C12+The+Chlor-Alkali+Industry

- Chlorine is a powerful oxidizing agent, except fluorine, very few chemical oxidizing agents could oxidize chloride ions to chlorine. - Uses electrons instead - Chlorine gas is formed during electrolysis of molten sodium chloride to produce sodium metal. - Chlorine gas is also formed during electrolysis of aqueous sodium chloride (brine/sea water) -> use less energy, more efficient and economical. - Products are Chlorine gas, hydrogen gas, sodium hydroxide. - __ THE DIAPHRAM CELL: __ - Brine is enter is a essential material - Chlorine gas is formed at the positive electrode (anode) - Hydrogen gas is formed at the negative electrode (cathodes) - Titanium is use as the positive electrode, steel is use as the negative electrode - The diaphragm helps to prevent the movement of OH - (from water H 2 O) to the positive electrode. - OH - is to stay on the negative electrode which combines with Na to give sodium hydroxide. - __ THE MERCURY CELL: __ - Mercury runs at the bottom - NaCl is ionized by the graphite positive electrode - Chlorine gas is formed and vaporize -<span style="font-size: 7pt; font-style: normal; font-variant: normal; font-weight: normal; line-height: normal;"> Na is left which formed Na/Hg(l) with mercury -<span style="font-size: 7pt; font-style: normal; font-variant: normal; font-weight: normal; line-height: normal;"> Na/Hg(l) when combine with water will give Na +, OH - , mercury and hydrogen gas. -<span style="font-size: 7pt; font-style: normal; font-variant: normal; font-weight: normal; line-height: normal;"> The mercury will be extract to be use again in the cell 1: NaCl -> Na + + Cl -
 * C.12.1 Discuss the production of chlorine and sodium hydroxide by the electrolysis of sodium chloride.**

Na + and H 2 O
 * Cathode (-): **

H 2 O + 2e- -> H 2 + 2OH- Water is oxidizing agent

Cl - and H 2 O
 * Anode (+): **

2Cl - -> Cl2 + 2e - Chloride ion is a reducing agent

2: CuSO 4 -> Cu 2+ (aq) + SO 4 2-

H 2 O and Cu2+(aq) (arrange follow the reactivity series)
 * Cathode (-): Reduction **

(Cu 2+ + 2e -  -> Cu(s)) x2 Cu 2+  ion is easier reduced than H 2 O Cu 2+  ion is a strong oxidizing agent (compare with H 2 O)

H 2 O and SO 4 2-
 * Anode (+): Oxidation **

2 H 2 O -> O 2 + 4H +  + 4e- When stop electrolysis: 4H + + 2SO 4 2-  -> 2H 2 SO 4

Overall equation: 2 CuSO4(aq) + 2H2O -> Cu(s) + O 2 + 2H 2 SO4

3: CuCl 2 -> Cu 2+ (aq) + 2Cl-

H 2 O and Cu 2+
 * Cathode (-): reduction **

Cu 2+ (aq) + 2e - -> Cu(s)

H 2 O and Cl -
 * Anode (+): oxidation **

2Cl - (aq) -> Cl 2 (g) + 2e-

Overall equation: CuCl 2 -> Cu(s) + Cl 2 (g)
 * ** Cathode (reduction) (-) ** || ** Anode (Oxidation) (+) ** ||
 * If the positive ions are before Al 3+ then H +  in H 2 O will be reduced, creating H 2  and OH -

2H 2 O + 2e - -> H 2 (g) + 2OH - (aq) || Negative ions (halide ions) with acid based without oxygen will give out electron to produce X 2 molecule

2Cl - -> Cl 2  + 2e -  || (nhận/accepted) Cu 2+ + 2e -  -> Cu || Negative ions with oxygen will not give away electrons, OH -  in H 2 O will give electrons creating O 2  and ion H + (nhường/removed) 2 H <span style="mso-ansi-language: ES; mso-fareast-language: KO; mso-text-raise: -3.0pt; position: relative; top: 3pt;">2 O -> O <span style="mso-ansi-language: ES; mso-fareast-language: KO; mso-text-raise: -3.0pt; position: relative; top: 3pt;">2 + 4H <span style="mso-ansi-language: ES; mso-fareast-language: KO; mso-text-raise: 3.0pt; position: relative; top: -3pt;">+  + 4e <span style="mso-ansi-language: ES; mso-fareast-language: KO; mso-text-raise: 3.0pt; position: relative; top: -3pt;">-  ||
 * If the positive ions are after Al 3+ then these positive ions will be reduced by the negative electrode

**C.12.2 Outline some important uses of the products of this process.** -<span style="font-size: 7pt; font-style: normal; font-variant: normal; font-weight: normal; line-height: normal;"> Chlorinated organic solvents -<span style="font-size: 7pt; font-style: normal; font-variant: normal; font-weight: normal; line-height: normal;"> Water purification -<span style="font-size: 7pt; font-style: normal; font-variant: normal; font-weight: normal; line-height: normal;"> Pesticides -<span style="font-size: 7pt; font-style: normal; font-variant: normal; font-weight: normal; line-height: normal;"> Feedstock for inorganic chemicals -<span style="font-size: 7pt; font-style: normal; font-variant: normal; font-weight: normal; line-height: normal;"> Bleaching paper

-<span style="font-size: 7pt; font-style: normal; font-variant: normal; font-weight: normal; line-height: normal;"> Mercury is dangerous in the environment -<span style="font-size: 7pt; font-style: normal; font-variant: normal; font-weight: normal; line-height: normal;"> The equation: Na/Hg(l) + H 2 0 -> Na + (aq) + OH - (aq) + 1/2H 2 (g) + Hg(l) only exist in theory -<span style="font-size: 7pt; font-style: normal; font-variant: normal; font-weight: normal; line-height: normal;"> In reality, not all of the mercury are recycled -<span style="font-size: 7pt; font-style: normal; font-variant: normal; font-weight: normal; line-height: normal;"> They leak out into the environment and harm organisms. -<span style="font-size: 7pt; font-style: normal; font-variant: normal; font-weight: normal; line-height: normal;"> Build up food chains toxic levels -<span style="font-size: 7pt; font-style: normal; font-variant: normal; font-weight: normal; line-height: normal;"> Ultraviolet light can break the C-CI bond at high altitude, release chlorine radicals -<span style="font-size: 7pt; font-style: normal; font-variant: normal; font-weight: normal; line-height: normal;"> Contribute to the depletion of ozone layer
 * C.12.3 Discuss the environmental impact of the processes used for the electrolysis of sodium chloride.**