Solvation is the process by which the solvent
molecules (often water) orient themselves around the solute (often a salt). During
the process, the solvent molecules have sufficient attraction for the
individual solute ions to break the ionic bond of the compound. The solvent
particles then surround the individual ions leading to the solid eventually
***NOTE: As you will no doubt be
required to explain the process in your own words, perhaps that becomes much
easier when you have a visual in mind.
Hopefully this video helps.***
First divide by 10^6 (to get rid of the ppm)….
3.5ppm / 10^6 = 3.5x10-6
This is the mass of Pb in grams
per 1 g of soln. We want the mass of Pb
per 25.0 grams of soln. So multiply by 25.0…
3.5x10^-6 g x 25.0 = 8.75 x 10^-5 g or 8.8
x 10^-5 g Pb if sigfigs are important
There are more than one type of percentage
designations for concentration (weight/weight, vol/vol, weight/vol). We’ll
assume weight per volume for this problem.
First use the def. of weight per
vol. (w/v) %...
mass solute (g) / vol soln (mL) x 100
Rearrange to solve for mass
(w/v) /100 x vol soln (mL) =
mass solute (g)
Plug n’ chug…
2.5 / 100 x 500 = 12.5 g NO3-
Finally we convert grams to mols.
The molar mass of nitrate is 62.004 g/mol…
12.5 g x (1 mol / 62.004 g) =
0.2015998 mols or if sigfigs are important = 0.2 mols NO3-
Convert 3.0 micro grams to grams…
3.0 x 10 -6 g
Divide by 20 g…
3.0 x 10^-6 g / 20 g = 1.5 x 10
Multiply by 10^9 to get ppb…
1.5 X 10^-7 x 10^9
= 150 ppb
or IF YOU USE THE FIVE-EVEN RULE
for rounding sigfigs… 200 ppb