In an experiment, potassium chlorate decomposed according to the following chemical equation. KClO3 → KCl + O2

(Molar mass of KClO3 = 122.5 g/mol; KCl = 74.55 g/mol; O2 = 31.998 g/mol)

If the mass of potassium chlorate was 240 grams, which of the following calculations can be used to determine the mass of oxygen gas formed?

(240 × 2 × 31.998) ÷ (122.5 × 3) grams
(240 × 3 × 31.998) ÷ (122.5 × 2) grams
(240 × 2 × 122.5) ÷ (31.998 × 3) grams
(240 × 3 × 122.5) ÷ (31.998 × 2) grams

In the experiment the potassium and chlorate decompose as per the chemical equation of KClO3 → KCl + O2.

Learn more about the potassium chlorate decomposed according.

link.

(240 × 3 × 31.998) ÷ (122.5 × 2) grams

Explanation:

To solve this problem, it is best to use the mole concept approach. Here find the number of moles of the given specie and use it to find that of the unknown.

Then convert the number of moles of the unknown to mass.

     Number of moles  =  

  Mass = number of moles x molar mass

Mass of potassium chlorate = 240g

The balanced reaction equation is given as:

              2KClO₃  →  2KCl  +  3O₂

Number of moles of KClO₃  =  

     Mole ratio:

              2 mole of KClO₃  will produce 3 moles of O₂

             mole of KClO₃ will produce   x 3 / 2 mole of O₂

So, mass of oxygen;

        Mass  =   x 3 / 2   x 31.998  =    x 3 x  x 31.998

 This gives (240 × 3 × 31.998) ÷ (122.5 × 2) grams

i believe you are right for all except the 3rd ( look at sqdancefan his answer is much better)

b is the correct answer

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