[Part 3]- C6- electrolysis💧

Question 1

What are aqueous solutions ?

Hint: _____ molecules ionise, forming what ions?

Hint: hydroxide

Answer 1

• aqueous solutions are dissolved in water- meaning they form when substances are dissolved in water
• and water molecules ionise/dissociate [split], forming hydrogen ion and hydroxide ions.

Question 2

What can you tell me about the formula of the copper sulfate solution, during electrolysis ? [of an aqueous solution]

Answer 2

• copper sulfate solution, has the formula CuSO4 (aq)- containing the copper ion: CU^2+ and the sulfate ion: SO4^2-
• because it’s dissolved in water, the hydrogen ion H^+ and the hydroxide ion OH^- needs to be considered.

Question 3

During the electrolysis of copper sulfate solution [an aqueous solution], what’s attracted to the cathode ?

Hint: rule- reactivity of hydrogen

Answer 3

• the copper sulfate solution, contains two positive ions that would be attracted to the cathode.
• ; the rule, is that hydrogen is (only) produced at the cathode, if the metal is more reactive than hydrogen.
• and because copper is less reactive than hydrogen, copper will be produced at the cathode.

Question 4

During the electrolysis of copper sulfate solution [an aqueous solution], what’s attracted to the anode ?

Hint: why

Answer 4

• and at the anode, oxygen gas is made- [because oxygen is usually produced at the anode, when aqueous solutions are electrolysed]

Question 5

Why are the electrodes inert ?

Answer 5

• the electrodes are inert [unreactive] because, it’s important that the electrodes don’t react, with the chemicals that are being made in electrolysis.
• otherwise, the electrodes will take part in the reaction

Question 6

What is the half-equation at the cathode, during the electrolysis of copper sulfate solution

Hint: 2e

Answer 6

• Cu^2+ 2e^- ————-> Cu
• this is a reduction reaction, as the copper ions are gaining electrons, to form copper atoms.

Question 7

What is the half-equation at the anode, during the electrolysis of copper sulfate solution ?

Hint: 4OH^- —> O2

Answer 7

4OH^- ———> O2 + 2H2O + 4e^-

OR

4OH^- ➖ 4e^- ———-> O2 + 2H2O

• four hydroxide ions react to form oxygen gas and water, using a total of four electrons in the process- therefore this is an oxidation reaction.

Question 8

What’s the rule to use, when predicting what will be produced at the cathode ?

Answer 8

• ; the rule, is that hydrogen is (only) produced at the cathode, if the metal is more reactive than hydrogen.

Question 9

What can you tell me about the formula of sodium chloride solution during electrolysis ? [of an aqueous solution]

Hint:

Answer 9

• sodium chloride solution, has the formula: NaCl^- containing the sodium ion: Na and the chloride ion Cl^-
• because it’s dissolved in water, the hydrogen ion H^+ and the hydroxide ion OH^- needs to be considered.

Question 10

During the electrolysis of sodium chloride solution, what’s attracted to the cathode

Hint: why?

Answer 10

• the sodium chloride solution, contains two positive ions that would be attracted to the cathode. [the sodium ion Na^+ and the hydroxide ion H^+]
• ; the rule, is that hydrogen is (only) produced at the cathode, if the metal is more reactive than hydrogen.
• and because sodium is more reactive than hydrogen, hydrogen gas will be produced at the cathode.

Question 11

During the electrolysis of sodium chloride solution, what’s attracted to the anode?

Answer 11

• and at the anode, there are two negative ions that could be attracted to it- [the chloride ion: Cl^- and the hydroxide ion OH^-]
• ; the rule for the anode is: that if the aqueous solution contains halide ions, then halogen will be produced at the anode. [otherwise it would typically be oxygen gas]
• therefore at the anode, chlorine gas is made- since the sodium chloride solutions, contains a halide ion [chloride]

Question 12

What is the half-equation at the cathode, during the electrolysis of sodium chloride solution ?

Answer 12

• H^+ ➕ e^- ———> H
• this is a reduction reaction, as the hydrogen ion is gaining one electron, to form a hydrogen atom.

Question 13

During the electrolysis of sodium chloride solution, what can else can you tell me about the cathode ?

Answer 13

• Since hydrogen atoms immediately pair up to form a hydrogen molecule [H2]- as hydrogen is a diatomic molecule, the half equation is doubled and now looks like this:
• 2H^+ ➕ 2e^- ———> H2

Question 14

What is the half-equation at the anode, during the electrolysis of sodium chloride solution ?

Answer 14

• Cl^- ———-> Cl + e^-
• ; as chloride atoms always pair to form a double molecule, the half-equation must be doubled:
• 2Cl^- ———-> Cl2 + 2e^-

OR

• 2Cl^- ➖ 2e^- ———-> Cl2
• this is an oxidation reaction, as chlorine loses one electron, to form a chlorine atom.

Question 15

What’s the rule to use, when predicting what will be produced at the anode ?

Hint: halide

Answer 15

• the rule for the anode is: that if the aqueous solution contains halide ions, then halogen will be produced at the anode.
• [otherwise it would typically be oxygen gas, as the hydroxide ions would be attracted to the anode]
• these halides ions are: fluoride (F −), chloride ( Cl −), bromide ( Br −), iodide ( I −) and astatide ( At −)

Question 16

List all the halide ions [5]

Answer 16

• fluoride (F −)
• chloride ( Cl −)
• bromide ( Br −)
• iodide ( I −)
• astatide ( At −)

Question 17

During the electrolysis of brine, what’s the equation for the change to electrolyte?

Hint: symbols

Answer 17

• NaCl [aq] ——-> NaOH [aq]

Question 18

What else can you tell me about the electrolysis of brine [sodium chloride solution] ?

Answer 18

• During the electrolysis of brine, hydrogen and chloride ions are removed from sodium chloride solution solution .
• ; sodium and hydroxide ions are left behind in solution.
• This means that sodium hydroxide is also formed during the electrolysis of sodium chloride solution.

Question 19

Why can the products of the electrolysis of brine be used ?

Hint: ions are removed

Answer 19

• Because hydrogen and chloride ions are removed from sodium chloride solution
• and sodium hydroxide is also formed, during the electrolysis of sodium chloride solution. [because sodium and hydroxide ions are left behind in solution.]
• the products of electrolysis of brine can be used

Question 20

What are the uses for the electrolysis of brine ? 🚀🏊‍♂️🧼

Answer 20

• hydrogen can be used for fuel cells and rockets
• chlorine can be used for bleach and swimming pools
• and sodium hydroxide can be used for: making soap, and unblocking drains.

Question 21

What is brine ?

Answer 21

• Brine is a solution of sodium chloride (NaCl) and water (H2O)

Question 22

What’s a word equation, for the electrolysis of a solution ?

Answer 22

Water (l) electicity ⟶ Hydrogen (g)+ Oxygen (g)

Question 23

What’s the test to show the change to the electrolyte ?

Answer 23

• litmus paper will turn blue at the anode

Question 24

When writing half-equations, what is the tip you must remember ?

Answer 24

• when writing half -equations, if there is a positively charged ion, the electron goes before the arrow to balance the charges

Question 25

What’s the rule when predicting what will be produced at the cathode, in the electrolysis of aqueous solutions ?

Answer 25

• [both hydrogen and metal ions are attracted to the cathode]
• though the rule is: if the metal is more reactive than hydrogen, hydrogen will be produced at cathode
• ; if the metal is less reactive than hydrogen, the metal will be produced at the cathode