paper 1 required practicals Flashcards
1
Q
how would you carry out a neutralisation reaction?
A
- take a dilute acid (e.g. hydrochloric acid) and put it in a beaker.
- heat it over a bunsen burner.
- keep adding an insoluble base (e.g. copper oxide), a little bit at a time.
- at first, the base will keep disappearing, as it reacts to forma salt (e.g. copper chloride).
- as you add more, the base will no longer disappear - at this point, the base must be in excess. we will have neutralised all of the acid.
- filter out the excess copper oxide, using a filter paper and funnel. we should now have the dissolved form of our soluble salt (in this case, copper chloride).
- gently heat up our now filtered solution, and evaporate off some water.
- stop heating it once you see crystals forming, and leave it to cool, causing more crystals to form.
2
Q
what are the hazards and risks of the making salts required practical?
A
- concentrated acid (i.e. hydrochloric acid) is corrosive, and if it makes contact with eyes, can result in burns and even blindness. wear goggles to prevent this.
- bunsen burner flames can cause burns on the skin if touched. to prevent this, be careful when handling it, never turn your back on it, and tie your hair up.
3
Q
describe the procedure for carrying out a titration:
A
- use a pipette to transfer 25cm³ of sodium hydroxide solution into a conical flask. (the conical flask reduces the risk of splashing).
> ensure you allow the liquid to drain
out of the pipette, instead of blowing it
out, as that could give you an incorrect
volume. - add 5 drops of an indicator (e.g. methyl orange) to the alkali in the conical flask. (other indicators could also be used, e.g. phenolphthalein).
- place the conical flask on a white tile, in order to see the colour change more clearly.
- fill a burette with sulfuric acid.
- add this acid to the alkali until the solution is neutral. we need to add just enough acid for this to happen.
> it’s important to swirl the solution to
make sure the acid and alkali mix.
> once we start to see a colour change,
add the acid drop by drop until the
solution is neutral.
> with methyl orange, the colour
change will be from yellow to red. - read the volume of acid added from the burette.
- repeat the titration several times, until you record two readings that are within 0.1 cm³ of each other.
- take a mean of these for our final volume.
4
Q
what is the correct way to read the burette during a titration?
A
ensure your eye is level with the surface of the liquid. the surface of the liquid naturally curves - scientists call this the meniscus. always read the value from the bottom of the meniscus, or a parallax error could occur.
5
Q
what is the point of a titration?
A
- before the titration, we already knew the volume and concentration of the alkali.
- now, we know the volume of acid needed to neutralise the alkali.
- from this, we can now calculate the concentration of the acid.
6
Q
what are the hazards and risks of the titration required practical?
A
- sodium hydroxide solution can cause skin and eye irritation. wear gloves and eye protection to prevent this.
- while filling the burette, sulfuric acid could be spilt, which could cause eye irritation. fill the burette slowly instead, using a funnel.
7
Q
describe the electrolysis required practical:
A
- pour approximately 50cm³ of copper (ii) chloride solution into a beaker.
- place a plastic petri dish over the beaker. the petri dish should have two holes.
- insert a carbon graphite rod into each hole, and these will act as electrodes.
> carbon graphite is unreactive, so
these electrodes are inert and won’t
interfere with the reaction.
> the two electrodes must NOT touch
each other, as that would produce a
short circuit, which can be hazardous. - attach crocodile leads to the rods, and connect the rods to the terminals (positive and negative) of a low voltage power supply.
- select four volts on the power supply, and turn it on.
- monitor the two electrodes.
> the cathode should be being coated
with copper, as if the metal is less
reactive than hydrogen, the metal is
produced at the cathode.
> the anode should be surrounded
by gas bubbles, and you might notice
the smell of chlorine in the air. this is
because chloride is a halide ion, and
is produced at the anode instead of
oxygen from the hydroxide ion.
8
Q
what would occur if you held a piece of damp blue litmus paper near the anode, during the electrolysis of copper (ii) chloride solution?
A
the blue litmus paper would become bleached, proving that the gas is chlorine.
9
Q
what are the hazards and risks of the electrolysis required practical?
A
- chlorine gas is toxic, and if inhaled too much, could damage health. ensure the room is well ventilated, switch off apparatus when not in use.
10
Q
describe the temperature changes required practical:
A
- use a measuring cylinder to to measure 30cm³ of dilute hydrochloric acid.
- transfer the acid into a polystyrene cup.
- stand the polystyrene cup inside a beaker, which stops the cup from falling over.
- use a thermometer to measure the temperature of the acid, and record this in a table.
- use a measuring cylinder to measure 5cm³ of sodium hydroxide solution, and transfer this to the polystyrene cup.
- fit a plastic lid to the cup, and place a thermometer through a hole in the lid. (the bulb of the thermometer must be in the solution).
- use the thermometer to gently stir the solution.
- look carefully at the temperature rise on the thermometer - when the reading on the thermometer stops changing, we record the highest temperature reached.
- rinse out and dry the polystyrene cup.
- repeat the whole experiment using 10cm³ of sodium hydroxide solution, and carry out the experiment several more times. (each time, increase the volume of sodium hydroxide solution by 5cm³, until we reach a maximum of 40cm³ of sodium hydroxide solution.)
- repeat the entire temperature one more time, to get a mean value for the maximum temperature reached for each volume of sodium hydroxide solution.
11
Q
why do we use a polystyrene cup with a lid in the temperature changes practical?
A
- we’re measuring the temperature in this experiment, so we want to reduce any heat losses.
- polystyrene is a good thermal insulator, which reduces heat loss from all sides.
12
Q
what are the hazards and risks of the temperature changes practical?
A
- hydrochloric acid and sodium hydroxide solution can both cause serious skin and eye irritation if contact is made. avoid contact with skin, and where protective clothing (e.g. gloves, goggles).
