Solutions Part II: Units of Concentration loosely from Chap' 12 Sec 5 of Brady

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SolutionsPart II Units of Concentration(loose
ly from Chap. 12 Sec 5of Brady Senese)

• Dr. C. Yau
• Fall 2009

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Units of Concentration
Molarity (M) Molality (m) Mass ppt, ppm,
ppb Mole fraction mole
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Mass Percent

• 15 w/w ?
• What does w/w mean?
• What is ppt? ppm? ppb?

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Example 12.2 p.492
Please dont waste time copying the question.
You can get it later from your textbook. Seawater
is typically 3.5 sea salt and has a density of
about 1.03 g mL-1. How many grams of sea salt
would be needed to prepare enough seawater
solution to completely fill a 62.5 L aquarium?
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Molality vs Molarity
Make sure you know EXACTLY what the difference is
between m and M! Know WHEN m is almost the same
as M...under what conditions?
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Ex 12.3 p.493
An experiment calls for a 0.150 m solution of
sodium chloride in water. How many grams of NaCl
would have to be dissolved in 500.0 g of water to
prepare a solution of this molality?
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Mole fraction mole percent

• You should have come across mole fraction when
  you studied the chapter on gases back in Gen Chem
  I. This is no different.
• How do you change mole fraction to mole percent?
• Remember that percent should always be thought of
  as part over whole x 100.
• Part over whole is a fraction. So you multiply
  mole fraction by 100 and you have by moles.

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Interconversion of Units of Concentration
Example 12.4 p. 494 What is the molality of 10.0
w/w aqueous NaCl?
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Example 12.5 p. 495

• A certain supply of concentrated hydrochloric
  acid has a concentration of 36.0 HCl. The
  density of the solution is 1.19 g mL-1. Calculate
  the molar concentration of HCl.

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p.514 12.44

• What is the molality of NaCl in a solution that
  is 3.000 M NaCl, with a density of 1.07 g mL-1?