why does dry Litmus Paper don't turn red when sodium chloride and concentrated sulphuric acid reacts ?
Answers
The colour of blue litmus paper changes only in the presence of ions like hydrogen (H+) or hydronium (H3O+) ions. HCl can produce these ions only when in the form of aqueous solution. Hence dry HCl gas does not change the colour of dry litmus paper.When concentrated sulphuric acid is added to NaCl, sodium bisulphate and HCl gas is formed. reaction also takes place at same time , that between NaCl and H2SO4 sodium sulphate and HCl.
NaCl + H2SO4 → NaHSO4 + HCl
2NaCl + H2SO4 → Na2SO4 + 2HCl
The gas released reaction is HCl acidic in nature acids turn blue litmus paper into red. hence the gas change the colour of litmus papaer from blue to red. it will have no effect on the colour of dry blue litmus paper. This is because colour of litmus paper is changed by the hydrogen ions. Dry HCl does not contains H+ ions. in this case, neither HCl is in aqueous form and not the litmus paper is wet, the colour of litmus paper doesn't change.