Chemistry practical Neco 2019

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I. Pink
ll. Colourless

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

(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

Neutralization reaction

I. Hofmann voltameter.
II. Kipp’s apparatus

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.

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

Average volume of A = 20.30+20.40+20.50/3

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

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

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

Molar mass of A = mass conc/molar conc
≅ 79gmol

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

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