The Foundations of Chemistry

A label that shows the analysis of

sulfuric acid.

3-7 Dilution of Solutions 107

Plan

The density of a solution, grams per milliliter, is numerically equal to its specific gravity, so
the density of the solution is 1.84 g/mL. The solution is 96.4% H 2 SO 4 by mass; therefore 100. g
of solution contains 96.4 g of pureH 2 SO 4. From this information, we can find the molarity of
the solution. First, we calculate the mass of one liter of solution.

Solution

1.84 103 g soln/L soln

The solution is 96.4% H 2 SO 4 by mass, so the mass of H 2 SO 4 in one liter is

1.77 103 g H 2 SO 4 /L soln

The molarity is the number of moles of H 2 SO 4 per liter of solution.

18.0 mol H 2 SO 4 /L soln

Thus, the solution is an 18.0 MH 2 SO 4 solution. This problem can also be solved by using a
series of three unit factors.



18.1 mol H 2 SO 4 /L soln 18.1 MH 2 SO 4

You should now work Exercise 68.

1 mol H 2 SO 4



98.1 g H 2 SO 4

96.4 g H 2 SO 4



100 g soln

1000 mL soln



L soln

1.84 g soln



mL soln

__? mol H 2 SO 4



L soln

1 mol H 2 SO 4



98.1 g H 2 SO 4

1.77 103 g H 2 SO 4



L soln

__? mol H 2 SO 4



L soln

96.4 g H 2 SO 4



100.0 g soln

1.84 103 g soln



L soln

__?g H 2 SO 4



L soln

1000 mL soln



L soln

1.84 g soln



mL soln

__? g soln



L soln

Problem-Solving Tip:Write Complete Units

A common pitfall is to write units that are not complete enough to be helpful. For in-

stance, writing the density in Example 3-19 as just doesn’t help us figure

out the required conversions. It is much safer to write , ,



96

1

.

0

4

0

g

g

H

s

2

o

S

ln

O 4

, and so on. In Example 3-19, we have written complete units to help

guide us through the problem.

1000 mL soln



L soln

1.84 g soln



mL soln

1.84 g



mL

DILUTION OF SOLUTIONS

Recall that the definition of molarity is the number of moles of solute divided by the
volume of the solution in liters:

molarity

Multiplying both sides of the equation by the volume, we obtain

volume (in L)molaritynumber of moles of solute

number of moles of solute



number of liters of solution

3-7

ANALYSIS

MAXIMUM LIMITS OF IMPURITIES

Appearance........Passes A.C.S. Test

Color (APHA)....................10 Max.

Residue after Ignition............4 ppm

Chloride (Cl)....................0.2 ppm

Nitrate (NO 3 )...................0.5 ppm

Ammonium (NH 4 ).................1 ppm

Substances Reducing KMnO 4 (limit about

2ppm as SO 2 ).........Passes A.C.S. Test

Arsenic (As)..................0.004 ppm

Heavy Metals (as Pb)..........0.8 ppm

Iron (Fe).........................0.2 ppm

Mercury (Hg).......................5 ppb

Specific Gravity...................~1.84

Normality.............................~36

Assay (H 2 SO 4 ) W/W...Min. 95.0%--Max. 98.0%

Suitable for Mercury Determinations

The small difference is due to

rounding.

See the Saunders Interactive

General Chemistry CD-ROM,

Screen 5.12, Preparing Solutions,

Dilution.