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NECO 2018 Chemistry Practical Answers
1ai) Tabulate
Titrations|Rough|first(1)|second(2)|third(3)
Final burette reading – |20.50|14.90|15.00|15.10|
Initial burette reading – |0.00|0.00|0.00|0.00|
volume of Acid used – |20.5|14.90|15.00|15.10|
1ai)
Average volume of Acid used=
1st+2nd+3rd/3
14.90+15.00+15.10/3=45/3=15cm³
1aii)
2HCL(aq)+Na2CO3(aq)—->2NaCl(aq)+H2O(aq)+CO2(aq)
1bi)
CA VA/CB VB =NA/NB
0.1moldm^-³*15cm³/CB*25cm³ *2/1
CB * 25cm^3*2=0.1moldm-³*15cm³*1
CB * 50=1.5
CB=1.5/50=0.03moldm-³
1bii)
25cm³—->0.03mole
1000cm³—->x
x=1000*0.03/25=30/25
x=1.2moldm-³
1biii)
concentration in mold-³=Con glm³ /molar mass
0.03moldm-³=x/106
x=0.03*106
x=3.18gldm³
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2a)
Tabulate
2ai)
OBSERVATION
i) C dissolves in water
ii) formation of white precipitate
iii) White precipitate dissolves in itel
INFERENCE
i)C is soluble in water
ii)CO3-²,SO4-³,SO3-²- suspected
iii)CO3²-,SO3²-, suspected
2bi)
OBERSVATION
i)effervescence occurs with the evolution of a gas
ii)the solutions turns to pink
INFERENCE
i)CO3²-,SO3²-, suspected
ii)CO3²-,Confrimed
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3ai)
Zinc chloride reaction with HaOH form white gelatinous precipitate solution in excess HaOH.
Ammonium trioxocarbonate(iv) on reaction with HaoH evolves a gas which turns red litmus paper blue and lime water milky.
Calcium trioxocarbonate(iv) on reaction with HaoH forms white powdery precipitate insoluble in excess HaOH.
3aii)
i) Boiling point to determine the purity in a liquid substance and
ii) Melting point to determine the purity in a solid substance
3bi)
Different between boiling n evaporation
Boiling
1. A process in which a substance changes its state from the liquid state to the gaseous state
2. Occurs throughout the liquid
Evaporation
3. Takes place only from the exposed surface of the liquid
3bii)
Carbon dioxide is use to extinguish fire because carbon dioxide molecules are heavier than oxygen molecules. When the liquid carbon dioxide inside the extinguisher expands into a gas, the carbon dioxide pushes out any oxygen surrounding the fire. Without oxygen available to fuel the chemical reaction, the fire goes out quickly.
3ci)
A 1 molar solution is a solution in which 1 mole of a compound is dissolved in a total volume of 1 litre. For example: The molecular weight of sodium chloride (NaCl) is 58.44, so one gram molecular weight (= 1 mole) is 58.44g.
3cii)
Acid Base indicators
3ciii)
i)methyl orange
ii)Phenolphthalein.
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