Question

using equations, explain each of the observations made at each electrode in part A....

These were our results for this experiment:

solution	pH+	observation at cathode	observation at anode	anode
NaCl	Base	A lot of bubbles	a little bit of bubbles	acid
NaBr	base	a lot of bubbles	tiny bubbles and it turned pae yellow	neautral
NaI	base	little bit of bubbles	turned dark yellow	base
AgNO3	acid	bubbles/ shiny silver	no change	neutral
CuSO4 (c electrode)	acid	red copper @tip	bubbling	acidic
CuSO4 (Cu electrode)	acid	lighter at electrode	darkter at electrode	acidic

This is what we used during our experiemnt:

experiment	solution	electrodes
1	0.1 M NaCl	graphite
2	0.1 M NaBr	graphite
3	0.1 M NaI	graphite
4	0.1 M AgNO3	graphite
5	0.1 M CuSO4	graphite
6	0.1 M CuSO4	copper

we used a u-tube for this experiment and inserted electrodes in each side

This is a post lab question and I need help writing equations for observations made at each electrode, thank you

Answer 1

1. Cathode reaction: 2H₂O + 2e --> H₂ + 2OH^-

The negative (–) cathode attracts the Na⁺ (from sodium chloride) and H⁺ ions (from water). Only the hydrogen ions are discharged at the cathode. The more reactive a metal, the less readily its ion is reduced on the electrode surface.

Anode: The positive anode attracts the negative hydroxide OH^– ions (from water) and chloride Cl^– ions (from sodium chloride). Only the chloride ion is discharged in appreciable quantities i.e. it is preferentially oxidised to chlorine.

2Cl^– ==> Cl_2(g) + 2e^–

Overall: 2NaCl(aq) + 2H₂O(l) ==> H₂(g) + Cl₂(g) + 2NaOH(aq)

2. Anode: 2Br^- ---> Br2(l) (pale yellow) + 2e

Cathode: 2H₂O + 2e --> H₂ + 2OH^-

3. Anode: 2I^- ---> I2(l) ( yellow) + 2e

Cathode: 2H₂O + 2e --> H₂ + 2OH^-

4. Cathode: Ag+ + e ==> Ag

Anode: 2H₂O_(l) – 4e^– ==> 4H⁺_(aq) + O_2(g)

5. The negative cathode electrode attracts Cu²⁺ ions (from copper sulfate) and H⁺ ions (from water). Only the copper ion is discharged, being reduced to copper metal. The less reactive a metal, the more readily its ion is reduced on the electrode surface.

Cathode: Cu²⁺_(aq) + 2e^– ==> Cu_(s)

The negative sulphate ions (SO₄^2-) or the traces of hydroxide ions (OH^–) are attracted to the positive electrode. But the sulfate ion is too stable and nothing happens. Instead either hydroxide ions or water molecules are discharged and oxidised to form oxygen.

Anode: 2H₂O_(l) – 4e^– ==> 4H⁺_(aq) + O_2(g)

6. The negative cathode electrode attracts Cu²⁺ ions (from copper sulfate) and H⁺ ions (from water). Only the copper ion is discharged, being reduced to copper metal. The less reactive a metal, the more readily its ion is reduced on the electrode surface.

A reduction electrode reaction at the negative cathode

(–) Cu²⁺_(aq) + 2e^– ==> Cu_(s) (Cu produces)

The negative sulphate ions SO₄^2- (from copper sulfate) or the traces of hydroxide ions OH^– (from water) are attracted to the positive electrode. But both the sulfate ion and hydroxide ion are too stable and nothing happens to them because the copper anode is preferentially oxidised to discharge Cu²⁺ copper ions.

Cu_(s) – 2e^– ==> Cu²⁺_(aq) (Cu dissolves)