Wednesday 6th June 2018
Practical – Chemistry – 10:00am – 12:00noon
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(1a)
Tabulate:
Titrations |Rough|1st |2nd |3rd |
Final burette reading |18.00|15.60|17.40|20.50|
Initial burette reading |0.00 |0.00 |2.00 |5.00 |
volume of Acide used |18.00|15.60|15.40|15.50|


(1ai)
Average volume of Acid used
VA = (VA1 + VA2 + VA3)cm3/3
VA = (15.60+15.40+15.50)/3
VA = 46.50/3
VA = 15.50cm3
(1aii)
2HCl(aq)+Na2CO3(aq)-->2NaCl(aq)+H2O(l)+CO2(g)


(1bi)
CA VA/CB VB =NA/NB
0.1moldm^-3 x 15.50cm3/CB x 25cm3 x 2/1
CB x 25cm3 x 2 = 0.1moldm^-3 x 15.50cm3 x 1
CB x 50 = 1.55
CB = 1.55/50 = 0.031moldm^-3


(1bii)
25cm^3---->0.031mole
1000cm^3---->x
x=10000.031/25=31/25
x=1.24moldm^-3


(1biii)
concentration in mold^-3 =Con glm^3 /molar mass
0.031moldm^-3=x/106
x=0.031106
x=3.286gldm^3


(2a)
Tabulate


(2ai)
OBSERVATION: C dissolves in water
INFERENCE: C is a soluble salt


(2aii)
OBSERVATION: White precipitate formed
INFERENCE: CO3²-, SO3²-, SO4²- suspected


(2aiii)
OBSERVATION: White ppt dissolves in excess of dil HCl
INFERENCE: CO3²- , SO3²- suspected


(2bi)
OBERSVATION: Effervescence occurs with the evolution of a gas
INFERENCE: CO3²- present


(2bii)
OBERSVATION: Solutions turns to pink
INFERENCE: CO3²- Confirmed


(3ai)
Zinc Chloride(ZnCl2) solution reacts with NaOH(aq) to form white ppt in drops. The precipitate dissolves in excess of NaOH.
Sodium hydroxide reacts with ammoniumtrioxocarbonate(iv) to form a solution which turns red litmus paper blue.
Calcium trioxonitrate(v) Ca(NO3)2 on reaction with sodium hydroxide forms a white powder precipitate insoluble in excess NaOH(aq)


(3aii)
I. Liquid substances - Boiling point of the substances.
II. Solid substances - The melting point of the substance.


(3bi)
(i) Evaporation takes place at almost all temperatures, while Boiling takes place at a specific temperature.
(ii) Only the surface of a liquid is involved in evaporation while the entire mass of the liquid is involved in boiling.


(3bii)
Carbon(iv)oxide does not support combustion.


(3ci)
A molar solution is an aqueous solution that contains one mole of solute in 1000cm³ of the solution.


(3cii)
Indicator.


(3ciii)
(i) Methyl orange
(ii) Phenolphthalein