Producing sulphur dioxide for using in a reaction
Note: Sulfur dioxide causes dyspnea. Prolonged inhalation of it may causes respiratory problems. So, reaction should be done under laboratory supervision.



The most common laboratory method of producing sulfur dioxide is the reaction of copper and sulfuric acid, both available in laboratories.

$$\ce{Cu(s) + 2H2SO4(l) → CuSO4(aq) + 2H2O(l) + SO2(g)}$$

Process: To a round bottom flask, 100 g of copper (small pieces, turnings, etc.) are placed. From a dropping funnel 100 ml of concentrated sulfuric acid is slowly added dropwise. The reaction flask is gently heated and obtained sulfur dioxide is dried by passing through a wash bottle with concentrated sulfuric acid. (Process taken from here. Read more to know how the reaction can be controlled and the precaution needed)

Alternatively, sodium sulfite can also be used.

$$\ce{Na2SO3 + H2SO4 -&gt; SO2 + Na2SO4 + H2O}$$

Process: Sodium sulfite is placed in the bottom of the 300 ml Erlenmeyer flask of the apparatus. The dropping-funnel is filled with dilute sulfuric acid, made by pouring one volume of concentrated sulfuric acid into an equal volume of water and cooling the mixture. The glass elbow is connected with a gas washing-bottle containing concentrated sulfuric acid, and the dry gas is collected by displacement in two or three empty cylinders. On allowing the dilute sulfuric acid to drop slowly upon the sodium acid sulphite, a very regular evolution of sulfur dioxide is obtained.



For full setup, check here.