paper 1 required practicals

Question 1

how would you carry out a neutralisation reaction?

Answer 1

1. take a dilute acid (e.g. hydrochloric acid) and put it in a beaker.
2. heat it over a bunsen burner.
3. keep adding an insoluble base (e.g. copper oxide), a little bit at a time.
4. at first, the base will keep disappearing, as it reacts to forma salt (e.g. copper chloride).
5. 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.
6. 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).
7. gently heat up our now filtered solution, and evaporate off some water.
8. stop heating it once you see crystals forming, and leave it to cool, causing more crystals to form.

Question 2

what are the hazards and risks of the making salts required practical?

Answer 2

• 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.

Question 3

describe the procedure for carrying out a titration:

Answer 3

1. 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.
2. 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).
3. place the conical flask on a white tile, in order to see the colour change more clearly.
4. fill a burette with sulfuric acid.
5. 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.
6. read the volume of acid added from the burette.
7. repeat the titration several times, until you record two readings that are within 0.1 cm³ of each other.
8. take a mean of these for our final volume.

Question 4

what is the correct way to read the burette during a titration?

Answer 4

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.

Question 5

what is the point of a titration?

Answer 5

• 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.

Question 6

what are the hazards and risks of the titration required practical?

Answer 6

• 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.

Question 7

describe the electrolysis required practical:

Answer 7

1. pour approximately 50cm³ of copper (ii) chloride solution into a beaker.
2. place a plastic petri dish over the beaker. the petri dish should have two holes.
3. 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.
4. attach crocodile leads to the rods, and connect the rods to the terminals (positive and negative) of a low voltage power supply.
5. select four volts on the power supply, and turn it on.
6. 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.

Question 8

what would occur if you held a piece of damp blue litmus paper near the anode, during the electrolysis of copper (ii) chloride solution?

Answer 8

the blue litmus paper would become bleached, proving that the gas is chlorine.

Question 9

what are the hazards and risks of the electrolysis required practical?

Answer 9

• 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.

Question 10

describe the temperature changes required practical:

Answer 10

1. use a measuring cylinder to to measure 30cm³ of dilute hydrochloric acid.
2. transfer the acid into a polystyrene cup.
3. stand the polystyrene cup inside a beaker, which stops the cup from falling over.
4. use a thermometer to measure the temperature of the acid, and record this in a table.
5. use a measuring cylinder to measure 5cm³ of sodium hydroxide solution, and transfer this to the polystyrene cup.
6. 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).
7. use the thermometer to gently stir the solution.
8. look carefully at the temperature rise on the thermometer - when the reading on the thermometer stops changing, we record the highest temperature reached.
9. rinse out and dry the polystyrene cup.
10. 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.

Question 11

why do we use a polystyrene cup with a lid in the temperature changes practical?

Answer 11

• 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.

Question 12

what are the hazards and risks of the temperature changes practical?

Answer 12

• 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).