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NECO Practical Chemistry Questions and Answers

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Today’s NECO Practical Chemistry Answers: (2020 Answers)

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Note: The answers below are not today’s answers.

2021 NECO Practical Chemistry answers loading…

(1) (2020 Answers)
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

(2ai)
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

(2aii)
TEST: To the first portion add NaOH solution in drys

OBSERVATION: Dark green gelatinous was formed

INFERENCE: Fe²+ present

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

2aiii)
TEST: then in excess

OBSERVATION: Precipitate is insoluble

INFERENCE: Fe²+ present

(2aiv)
TEST: To the second portion add K3Fe(CN)6 solution

OBSERVATION: A dark blue precipitate formed

INFERENCE: Fe²+ confirmed

(2bi)
TEST: To the third portion add AgNO³ solution

OBSERVATION: White Precipitate formed

INFERENCE: SO4²- , CL-, CO²- present

(2bii)
TEST: To the results obtained in add dilute HNO3 in drops , then excess

OBSERVATION: White Precipitate is insoluble

INFERENCE: CL- present

(2biii)
TEST: To the results obtained in add NH3 solution

OBSERVATION: White Precipitate dissolves

INFERENCE: CL- 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

(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.

CHEMISTRY PRACTICAL SPECIMEN:

Requirements:
(a) One burette (50cm³)
(b) One pippete (20cm³/25cm³). However, all
candidates in a center must use pipettes of the
same volume.
(c) The usual apparatus and reagents for
qualitative work including:
(i) Dilute sodium hydroxide solution
(ii) Dilute ammonia solution
(iii) Dilute hydrochloric acid
(iv) Barium chloride solution
(v) Distilled water
(vi) Red and Blue litmus paper
(vii) Phenolphtalein
(d) Methyl orange
(e) One boiling tube
(f) Five test tubes
(g) Filtration apparatus
(h) Source of heat
Each candidate should be supplied with the
following: Labelled An, Bn, Cn, where ‘n’ is the
candidate’s serial number.
(a) 150cm³ of chloride acid solution in a bottle
labelled “An”. The acid solution which should
be the same for all candidates will contain
3.4cm³ of the concentrated hydrochloric acid
per dm³ solution.
(b) 150cm³ of sodium hydroxide solution in a
bottle labelled “Bn”. The solution which should
be the same for all candidates will contain
4.0g of sodium hydroxide per dm³ of solution.
(c) One spatulaful of copper (ii)
tetraoxosulphate (vi) salt in a specimen bottle
labelled “Cn”.

The questions below are strictly for practice not the 2021 Chemistry expo.

All your burette readings (initials and final) as well as the size of your pipette must be recorded but no account of experimented procedure is required. All calculations must be done in your booklet.

1. A is O.200 moldm³ of HCI. C is a solution containing 14/3_g of Na₂CO₃. x H₂O in 500 cm³ of solution. (a) Put A into the burette and titrate it against 20.0 cm³ or 25.0 cm³ portions of C using methyl orange as indicator. Repeat the titration to obtain Consistent titre values. Tabulate your results and calculate the average volume of A used. The equation for the reaction is: Na₂CO₃ x H₂O + 2HCL_(aq) → 2NaCI_(aq) + CO2_(g) + (x+1) H₂O_(I).

(b) From your results and the information provided. Calculate the: (i) concentration of C in moldm^-3; (ii) concentration of C in gdm^-3; (iii) molar mass of Na₂CO₃, xH₂O; (iv) the value of x in Na₂CO₃ xH2O. [H = 1.0; C=12.0; O = 16.0; Na =23.0]

Credit will be given for strict adherence to the instruction, for observations precisely recorded and for accurate inferences. All tests, observations and influences must be clearly entered in the booklet in ink at the same time they are made.

2. F is a mixture to two inorganic salts. Carry out the following exercise on F. record your observation and identify any gas(s) evolved. State the conclusions you draw from the result of each test. (a) Put all of F in a beaker and add about 10cm³ of distilled water. Stir well and filter. Keep the filtrate and the residue. (b)(i) To about 2cm³ of the filtrate, add NaOH_(aq) in drops and then in excess (ii) To another 2cm³ portion of the solution, add a few drops of NHO_3(aq)followed by few drops of AgNO_3(aq). (d)(i) Put all the residue into a clean test-tube and add NHO_3(aq) followed by few solution from 2(d)(i) add NaOH_(aq) in drops and then in excess.

3. State what would be observed if the following reactions are carried out in the laboratory: (i) methyl orange is dropped into a solution of lime juice (ii) hydrogen sulphide gas is bubbled through iron (III) chloride solution; (iii) sulphur (IV) oxide gas is bubbled into acidified solution of KMnO4; (iv) ethanoic acid is added to a solution of K₂CO₃.

CHEMISTRY PRACTICALS ANSWERS

1. Indicator                                 =          Methyl Orange

Volume of the base used        =          25.00cm³

Average Titre              =          1^st + 2^nd + 3^rd/3

=          24.80 + 24.70 + 24.90/3

=          24.80cm³

Alternatively 2 concordant titres can be used to calculate average titre.

Equation of the reaction: Na₂CO₃ XH₂O + 2HCI_(aq) → 2NacI_(aq) + CO_2(aq) + (x+1)H₂O_(I)

C_AV_A/C_BV_B     =  n_A/n_B

C_A = Molar concentration of HCI_(aq) in moldm³

V_A = Volume of acid used in cm³ = 24.80cm³

C_B = Molar concentration of Na₂Cu₃ xH₂O in moldm³

n_A = 2

n_B = 1

(b)(i) concentration of C in moldm^-3 = ? From the equation of reaction:

C_AV_A/C_BV_B     =  n_A/n_B

C_A = 0.200 moldm³     V_A = 24.80cm³

C_B = ?                          V_B = 25.00cm³

Substitution of known values

0.200 x 24.80/ C_B x 25.00 = 2/1

C_B = 1×0.200×24.80/2×25.00

C_B­ = 0.0992 moldm^-3

(ii) Concentration of C in g dm^-3 = ?

500cm² → 14.3 g

1000cm3 →14.3/500 x 1000² g

= 28.6 g dm^-3

(iii) Molar mass of Na₂CO₃ xH₂O

Molar conc in moldm^-3 = conc in g dm^-3 / molar mass

Therefore: Molar mass g mol^-1 = conc in g dm^-3 / molar conc in moldm^-3

= 28.6 g dm^-3/0.0992 moldm^-3

= 288.3065

Approximately 288 g mol^-1

(iv) Value of x in Na₂CO₃ xH₂O?

[H = 1.0, C = 12.0, O = 16.0, Na = 23.0]

Na₂CO₃ xH₂O = 288

2(23) + 12 + 3 (16) + x (2(I) + 16) = 288

46 + 12 + 48 + 18x  = 288

106 + 18x        = 288

18x      = 288

18x      = 182

x       = 182/18

x       = 10.11

x approximately 10

3 (a)(i) Solution of lime juice turns to pink or red. (ii) The FeCI₃ solution changes colour from brown to green and a yellow deposit. (iii) The purple colour of the KMnO₄ solution turns colourless or decolourised. (iv) The solution of K₂CO₃ reacts with the addition of ethanoic acid to evolve a colourless, odourless gas with bubbling of effervescence.

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