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7/28/2019 Prelim P5 2012 Ans
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2. You are given a solid sample, Q, containing a mixture of two
salts. Carry out the
following tests on sample Q. Record your observations in the
table below. You
should test for any gas evolved. Do not breathe in any gas
produced.
(Salts: Copper(II) carbonate and Copper (II) nitrate)
Test
No.
Test Observations Remarks
1. Add a spatula of sample
Q into a clean and dry
test tube. Heat the
sample until there is no
further change.
Solid mixture turns
black. /Black solidformed.
Glowing splint
rekindled/ relighted.
White precipitate
formed in limewater. Brown gas is
produced.Do not accept yellow gas.
[4]
Students tend towrite yellow gas.Students onlytend to test
forCO2 and H2.
2. Add 1 - 2 spatula of
sample Q into a test
tube. Add distilled water
to the test tube till aboutthree-quarter full. Shake
well. Let the mixture
settle for 1 - 2 min.
Keep the mixture for
Test 3, 4 and 5.
Blue solution formed
with insoluble greensolid settle at the
bottom of the testtube.
[1]
Students are
unable toidentify the
colour of theinsoluble solidas they did notfully allow
themixture tosettle
3 (a) Transfer 2cm3 of thesolution from Test 2to a clean and
drytest tube.
(b) Add an equalamount of aqueoussodium hydroxide to
Moist/ Damp red
litmus paper turnsblue.
Black solid formed
upon heating./ blue pptturns black.
Do not accept bluesolution turns blackppt/black.
Students tend
to writesolution turnsblack.
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7/28/2019 Prelim P5 2012 Ans
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the test tube,followed by 2 - 3pieces of aluminiumfoil. Warm the
testtube gently and
carefully.
[2]
4. (a) Transfer 2cm3 of thesolution from Test 2to a clean and
drytest tube.
(b) Add aqueoussodium hydroxidedrop-wise till excessto the test
tube.
Blue ppt formed upon
adding sodiumhydroxide, which is
insoluble in excess..
[1]
5. (a) Transfer 2cm3 of the
solution from Test 2to a clean and drytest tube.
(b) Add about 1cm3 ofpotassium iodideinto the test tube,followed
by about
1cm3 of starchsolution.
Solution turns from
blue to brown uponadding potassiumiodide. acceptyellowish
Solution turns from
brown to blue-blackupon adding starchsolution./ blacksolution
formed/Solution turns black.
Do not accept purplesolution/ the word purple.
[2]
students tend
to writepurplish blackfor starch testand miss
outtheobservationafter addingpotassiumiodide.
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7/28/2019 Prelim P5 2012 Ans
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6. Add a spatula of sample
Q to a clean and dry test
tube. Add 3cm3 of dilute
hydrochloric acid into
the test tube.
Effervescence seen/
Bubbling of gasobserved.
White ppt formed in
limewater.
Solid mixture dissolves
in hydrochloric acid toform a blue solution.
[3]
students only
manage totest for CO2gas and didnot record the
observation ofthe soliddissolving.
Underlined keywords must be there to award the marks.
Conclusion:
Identify the ions present in the mixture. [2]
NO3-, CO3
2- , Cu2+ / nitrate, carbonate, copper(II)
Do not accept copper. If state more than the three ions, deduct
one mark.
3 correct - [2]
2 correct - [1]
1 correct - [0]
