If a 11.5 cm3 sample of lake water is found to have 178.5 ng As, what is the concentration of arsenic in the sample in parts per billion (ppb), assuming that the density of the lake water is 1.00 g/cm3?
To find the concentration of arsenic in parts per billion (ppb), we need to convert the given values into the appropriate units and then use the formula for concentration.
First, we need to convert the volume of the sample from cubic centimeters (cm³) to liters (L). Since 1 cm³ is equal to 0.001 L, we can do the following calculation:
11.5 cm³ * (0.001 L / 1 cm³) = 0.0115 L
Next, we need to convert the mass of arsenic from nanograms (ng) to grams (g). Since 1 ng is equal to 0.000000001 g, we can do the following calculation:
178.5 ng * (0.000000001 g / 1 ng) = 0.0000001785 g
Now, we have the volume of the sample (0.0115 L) and the mass of arsenic (0.0000001785 g). To find the concentration in parts per billion (ppb), we can use the following formula:
Concentration (ppb) = (mass of solute / volume of solution) * 10^9
Plugging in the values, we get:
Concentration (ppb) = (0.0000001785 g / 0.0115 L) * 10^9
Calculating this will give us the concentration of arsenic in ppb.