Chapter12-paper 62

Mixture: 2 or more substances that are mixed with each other and ration isn’t
important. They are without any chemical bonding.
Compound: a specific chemical formula in which elements have a fixed ratio
compared to others. They are bonded to each other chemically.
Solution: it is made up of a solvent & solute. The solute is dissolved in the
solvent & all chemical properties are the same.
 Comparing a solution & a mixture: every part of a solution has the same
chemical properties but, in a mixture, each different particle has a separate
chemical property.
Suspension: when particles aren’t dissolved in solvents so that the small
particles are visible.
Miscible: when 2 or more solvents dissolve in each other very well.

12-1~ Separating methods:

Solid from a liquid

a) Solid is b) Solid isnt

miscible. miscible.
(ex: wood & water)
(ex:salt in water) filtration

b) If solvent is wanted:
a) If salt is wanted:
distillation ==> evaporation
evaporation
and condesation

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Separating liquids

b) Liquids that arent

a) Liquids that are miscible
miscible. (ex: oil & water)
(ex: ethanol & water) Separating funnel
Fractional distillation
(The liquids have
different b.ps so they
turn into gas at different
temperatures)

Separating funnel:

 Separating solids: There are 4 methods

1. Separating based on density: after vibration they’ll separate from each
other based on their density, the lighter on top & the heavier sinks to the
bottom.
Ex: rice & sand
2. Separating based on magnetic properties: magnetic substances will be
attracted to the magnet & can be separated in this way.
Ex: iron & sand
3. Separating based on solution: when one solid is soluble in a solvent but
the other is not soluble, by using a solvent the soluble solid dissolves but
the other one wont. Then by filtration we can remove the insoluble solid.
Ex: sugar & sand
4. Separating based on sublimation: different solids have different
sublimation points. So, one of the solids becomes gas the other one
remains solid. The gas is turned back into solid by condensation.

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 Filtration:

Distillate: the liquid after condensation of gases in distillation process.

Chromatography: a technique to separate colored dyes.
Note: solvents start moving on the paper & different colors have different speed to
move, so they are separated from each other.
R.f value:

Note: if chromatogram has colorless spots so we will

place it in a locating agent then the spots become
colorful.

 Solubility of gases in liquids: there are 2 factors:

Pressure: the more the pressure, the higher the amount of gas dissolves in
liquids.
Temperature: the lower the temperature, the higher amount of gas dissolved
in liquids.

Titration: was discussed in chapter 3.

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Chemical analysis & investigation

12-2 Detection of cations:

If you add NaOH & nothing happens then Group 1 is present, or H+ , NH4+.
Further investigations for column 1:
Note: if nothing happens after adding NaOH, a red litmus paper is held above the
test tube, if it turns blue than NH4+ was present. If not, a blue litmus paper is
dipped in & it turns red meaning H+ is present.
If not, we will apply the flame test:
H+ + OH-  H2O(l)  neutral
+ -
NH4 + OH  NH3(g) + H2O(l)  NH3 is a basic gas
Li+ Crimson flame
Group 1 Na+ Yellow flame
K+ Lilac flame

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 Chapter12-paper 62

Ca2+ Brick-red flame

Group 2 Ba2+ Apple-green flame
Mg2+ White flame

Further investigations for column 2:

Cu2+  blue ppt
Fe2+  green ppt
Fe3+  red-brown ppt
Cr3+  grey-green ppt
To separate Fe(OH)2 & Cr(OH)3 we add excess NaOH.
Note: firstly, we will add excess NaOH, by doing this Cr(OH)3 dissolves to form a
green solution. On the other hand, Fe(OH)2 remains the same, that’s how we see
the difference.
By adding excess NaOH to Cu(OH)2 & Fe(OH)3 nothing happens as they are
insoluble ppt’s.
Further investigation By using ammonia with a fresh sample:

Note: by adding excess NH3, Cu2+ dissolves to form a blue solution. The rest
remain the same.
Further investigation for column 3:
~ As we add NaOH to all of column 3, a white ppt forms. As excess NaOH is
added, Al(OH)3 & Zn(OH)2 dissolve (because they are amphoteric oxides).
To distinguish between Zn2+ & Al3+ , we add NH3 to a fresh sample. A white
ppt forms for both. Then by adding excess NH3, Zn2+ dissolves but Al3+
remains as a ppt.

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To distinguish between Ca2+, Ba2+ & Mg2+, we should apply a flame test to
solids of the cations.
Mg2+  white flame // Ca2+  brick-red flame // Ba2+  apple-green flame
NaOH Excess NaOH NH3 Excess NH3
2+
Zn White Dissolves White Dissolves
Al3+ White Dissolves White No change
Ca2+ White No change No ppt No change
Ba2+ White No change White No change
Mg2+ White No change White No change

Positive ion (in solution) Effect of adding NaOH Effect of adding NH3
solution
Ammonium (NH4) Ammonia produced on
warming (test with damp -
red litmus paper)
Copper (II) (Cu2+) Light blue gelatinous ppt Light blue gelatinous ppt,
of copper hydroxide, dissolves in excess NH3
insoluble in excess giving a deep blue
NaOH solution
Iron (III) (Fe3+) Rust-brown gelatinous Rust-brown gelatinous
ppt of iron (II) hydroxide, ppt, insoluble in excess
insoluble in excess
Chromium (III) (Cr3+) Grey-green ppt of Grey-green ppt, insoluble
chromium (III) in excess
hydroxide, soluble in
excess
Calcium (Ca2+) White ppt of calcium No ppt (or only a very
hydroxide, insoluble in slight ppt)
excess
Magnesium (Mg2+) White ppt of magnesium White ppt, insoluble in
hydroxide, insoluble in excess
excess
Zinc (Zn2+) White ppt of zinc White ppt, soluble in
hydroxide, soluble in excess
excess giving a colorless
solution

