Question

6 grams of carbon 40 grams were fully burnt in the atmosphere of oxygen. What percentage of oxygen left?

Answer 1

5percent of oxygen is left

Acc to icse syllabus!

Hope this helps

Answer 2

Gram molecular wight of carbon = 12gms

In other words,

12 gms of carbon =1 mole carbon  

Therefore,  6 gms of carbon = 0.5 moles of carbon

Gram molecular weight of oxygen = 32 gms

In other words,

1 mole of oxygen = 32 gms

The chemical reaction between carbon and oxygen is as follows:

C + O₂ = CO₂

i.e 1 mole of carbon will react with 1 mole of oxygen

=> 0.5 mole of carbon will react with 0.5 mole of oxygen

hence oxygen consumed in the reaction = 0.5 mole = 16 gms

so oxygen left = 40 - 16 = 24 gms

% of oxygen left = 24 x 100/40 = 60%

Hence 60% of oxygen will be left.