How to add salt to an acid in a basic Acid+Insoluble Base reaction?
1. Spatula
Why is heat not required sometimes in a Acid+Insoluble Base reaction?
1. Reaction is fast enough at room temperature
Define ‘in excess’
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unreacted
still solid
insoluble
How to form crystals from an aquoues solution of a salt?
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fiilter out unreactant excess
heat or evaporate till saturated
to crystallisation point or until saturation point to conduct the glass rod test
Errors in titration process
1. using a measuring cylinder to measure solution
2. only carrying out the experiments once
3. going past the end-point
How to avoid errors
1. repeat the experiment
2. improvement linked to going past the end-point – be vigilant and register changes in
solution
3. change in apparatus or method
1. e.g. use a pipette / burette
2. use insulation / lid
3. as more accurate / precise, than a measuring cylinder.
4. Reduce heat losses – polyseterene cup
Describe a flame test
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blue /roaring/ hot flame
use of a splint /wire to introduce the solid into the flame
use of (concentrated) hydrochloric acid to wash the wire initially
Why is it necesary to gently heat the solid in tube at first?
1. solid spits out of the tube / the tube might crack
Define Solubility
1. This is the maximum amount of solute a solvent can hold/dissolve at a given temperature.
Obtaining pure water from a mixture:
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Heat/boil mixture
condnse the vapor
Obtaining sand from a mixture:
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filter/decant after dissolving soluble substance into water
Clean with water
dry
Color of salts in solid form:
What is the purpose of the water above?
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Condense the vapours
from gaseous to liquid state
Why is thermometer bulb placed as shown and not in the mixture of alcohols?
1. to measure the temperature of the vapour/ temperature of liquid would not be constant
Give an advantage and disadvantage of using a measuring cylinders?
Adv- Quick and easy to use
Disadv- not accurate
Ways to improve a reaction
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use of burette
pipette
gas syringe
weighed amount of limting reagent
repeat experiment (and average)
clean the reactant/remove oxide layer
When a solid substance has no obvious cation we have learned it is:
-probably a transition metal compound
– is an catylat for the other reactions that occured
Describe how you would
● obtain a sample of tin from a large lump of cassiterite in the laboratory,
● determine the percentage by mass of tin present in cassiterite.
Tin is similar in reactivity to iron. (Cassiterite is a naturally occurring form of tin oxide.)
Your answer should include any apparatus and chemicals used and the conditions required:
A: • crush lumps with pestle and mortar
• weigh cassiterite
• heat /reduce
• with carbon /CO/ more reactive metal, e.g. Zn
• weigh tin
• (mass of tin/ initial mass) × 100 (%)
How would results be improved by taking repeated measurements?
1. can take average or mean / can spot anomalies /more reliable
Name a suitable indicator that could be used in titration
1. methyl orange / thymolphthalein / litmus
Potassium chloride is a salt that dissolves in water. The solubility of a salt is the mass in grams of the salt that dissolves in 100 cm3 of water
at a particular temperature.
Plan an investigation to determine the solubility of potassium chloride in water at 40 °C. You are provided with potassium chloride and
common laboratory apparatus.
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Method 1: evaporation
• measured volume of water using measuring cylinder / pipette / burette
• heat to 40 °C / heat to >40 °C
• add KCl until no more dissolves / add excess KCl
• stir
• filter mixture (if heated to >40 °C then need to cool and filter)
• evaporate filtrate to dryness
• weigh solid
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Method 2 mass not used
• measured volume of water using measuring cylinder / pipette / burette
• heat to 40 °C
• add KCl until no more dissolves
• stir
• weigh KCl not added
• weigh KCl before adding any to water – only awarded if weighed mass not used after
• difference in mass of KCl is mass dissolved
 Method 3 mass undissolved
• measured volume of water
• using measuring cylinder / pipette / burette
• heat to 40 °C
• stir
• filter
• weigh residue (do not award if residue washed)
• add weighed (excess) KCl to water – only awarded if mass of residue measured • mass KCl
dissolved = initial mass – final mass
Describe a test for carbon dioxide.
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limewater / calcium hydroxide solution
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Turns milky / cloudy / white ppt.
Suggest how the reliability of the results could be checked.
1. Repeating experiment and comparing/taking average
What is this process?
• evaporate;
• until crystallisation point/ crystals (start to) form/ saturated;
• leave to cool;
Suggest one advantage of putting a layer of chromium on a spoon.
1. prevent rusting/ corrosion/attractive appearance/ shiny;
Why must the electrolysing object be very clean and free of grease?
1. coating will not stick / be even / dirt or grease will be trapped;
Why was the burette washed with- (i) Distilled water, (ii) Acid to be added
(i) to remove intial liquid/residue/ impurities / to clean it;
(ii) to remove water/ so acid is not diluted;
If the composition of a salt is not clear just mention general observations like:
hydrated/water;
Acidic
Basic
Anhydrous Copper Sulphate + Water
Exothermic – temperature increase
Color change – white to blue
Cobalt Chloride + Water
Endothermic – heat is applied for color change
Color change – from pink to blue
Dilute sulfuric acid reacts rapidly with magnesium ribbon. The
magnesium ribbon gets smaller and eventually disappears.
Plan an investigation to show how the rate of this reaction changes using
different concentrations of sulfuric acid. You are provided with
common laboratory apparatus, sulfuric acid, water and magnesium
ribbon.
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uses different (at least two) concentrations of sulfuric acid;
made by diluting with water;
same total volume of (diluted) sulfuric acid;
same mass / amount/ size/ length/ surface area of magnesium (ribbon);
measure time (or run at the same time);
for magnesium to dissolve or react or disappear/ cm3 gas to collect/ volume collected (set
time)/ bubbles to stop/ mass to decrease by g/mass to stop decreasing;
compare times of reaction/results;
“Using a measuring cylinder, 30 cm3 of aqueous sulfuric was poured into a beaker. The stop
clock was started and a 4 cm length of magnesium was added to the sulfuric acid in the beaker.
