Question - Suppose you want to test for the presence of lead coming from two dif
ID: 904151 • Letter: Q
Question
Question - Suppose you want to test for the presence of lead coming from two different sinks in your home. Thinking about the techniques learned in this experiment and in previous experiments how would you test?
A.) Whether lead was present or not? Be specific;
B.) Which sink had more lead per liter? Be specific about the procedures you would use.
C.) Suppose the concentration of lead in your sink water is very low. How could you increase its concentration in the samples you are testing so that the lead concentration is easier to detect? Be Specifc..
Any Help would be greatly appreciated
The experiment we preformed this week was an oxygen and hydrogen reaction in a bottle, to create a small explosion. We also preformed/created a net ionic equations table with mystery solutions. Other than that, this is the whole question.. What other information is needed to help try and complete this problem, if any?
Explanation / Answer
a) Lead (II) ions form insoluble compounds with a number of anions. Lead (II) chloride is insoluble, as are lead (II) sulfate and lead (II) hydroxide. But, as there will be very little lead in a sample of water as we expect, you need to find the mist insoluble lead compound and use that anion.
For that we need to look at a table of Ksp values of various lead salts. The lead salt with the smallest Ksp will precipitate even at a very low concentration of Pb(II). If you check for Ksp values of all lead salts, it will be Lead(II) sulfide PbS with the least Ksp value of 3 x 10-28.
Now, just ass Na2S to the water from the sink and if there are any traces of Pb(II), then a black precipitate of PbS will be formed.
b) Take equal volumes of water from sink (say 2ml) and use equimolar Na2S salt to test Part a. Now, the sink having more lead per liter will have the higher amount of precipitation.
c) Suppose the concentration of lead in your sink water is very low. Then, you can use a certain volume of water and heat it to reduce the volume to half, say. Now, using M1V1=M2V2, as the volume is reduced to half, the concentration of salt Pb(II) will be increased to double the amount than the original soltuion. You can repreat this procedure till you get a observable amount of precipitation in the baove tests.