Question

How many grams of hydrogen peroxide (H2O2) are needed to form 32.8 grams of oxygen gas?

hydrogen peroxide (H2O2)(aq) ---> water(ℓ) + oxygen(g)

Answer 1

Step 1) Molecular formula of water is H₂O and moleculalr formula of gaseous oxygen is O₂.

So the reaction is

H₂O₂(aq) ---------------> H₂O(l) + O₂(g)

In this reaction H is balanced on both the side, but O is not balanced.  

O can be balanced by giving proper coefficient to O₂, The coefficient can be whole number 1,2,3... or

a fraction 1/2, 3/2, 5/2....

Here we can balance O by giving coefficient 1/2 to O₂, So we have

     H₂O₂(aq) ---------------> H₂O(l) + 1/2 O₂(g)

Multiplying both the side by 2 we have

   2*( H₂O₂(aq) ---------------> H₂O(l) + 1/2 O₂(g) )

    2 H₂O₂(aq) ---------------> 2 H₂O(l) + O₂(g). This is the balanced reaction.  

Step 2 : Convert 32.8grams of O₂ to moles.  

molar mass of O₂   = 31.998g/mole

32.8g O₂ x   1mole O₂ = 1.025mole of O₂.  

31.998g

So there are 1.025mole of O₂ in 32.8g O₂.  

Step 3 : Find the moles of H₂O₂ from moles of O₂ .

mole ratio of  H₂O₂ and O₂   from the balanced reaction is 2:1.  

1.025mole of O₂ x 2mole of H₂O₂ = 2.050mole of  H₂O₂  

1mole of  O₂ .  

So 2.050mole of H₂O₂ is formed from 1.025 moles of O₂  

Step 4 Convert 2..050mole of H₂O₂ to grams

Molar mass of  H₂O₂ = 34.014g/mole

2.050mole of  H₂O₂ x 34.014g  H₂O₂ = 69.73g  H₂O₂   

1mole of H₂O₂

So 69.7g of Hydrogen peroxide  is required to form 32.8grams of oxygen gas