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1. QUALITATIVE ANALYSIS OF CATIONS
Cation and anions can be identified by colour of precipitation and/or whether a precipitate is formed or not. Common tested cations include: potassium (K+), sodium (Na+), calcium (Ca2+), magnesium (Mg2+), aluminium (Al3+), lead (Pb2+), zinc (Zn2+), iron(II) (Fe2+), iron(III) (Fe3+), barium (Ba2+), copper (Cu2+) ,ammonium NH 4 +^ and silver (Ag+) When writing the formula of the ions, ensure that The first letter is capital, the second letter is small The letters are not joint The letters are not fancy The ions have the correct charge When writing radicals, ensure that Both letters are capital The radical has the correct charge a) Put the solid into a boiling-tube, add water and shake thoroughly. Observation Inference A colourless solution Fe2+, Fe3+, Cu2+^ absent Pale green solution Fe2+^ present Brown solution Fe3+^ present Pale blue solution Cu2+^ present b) Put the solid into a boiling-tube, and water and shake thoroughly. Filter. Retain both residue and the filtrate for further tests. Observation Inference A colourless solution and a white residue Fe2+, Fe3+^ ,Cu2+^ absent in both filtrates and residue Divide the solution into portions of about 2cm^3. c) Add NaOH(aq) dropwise till in excess Observation Inference No white ppt is formed Al3+, Pb2+, Zn2+^ Mg2+, Ca2+^ absent White ppt soluble in excess sodium hydroxide Al3+, Pb2+, Zn2+^ present
White ppt insoluble in excess sodium hydroxide Al3+, Pb2+, Zn2+^ absent Mg2+, Ca2+^ present Pale blue ppt formed insoluble in excess sodium hydroxide Cu2+^ present Pale green ppt formed insoluble in excess sodium hydroxide Fe2+^ present Pale brown ppt formed insoluble in excess sodium hydroxide Fe3+^ present d) Add Aqueous Ammonia (NH3(aq)) dropwise till in excess Observation Inference No white ppt is formed Al3+, Pb2+, Zn2+^ absent White ppt soluble in excess in ammonia solution Zn2+^ present White ppt insoluble in excess in Ammonia solution Al3+, Pb2+, Mg2+^ present Zn2+^ absent Pale blue ppt soluble in excess Ammonia to a deep blue solution Cu2+^ present Pale green ppt formed insoluble in excess Fe2+^ present Pale brown ppt formed insoluble in excess Fe3+^ present e) Add three drops NaOH(aq) and heat the solution. Test for any gas produced using moist/wet litmus paper Observation Inference A colourless gas with a pungent smell and turns moist red litmus paper blue NH 4 +^ present f) Add Na 2 SO4(aq) or any soluble sulphate or dilute H 2 SO4(aq) Observation Inference White precipitate formed Pb2+, Ba2+^ present No white precipitate formed Pb2+, Ba2+^ absent g) Add NaCl(aq) or HCl(aq) and warm/boil Observation Inference White precipitate formed which dissolve on Pb2+^ Present
m) Add few drops of Ba(NO 3 )2. Observation Inference White precipitate formed SO 4 2-, SO 3 2-, CO 3 2-^ present No white precipitate formed SO 4 2-, SO 3 2-, CO 3 2-^ absent n) Add few drops of Ba(NO 3 ) 2 followed by dilute HNO3(aq) /HCl(aq) Observation Inference White precipitate formed soluble in dilute HNO3(aq). SO 3 2-, CO 3 2-^ present White precipitate formed insoluble in dilute HNO3(aq). SO 4 2-^ present SO 3 2-, CO 3 2-^ absent o) Add 0.01M silver nitrate solution. Observation Inference White precipitate. Cl-^ present No white precipitate. Cl-^ absent. p) Add a few drops of acidified potassium manganate (VII) KMnO4(aq) solution. Observation Inference Purple acidified KMnO4(aq) turns to colourless SO 3 2-,present Purple acidified KMnO4(aq) remains purple SO 3 2-^ absent q) Add a few drops of acidified potassium dicromate(VI) K 2 Cr 2 O7(aq) solution. Observation Inference Orange acidified potassium dicromate(VI) K 2 Cr 2 O7(aq) turns green SO 3 2-, present Orange acidified potassium dicromate(VI) K 2 Cr 2 O7(aq) remains orange. SO 3 2-^ absent r) Add a few drops of dilute HCl(aq) or dilute HNO3(aq) to the solid/solution. Observation Inference Effervescence of a colourless gas SO 3 2-, CO 3 2-^ present
No effervescence of a colourless gas SO 3 2-, CO 3 2-^ absent s) Add 2cm^3 freshly prepared iron(II)sulphate(FeSO 4 ) to the solution. Hold the test tube in a slanting position and carefully add concentrated sulphuric acid along the wall of the test tube. Observation Inference A brown ring is formed at the junction of sulphuric acid and the mixture NO 3 -^ present t) Heat the solid in a dry test tube. Test the gas produces with glowing splint. Observation Inference A gas that relight a glowing splint Brown residue NO 3 -^ , ClO 3 -^ , O2-^ present u) To the solution add 3 drops of NaOH. put a piece of aluminium and shake the mixture. Warm the mixture and test any gas produced with both red and blue litmus papers. Observation Inference Effervescence A gas that red litmus paper to blue. NO 3 -^ present
3. Heating Test
