C2.5 Salts and electrolysis Flashcards
(27 cards)
What is a base?
substances that neutralise acids
What is an alkali?
a soluble hydroxide , produces OH- ions when added to water
What does the pH scale show?
how acidic or alkaline a substance is
What ions make something acidic?
H+ ions
What is produced when an acid and metal react?
Acid + Metal = salt + hydrogen
What is produced when and acid and base react?
Acid = Base = salt + water
What is the reaction between an acid and base called?
a neutralisation reaction
What is electrolysis?
the separation of substances using electricity
What does adding ammonium solution to an acid produce?
an ammonium salt (eg. ammonium nitrate) and water
What is the positive electrode called?
anode
What is the negative electrode called?
cathode
How can an insoluble salt be made?
reacting two solutions to produce a precipitate
What can be electrolysed?
Ionic compounds when they are molten or in a solution this is because their ions are then free to move to the electrodes
Which ions move where during electrolysis?
negative ions (an ions) move to the positive electrode (anode) positive ions(cat ions) move to the negative electrode (cathode)
What happens at the electrodes?
negative(cathode)-reduction, positive ions are reduced
positive(anode)-oxidation, negative ions are oxidised
What effect does water have on electrolysis?
The less reactive element between hydrogen and the metal is usually produced at the negative electrode.
At the positive electrode, hydroxide usually discharges, giving off oxygen gas (except when there is large concentration of halide ions in solution(group 7) in this case the halide is discharged)
How is electrolysis used to extract aluminium?
aluminium oxide is electrolysed when manufacturing aluminium metal
it is mixed with molten cryolite to lower its melting point
aluminium forms at the negative electrode and oxygen at the positive electrode
What are the electrodes replaced often during the electrolysis of aluminium?
because they are made of carbon and this is gradually burnt/worn away by the oxygen forming carbon dioxide
What are the product when we electrolyse brine?
hydrogen, chlorine and sodium hydroxide solution
What is formed at the negative electrode when electrolysing brine?
Hydrogen ions (H+) formed when water breaks down are attracted as well as sodium ions (Na+) but as hydrogen is less reactive it is formed here as a gas (H2)
What is formed at the positive electrode when electrolysing brine?
Chloride ions (Cl-) are attracted to the positive electrode
they are lose one electron and the ions are oxidised
they bond together in pairs and are given off as chlorine gas (Cl 2)
What are the uses of hydrogen?
useful in food industry (very pure hydrogen)
make margarine by reacting with vegetable oils
What are the uses of chlorine?
can react with sodium hydroxide to make bleach (good at killing bacteria)
makes disinfectants, and plastics eg. PVC
What are the uses of sodium hydroxide?
used to make soap and paper
also used with chlorine to make bleach
