MOCKS Flashcards
why use an instrumental method to measure something?
accurate
sensitive
Explain the difference between the processes in electrolysis and in a
chemical cell.
electrolysis uses electricity to produce a chemical reaction
a cell uses a chemical reaction to produce electricity
Some of the copper produced did not stick to the negative electrode but fell to the bottom of the beaker.
Suggest how the students could find the total mass of copper produced.
Filter the mixture
wash and dry copper
weigh copper
add to increase in mass of electrode
Copper nitrate solution is blue.
Suggest why the blue colour of the copper nitrate solution fades during the electrolysis.
copper ions are discharged from the solution
Observation if metal produced at the negative electrode
solid produced
Observation if gas produced at the positive electrode
bubbles/effervescence
Why is graphite used for the electrodes?
graphite conducts electricity
graphite is inert
Bauxite contains between 15% and 25% aluminium.
How does this show that bauxite is a mixture and not a compound?
it contains a varying percentage of aluminium
Copper chromate contains yellow coloured CrO4^2–ions
Explain why the colour changed at the positive electrode.
chromate ions moves to positive electrode as opposite charges attract
Explain why a mixture of aluminium oxide and cryolite is used as the electrolyte instead of using only
aluminium oxide.
lowers the melting point
so less energy needed
Sodium metal and chlorine gas are produced by the electrolysis of molten sodium chloride.
Explain why sodium chloride solution cannot be used as the electrolyte to produce sodium metal.
hydrogen is produced
as sodium is more reactive than hydrogen
Why can solid zinc chloride not be used as an electrolyte?
solid (zinc chloride) does not conduct (electricity)
as ions cannot move in the solid
Why can solid zinc chloride not be used as an electrolyte?
solid (zinc chloride) does not conduct (electricity)
as ions cannot move in the solid
Why can graphite conduct electricity?
each carbon / atom forms 3 (covalent) bonds
one electron per carbon / atom is delocalised
(so) these electrons carry charge through the graphite
How should the solution be heated gently in crystallisation?
using a water bath
Why do you warm the acid in crystallisation?
to speed up the reaction
Why do you stir the mixture in crystallisation?
to make sure all acid reacts
Why do you filter the mixture in crystallisation?
to remove (e.g. magnesium oxide) in excess
Explain why an acid can be described as both strong and dilute.
(strong because) completely ionised (in aqueous solution)
(dilute because) small amount of acid per unit volume
Explain why the student should use a pipette to measure the dilute sulfuric acid and a burette to measure the sodium hydroxide solution in titration.
pipette measures a fixed volume
burette measures a variable volume
What is a weak acid?
produces H+ ions in aqueous solutions
only partially ionised
The student repeated the experiment with potassium carbonate.
The limewater did not bubble.
Suggest why there were no bubbles in the limewater.
Potassium carbonate does not decompose to produce carbon
dioxide
Advantages of using hydrogen fuel cells over rechargeable cells
no loss of efficiency over time
take less time to refuel (than to recharge rechargeable batteries)
no toxic chemicals to dispose of at the end of cell’s life
Suggest factors that could affect the voltage produced in a fuel cell.
concentration of electrolyte
temperature of electrolyte
Suggest why trains using hydrogen fuel cells are referred to as ‘steam trains’?
hydrogen is oxidised
water is released as a gas
Why can alkaline batteries not be recharged?
the reaction cannot be reversed
Why do non-rechargeable cells stop producing electricity?
the reaction stops as reactants are used up
