law

R = [Br] []

Consider the equilibrium reaction

=  [B]

 =  [Br] ²

At equation:

 =

[B] =  [Br]²

[B] =[ Br]²

[Br] = [Br]^1/2

R= K₀Br^1/2

R= K [Br []

K_h =

CCOONa   →  CCO + N

Start    0.1                 0          0

0.1 – x           x          x

K_h =

α = × 100

[H COONa] =

Let added volume be x

[H COONa] =

0.1=

n=0.1x

[H COONa] =

[HCOOH] =

14. Explain the meaning and significance of colloids

15. Discuss the properties of soil colloids

               –  Surface area

               –   Electric charge

               –   Ion exchange (diagram)

16. Explain the mechanism of ion exchange in soil

17. Calculation of percentage base saturation of a soil sample. With worked examples (how to calculate)

18. Aluminum has high polarizing power hence the compound formed between Al and carbon will be unstable therefore it will decompose immediately after formation.

The chloride outside is not part of the complex meaning that it is ionization. Therefore Ag will react. In [ p(NH₃)₂ cL₄)] the chloride is part of the complex hence there is no ionizable chloride ion and there no reaction

19. (a)(i)  CH₃ – C-CH₃ + CH₃ Mg CL CH₃ –C- CH₃

(ii) CH₃ –C- C-CH₃ +NaOH + I₂        CHI₃ + NaOOC – CONa + NaI
(iii) CH₃ CH₂ C – NH₂
CH₃ CH₂ NH₂ + KBr +CO₂ +H₂O
(iv) CH₃ CH₂ NH₂ + CHcL₃
CH₃ CH₂ N =C + HCL

20. Distinguish between

When Br₂/H₂O is added to phenol, white ppt is formed

When Br₂/H₂O is added, no reaction

(iv) CH₃ CH₂ OH +I₂ + NaOH       No reaction

22. With the aid of chemical equations explain the following

(i)   Mercury(ii) iodide solution but not in potassium iodide solution but in water

(ii)  The pink solution of cobalt (ii) chloride turns blue when conc. HCL is added gelatinous  ppf of

(iii)  Copper (ii) hydroxide turns deep blue in excess ammonia

(iv)  ZnO and Pbo dissolves in hot conc sodium hydroxide solution

23. using relevant balanced chemical equation describe the process of extracting copper from copper pyrite under the following heading.

 (i) Concentration

(ii) Roasting

 (iii) Removal of ion impurities

(iv) Self- reduction reaction

24.  Cobalt copper, Iron and manganese are d-block elements

a.            What is meant by the term d- block element

b.            Write E.C of Cu,  Fe²⁺, Mn²⁺

 (i)   Explain in terms of E.C why Fe²⁺ ions are readily oxidized to Fe³⁺ ions but manganese (ii) ions are not readily oxidized to Mn³⁺

25.  2.5 x 10^-3 moles of a compound with a formula was dissolved in 0.1M a silver nitrate solution. 50 cm³ were required for complete precipitation of the chloride ions present.

      (i) Deduce the ionic formula of the compound

      (ii) Draw the structure of the complex ion present and name it

26.  Write the formula of the following complexes

     (i) Tetra ammine copper(ii)  Sulphate mono hydrate

     (ii)Potassium

27.  Write down a balanced chemical equation for the following

       (i)  Adding of excess ammonia solution to aluminium ion

       (ii)  Ion(iii) oxide is heated with aluminium power

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