A 0.1430 g sample of copper was dissolved in 20 ml of 6 mol/L HNO_3 and diluted

Question

A 0.1430 g sample of copper was dissolved in 20 ml of 6 mol/L HNO_3 and diluted to 100.0 mL in a volumetric flask. What is the concentration of copper in g/L in the flask? The solution prepared in Q .1 was diluted one hundred times Now what is the concentration of copper in units of g/L? The standards were then prepared as described in the procedure and a 5 mL aliquot of unknown was pipetted into each of them. The intercept on the x axis was -4.12mL' How many grams of copper were introduced in the 5 mL addition to each standard? What is the original concentration of Cu in the unknown in g/L? What is the original concentration of the unknown in ppm**. This means that there is exactly as much copper in 4.12 mL of standard as there is in 5 mL of unknown. ** In dilute aqueous solution 1 ppm = 1 mg/L

Explanation / Answer

Q1)

note that all moles of Copper remain, since they change from:

Cu(s) = Cu+2(aq)

so...

C = mass/Volume

C = (0.143 g) / (100 mL) = 1.43 gL

Q2.

diluted 100 times means---

Cnew = 1/100*C1 = 1.43/100 = 0.0143 g/L

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