Multiple choice

By the reaction of carbon and oxygen, a mixture of $CO$ and $CO_{2}$ is obtained. The mass ratio of the mixture obtained when $20$ g of $O_{2}$ reacts completely with $12$ g of carbon is:

  1. $m_{CO}: m_{CO_{2}} = 21:11$
  2. $m_{CO}: m_{CO_{2}} = 11:21$
  3. $m_{CO}: m_{CO_{2}} = 22:14$
  4. $m_{CO}: m_{CO_{2}} = 14:22$
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AI explanation

Divide the carbon and oxygen into two simultaneous reactions where x moles of carbon become CO and y moles become CO2, based on the given masses of 12 grams of carbon (1 mole) and 20 grams of oxygen (1.25 moles). This establishes the system of equations x + y = 1 and x + 2y = 1.25. Solving this system gives x = 0.75 moles of CO and y = 0.25 moles of CO2. Multiplying by their respective molar masses of 28 and 44 gives a mass of 21 grams of CO and 11 grams of CO2, establishing the ratio 21:11.

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