Question #9ecfa
1 Answer
Explanation:
The first thing to do here is to use the density of the water sample to determine its mass
#12.3 color(red)(cancel(color(black)("cm"^3))) * "1.00 g"/(1color(red)(cancel(color(black)("cm"^3)))) = "12.3 g"#
Now, in order to find the concentration of arsenic in parts per billion, you need to figure out how many grams of arsenic would be present in
Alternatively, you can say that a concentration of
In other words, all you need to do now is to use the known composition of the lake water to find how many nanograms of arsenic you have in
#1 color(red)(cancel(color(black)("g lake water"))) * overbrace("178.3 ng As"/(12.3color(red)(cancel(color(black)("g lake water")))))^(color(blue)("the given composition")) = "14.5 ng As"#
So, you now know that
#color(green)(bar(ul(|color(white)(a/a)color(black)("concentration As " = " 14.5 ppb")color(white)(a/a)|)))#
The answer is rounded to three sig figs.