2019/2020 CHEMISTRY TRIAL

*CHEMISTRY GENUINE TRIALS WASSCE 2019*

_Brought to you by:_
*Mr Gabriel*
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*Question*
a)  Give the  IUPAC  names of each of the following substances.
i)   SO32- .        
ii)   CuSO4.5H2O.               
iii)  KMnO4.

b)   Define each of the following terms:
i)    standard  solution.
ii)   saturated  solution.
iii)   standard  enthalpy of formation.

c)    A  250cm3 solution of  K2Cr2O7 with concentration 0.025m0l dm-3 is to be prepared from  a stock solution with concentration  0.04mol dm-3. Calculate the volume of the stock solution required.

d)    Account for the followingb observations:
i)   The enthalpy of neutralization between strong acids and strong bases is constant but that between weak acids and weak base varies and  it also low.

ii)       Washing down the acid or base splashed on the walls of  a conical flask with a little distilled  water  during  volumetric  analysis does not have any effect on the titre values.
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*_ANSWERS_*
a)  
i)      SO32-   =    Trioxosulphate (IV) ion

ii)     CuSO4.5H2O =  Copper (II) tetroxosulphate (VI) pentahydrate.

iii)     KMnO4  =   Potassium tetraoxomanganate  (VII).

b)    
i)    Standard solution is a solution whose concentration is accurately known.

ii)    A saturated solution is one which cannot dissolve any more solute at a given temperature.
  OR:  A solution in which dissolved and undissolved solute are in dynamic equilibrium at a  Given temperature.

iii)      Standard  enthalpy of formation is the enthalpy / heat  change when one mole of a substance  is formed from its constituent elements in their standard states and under standard conditions of 298K temperature and 1.0 atm pressure.

c)     From the law of dilution. C1V1 =  C2V2.  Where C1. and C2 are the initial and final concentrations and V1 and  V2  are the initial and final volumes of the solutions respectively.
   C2  =  0.025 mol dm-3,  V2  =  250cm3.  C1 = 0.04 mol dm-3.  V1 = ?

O.O4V1 =  0.025 X 250   
               
V1 = 250 x 0.025   =   156.25cm3.
                0.04

d)    Strong acids and strong  bases are fully ionized in aqueous solution to give H+ and OH- ions  respectively. Therefore reaction between strong acids and strong bases  is basically
  H+(aq)   +  OH-(aq)    →     H2O(l)  and hence has a constant enthalpy change.

Weak acids and weak bases ionize partially in aqueous solution and the degree   of  ionization varies. Different endothermic amounts of energy are required to ionize them  fully  before the actual neutralization reaction occurs. Thus their overall enthalpy of neutralization is low and varied.

*_MR GABRIEL_* 🦅🦅
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