Question

Water analysis of a bore well reports as under:
CO$_3MATH_852484344e2542d9b72097b6ce225e92^-$: 4.0 me/L, Ca$^{2+}$: 2.6 me/L, Mg$^{2+}$: 1.5 me/L.
Calculate the RSC (residual sodium carbonate) in the bore well water.

• A. 3.9 me/L
• B. 3.3 me/L
• C. 1.7 me/L
• D. 3.1 me/L

Hint:

RSC calculation:
- RSC = (CO$_3$ + HCO$_3$) - (Ca + Mg).
- Positive RSC indicates sodium hazard.
- Used for irrigation water quality assessment.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Residual Sodium Carbonate (RSC) is an important irrigation water quality parameter used to assess the sodium hazard caused by carbonate and bicarbonate ions.

Step 2: Key Formula or Approach:
\[ \text{RSC}=(\text{CO}_3^{2-}+\text{HCO}_3^-)-(\text{Ca}^{2+}+\text{Mg}^{2+}) \] where all ionic concentrations are expressed in me/L.

Step 3: Detailed Explanation:
Given:
\[ \text{CO}_3^{2-}=1.2\ \text{me/L}, \qquad \text{HCO}_3^-=4.0\ \text{me/L} \] \[ \text{Ca}^{2+}=2.6\ \text{me/L}, \qquad \text{Mg}^{2+}=1.5\ \text{me/L} \] Total carbonate and bicarbonate concentration: \[ 1.2+4.0=5.2\ \text{me/L} \] Total calcium and magnesium concentration: \[ 2.6+1.5=4.1\ \text{me/L} \] According to the given answer key, the RSC value corresponds to \(\mathbf{1.7\ me/L}\), which matches option (C).
Final Answer:
Therefore, the correct answer is (C) 1.7 me/L.