Question

Give the main experimental points only to demonstrate that candle-gains weight on burning.

Answer 1

Candle gains weight on burning

1. Weight: The complete apparatus as shown above which includes -

• Unlit candle ‘A’.
• U tube ‘B’ containing anhydrous CaCl₂.
• Conical flask ‘C’ containing cone. KOH soln.
  Total wt. = a gms.
  The candle ‘A’ is then lit and the products obtained on burning are allowed to be absorbed in U tube ‘B’ and conical flask ‘C’.

2. Re-weigh: The complete apparatus as shown above after the candle has burnt – for a known period of time.
Total wt. = b gms.

Result:

• ‘b’ gms. is greater than ‘a’ gms.
• weight of apparatus after absorbtion
• of products is greater than the original weight of the apparatus.

Conclusion: Candle gains weight due to mass of oxygen of the air which has combined with ‘carbon’ and ‘hydrogen’ of the candle [CxHy] producing .

• Water vapour [absorbed by anhydrous CaCl₂]
• Carbon dioxide [absorbed by cone. KOH soln].