C6 Electrolysis Papers Part 2 Flashcards
What is the Reaction to produce iron from iron oxide
Carbothermal reduction
Why electrically conductive aluminium is used to make cans
Low density
Less resistance to corrosion
Why the positive electrode must be continually replaced
Electrode reacts with oxygen
Calculate the mass of oxygen produced when 2000 kg of aluminium oxide is completely electrolysed
2 Mr of Al2O3 = 204
204 (kg of Al2O3) gives 96 kg of O2
(2000 ➗ 204) x 96 = 941kg
Why sodium chloride solution can’t be used as the electrolyte to produce sodium metal
Hydrogen would be produced instead of sodium as sodium is more reactive than hydrogen
Calculate the volume of 150 kg of chlorine gas at room temperature and pressure
The volume of one mole of any gas at room temperature and pressure is 24.0 dm3
Relative formula mass (M.): Cl = 71
150,000
_________ x 24 = 50,704dm3 so 50,700dm3
71
Which line in figure 3 shows volume of gas collected is directly proportional to time
Hydrogen line only
Why can graphite conduct electricity
Has delocalised electrons
What is produced at cathode/anode molten zinc chloride
Cathode - zinc as zinc is more reactive than hydrogen
Anode - chlorine as it is halide so chlorine is produced not oxygen
What is produced at cathode/anode potassium bromide
Cathode - hydrogen as potassium is more reactive than hydrogen
Anode - bromine as it is halide
Why wouldn’t electrolysis work if was solid sodium chloride
Solid zinc chloride does not conduct electricity as ions cannot move in solid
How graphite conducts electricity answer in terms of structure and bonding in graphite
Each carbon atoms forms 3 covalent bonds
1 electron per carbon atom is delocalised
So these electrons carry charge through the graphite
The student made an error in selecting the apparatus for this investigation
How should the apparatus be changed
Give one reason for your answer
Use measuring cylinders instead of test tubes as test tubes can’t measure volume
Describe trends in results above of hydrogen and chlorine increasing graph
Volume of hydrogen collected is directly proportional to time
Rate of collection of hydrogen is 0.45 cm/min
Up to 8 minutes chlorine is collected at increasing rate
No gas escapes from the apparatus
Suggest one reason for the difference in volume of each gas collected
Chlorine reacts with water
Calculate the amount in moles of chlorine collected after 20 minutes
Use Figure 3
The volume of one mole of any gas at room temperature and pressure is 24.0 dm
6.6 ➗ 1000 = 0.0066
0.0066 ➗ 24 = 2.75 x 10^ -4
Independant variable
The variable that changes during an experiment
Dependant variable
Variable being tested or measured
Control variable
Variable that is kept the same during scientific experiment
Independant variable for electrolysing salt solutions with inert electrodes
Salt solutions
Observation for electrolysing salt solutions with inert electrodes
Solid/metal deposit on negative electrode
Why the product at negative electrode is not always a metal
Hydrogen produced when metal is more reactive than hydrogen
Why does iodine have higher boiling point than chlorine
Forces between iodine atoms are stronger
Predict the boiling point of bromine
Anything in range +30 to +120
Trend in boiling point group 1 and halogens
Group 1 - decreases as goes down group
Halogens - increases as goes down group
Why trend in reactivity decreases halogens as go down group
Atomic mass of the halogens increases
Increase in electron shells
Atoms get larger as go down group
Attraction to outer electron from nucleus decreases
Why trend in reactivity increases group 1 as go down group
Atoms become larger
Outer electron becomes further from the nucleus
Attraction between nucleus and outer electron gets weaker so electron is more easily lost
Why trend in boiling point increase down group 7
Atoms increase in size as they gain extra electron shells
Intermolecular forces become stronger
More energy is required to break these forces
Why trend in boiling point decrease down group 1
Additional shell being added to the previous element causes atomic radius to increase
The increasing atomic radius means weaker forces between atoms so lower melting and boiling point
What colour is final solution of reaction chlorine added to potassium iodide solution
Brown
REACTIVITY SERIES
Potassium
Sodium
Lithium
Calcium
Magnesium
Aluminium
CARBON
Zinc
Iron
Tin
Lead
HYDROGEN
Copper
Silver
Gold
Platinum
Ionic equation for reaction of chlorine with potassium iodide
2I- + Cl2 ———> I2 + 2Cl-
Why is potassium not included in
Ionic equation for reaction of chlorine with potassium iodide
It is a spectator ion and dissociates in aqueous solution
Potassium ions do not undergo any chemical change during reaction and don’t affect redox process therefore excluded from net ionic equation
Spectator ion
Ions that are present in the reaction mixture but don’t participate in the chemical reaction
They remain unchanged throughout the process
Why potassium iodide conducts electricity
Contains ions which can move
Transition metals ions
+2
Which electrode does oxidation happen in
Positive anode
Which electrode does reduction happen in
Negative cathode
Why zinc ions move towards negative electrode
Zinc ions are positive and opposite charges attract
What type of reaction occurs when the zinc ions gain electrons
Reduction
Why alloy is harder than pure zinc
Different sized atoms
No layers or rows so can’t slide
Alloys can be bent. Some alloys return to their original shape when heated
What name is used for these alloys
Shape memory
What happens when a magnesium atom reacts with chlorine atoms to produce magnesium chloride.
Magnesium loses 2 electrons and chlorine gains 1 electron
Forms ionic bonds
Electrostatic attraction between ions
8 electrons in outer shell
Why magnsium chloride must be molten or dissolved in water to be electrolysed
Ions can move to electrodes and carry charge
How magnsium is produced at negative electrode
Magnesium ions attracted to electrode so magnsium ion gains 2 electrons
Why magnesium is not produced at negative electrode
Magnesium is more reactive than hydrogen
Complete and balance the half equation for the reaction at the positive electrode.
_______ Cl- ———-> Cl2 + _________
2Cl- ——-> Cl2 + 2e-
Why metals can be bent and shaped
Layers of particles can slide
