2020 NECO-CHEMISTRY-PRACTICALS-ANSWERS

NECO-CHEMISTRY-PRACTICALS-ANSWERS

(1)

Indicator used is methyl orange.

Volume of pipette used is 25cm³

Tabulate. 

Titration; Rough|1st|2nd|3rd|

Final burette reading cm³|23.50|23.00|23.00|33.00|

Initial burette reading cm³| 00|0.00|0.00|10.00|

Volume of acid used(cm³) |23.50|23.00|23.00|23.00|

Average volume of A used = 23.00+23.00+23.00/3 =23.00cm³

Equation for the reaction 

X²Co³(aq)+2HCl(aq)---->2XCl(aq)+H²O(s)+Cl(s)

(1i)

Concentration of A in moldm³ =concentration in gldm³.

3.6g of A =500cm²

Xg of A will be = 10000³

Xg=3.65*1000/500 =36.5/5 =7.3gldm³

Molar Mass of A HCl=1+35.5=36.5

Concentration of A =7.3gldm³/36.5gldm³

=0.20moldm³

(1ii)

Concentration of B in moldm³

concentration of A in moldm³ CA=0.20

Volume of used VA=23.00

Concentration of B in moldm³ CB=?

Volume of B used VB= 25.00

CAVA/CBVB = n(A)/n(B) =2/1

0.20*23.00/CB*25.00=2/1

2*CB*25.00=0.20*23.00*1

CB=0.20*23.00/50

Cb=46/50=0.092moldm-³

(1iii)

Molar mass of B in glmol

Concentration of B(moldm-³)= conc gldm³/molar mass

0.092=10.60gldm³/molar mass

0.092 * molar mass =10.60gldm³

Molar mass =10.60gldm³/0.092

=115.2glmd

(1iv)

Relative atomic mass of X in X²CO³

X²+12+3(16)=115.2

2x+12+48=115.2

2x+60=115.2

2x=115.2÷60

2x=55.2

x=55.2/2=276

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(2i)

Tabulate.

TEST; C + 5cm³ of distilled water and shake thoroughly. Divide the solutions into three portions.

OBSERVATION; A pale green solution results 

INFERENCE; salt is soluble 

(2ii)

TEST; To the first portion add NaOH solution in drys 

OBSERVATION; Dark green gelatinous was formed 

INFERENCE; Fe²^+ present

(2iii)

TEST; then in excess 

OBSERVATION; precipitate is insoluble 

INFERENCE; Fe²^+ present

(2iii)

TEST; To the second portion add K3Fe(CN)6 solution

OBSERVATION; A dark blue precipitate formed 

INFERENCE; Fe²^+ confirmed

(2iv)

TEST; To the third portion add AgNO³ solution 

OBSERVATION; White Precipitate formed 

INFERENCE; SO4²^- , CL^- CO²^- present

(2v)

TEST; To the results obtained in add dilute HNO3 in drops , then excess 

OBSERVATION; White Precipitate is insoluble 

INFERENCE; CL^- present

(2vi)

TEST; To the results obtained in add NH3 solution

OBSERVATION; White Precipitate dissolves 

INFERENCE; CL^- Confirmed

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(3ai)

Filtration

(3aii)

Diagram.

(3bi)

I. Methyl Orange

II. Methyl orange

III. Phenolphthalein

(3bii)

A white Precipitate is observed. Effervescence occurs a gas is evolved which change lime water milky.

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Completed.

Screen shots

QUESTIONS