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Aluminium (Al3+) White ppt of aluminium White ppt, soluble in

hydroxide, soluble in excess
excess giving a colorless
solution

Detection of anions:
To detect anions, first we add silver nitrate then acid & finally specific tests
of SO42- & NO3- are done.
Silver Nitrate is used to detect Cl-, Br -, I-, & Cr2O72-.
 To detect halide ions, we have to add AgNO3 (silver nitrate), then a colorful
ppt forms.
Note: nitric acid is also added, however it does nothing except providing an
acidic media.
Na+Cl- + AgNO3  AgCl (white ppt) + NaNO3
Na+Br- + AgNO3  AgBr (crème ppt) + NaNO3
Na+I- + AgNO3  AgI (yellow ppt) + NaNO3
 To detect Cr2O72- we have to add AgNO3 (& nitric acid) & an orange ppt
forms.
Na2+Cr2O72- + AgNO3  Ag2Cr2O7 (orange ppt) + NaNO3
 To detect CO32-, by adding a dilute acid, H2CO3 will form and this acid
decomposes immediately to water & CO2. Fizzing of CO2 is the evidence of
carbonate.

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 To detect SO32- (sulfite), we will add any acid & sulfur dioxide will be
released which is the evidence for presence of SO32-.

 To detect SO2 gas, we can place a paper in a solution of KMnO4 and it burns
to purple. Then we will place it above the test tube of SO2 gas fizzing & the
paper will become colorless as it bleaches the paper.

 To detect SO42- (sulfate), we add a solution of barium (Ba2+) (chloride or

nitrate), then a white ppt (BaSO4) will form.

 To detect NO3- (nitrate), we have to place aluminium foil & NaOH in the
test tube, then apply heat with a Bunsen burner. Then ammonia as a gas is
released.

Detection of gases:
Hydrogen (H2): by using a lit matchstick, it starts popping (burning of hydrogen).
(It’s a colorless & odorless gas).
Oxygen (O2): a glowing matchstick will relight.
Carbon dioxide (CO2): it’s a colorless & odorless gas. There are 2 methods to
detect CO2:
- We add CO2 to limewater, the transparent solution will turn milky (opaque).
CO2(g) + Ca(OH)2(aq)  CaCO3(s)
- Turns off lit matchsticks (not a reliable method)

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Chlorine (Cl2): it’s a yellowish-green gas, very dangerous to smell. To detect it we

will use any type of damp litmus paper, it has bleaching properties so it will
decolorize the paper (it will turn white).
Sulfur dioxide (SO2): its an acidic gas, it also has a bad/pungent smell & its
colorless. Detection was discussed in anions.
Ammonia (NH3): it is a pungent gas (has a very bad smell). It turns damp red
litmus paper blue (only alkaline gas in O-level).
Note: when adding an acid to an unknown solution, if fizzing occurs, two gases are
possibly present: CO2 & SO2.

Quantitative: total amount of gas is needed.

Methods to collect gases:

Qualitative: just a sample of the gas is enough

~ Drying Agents: some chemicals which are able to absorb gases towards
themselves like water.
Examples: Concentrated H2SO4 (not usually used); Anhydrous copper sulfate;
Anhydrous calcium chloride; calcium oxide
Any anhydrous salt can be used as a drying agent
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For testing pH  there are some indicators & digital pH meters to identify the pH
(litmus paper is general, only indicates acidic, basic, neutral properties).

Test for presence of water:

There are 2 reactions to detect it:

~ Plotting graphs
 The dependent variable is the result of independent
variables.
 Dependent variable is on the y-axis & independent
is on the x-axis.
Example: changing concentration has an effect on rate of
reaction, in this case concentration is independent & rate is
dependent.
We can use a line of best fit/ a cure on graphs

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~ Errors

Random- close results to

accurate value, source of
error is personal
2 main errors
Systematic - results are
far from accurate, its
source is systematic

Removing errors: Random  repeat at least 3 times & find average

Systematic  adjust instruments
Example: Random error  reading different temps/burette values
Systematic error  wrong adjustment of different instruments
Test for saturation of organic compounds:
If we add bromine water, saturated hydrocarbon isn’t able to decolorize it, whereas
unsaturated hydrocarbons since they have a double bond, they can make the
bromine water colorless.

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ATP: there are 4 questions in this paper.

Q1) Less than 8 marks, mostly naming equipment & very easy chemical processes
like evaporation etc.
Q2) Main question: around 15-17 marks, base of the question is from chapter rate.
Q3) Related to qualitative chemistry, detecting cations or anions. It has two parts,
both related to the identification of ions. One part related to a known sample,
another for an unknow sample. Around 10-15 marks.
Q4) Around 6 marks, might be from any chapter ~ a creative question
Example for question 4) Find purity percentage of limestone in a sample which has
an overall mass of 35g. You are provided with a chem lab.

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Answer: CaCO3 is a base so we react it with a known acid, then the mole of CaCO3
can be calculated based on mole of acid (HCl). Finally, we convert it to mass &
purity percentage.
CaCO3 + HCl  CaCl2 + H2O + CO2
Chemistry apparatus:

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Chemical safety symbols:

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