AS Live Session Spring 2024

Spring 2024 AS Sessions:

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Session 1 – Radioactivity and Ionisation Energies (NS)

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Session 2 – Gravimetric Practical (PB)

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Session 3 – Instrumental Analysis (NS)

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Session 4 – Making up a Standard Solution and Titrations (PB)

Gravimetric Analysis

(AS Chemistry)

A 1.22g sample of impure lead nitrate was dissolved in 40.0ml of distilled water and analysed by gravimetric analysis to determine the percentage by mass of lead present. Excess sodium sulphate was added from a burette to form a precipitate of lead sulphate.

The precipitate was filtered, washed and dried before being weighed on a pre-weighed piece of filter paper. After heating to constant mass a precipitate of lead sulphate weighing of 1.44g was collected.

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Use this information to determine the mass of lead by % mass in the sample

equation

lead + sodium

Nitrate sulphate

lead + sodium

suphate nitrate

Pb(NO₃)_2(aq) Na₂SO_4(aq) PbSO_4(s) 2 NaNO_3(aq)

_{Ar 207.2 Mr = 303.26}

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Moles PbSO_4(s) =

1.44/303.26 = 4.75 x 10^-3

Mass Lead =

4.75 x 10^-3 x 207.2 = 0.984g

% mass = 0.984/1.22 x 100 = 80.7%

Titration

(AS Chemistry)

Summer 2022

24.20

24.20

23.60

23.6

0.4

5

0

23.25

23.90

0.30

23.60

Average titre = 23.60ml

nHCl =

0.100x 23.60/1000 = 2.36 x 10^-3

n M₂CO₃ =

2.36 x 10^-3 /2 = 1.18 x 10^-3

4.72 x 10^-3

Mass of carbonate = 1.25g

M_r =

1.25/1.18. x 10^-3

= 1059.3

???????

Titration moles in 25cm3 = 1.18 x10^-3

Moles in 1.25g of carbonate =

1.18 x 10^-2

Mass of carbonate = 1.25g

M_r =

1.25/1.18. x 10^-2

= 105.9

n carbonate needed =

0.05 x 250/1000 = 1.25 x 10^-2

Mass carbonate =

1.25 x 10^-2 x 106 = 1.325g

procedure

weigh

dissolve

transfer

Rinse!!

pipette/meniscus

AGITATE

PIPETTE

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TITRATE INDICATOR X 3

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MEAN VOLUME

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REPEAT NO INDICATOR

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EVAPORATE