Presentation on theme: "a.What four ions are present in sodium chloride solution? 3 Na + (aq), Cl - (aq), H + (aq), OH - (aq) b.In Figure 21.3, write the ionic equation for the."— Presentation transcript:
a.What four ions are present in sodium chloride solution? 3 Na + (aq), Cl - (aq), H + (aq), OH - (aq) b.In Figure 21.3, write the ionic equation for the reactions at: 2Cl - (aq) Cl 2 (g) + 2e - (i).the anode
2H + (aq) + 2e - H 2 (g) (ii).the cathode Chloride ions and hydrogen ions are removed, leaving sodium ions and hydroxide ions, i.e. sodium hydroxide. c.Explain why sodium hydroxide forms during the electrolysis.
Oxygen gas is formed instead of chlorine gas. Chlorine is needed to react with the sodium hydroxide solution. 4To prepare a solution of chlorine bleach, dilute sodium chloride solution is not electrolysed. Give the reason.
1.Different electrodes. 2.No porous membrane in laboratory cell. 3.Three products separated in industrial cell. 4.Bleach formed inside the laboratory cell, separately from the industrial cell. 5.Industrial product is purer (cf. Class Practice 6). 5State some differences between the laboratory preparation and the industrial manufacture of bleach.
6In the industrial manufacture, the chlorine at the anode is not mixed with the sodium hydroxide solution inside the cell. Why not? The bleach formed is mixed with other substances (e.g. NaOH, NaCl) and so is not pure.
mercury cathode, graphite (sometimes titanium) anode 7The electrolysis of brine is also carried out in a mercury cathode cell. a.What electrodes does this cell use? Cathode - sodium Anode - chlorine b.What is formed at each electrode?
Sodium (dissolved in the mercury) is removed and reacts with water. c.How is sodium hydroxide formed?
a.In the industrial electrolysis of brine, name: 8 solid salt (i).the raw materials; and (ii).all the products. hydrogen, chlorine, sodium hydroxide solution
No. Hydrogen is used to make hydrochloric acid; chlorine and sodium hydroxide form bleach. b.Is there any waste substance in this process?