Electrolysis Flashcards
Definition of electrolysis
The passage of electricity through a chemical substance causing a chemical change and the formation of new substances at the electrodes
for the bulb to light there must be?
a complete circuit
Ionic substances dissolve in water to form what?
An aqueous solution
The ions in the ionic substance become what>
Mobile
if the aqueous solution is connected in a circuit what will happen?
an electric current will flow
The aqueous solution is an example of what?
An electrolyte
Give three examples of an aqueous solution
Sodium chloride solution
dilute sulphuric acid
copper sulphate solution
electrolysis of sodium chloride solution observation at the anode (positive electrode)
fizzing and chlorine smell
electrolysis of sodium chloride solution observation at the cathode (negative electode
hydrogen
half equation for oxygen
4OH(-) - 4E- = 02 + 2H(2)0
half equation for hydrogen
2H+ (+) 2E- = H2
What are the ‘rules’ for the anode (positive electrode)
- halide ions always lose their electrons before hydroxide ions
- hydroxide ions will lose their electrons before sulphate or nitrate ect
what are the ‘rules’ at the cathode?
metal ions below hydrogen in the reactivity series always gains electrons before H+ ions
-H+ ions always gain electrons before metal ions that are above it in the reactivity series
Definition of the electrolysis of brine
a very important electrolysis of concentrated sodium chloride solution used in the industry
what does the electrolysis of brine produce?
- Chlorine Gas
- Hydrogen Gas
- Sodium Hydroxide Solution
What are the ions present in brine
Sodium
chlorine
hydroxide
hydrogen
whats happens when an electrical current passes through brine at the cathode (-)
sodium and hydrogen ions move to the cathode
-H+ ions gain electrons and H+ gas is released
Na+ ions remain in solution
What happens when an electrical current passes through brine at the Anode (+)
- chloride and hydroxide ions move to the anode
- chloride ions lose electrons and chlorine gas is released
- hydroxide ions remain in solution
What is made in the electrolysis of brine and at which electrode or other>
- Hydrogen gas at the cathode
- Chlorine Gas at the anode
- sodium hydroxide solution left in the container
What is Hyrogen Gas used for?
- harden veg oil into margarine
- make hydrochloric acid for use in pharmacy industry
What is chlorine gas used for?
(poisonous) -to kill bacteria in drinking water and pools
- to make bleach + pvc/plastics
- to make disinfectant
what is sodium hydroxide solution used for?
- soap
- paper
- bleach
What is the test for hydrogen?
insert a lighted splint
gas burns with a pop
HAZARD- in air a spark causes explosion
test for oxygen?
insert a glowing splint
the splint relights
Test for carbon dioxide
- bubble the gas through limewater
- the limiter turns milky
test for chlorine
- put damp BLUE litmus paper in the gas
- the litmus turns pink and then BLEACHES
test for Ammonia
put red litmus in the gas
-the litmus turns blue the gas is alkaline
HAZARD= alkaline very soluble in water danger of suck back
Hydrogen chloride test
put the gas ned to a bottle of ammonia solution
the gas gives dense white fumes of ammonium chloride
test for water x2
add to anhydrous copper sulphate(white) add to blue cobalt chloride paper
-anyhydrous copper sulphate turns blue
blue cobalt chloride paper turns pink
Test for pure water
boils at 100C
freezes at 0C
test for Alkenes C=C double bonds (unsaturated hydrocarbons)
shake with bromine water
-bromine water decolourises turns from yellow/brown to colourless
definition of an electrolyte
a liquid or gel which contains ions and can be decomposed by electrolysis, e.g. that present in a battery.
definition of conductor
a metal that conducts electricity when it is solid as it does not have mobile ions
In a circuit which way do the electrons go
negative to positive
Why does solid Lead (II) not undergo electrolysis
It doesn’t have mobile ions
Describe what you would observe in the electrolysis of lead (II)
lead- a shiny substance would form at the cathode and bromine gas and fizzing would be given off at the anode
