| Oxidant strength | oxidants | reductants | Reductant strength |
very strong moderate | F2 (fluorine) | F– (fluoride) | very weak moderate |
| Cl2 (chlorine) | Cl– (chloride) | ||
| conc H2SO4 | |||
| Br2 (bromine) | Br– (bromide) | ||
| I2 (iodine) | I– (iodide) |
Both I– and Br– are sufficiently strong reductants to donate electrons to sulfuric acid.
Both F– and Cl– are weaker reductants and do not donate electrons to sulfur in sulfuric acid.
Both F– and Cl– are weaker reductants and do not donate electrons to sulfur in sulfuric acid.
How do chlorides and fluorides react with concentrated sulfuric acid?
The halide ions can accept a proton to give the corresponding hydrogen halide.
F– is the only halide that is sufficiently basic to accept H+ from H2SO4 in aqueous solution.
However in the absence of water (concentrated sulfuric acid) reaction occurs with both fluoride and chloride salts to generate the corresponding hydrogen halide. These are proton-transfer reactions. The product arising from the sulfuric acid can be HSO4– or SO42– depending upon the relative amounts of the reactants used.
H2SO4(l) + NaF(s)
H2SO4(l) + CaF2(s)
H2SO4(l) + NaCl(s)
These reactions are exothermic and the colourless gases escape from the test tube. The reaction to produce hydrogen chloride is used as a source of small amounts of this gas for laboratory applications. The reaction with the naturally occurring calcium minerals containing fluoride is the commercial source of HF.
F– is the only halide that is sufficiently basic to accept H+ from H2SO4 in aqueous solution.
However in the absence of water (concentrated sulfuric acid) reaction occurs with both fluoride and chloride salts to generate the corresponding hydrogen halide. These are proton-transfer reactions. The product arising from the sulfuric acid can be HSO4– or SO42– depending upon the relative amounts of the reactants used.
H2SO4(l) + NaF(s)
HF(g) + NaHSO4(s)
H2SO4(l) + CaF2(s)
2HF(g) + CaSO4(s)
H2SO4(l) + NaCl(s)
HCl(g) + NaHSO4(s)
These reactions are exothermic and the colourless gases escape from the test tube. The reaction to produce hydrogen chloride is used as a source of small amounts of this gas for laboratory applications. The reaction with the naturally occurring calcium minerals containing fluoride is the commercial source of HF.