Calculating alkalinity and expressing it in as CaCO3

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The discussion focuses on converting various ions' concentrations from milligrams per liter to milligrams per liter as CaCO3. The calculations for Ca2+, Mg2+, CO2, HCO3-, and CO32- show slight discrepancies when compared to textbook answers, attributed to differences in molar mass used. The calculated values for each ion are close to the book's figures, with differences generally below 0.1 mg/L. The user expresses concern over the accuracy of their results, seeking confirmation on the negligible nature of the differences. Overall, the conversation highlights the importance of precision in alkalinity calculations and the potential for minor variations in results.
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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-


Homework Equations





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
 
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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.
 
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