2020 NABTEB GCE CHEMISTRY VERIFIED ANSWERS

2020 NABTEB GCE CHEMISTRY VERIFIED ANSWERS

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(1ai)

To have two or more concurrent result or values

(1aii)

Average Volume titre=20.00 + 20.10 / 2

=20.05

(1aiii)

HNO3 + XOH  ----->  XNO3 + H2O

(1bi)

When number of acid (na) = 1, and the number of base (nb) = 1

Using CaVa/CbVb=na/nb

Given:

Ca=0.0499

na=1

nb=1

Va=20.05

Vb=20.00cm³

Use your school titre value and volume of base used(i.e 25cm³)

Cb=?

Using the equation

CaVa/CbVb=na/nb

Cb= 0.0499 × 20.05 × 1 ÷ 20 × 1

Cb=0.050 mol/dm³

≈0.1mol/dm³

(1bii)

1.4g  –––– 250cm³

x –––– 1000cm³

x=1.4×1000/250

x=5.6g

Mass conc = molarity × Molar mass

5.6=0.1 × Molar mass

Molar mass= 5.6/0.1

=56g

(1biii)

Molar mass = 56g

The Molar mass of x = x + 16 + 1

:. 56 = x + 17

x = 56 – 17

x = 39

Relative atomic mass of x = 39, the element  x js potassium and the alkali is potassium hydroxide

(1biv)

Methyl orange

(1ci)

To Ensure High Accurate of the titre Value

(1cii)

Using an acid will alter the volume of the acid used and affect the reading in the final result.

(1ciii)

This is to avoid movement of air, which may lead to the sucking of the base solution

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(2i)

(i)  W     is Copper (Cu)

(ii)  X     is  Iron  (fe)

(iii) Y    is Zinc (Zn)

(iv)  Z   is Lead  (Pb)

(2ii)

(i)  W     is Cu^2+

(ii)  X     is Fe^3+

(iii) Y     is Zn^2+

(iv)  Z    is Pb^2+

(2iii)

TABULATE: 

• W 

TEST APPLIED

W + NH3 in drop

And in excess

OBSERVATION

Blue precipitate form in drop of NH3

And Blue precipitate in excess

INFERENCE

Cu^2+ is present

• X

TEST APPLIED

X + NH3 in drop

And in excess

OBSERVATION

Light green precipitate form both in drop and in excess of NH3

INFERENCE

Fe^2+ is present

• Y

TEST APPLIED

Y + NH3 in drop 

And in excess

OBSERVATION

White Gelatinous precipitate soluble in excess

INFERENCE

Zn^2+ is present

• Z

TEST APPLIED

Z + NH3 in drop 

And in excess

OBSERVATION

White powdery precipitate insoluble in excess

INFERENCE

Pb^2+ is present

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(3a)

(i) Pick the solute

(ii) Dissolve the solute

(iii) Decolorize the solution

(iv) Filter any solids from the hot solution

(v) Crystallize the solute

(vi) Collect and wash the crystals

(vii) Dry the Crystals

(3bi)

TEST TUBE A

The colour of the tube A changes to blue black because it is in carbohydrate and starch was present

(3bii)

TEST TUBE B

The solution TUBE B turned clear, Meaning that starch was gone

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Completed!!

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