# Calculating alkalinity and expressing it in as CaCO3

• Jim4592
In summary, the conversation is about converting various substances from milligrams per liter as the ion to milligrams per liter as CaCO3. The speaker has performed calculations and is comparing their answers to the book's answers, noting slight differences due to different molar masses used. They conclude that the differences are negligible and within the expected precision for determining alkalinity experimentally.
Jim4592
Calculating alkalinity and expressing it in "as CaCO3"

## Homework Statement

Convert the following from milligrams per liter as the ion to milligrams per liter as CaCO3.

A) 83.00 mg/L Ca2+
B) 27.00 mg/L Mg2+
C) 48.00 mg/L CO2
D) 220.00 mg/L HCO3-
E) 15.00 mg/L CO32-

## The Attempt at a Solution

I think I did the calculations correctly, but there's a slight difference between my answer and the book's answer...I was hoping someone could look and see if I did the steps correctly and if so is it difference negligible?

A) (83.00 mg Ca{2+} / L) x (1 mmole Ca{2+} / 40.078 g) x (2 meq Ca{2+} / mmole Ca{2+}) x (100 mg CaCO3 / 2 meq) = 207.096 mg/L as CaCO3, book answer = 207.25

B) (27.00 mg Mg{2+} / L) x (1 mole Mg{2+} / 24.305 g) x (2 meq Mg{2+} / mmole Mg{2+}) x (100 mg CaCO3 / 2 meq) = 111.088 mg/L as CaCO3, book answer = 111.20

C) (48.00 mg CO2 / L) x (1 mmole CO2 / 44.0095 g) x (2 meq CO2 / 1 mmole) x (100 mg CaCO3 / 2 meq) = 109.067 mg/L as CaCO3, book answer = 109.18

D) (220 mg HCO3{-} / L) x (1 mmole HCO3{-} / 61.01684 g) x (1 meq / 1 mmole) x (100 mg CaCO3 / 2 meq) = 180.278 mg/L as CaCO3, book answer = 180.41

E) (15.00 mg CO3 / L) x (1 mmole CO3 / 60.0089 g) x (2 meq / 1 mmole) x (100 mg CaCO3 / 2 meq) = 24.996 mg/L as CaCO3, book answer = 25.02

Obviously book uses slightly different molar masses. I wouldn't care too much, differences are below 10-3, that's about as precise as you can determine alkalinity experimentally.

alright thank's borek, I thought I would be able to just write it off but that's the farthest off we've ever been, so I figured I'd ask for a second opinion.

## 1. What is alkalinity and why is it important to calculate it?

Alkalinity is a measure of the capacity of a solution to neutralize acids. It is important to calculate alkalinity because it can indicate the ability of a solution to resist changes in pH, which is crucial for maintaining a stable environment for living organisms.

## 2. How is alkalinity calculated?

Alkalinity is typically calculated by titrating a sample of the solution with a strong acid until the pH reaches a specific endpoint. The amount of acid required to reach the endpoint is then used to calculate the alkalinity in terms of CaCO3 equivalents.

## 3. What is the significance of expressing alkalinity in terms of CaCO3 equivalents?

Expressing alkalinity in terms of CaCO3 equivalents allows for easier comparison between different water samples. It also provides a common unit of measurement that is widely recognized and understood in the scientific community.

## 4. Can alkalinity be expressed in units other than CaCO3 equivalents?

Yes, alkalinity can also be expressed in units of milligrams per liter (mg/L) or parts per million (ppm). However, these units may not be as universally understood and can vary depending on the specific method of titration used.

## 5. How is alkalinity used in environmental and water quality assessments?

Alkalinity is an important parameter in assessing the health of aquatic ecosystems and the quality of drinking water. It can help determine the potential for acidification, the presence of certain ions, and the effectiveness of water treatment processes.

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