The mixture was stirred constantly. The time taken for all of the magnesium to react and
disappear was measured.”
Indicator Types
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Universal indicator.
Litmus.
Phenolphthalein.
Methyl orange.
Anamolous in titration reactions caused by:
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measuring or recording error
manual error with burette
overshot end-point
What could have been used to apply a mixture onto the paper in chromotagraphy?
1. (teat) pipette/ capillary tube;
Possible solvent that could be used for paper chromotagraphy
1. water/ organic solvent;
Why does sometimes the mixture on the baseline in paper chromotagraphy not move?
Compound is insoluble in given solvent
Why does increased temperature increase rate of reaction?
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particles have more energy / move faster;
more (chance of/ successful) collisions;
Explain why cotton wool was used in the neck of the conical flask
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to prevent escape of/ splash of acid;
to allow carbon dioxide/ gas to escape;
You are provided with samples of three metals, tin, zinc and silver. Plan an investigation
to show the order of reactivity of these three metals. You are provided with common
laboratory apparatus and dilute acids.
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o
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Method 1:
Monitoring the reaction of the metal with acid
named acid;
same or stated volume of (same concentration of) acid;
fair test idea, i.e. same surface area/ size/ mass / amount
metal;
measure volume of gas / count bubbles / temperature
change/ observe complete reaction;
suitable reference to time;
conclusion/ comparison, e.g. most effervescence = most
reactive;
Method 2:
o Displacement reaction from:
o react each metal;
o with named acid;
o
o
o
to prepare salt solution of each;
react each metal with each solution of salt; observe if
displacement occurs;
conclusion/ comparison;
Suggest what could be used to hang the piece of limestone from the stand over the heat.
Explain your answer.
1. Wire – with high melting point
In what position should the air hole of the Bunsen burner be?
1. Open
Inert Electrodes
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Platinum
Graphite(carbon)
Gold
Rhodium
Reactive (or involved) Electrodes
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Copper
Zinc
Lead
Silver
Explain why electrolysis of concentrated hydrochloric acid experiment is carried out in
a fume cupboard.
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chlorine produced;
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poisonous /toxic;
What type of chemical reaction occurred when magnesium reacted with sulfuric acid?
1. exothermic / redox / displacement
An oxidising agent was added iron(II) chloride solution. Aqueous sodium hydroxide
was then added to the mixture.
1. Brown Precipitate
Toothbright toothpaste contains three compounds, sodium fluoride, calcium carbonate and water. Calcium
carbonate is insoluble in water and sodium fl uoride is soluble in water.
Plan an investigation to fi nd out the percentage of calcium carbonate present in this toothpaste. You are
provided with common laboratory apparatus.
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weighed amount/ xg of toothpaste
add water;
stir/ heat;
filter (to obtain calcium carbonate)
Wash
dry
weigh residue
calculate percentage calcium carbonate; Mass of Calcium
Carbonate/Mass of Toothpaste X 100
A solution of dilute sulfuric acid was electrolysed for 1 hour. Suggest why the pH of the
solution decreased during the electrolysis
solution became more acidic / more concentrated
 water was broken down/ electrolysed
1. measure initial temperature of (solid) ammonium chloride /
barium hydroxide
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add barium hydroxide / ammonium chloride AND mix / stir
use a thermometer
measure the temperature of the mixture / final temperature
temperature decreases /test-tube feels cold
Test for Ammonia
Ammonium ions can be identified in a solution by adding dilute
sodium hydroxide solution and gently heating. If ammonium ions are
present, they will be converted to ammonia gas. The gas will turn red
litmus paper blue.
How would you know when to stop heating a solution in an evaporating dish?
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solid/ crystals appearing on edge
glass rod test;
What if there is no reaction when testing something?
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no reaction/ change/ precipitate
The label on a bottle of orange drink stated ‘contains no artificial colours’. A scientist thought that the orange
colour in the drink was a mixture of two artificial colours: • Sunset Yellow E110 • Allura Red E129
Plan an investigation to show that the orange colour in the drink did not contain these two artificial colours. You
are provided with samples of E110, E129 and the orange colouring from the drink. You are also provided with
common laboratory apparatus. You may draw a diagram to help answer the question.
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chromatography;
(pencil) baseline/ origin;
apply orange colour to paper;
and samples of both E110 and E129;
solvent/ named solvent;
check heights of spots of E colours against orange drink;
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conclusion/ allow comparison to known Rf values;
Suggest why small glass beads are used in the fractionating column instead of large glass
beads.
1. Larger surface area of overreactive higher boiling point liquids to
condense and fall back into the flask to liquid.
Give a test to show that a liquid is acidic.
1. named indicator/ pH meter/ pH paper
2. result: correct colour change/ pH < 7 (1)
The gas given off was tested with damp litmus paper (2 marks)
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indicator paper turns blue
pungent/ sharp smell
Ethanedioic acid dihydrate, H2C2O4.2H2O, is a white crystalline solid. This acid is
water-soluble and is found in rhubarb leaves. Plan an investigation to obtain crystals of
ethanedioic acid dihydrate from some rhubarb leaves. You are provided with common
laboratory apparatus, water and sand.
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extraction
cut leaves up/ small pieces / grind/ crush
use of pestle/ mortar
add water
sand
boil/ heat/ stir/ mix / shake
separation decant/ filter
obtaining crystals evaporate/ heat solution
to crystallising point/until crystals start to form
leave to cool