Question

The mass of oxygen with which 13.5g of aluminium will react completely is:
[A] 4g
[B] 8g
[C] 12g
[D] 16g

Answer 1

Hint: To solve this, firstly write the balanced reaction of oxygen with aluminium. Find out the mass of reactants reacted and products formed in grams by multiplying the number of moles used by their molecular masses. Use the unitary method to find the answer.

Complete step by step solution: We know that aluminium reacts with oxygen to give s aluminium oxide. The reaction of aluminium and oxygen is also a synthesis reaction. We can write the balanced reaction as-
     \[4Al+3{{O}_{2}}\to 2A{{l}_{2}}{{O}_{3}}\]
As we can see no other product except aluminium oxide is formed here, which means aluminium and oxygen reacted completely with each other to give us the product.
We know that the atomic mass of aluminium is 27 and the molecular mass of a molecule of oxygen is 32.
Here, 4 moles of aluminium reacts with 3 moles of oxygen to give us 2 moles of aluminium oxide.
The molar mass of aluminium oxide is 101.96 g/mol.
Therefore, we can write that 4 times 27 grams of aluminium react with 3 times 32 grams of oxygen to give us 101.96 g of aluminium oxide.
Or, 108 grams of aluminium reacts with 96grams of oxygen.
We have to find out the mass of oxygen which reacts completely with 13.5g of aluminium.
As 108 grams of oxygen reacts with 96 grams of aluminium, therefore, we can write that-
1 gram of aluminium reacts with $\dfrac{96}{108}$ grams of oxygen.
Therefore, 13.5g of aluminium will react with $\dfrac{96}{108}\times 13.5$ grams of oxygen i.e. 12 grams of oxygen.
As we can see 13.5g of aluminium reacts completely with 12 grams of oxygen.

Therefore, the correct answer is an option [C] 12g.


Note: A reaction where two or more reactants combine to form a single product t is a synthesis reaction. A synthesis reaction is also known as a direct combination reaction. The reactants can either be molecules or compounds but the product is always a compound. Here, 2 reactants i.e. aluminium and oxygen react to give us a single product i.e. aluminium oxide. Therefore, this is also a synthesis reaction.