A sample of hard water contains 20 mg of `Ca^(2+)` ions per litre. How many milliequivalents of `Na_(2)CO_(3)` would be required to soften 1 litre of sample ?

Explanation

To solve the problem of how many milliequivalents of `Na2CO3` are required to soften 1 liter of hard water containing 20 mg of `Ca^(2+)` ions, we can follow these steps:

### Step 1: Write the Reaction
The first step is to write the chemical reaction that occurs when `Na2CO3` reacts with `Ca^(2+)` ions:
\[ \text{Ca}^{2+} + \text{Na}_2\text{CO}_3 \rightarrow \text{CaCO}_3 + 2\text{Na}^+ \]

### Step 2: Determine Molar Masses
Next, we need to find the molar masses of `Ca` and `Na2CO3`:
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