NABTEB CHEMISTRY PRACTICALS ANSWER

 NABTEB CHEMISTR PRACTICALS ANSWERS

1a) Volume of pipette used =25cm^3

Indicator used = Methyl Orange

Table of observation

Burette Reading | Rough | 1st | 2nd |3rd

Final Reading|24.50 |23.50 |23.40 |23.60

Initial Reading (Cm^3)| 0.00| 0.00| 0.00| 0.00

Volume of Acid Used|24.50| 23.50| 23.40| 23.60

Average volume of acid used =1st + 2nd + 3rd/3

=23.50 + 23.40 + 23.60/3

=70.5/3 = 23.50cm^3

1b) Concentration of solution B in Mol/dm^3

CAVA/CBVB=nA/nB

CA= 0.03mol/dm^3, VA=23.50cm^3, nA=2, nB=1, VB= 25cm^3, CB= ?

CB= CAVAnB/VBnA

CB= 0.03 x 23.5 x 1/25 x 2

=0.705/50 =0.0141

Concentration of Solution B in mol/dm^3=0.0141mol/dm^3

1bii) Molar mass of Nacl

=23 + 35.5 = 58.5g/mol

Na2Co3 in 1dm^3 of B = Molar Conc x Volume

=0.0141 x 1

=0.0141mole

[12/05 13:44] ‪+234 903 620 3423‬: From the equation

Na2Co3 + 2Hcl——>2Nacl + H2O + Co2

1mole of Na2Co3 produces 1mole of Nacl

0.0141mole of Na2Co3 librates

2 x 0.0141mol of Nacl

=0.0282mol

Mass of Nacl =0.0282 x 58.5

=1.6497g

=1.65g

1biii) From the equation:

1mole of Na2Co3 produces 1mole of Co2 at S. T. P

1mole of Na2Co3 produces 22.4dm^3 of Co2 at S.T.P

Therefore, 0.0141mole of Na2Co3 will produce 22.4 x 0.0141

Volume of Co2=0.316dm^3

1bix) Molar Mass of H2x=(2 x 1) + X=(2 + X)g/mol

[12/05 13:44] ‪+234 903 620 3423‬: 2) TEST | OBSERVATION | INFERENCE

a) C+ water mixed thoroughly and filtered | Partially Soluble in water with colourless filtrate and white residue | C is a mixture of soluble and insoluble salts

[12/05 13:44] ‪+234 903 620 3423‬: bi) Filtrate + NaOH(aq) in drops, then in excess | White precipitate is formed. The precipitate soluble in excess NaOH(aq)| Pb^2+, Zn^2+ or Al^3+ present

bii) Filtrate of NH3(aq) in drops, then in excess | White is formed. The precipitate is insoluble in excess NH3(aq)| Pb^2+ or Al^3+ present

biii) Filtrate + KI(aq) + warm and allow to cool| Yellow precipitate is formed. The precipitate reappears after cooling| Pb^2+ confirmed

c) Residue + HCL(aq)| The residue dissolves ,librating a colourless gas which turns lime water milky| Gas is Co2 from Co3^2-is present

[12/05 13:44] ‪+234 903 620 3423‬: d) Residue + NH3(aq) in drops, then in excess | White gelatinous precipitate is formed. The precipitate is soluble in excess NH3(aq)| Zn^2+ confirmed

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3a)

NH4CL and NaN03 dissolves readity in cold water

3aii)

CuCO3 have a black residue on heating

3bi)

E=Cu0

3bii)

blue precipitate is formed the precipitate dissolves in aqeous ammonia to give a deep blue solution

3biii)

G is water (H20)

3biv)

A dark brown precipitate is formed at the bottom of the test tube which shows that copper has been displaced by zinc from its solution

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