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:star: Chemical Tests :star:, :green_cross:Cations & Anions :green…
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Chemical Tests
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:green_cross:
Cations & Anions
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Cations Tests
Test for: Iron (II), Iron (III) and Copper 2+
Add a few drops of Sodium Hydroxide (NaOH). It will form a specific coloured precipitate.
Iron (II) makes
Green
: FeCl3 + 3 NaOH -> Fe(OH)3 + 3NaCl
Iron (III) makes
Brown
: FeCl2 + 2NaOH -> Fe(OH)2 + 2NaCl
Copper 2+ makes
Blue
: CuSO4 + 2NaOH -> CuOH2 + Na2SO4
Additional Test for
calcium chloride
:
white cloudy precipitate
Test for: Ammonium (NH4+)
Add
Sodium Hydroxide (NaOH)
to the substance.
No precipitate
is formed gas (ammonia) is. Perform the
ammonia test
(damp red litmus paper). If positive, the substance contains Ammonium cations
Anions Test
Sulphate anions (SO4
2–)
Use the hydrochloric acid to remove carbonates which could result in
false positives
.
Add
hydrochloric acid
first to acidify the substance. Then add
barium chloride
solution.
Sulfate Present - Precipitate colours: White
Ba2+(aq) + SO42-(aq) → BaSO4(s)
Carbonate anions (CO3 2-)
Add (
dilute
) hydrochloric acid then bubble the gas through lime water. If it becomes cloudy, it contains CO2 which means the substance contains carbonate ions.
Do the carbon dioxide test:
calcium carbonate + hydrochloric acid → calcium chloride + carbon dioxide + water
Halide anions (Cl- Br- and I- ions)
Add
nitric acid
then
silver nitrate
solution to detect halide ions.
Precipitate Colours
Ag+(aq) + I-(aq) → AgI(s)
(silver iodide is pale yellow)
Ag+(aq) + Br-(aq) → AgBr(s) (
silver bromide is cream
)
Ag+(aq) + Cl-(aq) → AgCl(s)
(silver chloride is white
)
Use the nitric acid to remove the carbonate in the substance as it could result in
false positives
.
Anions are negatively charged. Cations are positively charged!
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Water Tests
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Physical Test: Boil or Freeze the water. Boiling point is
100 degrees and freezing point is 0 (Celsius)
:warning: Impure water has a higher boiling point and lower freezing point. :warning:
Equation for Water: 2 H2 + O2 -> 2 H2O
Chemical Test: Water reacting with anhydrous copper sulphate. Turns to blue hydrated copper sulphate.
CuSO4 (s) + 5 H2O (l) -> CuSO4.5H2O (s)
:warning:
The reaction is reversible
:warning:
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Gas Tests
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Gases
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Carbon Dioxide
(CO2)
Poisonous
but has many other uses: Used in
fire extinguishers
as it is not flammable and in
fizzy drinks.
To test for it:
use lime water. Carbon dioxide is bubbled in lime water.
Observations:
Bubbles in test tube. Test tube becomes milky and cloudy.
Hydrogen
(H2)
Highly explosive
but is a
good fuel source.
To test for it:
Light a Splint inside an empty test tube.
Observations:
and audible
Squeaky Pop
can be heard.
Oxygen
(O2)
Vital for life for respiration
. In very
high concentrations
it can be
poisonous
. It causes things to
ignite
(burn).
To test for it:
Placing a
glowing, almost burnt out
, splint into a test tube filled with manganese dioxide powder.
Observations:
When splint is inside the test tube the
splint reignites
due to the oxygen.
Chlorine
(Cl2)
Has multiple industrial uses such as
fertilizer
. Is
poisonous.
To test for it:
Place
Damp blue
litmus paper into chlorine. It will form hydrochloric acid.
Observations:
Upon touching the chlorine, the damp blue litmus paper turns to a
red/pink colour
to indicate it is acidic (HCl if formed). Then the paper is
bleached and become colourless
since chlorine is an effective bleaching agent.
Ammonia
(NH3)
Important for the
manufacturing of explosives
but is
smelly
and
poisonous
.
To test for it:
Use Damp red litmus.
Observations
: Litmus paper turns
blue
indicating ammonia is
alkali
.
:warning:
Litmus Paper is
damp
so the gas can be dissolved into the liquid. Used to identify its pH levels
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Flame Tests
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Steps to all of the Tests:
Step 1: Dip
nichrome wire
loop into
dilute HCl
and place blue
(non-luminous)
Bunsen flame to learn it.
:warning: Nichrome wire is used to not emit a very bright colour (easier to detect colours). Hydrochloric acid is used to make sure the items tested becomes soluble. Blue (non-luminous) is used to help identify colour of reactant. Anything brighter you cannot see the colour.
Step 2: Dip into HCl again and then add the compound you are testing.
Step 3: Place the substance in the Bunsen burner flame.
Step 4: Note down the colours observed.
Li+
is Red
Na+
is yellow
K+
is lilac
Ca2+
is red/orange
Cu2+
is blue-green
:warning:
Iron
was not tested because it does not give a distinct/unique colour specific enough to identify itself with.
The other metals tested resulted in unique colours.
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