v) Heat a small amount of solid gently then strongly in a boiling tube and test any gases given out. Observation Inference Colourless vapours condenses on the cooler parts of the test tube, Hydrated salt A brown gas that turn moist blue litmus paper red NO 3 -^ present Colourless gas that extinguishes a burning splint/forms a white ppt with lime water CO 3 2-^ or HCO 3 -^ present A gas that turns red litmus paper to blue NH 4 +^ present Solid turn yellow when hot and white and Zn2+^ present
absent c) Add a few drops of acidified potassium dicromate(VI) K 2 Cr 2 O7(aq) solution. Observation Inference Orange acidified potassium dicromate(VI) K 2 Cr 2 O7(aq) turns green R-OH, present Orange acidified potassium dicromate(VI) K 2 Cr 2 O7(aq) remains orange. R-OH absent d) Add a few drops of bromine water. Observation Inference Yellow/orange colour of bromine water turn colourless , present Yellow/orange colour of bromine water turn colourless , absent e) Test the pH of the solution using universal indicator solution/paper Observation Inference pH is 1,2,3 Strongly acidic pH is 4,5,6 Weakly acidic pH is 10,11,12 Strongly alkaline f) Put a piece of Mg/Na 2 CO 3 /NaHCO 3 into the solution. Observation Inference Effervescences , H+^ present No effervescences , H+^ absent g) Put some of the compound into an evaporating dish and ignite. Observation Inference Burn with a blue non sooty flame , absent h) Put some of the compound on a metallic spatula, ignite with a Bunsen burner flame Observation Inference Solid melt and burn with a yellow sooty flame , present
i) To the solution add 5 drops of concentrated Ethanoic acid followed by 3 drops of concentrated sulphuric acid. Shake the mixture and warm the mixture. Observation Inference Oily sweet-smelling compound formed present
5. REACTION RATES
The six factors which affect the rate of reaction Concentration Temperature Catalyst Surface area Light Pressure. When any of the above factors increases, the rate of increases and vice versa. Concetration and temperature are possible to vary and therefore are tested in chemistry paper 3. Concentration is changed by adding varying amount of water. Temperature is varied by heating of cooling the reactants. The value of time obtained in the table should either increase or decrease and not and the mixture of the two. Common reactions used to measure rates of reaction Reaction of magnesium ribbon with various concentration of HCl or H 2 SO 4 Mg(s) + 2HCl(aq) MgCl2(aq) + H2(g) Mg(s) H 2 SO4(aq) MgSO4(aq) + H2(g) Formation of yellow precipitate of sulphur when sodium thiosulphate react with various concentrations of HCl
Na 2 S 2 O 3 + 2HCl NaCl(ag) + SO2(g) + H 2 O(l) + S(s)
5 10 15 20 25 30 35 40 0 5 10 15 20 25 30
A plot of concentration/volume
of acid versus time
time (sec) volume of acid (cm3)
A plot of rate (1/time) against volume of acid/concentration
0 5 10 15 20 25 30 0 2 4 6 8 10 12 14 16 volume of acis (cm3) 1/TIME (sec-) ×10-
b) When temperature decreases, time taken increase thus rate of reaction decreases.
ENERGY CHANGES-THERMODYNAMIC
Reactions can be classified as either endothermic or exothermics.
Exothermic reactions
Heat of neutralization
Heat of displacement
Heat of solution e.g. dissolving sulpuric acid in water
Exothermic reactions
Heat of solution e.g. dissolving sodium nitrate in water
Reaction between Sodium hydrogen carbonate and hydrochloric
acid.
Temperature change is obtained from graph by extrapolation and from the
table.
Heat change = mass of solution × specific heat capacity × temperature
change
ΔH = m × C × ΔT
Molar heat must have the correct sign (- for exothermic and + for
endothermic)
Molar heat must have the correct units. (j/mole or kj/mole)
Examples:
Temperature of Na 2 S 2 O 3 (oC) rt 30 40 50 60 Time taken for the cross to become invisible (sec) 1/time (sec)
0 50 100 150 200 250 300 0 5 10 15 20 25 TIME (SEC) TEMPERATURE (OC) c) Gradual rise and then gradual in exothermic e.g.
Time (sec) 0 30 60 90 120 150 210 240
Temp (oC) 25.0 26.0 27.0 28.0 29.0 29.0 27.0 26.
0 50 100 150 200 250 300 24 25 26 27 28 29 30 time (sec) temperature (oC)c
6. SOLUBILITY AND SOLUBILITY CURVE
Defination of solubility must include 100g of water.
Plotted point are joined to obtain a curve and not a straight line
Mass of crystals is given in grams
Show how you have obtained the answer on the curve using dotted lines.
Example
Volume of water in
the boiling tube
Temperature at which
crystals of solid appear (oC)
Solubility of solid M
(g/100g of water)
0 0.5 1 1.5 2 2.5 3 3. 70 72 74 76 78 80 82
freezing point graph
time (min) temperature (oC)
8. TITRATION
Ensure that:
Titration table is completely filled
All values in the table are to one decimal places.
Titre values do not vary by more that 0.
When calculating:
Transfer all answers intact
Average volume should be in-2dps
Moles in mole-4dps
Molarity-3dps
Mass-2dps
Temperature-1dp
Time-1dp
1/time- 3dps.
When calculating moles
R.A.M and R.F.M do not have units.
No of moles n = mass/molar mass and not n= mass/RFM.
Equations are necessary when esterblishing the mole ratio of reactants and
productst but are not compulsory
If an equation is written, it must correct, balanced, and have state symbols.
