C2.5 Salts and electrolysis Flashcards Preview

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Flashcards in C2.5 Salts and electrolysis Deck (27):

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?



What is the negative electrode called?



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


What is electroplating?

covering an object with a thin layer of metal by electrolysis


How does electroplating work?

the object to be electroplated is made the negative electrode in electrolysis cell
the plating metal is made the positive electrode
the electrolyte contains ions of the plating metal


Why do we electroplate objects?

to improve their appearance
protect their surfaces
use smaller amounts of precious metals