Calculate the mass of calcium carbonate present in a 50.00 ml sample of an aqueous calcium carbonate standard, assuming the standard is known to have a hardness of 75.0 ppm (hardness due to caco3). also given is the density of the sample (0.9977g/ml) and the molar mass of caco3 (100.0g/mol).

Given the volume and density of the sample, we can calculate its mass.
mass = density * volume
mass = 0.9977 * 50
mass = 49.885 g
75 ppm Calcium Carbonate means that when there is 75 parts of Calcium Carbonate every one million parts of standard. Let one part be one gram.
So,
75 × 10⁻⁶ g CaCO₃ every gram of standard
grams of standard = .49.885
mass of CaCO₃ = 3.74 × 10⁻³ grams

The third choice .. (:

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