Question

water sample was found to have 14 mg caco₃ in a 100.0 ml sample. calculate the concentration of caco₃ in units of grains per gallon.
concentration of caco₃ = gpg
what is the hardness classification based on the scale given in table 1 of the lab procedure?
○ moderately hard
○ very hard
○ hard
○ slightly hard
○ soft

Explanation:

Step1: Convert mL to gallons

We know that 1 gallon = 3785.41 mL, so 100.0 mL = $\frac{100.0}{3785.41}$ gallons $\approx 0.0264172$ gallons

Step2: Convert mg to grains

1 grain = 64.79891 mg, so 14 mg = $\frac{14}{64.79891}$ grains $\approx 0.21605$ grains

Step3: Calculate gpg concentration

Concentration (gpg) = $\frac{\text{Total grains}}{\text{Total gallons}}$
$\text{Concentration} = \frac{0.21605}{0.0264172} \approx 8.18$ gpg

Step4: Classify water hardness

Standard water hardness scale: Soft (0-1 gpg), Slightly hard (1-3.5 gpg), Moderately hard (3.5-7 gpg), Hard (7-10.5 gpg), Very hard (>10.5 gpg). 8.18 gpg falls in the hard range.

Answer:

Concentration of $\text{CaCO}_3$ = 8.18 gpg
hard