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Spring 2024 AS Sessions:

Session 1 – Radioactivity and Ionisation Energies (NS)

Session 2 – Gravimetric Practical (PB)

Session 3 – Instrumental Analysis (NS)

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

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Gravimetric Analysis

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Silver Nitrate

M_r

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?

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Gravimetric method – to find moles XCl

XCl_(aq) + AgNO_3(aq) 🡪 AgCl_(s) + XNO_3(aq)

Cl-_(aq) + Ag+_(aq) 🡪 AgCl_(s)

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XCl (aq)

EXCESS

Remember

nAgCl = nXCl

XCl_(aq) + AgNO3_(aq) 🡪 AgCl_(s) + XNO3_(aq)

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XCl_(aq) + AgNO3_(aq) 🡪 AgCl_(s) + XNO3_(aq)

n(XCl) = 0.00407 mol

0.305

Molar mass = 0.305

0.00407

XCl =74.94

X = 74.94 – 35.5 = 39.43

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Summary

Moles XCl = mass of silver chloride

Mr of silver chloride

Mr XCl = mass of XCl

moles of XCl

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Applying to a similar situation

What is M in

M₂CO₃

Questions

What is the charge of the carbonate ion?

What does this tell us about the group of M?

In practical tems how will gravimetric analysis be done to establish M’s identity?

Accurately weigh the carbonate M2CO3

Form a ppt of CaCO3 from the M2CO3

Filter, dry to constant mass and weigh ppt

of CaCO3

Find moles of CaCO3 ppt formed

Use ppt equation to relate to moles of CaCO3 to moles of M2CO3

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Making the precipitate

Add CaCl_{2 (aq)}

M₂CO_3(aq) + CaCl_2(aq)

CaCO_3(s) + 2 MCl_(aq)

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Filter, dry to constant mass and weigh ppt

Find moles of CaCO3 ppt formed

Moles of CaCO3 = 1.838/100.1

= 0.01836

Mass of CaCO3 formed = 1.838g

Use eqn to find moles of M2CO3

Moles of M2CO3 = 0.01836

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Moles of M2CO3 = 0.01836

Mr (M2CO3) = mass/moles

Calculation to find Mr

Mr = 1.972/0.01836

= 107.4

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Identity of M in M₂CO₃

M= 107 – 60 = 23

2

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Mass of boat and contents

= 1.4614g

Mass of emptied boat

= 0.9662g

Mass added = 1.4614-0.9662

= 0.4952g

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Mass added = 1.4614-0.9662

= 0.4952g

Error in weighing = 0.5246-0.4952

= 0.0294g

% error = 0.0294/0.4952 x 100

= 5.94% !!!

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Spring 2024 AS Sessions:

Session 1 – Radioactivity and Ionisation Energies (NS)

Session 2 – Gravimetric Practical (PB)

Session 3 – Instrumental Analysis (NS)

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