Question

Orthophosphate sample IDs: #1 phosphate 1 #2 P 107 (orange) wavelength used 622 nm VOLUME WATER (ML) VOLUME STANDARD OR SAMPLE (ml) CONCENTRATION OF SAMPLE (ppm, ug/mL) ABSORBANCE 10 0 0.0946 standards 0.1504 0.2689 1.2 0.5151 | 10 10 0.6249 0.4571 2.1 sample - sample 2 DOT 8.1 0.95 1.678 0.2144 * Only do the 1/10th dilution if the original sample was over 3 ppm concentration Analysis 4a. (See page 89.). As seen in the data table, Sample 1 had a phosphate concentration of 2.1 ppm Convert this concentration from ppm units to molar concentration (in units of moles/L).

Answer 1

2.1 ppm= 2.1 grams (g) solute per 106 g solution= 2.1 milligrams (mg) solute per 1000 g solution= 2.1 mg solute per 1 L solution

(assuming density ~1 g/mL, since concentration is too small)

Therefore,

2.1 ppm= 2.1 mg solute per 1 L solution= 0.0021 g solute per 1 L solution

Dividing by the molar mass of phosphate for converting it to moles,

2.1 ppm= 0.0021/94.9= 0.000022 moles per 1 L solution= 22 micromoles per 1 L solution

Hence, in units of moles/L, 2.1 ppm equals 22*10-6 moles/L.