Question

PO, 3- Oxygen (0) X PO, • H* ions PO 3- 02-02 Pb2+ Pb2+ Pbº water pipe Phosphate (yellow stars, PO3-) binds to lead pipe making protective layer. If phosphate is not continually added, Pbº is exposed to dissolved oxygen (O2). O2 oxidizes or steals electron from Pbº to make Pb2+ ions. Pb2+(OH)2 H0 1,0 Pb2+(OH)2 Pb2+ Pb2+ 02. picks up protons dissolved in H2O to make hydroxide ions (OH) and more H20. Pb2+ floats away in the drinking water as lead hydroxide, Pb(OH)2.

YOU ONLY NEED TO ANSWER THESE:

3. What is the molarity (M) of Pb2+ at 13,000 ppb

4. If we want to know how many ppb of Pb2+ at the same molarity can be found in a solvent other than water, say ethanol, CH3CH2OH, what piece of information do you need to look up to answer this question?

5. The molarity of Pb would be higher or lower in ethanol than in water?

Answer 1

Answer 3: The concentration of Pb2+ is given in 13,000 ppb (parts per billion)

This means, 1 g of Pb2+ per 1,000,000,000 g of solute

or 0.000001 g of Pb2+ per 1,000 g of solute

Therefore 13,000 ppb = 13000 x 0.000001 mg = 0.013 g is dissolved in 1 L of solution (0.013 g/L)

Hence molarity = 0.013 g/L / 207.20 g/mol =0.00062 mol / L

Answer 4: If we want to know the concentration of Pb2+ at ppb level in ethanol, we need to know the mass of ethanol as concentration in ppb means 1 g of Pb2+ per 1,000,000,000 g of solute. Thus in order to know the mass of ethanol, we need to know it's density to calculate it's mass in desired volume of ethanol.

Answer 5 Since the density of ethanol (0.79 g/L) is lower than the water (1.0 g/L), thus volume of ethanol in a given concentration will be larger than the water and consequently will have lower concentration.