Question 1 Answer

(i)  Average volume of acid used.

(ii)  MgCO3+H2SO4→ MgSO4 + H2O+ CO2

(iii)
0.2 mol in 1000cm3

x mol  in 250 cm3

x = 0.2mol x 250cm3

1000cm3

= 0.005 mol

(iv)

From eqn 1 mol MgCO3 : 1 mol H2SO4

Therefore 0.005 mol MgCO3 : 0.005 mol H2SO4

(v)

0.005 mol of MgCO3 in 25 cm3

X mol   of MgCO3 in 250cm3

X mol = 0.005 x 250cm3

25 cm3

X mol = 0.05 mol

(vi)

Mass = mol x RMM of MgCO3

= 0.05 mol x 24 + 12+ 16 x 3

= 4.2g

(vii) Method A

Use a titration method to prepare Anhydrous magnesium Sulphate.

Determine volume of sulphuric acid from a burette needed to neutralize a fixed volume of magnesium carbonate solution measured in a pipette.

Repeat the titration using a phenolphthalein as an indicator until three volumes of acid are the same.

Evaporate some of the water using an evaporating dish and Bunsen burner.

Leave to crystallize

Rinse and dry crystals.

Method B

Use a metal and acid method.

Add fixed amount of magnesium metal to a fixed volume of sulphuric acid in a beaker, warming if necessary until effervescence stops and excess metal is present.

Filter to remove excess magnesium metal, collect filtrate.

Evaporate some water using an evaporating dish and Bunsen burner.

Leave to crystallize

Rinse and dry crystals

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