[Tempeste1204]

What is the mass of potassium oxide produced when 9.75g of potassium is burnt completely in the oxygen?

I got the answer 11.75g but the book says its 23.5g
The attachment below is my calculation and the other is the calculation my friend provided me. Which one is correct?

[thetada]

I'm reluctant to say the book is wrong but your calculation looks better. Your friend hasn't considered the stoichiometry whereas you have. Maybe you could Google the book to see if anyone else has had problems with it.

[Hunter2]

The book and also the calculation of your friend is wrong. Correct is 11,75 g.

In your friend calculation it is not considered that  potassiumoxide has two potassium atoms.

The 0,25 mol potassium is correct. But 1 mol K correspond to 0.5 mol K₂O, what means the calculation must be (39+39+16) g/mol x 0,25 mol/2 = 11,75 g

But this exercise is anyway akademic, because potassiumoxide can not be obtained by burning of potassium. The products are potassium peroxide K₂O₂ and potassium suboxide KO₂.

[Tempeste1204]

Thank you guys, really appreciate it ! 

[Borek]

Technically neither of these answers is correct. Potassium reacting directly with air oxygen doesn't produce K₂O, but rather a mixture of K₂O₂ and KO₂.

[Hunter2]

What I already described above.

[Tempeste1204]

Forgot to mention that the equation given was provided by the book.Just want to know which person did it correctly