Let's solve this step by step.
---
Given Reaction:
$$
\text{Na}_2\text{SO}_4 + \text{CaCl}_2 \rightarrow \text{CaSO}_4 + 2\text{NaCl}
$$
Given Data:
- Mass of Na₂SO₄ = 40 g
- Mass of CaCl₂ = 35 g
- Mass of CaSO₄ produced = 20 g
- Find: Mass of NaCl formed = ?
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Step 1: Use the Law of Conservation of Mass
In a chemical reaction,
mass is conserved. That means:
> Total mass of reactants = Total mass of products
So:
$$
\text{Mass of Na}_2\text{SO}_4 + \text{Mass of CaCl}_2 = \text{Mass of CaSO}_4 + \text{Mass of NaCl}
$$
Plug in the known values:
$$
40\, \text{g} + 35\, \text{g} = 20\, \text{g} + x
$$
$$
75\, \text{g} = 20\, \text{g} + x
$$
Now solve for $x$:
$$
x = 75\, \text{g} - 20\, \text{g} = 55\, \text{g}
$$
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✔ Answer: 55 grams of NaCl are formed.
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Explanation:
Even though we're given a balanced chemical equation, and you might think stoichiometry is needed, the problem gives
actual masses of all reactants and one product, and asks for the other product. So,
conservation of mass is sufficient here.
The total mass of reactants is 75 g. One product (CaSO₄) is 20 g, so the remaining mass must be NaCl → 55 g.
---
Note:
This assumes that
all reactants are completely consumed and the reaction goes to completion — which is implied by the data provided.
✔ So,
55 grams of NaCl are formed.
Parent Tip: Review the logic above to help your child master the concept of law of conservation of mass example problems.
