Please show work. How much systematic error is introduced by the determination o
ID: 817335 • Letter: P
Question
Please show work.
How much systematic error is introduced by the determination of the lead content of seawater due to the lead impurities in HC1 that is used to acidify the sample before atomic absorption measurement? Assumption: The sea water lead concentration is 40 ng Pb/kg seawater. The density of seawater is 1.025 g/cm3 Protocoll: 60 ml seawater is acidified with 1 ml HC1 before the measurement. For this task highest quality HC1 is used (Merck suprapure). The label on the Merck HC1 claims 0.005 ppm lead impurity. ppm means: parts per million or fig/g; i.e., 1.0 ppm lead impurity means 1.0 pg lead in 1.0 g HC1. The density (rho hcl) degree of the HC1 is 1.15 g/cm3.Explanation / Answer
so, in sodium acetate solution , we have 0.05 ppm of lead impurity,
so in 1 kg of sodium acetate salt , we have 0.05 mg of lead.
in 1000 gms of sodium acetate salt , we have 0.05 mg of lead.
In 1 gm of sodium acetate salt , we have 0.00005 mg of lead.
so, in 10 ml , 1 mol/L sodium acetate solution , we have 10 *0.001 = 0.01 moles of sodium acetate
weight of 0.01 moles of sodium acetate = 0.01 * 82.03 = 0.8203 gms.
so, in 0.8203 gms of sodium acetate , we have 0.8203 * 0.00005 mg of lead = 0.000041015 mg
In 1 ml of blood we have 300 ng of lead.
here we are adding an additional 0.000041015 mg of lead = 41.015 ng of lead.
so error = 41.015 ng .
percentage error = (41.015)/(300) * 100 = 13.67166 %