required practicals

Question 1

electrolysis required practical
aim

Answer 1

investigate what happens when aqueous solutions are electrolysed using inert electrodes

Question 2

electrolysis required practical
equipment

Answer 2

equipment

• copper chloride solution
• copper sulfate solution
• sodium chloride solution
• sodium sulfate solution
• 100cm3 beaker
• petri dish lid
• two carbon rod electrodes
• two crocodile/4 mm plug leads
• low voltage power supply
• blue litmus paper
• tweezers

Question 3

electrolysis required practical
process

Answer 3

method

• pour copper chloride solution into the beaker to about 50cm3
• add the lid and insert carbon rods through the holes the rods must not touch each other
  attach crocodile leads to the rods and connect the rods to the dc (red and black) terminals of a low voltage power supply
• select 4v on the power supply and switch on
• observe both electrodes; is there bubbling at neither, on or both electrodes
• with tweezers hold a piece of blue litmus paper in the solution next to the positive electrode (one connected to the red terminal)
  *if the gas produced at the +ve electrode doesn’t bleach the litmus paper then it’s oxygen
  *gas produced at the -ve electrode is hydrogen
• after no more than 5 minutes, switch off the power supply
  –> observe the -ve terminal, is there metal coating on it - this is pure copper
• clean the equipment carefully and repeat the steps for copper sulfate, sodium chloride, sodium sulfate

Question 4

electrolysis required practical
findings

Answer 4

findings

copper chloride
- +ve electrode (anode) –> bubbled, chlorine
- -ve electrode (cathode) –> copper formed

copper sulfate
- +ve electrode (anode) –> bubbled, oxygen
- -ve electrode (cathode) –> copper formed

sodium chloride
- +ve electrode (anode) –> bubbled less, chlorine
- -ve electrode (cathode) –> bubbled lots, hydrogen

sodium sulfate
- +ve electrode (anode) –> bubbled, oxygen
- -ve electrode (cathode) –> bubbled more, hydrogen

Question 5

electrolysis required practical
safety

Answer 5

safety

wear goggles throughout

Question 6

neutralisation required practical
aim

Answer 6

investigate to find the concentration of a dilute sulfuric acid solution using a sodium hydroxide solution of known concentration

Question 7

neutralisation required practical
equipment

Answer 7

equipment

• 25cm3 volumetric pipette and pipette filler
• burette
• small funnel
• clamp stand
• 250cm3 conical flask
• white tile
• dilute sulfuric acid of unknown concentration
• 0.1 mol/dm3 sodium hydroxide solution
• methyl orange indicator

Question 8

neutralisation required practical
method

Answer 8

method

• use the pipette and pipette filler to put exactly 25cm3 sodium hydroxide solution into the conical flask and stand it on a white tile
• clamp the burette vertically in the clamp stand halfway up its length
• close the burette tap and use a funnel to fill the burette with dilute sulfuric acid to the 0cm3 line
• put 5-10 drops of phenolphthalein into the conical flask, swirl to mix and place under burette ontop of tile
• open the tap so the sulfuric acid flows at a drop by drop rate into the flask
• constantly swirl the flask while the acid is being added and look out for the change from pink - colourless
• close the tap as soon as the colour changes and read the burette to record the amount of acid added
• repeat steps 1-7 twice more and record results in a table
• calculate the mean volume of acid needed to neutralise 25cm3 of the sodium hydroxide solution
• use this to calculate the concentration of the acid in mol/dm3 and g/dm3

Question 9

neutralisation required practical
findings

Answer 9

trial 1
12.80

trial 2
12.50

trial 3
12.50

mean
12.50

Question 10

neutralisation required practical
calculation

Answer 10

n = c x v/100

n = number of moles
c = concentration in mol/dm3
v = volume in cm3

step 1 - work out the moles of sodium hydroxide in 25cm3 with the equation:
moles = concentration x volume
= 0.1 mol/dm3 x (25 ÷ 1000)
= 0.0025

step 2 - look at the equation

2NaOH + H₂SO₄ —> Na₂SO₄ + 2H₂O
two moles of sodium hydroxide neutralise one mole of sulfuric acid

so - moles of sulfuric acid used:
0.0025/2 = 0.00125

step 3 - work out the concentration of sulfuric acid (mol/dm3) with the equation:

concentration of sulfuric acid (mol/dm3)
= moles ÷ mean volume of acid
= (step 2 answer) ÷ (mean volume ÷ 1000)
= 0.00125 ÷ 12.5 x 1000
= 0.1

step 4 - work out the RFM of H₂SO₄

RFM of H₂SO₄ = 98.09

step 5 - work out the concentration of sulfuric acid (g/dm3) with this equation:

(answer from step 3) x (RFM of H₂SO₄)
= 0.1 x 98.09
= 9.809

Question 11

temperature changes
aim

Answer 11

investigate the variables that affect temperature change in reacting solutions such as e.g. acid plus metals, acid plus carbonates, neutralisations, displacement of materials

Question 12

temperature changes
equipment

Answer 12

equipment

• hydrochloric acid of
  0.1 mol/dm-3
  0.5 mol/dm-3
  1 mol/dm-3
  2 mol/dm-3
• magnesium ribbon in 2cm pieces
• expanded polystyrene cup + lid
• 25 cm3 measuring cylinder
• thermometer

Question 13

temperature changes
method

Answer 13

method

• measure 15cm3 of acid into a polystyrene cup
• use a thermometer to record the initial temperature of the acid
• add 2cm length of the magnesium ribbon and put the lid on
• record the MAX temperature reached
• repeat steps for each concentration of acid

Question 14

temperature changes
findings

Question 15

temperature changes