ZnCO3 → ZnO + CO2
2NaNO3 → 2NaNO2 + O2
(NH4)2Cr2O7 → N2 + Cr2O3 + 4H2O
Precipitation Reactions
- Solubility Rules (in water)
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Na, K and NH4 compounds are all soluble.
- All nitrates are soluble.
- Most chlorides are soluble. Exceptions include Pb and Ag.
- Most sulphates are soluble. Exceptions include Pb and Ba.
- Most oxides, hydroxides and carbonates are insoluble in water.
Experiment 1.1b
Mix each of the following compounds with 5 cm3 water. Answer the questions on page 5. To those that form solutions add a few drops of 0.4M NaOH. Record results.
Compounds used:
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CuCl2 — dissolves, blue ppte with NaOH
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FeSO4 — dissolves, green ppte with NaOH
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MgCO3 — doesn’t dissolve
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Fe(NO3)3 — dissolves, orange/red ppte with NaOH
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Fe2O3 — doesn’t dissolve
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K2CO3 — dissolves, no ppte with NaOH
Interpretation of Precipitation
Pupils to read and make brief notes. Include ionic and full equations where relevant [Study Task, bottom of page 6.]
Experiment 1.1b (contd)
Further experiments using solubility rules, writing equations, etc.
Redox Reactions
REDOX = REDuction and OXidation
Expt. 1.1c Demonstration of Thermit Reaction
Write a balanced equation and calculate sensible amounts (0.05 moles Fe2O3). Procedure as in book.
Interpretation
Al has gained oxygen, thus is oxidised. Fe has lost oxygen, thus is reduced. Both processes occur simultaneously.
Zn can also reduce iron(III)oxide to Fe [position in the reactivity series], but Cu could not.
These reactions release considerable amounts of energy [equations and energy changes shown on page 9]. A reaction which releases energy [exothermic reaction] is given a negative value because the products contain less energy than the reactants [energy change = products energy – reactants energy]. Note that the Copper reaction is endothermic and, therefore, unlikely to ‘go’. Much more about this later!!
Thermit Reaction — read and make brief notes (page 9).
But redox reactions are more than just loss or gain of oxygen — this would be rather limiting!! Iron forms two different series of compounds, each containing a different iron ion [Fe2+ and Fe3+]. Transition elements (of which iron is one) frequently contain more than one type of ion.
If the charge on an ion becomes more positive (e.g. Fe2+ to Fe3+) then the ion is said to have been oxidised [i.e. it has undergone oxidation]. If the charge becomes more negative, then the ion has been reduced [i.e. it has undergone reduction].. Remember that oxidation and reduction must occur simultaneously.
Does this fit with what we know about oxygen addition or removal??? Consider the Thermit reaction. The iron goes from 3+ in the oxide to 0 as the metal, so is reduced. The aluminium has 0 charge as the metal, but is 3+ in the oxide, hence it has been oxidised. Thus, the same pattern applies.
Expt. 1.1.d Redox Reactions
Essentially...................
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Oxidise fresh acidified FeSO4 using the following oxidising agents:
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H2O2
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KMnO4
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conc. HNO3 then warm
Test products with NaOH.
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Reduce fresh acidified Fe2(SO4)3 using the following reducing agents:
Test products with NaOH.
Displacement reactions are one type of redox reaction. One example is the reaction of iron metal with copper ions. However, we could construct two possible equations for the reaction, namely
Fe(s) + Cu2+(aq) → Fe2+(aq) + Cu(s)
2Fe(s) + 3Cu2+(aq) → 2Fe3+(aq) + 3Cu(s)
In the first equation one mole of iron produces one mole of copper. The ratio in the second is one mole of iron produces 1.5 moles of copper. Thus, weighing the iron and the copper should allow us to determine the reaction that occurs. [Could we not also use NaOH?? What problems might there be with the NaOH approach??]
Expt. 1.1e Deciding which equation is correct
Details on pages 11/12. Calculate moles of iron used, and moles of pure, dry copper formed. Which ratio is correct?
It is, perhaps, helpful to remember OIL RIG. Oxidation Is Loss of electrons, Reduction Is Gain of electrons.
Section 1.2 Making Salts
Experiment 1.2a Preparation of Nickel Sulphate, NiSO4.7H2O
NiCO3(s) + H2SO4(aq) → NiSO4(aq) + CO2(g) + H2O(l)
See book for details.
Expt. 1.2b Preparation of Mohr’s salt, Ammonium Iron(II) Sulphate, (NH4)2SO4.FeSO4.6H2O
Fe → FeSO4 NH3 → (NH4)2SO4 Mix, crystallise.
See book for details.
Section 1.3 Toolkit: Writing Formula & Balancing Equations
Standard GCSE stuff — use GCSE notes where necessary.
Section 1.4 Toolkit: The Mole, Molar Mass & Molar Volume
Standard GCSE stuff — use GCSE notes where necessary.
Section 1.5 Background Reading: A Golden Opportunity
Answers to Questions:
1.
Key Skills
Communication [Background Reading]
Number [Expts 1.2a&b]
Topic Review
1. List the key words or terms in definitions.
2. Summarise key concepts as simply as possible.
Review Questions
1. Name compounds of given formula.
2 Give formula and state of element.
3. Give formulae of given compounds.
4. Write and balance (simple) decomposition equations.
5. Write and balance precipitation ionic equations.
6. State type of reaction & reason.
7. Write balanced equations.
8*. Calculate molar masses of compounds.
9*. Calculate mass of x moles of substance.
10*. Calculate number of moles.
11*. Calculate masses or volumes.
12*. Preparation of hydrated magnesium chloride.
Examination Questions
13. Preparation of hydrated zinc sulphate.
14. Preparation of vanadium alum.
15. Manganese — reactions and properties.
