---
title: "Non-carbonate hardness: TH 150, CH 60"
subject: "Water Supply Engineering"
chapter: 4
key: "semester_5/water_supply_engineering:hardness-c72"
source: https://www.bctengineer.com/q/semester_5/water_supply_engineering/hardness-c72
site: BCT Engineering
---

# Non-carbonate hardness: TH 150, CH 60

Water Supply Engineering · Chapter 4: Quality of Water

- Asked in: 2072 Chaitra, 4 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/water_supply_engineering/hardness-c72
- Whole chapter: https://www.bctengineer.com/md/semester_5/water_supply_engineering/chapter-4

## Question

The total hardness of water is 150 mg/l and carbonate hardness is 60 mg/l. All the three bi-valent metallic ions causing hardness are same. Determine the non-carbonate hardness, alkalinity and concentration of bi-valent metallic ions.

## Short answer

Non-carbonate hardness = 150 – 60 = 90 mg/L; alkalinity = 60 mg/L as CaCO3. Let equal concentration x of Ca, Mg, Sr; total hardness factor sum 7.752×x = 150, so x = 19.35 mg/L.

## Answer

Total hardness (TH) $= 150$ mg/l, carbonate hardness (CH) $= 60$ mg/l. The three bivalent metallic ions are taken as Ca$^{2+}$, Mg$^{2+}$ and Sr$^{2+}$ present in equal concentration $x$ mg/l (equivalent weights 20.04, 12.15 and 43.81).

#### Non-carbonate hardness
$$
\text{NCH} = \text{TH}-\text{CH} = 150-60 = 90\ \text{mg/l as CaCO}_3
$$

#### Alkalinity
Total hardness is greater than carbonate hardness, so all alkalinity is used in carbonate hardness: alkalinity = CH $= 60$ mg/l as CaCO$_3$.

#### Concentration of the bivalent ions
$$
\begin{aligned}
\text{TH} &= x\left(\frac{50}{20.04}+\frac{50}{12.15}+\frac{50}{43.81}\right) = x(2.495+4.115+1.141) = 7.752x = 150\\
x &= 19.35\ \text{mg/l}
\end{aligned}
$$

**Answer: NCH = 90 mg/l as CaCO$_3$; alkalinity = 60 mg/l as CaCO$_3$; each bivalent ion = 19.35 mg/l.**

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. NCH = TH - CH =
   A. 90 mg/l
   B. 210 mg/l
   C. 60 mg/l
   D. 150 mg/l
   Answer: A. 150 - 60. (Key point: NCH)

2. Since TH > CH, alkalinity equals:
   A. TH = 150
   B. CH = 60 mg/l
   C. NCH = 90
   D. 0
   Answer: B. All alkalinity is used as carbonate hardness. (Key point: Alkalinity)

3. Sum of 50/EW for Ca, Mg, Sr is:
   A. 6.610
   B. 2.495
   C. 7.752
   D. 4.115
   Answer: C. 2.495+4.115+1.141. (Key point: Equation)

4. Each ion = 150/7.752 =
   A. 50 mg/l
   B. 7.75 mg/l
   C. 30 mg/l
   D. 19.35 mg/l
   Answer: D. x = TH/7.752. (Key point: Ion conc)

## Close variants set in other exams

- [Non-carbonate hardness: TH 160, CH 70](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Ahardness-b78) — Water Supply Engineering, chapter 4, asked 2×

## Related in Water Supply Engineering

- [Alkalinity and Ca, Mg: TH 280, CH 75](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Ahardness-s73) — Water Supply Engineering, chapter 4
- [Hardness with Ca, Mg, Sr equal, TH 150](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Ahardness-as70) — Water Supply Engineering, chapter 4
- [Ca and Mg concentration, NCH, alkalinity: TH 400 ppm](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Ahardness-bk79) — Water Supply Engineering, chapter 4
- [Ca and Mg concentration, alkalinity (300 mg/l hardness)](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Ahardness-ca-mg-equal-300) — Water Supply Engineering, chapter 4, asked 2×
- [Hardness of well water with strontium 25.26 mg/l](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Ahardness-bk81) — Water Supply Engineering, chapter 4