Other Ways of Expressing the Concentration of Solutions percent concentration, ppm, ppb.
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Other Ways of Expressing the Concentration of Solutions percent concentration, ppm, ppb
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Transcript of Other Ways of Expressing the Concentration of Solutions percent concentration, ppm, ppb.
Other Ways of Expressing the Concentration of Solutions
percent concentration,
ppm, ppb
Percentage Concentration
Can be expressed as:
1. % mass/volume, or % m/v;
2. % mass/mass, or % m/m;
3. % volume/volume, or % v/v.
1. % mass/volume, or % m/v
% m/v = mass of solute (g)100 mL solution1
—or— mass of solute (g) * 100% vol of solution (mL)
1solution = solute + solvent
sample problem 1
What is the % concentration when 4.52 g KNO3 is dissolved in 250 mL of solution?
Answer:
(4.52 g/250 mL) * 100% = 1.81%
—or—4.52 g = ? g .
250 mL 100 mL
? = 1.81 g/100 mL or 1.81 %
sample problem 2
Na3PO4 is sold in hardware stores under the (incorrect) name “Trisodium phosphate”, or TSP.
A 1.7% (m/v) solution of TSP is recommended for cleaning walls before painting or putting up wallpaper.
What mass of TSP is needed to make 2.0 L of solution?
Answer: 1.7% (m/v) means
1.7 g per 100 mL or
? g per 2000 mL
cross-multiplying gives
? = (1.7 g * 2000 mL)/100 mL
= 34 gUse 34 g TSP to make 2.0 L of cleaning sol’n.
NB. Solutions of TSP are VERY BASIC.
Wear Gloves!!
2. % mass/mass, or % m/m
% m/m = mass of solute (g)100 g solution1
—or— mass of solute (g) * 100% mass of solution (g)
1solution = solute + solvent
sample problem 3
CaCl2 is often used as an ice-melter.
If 45.3 g of slush (snow, ice, CaCl2) was evaporated to yield 6.37 g CaCl2, calculate the % m/m CaCl2 in the slush.
Here, the slush represents the
solution.
Answer:
% CaCl2 = (6.37 g CaCl2/45.2 g slush)*100%
CaCl2 = 14.1 % (m/m)
3. % volume/volume, or % v/v
% v/v = volume of solute (mL)100 mL solution1
—or— volume of solute (mL) * 100%
volume of solution (mL)
1solution = solute + solvent
sample problem 4
Rubbing alcohol is a 70% (v/v) solution of isopropyl alcohol in water.
What volume of isopropyl alcohol is required to prepare 350 mL of rubbing alcohol?
Answer:
70 mL isopropyl alcohol = ? mL
100 mL rubbing alcohol 350 mL
? = (70 mL * 350 mL)/100 mL
= 245 mL isopropyl alcohol in 350 mL
Practical Application
The concentration of alcohol (ethanol) in alcoholic beverages is stated as % (v/v).
Regular beer is 5.0% (v/v) ethanol;
“lite” beer is 4.0% (v/v).Express the % ethanol in “lite” beer as % (m/v).
What information do you need?
Density of ethanol = 0.80 g/mL.
Answer:4.0% (v/v) =
4.0 mL ethanol/100 mL
We need to convert 4.0 mL ethanol mass.4.0 mL*(0.80 g·mL-1) = 3.2 g ethanol/100 mL
% ethanol (m/v) in “lite” beer = 3.2%
If you were the brewer, would you label % ethanol in “lite” beer as m/v or v/v?
ppm concentration*ppm =mass of solute * 106
mass of solution
or
mass of solute = . ? g .
mass of solution 106 g solution
(*parts per million—106)
ppb concentration*
ppb = mass of solute * 109
mass of solution
or
mass of solute = . ? g . mass of solution 109 g solution
(*parts per billion—109)
sample problem 5
Symptoms of mercury poisoning become apparent after the ingestion of more than 20 mg of Hg. For a 70 kg person, convert this to
a) % m/m
b) ppm
c) ppb
Answer:a) % m/m = (20 x 10-3 g/70 x 103 g) * 100%
= 2.9 x 10-5 is percent Hg in body
b) ppm = (20 x 10-3 g/70 x 103 g) * 106
= 0.29 ppm Hg
c) ppb = (20 x 10-3 g/70 x 103 g) * 109
= 2.9 x 102 ppb Hg
HW
P 371 to 377, do several problems from each set.
