Paper 6
https://www.IGCSEvideos.com
Dr. Nervana Ehab
General tips for paper 6
experiments
Make sure to tell the examiner:
1. The apparatus you will need.
o e.g. beaker, conical flask
2. What are you measuring?
o e.g. time, volume, temperature, weight
3. How are you measuring it?
o e.g. stop clock, gas syringe, thermometer, balance
4. Factors to keep constant, so experiment is fair (if you are
comparing 2 or more things)
o e.g. distance from heat source, temperature, mass
5. When are you going to stop the experiment? or Describe
procedure of experiment. e.g.:
o when mass becomes constant
o specific time is passed
o when you use up a certain amount of the chemical
o when no more gas is collected
6. Calculate results, e.g.
o mass 1 – mass 2
o final temp – initial temp
7. Conclusion
o what do results tell us?
o e.g. acid A is stronger than acid B
o metal A is more reactive than metal B
o Solution A produces more gas than solution B
o fuel A produces more energy than fuel B
Page 1 of 8
Paper 6
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Dr. Nervana Ehab
summary of colours
Metals & ionic compounds:
• All metals are silvery grey, except
o Gold → yellow
o Copper → red-brown
• Compounds of non-transition metals → white
• Compounds of transition metals → coloured
• All copper compounds are blue except:
o CuCO3 → green
o CuO → black
• Fe2+ salts → green
• Fe3+ salts → red-brown
• KMnO4 → Purple
• K2Cr2O7 → Orange
Covalent compounds:
•
•
•
•
Noble gases → colorless gases
Carbon (graphite, coal, coke) → black solid
Sulfur → yellow solid
Halogens:
o Fluorine → pale-yellow gas
o Chlorine → yellow-green gas
o Bromine → red-brown liquid
o Iodine:
▪ at room temperature → grey solid
▪ sublimes to give → purple gas
▪ dissolves in water → brown solution
Page 2 of 8
Paper 6
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Dr. Nervana Ehab
safety precautions
• Toxic gases (e.g. halogens)
o Use of fume cupboard
o Ventilated area
crucible
• Heat solids in crucible
• Stir with glass rod not spatula
o spatula may react with the solution
• Suck-back: occurs when you stop heating and the liquid
returns back (flows back)
o problem: can cause the cracking of the hot test tube
o prevent it by: removing delivery tube from liquid before
you stop heating
hot content
water flows back to test
tube when air shrinks
gas
air inside test tube is
expanded due to heat.
Upon cooling, air shrinks
back to normal volume
Page 3 of 8
Paper 6
https://www.IGCSEvideos.com
Dr. Nervana Ehab
accuracy of measurements
• Repeat the experiment and take the average to improve
accuracy → improves reliability
• To collect gas: gas syringe is more accurate than measuring
cylinder
• Pipette is the most accurate, however:
o slow → don’t know when to start the stop watch
o measures only fixed volumes
• Burette: accurate & can measure any volume, however:
o slow to run out the solution
• Measuring cylinder
o convenient and fast to use
o However: less accurate
Page 4 of 8
Paper 6
https://www.IGCSEvideos.com
Dr. Nervana Ehab
separating chemicals
• To keep a liquid separated from other chemicals in a testtube, hold the liquid using ceramic wool or cotton
• To keep oxygen from entering the
fermentation container (to prevent
oxidation of alcohol), use airlock.
o Air lock allows CO2 to escape, but
prevent air from entering
• To separate a liquid from other chemicals in a conical flask:
o Place the liquid in a funnel connected to
separating
the conical flask through a rubber stopper.
funnel
When you want to mix the chemicals (to
start the reaction), open the tap of the
funnel.
o Place the liquid in a test tube and hold the
test tube with thread. When you want to
mix the chemicals, let the thread fall so
liquid leaves the test tube.
Page 5 of 8
Paper 6
https://www.IGCSEvideos.com
Dr. Nervana Ehab
titration experiments
• The zero mark is at the top of the burette, the 50 cm 3 mark is
at the bottom near the tap
• Readings in burette may start from 0 or from any other
starting point
o final – initial reading = volume used
12.8 cm3
39.2 cm3
Therefore, volume used from burette =
final – initial
= 39.2 – 12.8
= 26.4 cm3
Page 6 of 8
Paper 6
https://www.IGCSEvideos.com
Dr. Nervana Ehab
Example #1: unknown solutions in conical flask
NaOH used for
neutralization
NaOH used for
neutralization
Acid A
Acid B
unknown
concentration
Solution B required more NaOH from the burette for
neutralization, therefore it is more concentrated
Page 7 of 8
Paper 6
https://www.IGCSEvideos.com
Dr. Nervana Ehab
Example #2: unknown solutions in burette
NaOH used for
neutralization
NaOH used for
neutralization
Only a small volume of NaOH
was enough for neutralization
because this NaOH is
concentrated, so few drops
contain many ions
Large volume of NaOH was
needed for neutralization
because this NaOH is dilute
Page 8 of 8