Practice Questions on Reacting masses

Solve the following Practice Questions on Reacting masses using balanced Chemical equations

Q.1 20 g Magnesium ribbon is burnt in air with white light. Calculate the mass of Magnesium oxide (MgO) formed in this reaction.

Hint: Write the balanced chemical equation for the reaction between Mg and Oxygen gas.

2Mg(s) + O₂ (g) → 2MgO(s)

Use the Molar mass of Mg and MgO according to balanced equation and calculate the mass of MgO.

Mr of Mg= 24 g/mol

Mr of O = 16 g/ mol

So MgO = 24+16 = 40 g/mol

2Mg(24×2) + O₂ (g) → 2MgO(40×2)

So According to balanced equation,

48 g Mg forms MgO = 80 g

Hence 20 g Mg will form MgO = (20X80)/48

=33.33 g thus 20 g Mg will form 33.33 g MgO

We did not take Oxygen in to account because the Oxygen is not a limiting reactant and it is enough in the reaction.

Q2. 25 g Li₂O(s) is reacted with 100 cm^{3 of}  0.75mole/dm³  HCl solution as per below equation:

Li₂O+ 2HCl(aq) → 2LiCl (aq) + H₂O(l)

Calculate the amount of LiCl formed in the reaction.

Q3. 2.5 moles of MgO  reacts with  2.5 moles of HCl. Determine the limiting reactant and calculate the amount of  MgCl₂ formed in the reaction.

MgO(s) + 2HCl (aq) → MgCl₂(aq) + H₂O(l)

Q.4  150g Phosphorus reacts with 200 g Oxygen gas , determine the limiting reactant and calculate the mass of Phosphorus oxide(P₄O₁₀ ) formed in this reaction.

Read Mole concept.