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2019 NECO Chemistry Practical Answers Expo

Last modified about 3 weeks ago by . Posted in Neco |

NECO 2019 Chemistry Practical Question & Answers Expo.

===COMPLETED===

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(2)
Fill in the space.
(2i)
Observation;
Solution turns blue

Inference;
Copper salt suspected.

(2ii)
Observation;
Blue gelatinous precipitate

Insoluble in excess NaOH

Inference;
Cu²+ suspected

Cu²+ Confirmed

(2iii)
Observation;
Blue gelatinous precipitate

Soluble in excess NH³

Inference;
Cu2²+ Suspected

Cu²+ Confirmed

(2iv)
Observation;
White precipitate

Inference;
SO4²- Suspected

(2v)
Observation;
Precipitate insoluble in excess

Inference;
SO4²- confirmed

========================

(1)
CLICK HERE FOR THE IMAGE
CLICK HERE FOR THE CONTINUATION

TAKE NOTE ON THIS NUMBER (1)
Pls note that each school have their titre value or end point. In our solution, we used 20.40cm3. So make sure you use ur school’s titre value. Ask your chemistry teacher. Some school got 24.50, 24.20, 22.10, 22.40, etc. Make sure your average titre value tallies with that of ur school’s. Anywhere you see 20.40 in my work, edit it and re-solve with ur school’s value.
This is very important.
Thanks.
=====================================

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(1)
The volume or pipette used 25.00cm³

In a tabular form
Titrations |rough |1st|2nd|3rd|
Final reading |21.00|41.30|20.40|40.90
Initial reading|0.00|21.00|0.00|20.40
Vol of A used |21.00|20.30|20.40|20.50

(1ai)
Average volume of A = 20.30+20.40+20.50/3
=61.2/3
=20.40cm³

(1aii)
H2X(aq) + 2NaOH(aq)–>Na2X(aq) + 2H2O(l)

(1bi)
Mass conc. of B = 1g/250cm³
= 1g/0.25dm³ = 4g/dm³
Using :
Molar conc. = mass conc./molar mass
= 4/(23+16+1) = 4/40 = 0.1mol/dm³

(1bii)
Using CAVA/CBVB = nA/nB
CA = CBVBnA/VAnB
CA = 0.1×25×1/20.4×2
Concentration of A = 0.06127mol/dm³

(1biii)
Molar mass of A = mass conc/molar conc
=4.85/0.6127
=79.15
? 79gmol

(1c)
(i)it might contain traces of impurities which must be removed before being weighed
(ii)it is hygroscopic which readily absorb moisture from atmosphere
================================

(3ai)
phenolphthalein

(3aii)
I. Pink
ll. Colourless

(3aiii)
(i)To give a sharp change in colour at the end of the acid base reaction

(3aiv)
(i)the burette must be rinsed with the acid or allow it to drain after rinsing with distilled water
(ii)Air bubble must not be allowed in the burette

(3av)
Neutralization reaction

(3bi)
I. Hofmann voltameter.
II. Kipp’s apparatus

(3bii)
Because silver nitrate is photosensitive (i.e.sensitive to light) Therefore,if the silver nitrate is left in sunlight or any bright light, it breaks down (hydrolyses) to give black/brown silver oxide and nitric acid.

More Answers Loading…….100%

make sure you use your school titre value

For example, if your school uses 23.50

Our own solution centre may use 24.00

Pls don’t be confused, just make adjustment from the beginning where you will need to find the *

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