**Passage 7:** mL of a water sample required mL of for titration of total and ions. Another mL requi — Redox Reactions and Volumetric Analysis Chemistry Question
Question
**Passage 7:** $100$ mL of a water sample required $10$ mL of $0.01 M$ $Na_2EDTA$ for titration of total $Ca^{2+}$ and $Mg^{2+}$ ions. Another $100$ mL required $6$ mL of the same $EDTA$ after precipitating $Mg^{2+}$. <br> **Q1:** The hardness due to $Ca^{2+}$ in ppm is:
Answer: A
💡 Solution & Explanation
**Step 1:** $1$ mole $EDTA \equiv 1$ mole $Ca^{2+}$. <br>**Step 2:** Moles $Ca^{2+} = 6 \times 0.01 / 1000 = 6 \times 10^{-5}$ in $100$ mL. <br>**Step 3:** Moles in $1$ L = $6 \times 10^{-4}$. <br>**Step 4:** Mass $CaCO_3 \text{ equiv} = 6 \times 10^{-4} \times 100 = 0.06$ g = $60$ mg/L = $60$ ppm.
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