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Safe Amount Of Arsenic In Drinking Water

The standard for arsenic content in public water supplies is less than or equal to 10 parts per billion (ppb) arsenic. Assuming that this arsenic is present as arsenate ASO_{4}^{3-},

What mass of sodium arsenate would be present in a 1 L sample of drinking water that just meets the stadard?

**The strings**:

S_{7}P_{1}A_{15} (containership - mass).
**The math**:

Pj Problem of Interest is of type *containership* (mass).

1 ppb = 1μg/L = (1 x 10^{-6}) g /L

So, 10 ppb = 10 x 10^{-6} g/L

So, mass of arsenic in 1 L sample of drinking water = 10^{-5} g.

Molar mass of arsenic = 74.92 g

So mol of arsenic in 1 L = (1/74.92)(10^{-5}) = 0.01335 x 10^{-5} mol

Na_{2}AsO_{4} -------> 3Na^{+} + AsO_{4}^{3-}

Mole ratio Na_{3}AsO_{4}:AsO_{4}^{3-} = 1:1

So, mol of Na_{3}AsO_{4} in 1 L sample of drinking water = 0.01335 x 10^{-5} mol.

Molar mass of Na_{3}AsO_{4} =3x23 +74.92 + 4x16 = 69 + 74.92 + 64 = 207.92 g

So, mass of Na_{2}AsO_{4} in 1 L sample of drinking water = 207.92(0.01335)(10^{-5}) = 2.8 x 10^{-5} g of Na_{2}AsO_{4}.

Math

The *point* **.** is a mathematical abstraction. It has negligible size and a great sense of position. Consequently, it is front and center in abstract existential reasoning.

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