Brine is a concentrated solution of aqueous sodium chloride
It can be electrolysed using inert electrodes made from platinum or carbon/graphite
When aqueous sodium chloride is electrolysed, it produces bubbles of gas at both electrodes as chlorine and hydrogen are produced, leaving behind sodium hydroxide solution
The products of electrolysis of aqueous sodium chloride all have important industrial uses:
Chlorine is used to make bleach
Hydrogen is used to make margarine
Sodium hydroxide is used to make soap and detergents
Product at the Negative Electrode (aqueous sodium chloride):
The H+ ions are discharged at the cathode as they are less reactive than sodium ions
The H +ions gain electrons to form hydrogen gas
Product at the Positive Electrode (aqueous sodium chloride):
The Cl- ions are discharged at the anode
They lose electrons and chlorine gas forms
The Na+ and OH- ions remain behind and form the NaOH solution
Product of electrolysis of aqueous sodium
A) Hydrogen gas
B) chlorine gas
C) sodium chloride
D) brine
E) sodium
F) hydroxide
Dilute sulfuric acid can be electrolysed using inert electrodes made from platinum or carbon/graphite
Bubbles of gas are seen at both electrodes
Product at the Negative Electrode (dilute sulfuric acid)
H+ ions are attracted to the cathode, gain electrons and form hydrogen gas
Product at the Positive Electrode
OH- ions are attracted to the anode, lose electrons and form oxygen gas and water
If the gas produced at the anode relights a glowing splint dipped into a sample of the gas then the gas is oxygen
If the gas produced at the anode bleaches damp litmus paper then the gas is chlorine
A) blue
B) red
C) white
D) chlorine
If the gas produced at the cathode burns with a 'pop' when a sample is lit with a lighted splint then the gas is hydrogen
Water is a poor conductor of electricity
very small number of water molecules ionize to form H+ and OH- ions
water can conduct if it contains salt impurities
Electrolysis of water with some sulfuric acid (H2SO4)
A) double the gas
B) hydrogen
C) carbon
D) cathode
E) oxygen
F) platinum
G) anode
Electrolysis of water with some sulphuric acid (in a circuit)
A solution of sodium chloride in water contains the following ions:
H+ (aq) and OH-(aq) from the water
Na+ (aq) and Cl-(aq) from the sodium chloride
Both positive ions migrate to the negative electrode and both negative ions move to the positive electrode
cations → cathode
anions → anode
at each electrode, one or both of the ions may be discharged
Metals (cations), if produced, are discharged at the cathode electrode
Hydrogen is produced at the cathode electrode only and is produced in preference to metals unless unreactive metals such as Cu and Ni are present
Other non-metals (anions) are produced at the anode electrode
Reactive metals tend not to be formed at the cathode during electrolysis of aqueous solutions
Investigating electrolysis of aqeuous solutions
A) products
B) oxygen
C) chlorine
D) bromine
E) iodine
F) positive electrode
G) anode
H) solution
I) negative electrode
J) cathode
K) tested
L) products
M) hydrogen
N) copper
O) lead
P) silver
Flowchart
A) non-metal
B) metal
C) oxygen
D) dilute
E) oxygen
F) concentrated
G) halogen
H) lower
I) metal
J) higher
K) H2
Flowchart
Anode
If a dilute halide or OH- is present, oxygen is formed
If a concentrated halide is present, halogen is formed e.g. bromide → bromine, iodide → iodine
Cathode - metal must be less reactive than H to give the metal otherwise H2 is produced
metal or H+ formed
Reactivity Series Mnemonic
Lovely - Li
Katie - K
Never - Na
Could - Ca
Manage - Mg
A - Al
Zebra - Zn
For - Fe
She - Sn
Punishes - Pb
Him - H
Cruelly - Cu
Ag
Au
P+
Ag, Au and P+ are less reactive
which electrode does reduction take place?
Cathode
which electrode does oxidation take place?
Anode
What is the half equation for chloride?
2Cl- = Cl2 + 2e-
Where does the hydrogen come from in the reaction of sodium chloride (NaCl)?
Water
What are the solutions left behind after the electrolysis of concentrated sodium chloride?
sodium hydroxide
What are the solutions left behind after the electrolysis of dilute sodium chloride?
remaining solution of sodium chloride and the water is decomposed
Ions in the concentrated NaCl are:
water - H+ and OH-
NaCl - Na+ and Cl-
NaCl at the anode:
2Cl- → Cl2 + 2e-
Cl- oxidised to Cl2
NaCl at the cathode:
2H+ → H2
H+ reduced H2
Electrolysis of concentrated aqueous NaCl
leaves a high concentration of OH- around the cathode
sodium ions are drawn through the membrane where OH- react to form NaOH
Electrolysis of concentrated aqueous NaCl
A) chlorine
B) hydrogen
C) water
D) sodium hydroxide
E) solution
F) nickel cathode
G) membrane for separation
H) titanium anode
I) salt
J) solution
K) concentrated salt
Electrolysis is an important industrial process as it produces 3 important products which are used to make other products:
H2 - makes HCl and CH4, fuel for rocket shops and some vehicles, NH3 for fertilizers
Cl2 - cleaning pools, kills bacteria, makes HCl, makes bleachh
NaOH - paper, soap
Hydrochloric acid is a strong acid and completely ionizes
HCl → H+ + + Cl-
Ions mitagate to the oppositely charged electrode and turn into molecules in the reaction of hydrochloric acid