ENV-32

Total hardness as CaCO3

TH = 2.497 [Ca] + 4.118 [Mg] in mg/L as CaCO3.

Reading speed

Water chemistryAPHA 2340

Governing equation

\mathrm{TH}=2.497[\mathrm{Ca}]+4.118[\mathrm{Mg}]

where

[Ca]: Calcium (mg/L)
[Mg]: Magnesium (mg/L)
TH: Total hardness (mg/L as CaCO3)

Lecture brief

Historical brief

Streeter–Phelps (1925) oxygen sag, settling theory and Guldberg–Waage kinetics made water and air quality a rate problem. The lab computes sag, overflow and a snapshot of reactor mass balance. This sheet (ENV-32 — Total hardness as CaCO3) is the form associated with APHA 2340. Working symbols: $[Ca]$ , $[Mg]$ $\rightarrow$ $TH$ . Hardness is the equivalent CaCO3 of divalent cations. The factors convert mg/L Ca and Mg to mg/L CaCO3.

Purpose

Purpose: compute

TH

from

[Ca]

[Mg]

in Environmental via

\mathrm{TH}=2.497[\mathrm{Ca}]+4.118[\mathrm{Mg}]

TH = 2.497 [Ca] + 4.118 [Mg] in mg/L as CaCO3. Use it when a real environmental question must be answered in SI before a code check.

Live realistic example

In symbols

Live case. Given

[Ca] = 40.000\,\mathrm{mg/L}

[Mg] = 12.000\,\mathrm{mg/L}

, the governing relation

\mathrm{TH}=2.497[\mathrm{Ca}]+4.118[\mathrm{Mg}]

yields

TH = 149.3\,\mathrm{mg/L as CaCO3}

. A beaker, Ca and Mg bars, a hardness scale. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

Calcium [Ca]40 mg/LMagnesium [Mg]12 mg/L

Outputs

Total hardness TH149.3 mg/L as CaCO3

Reading speed

Watch on YouTube

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Narration of this film

A beaker, Ca and Mg bars, a hardness scale.

Hardness is the equivalent CaCO3 of divalent cations. The factors convert mg/L Ca and Mg to mg/L CaCO3.

Reading speed

Watch on YouTube