CHEM 1405

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CHEM 1405

• Class Meeting 18

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Assignments and Reminders

• Reading Assignment
• Chapter 9 by Thursday April 6th
• Homework Problems due Thursday Mar 30th
• Chapter 8 Problems 1 through 29 except 3 and
  4
• Possible quiz on Thursday
• EXAM III week of April 4th
• Coverage Chapter 7 and 8
• Class website
  http//iws.ccccd.edu/jstankus/

Next week!
Please use only one side of the page when
submitting Homework
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Chemistry Help Resources

• My office hours
• Tuesdays after class in Lecture room
• Thursdays 1-2 in Math Lab
• Free Tutoring through college
• Students must submit a tutor request form in
  order to receive detailed information about the
  available tutoring services.  The form is
  available on Collin's website and in the
  following offices
• CPC room A108 (ask for Sonia Castillo)
• PRC room F109 (ask for Shontel Penny or Mary
  Eldridge)
• SCC rooms G200 and G141
• There are group tutoring services available for
  the following courses (SUBJECT TO CHANGE!)
• CHEM 1405, 1411, 1412, 2423,
•  
• Also available will be online tutoring in the
  following courses (SUBJECT TO CHANGE!)
• CHEM 1412 below

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Objectives

• 1. What are different ways of expressing the
  concentration of a solution? When is each used?

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Solutions

• Solutions are homogeneous mixtures of two or more
  substances
• Homogeneous thoroughly mixed, even composition
  throughout
• Solute substance being dissolved
• Solvent substance doing the dissolving

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Quantities of Solutes in Solution

• A dilute solution is one that contains relatively
  little solute in a large quantity of solvent.
• A concentrated solution contains a relatively
  large amount of solute in a given quantity of
  solvent
• A saturated solution contains the maximum amount
  of solute that can be dissolved in a particular
  quantity of solvent at equilibrium at a given
  temperature.

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Solution Concentrations

• Need something more specific than concentrated
  and dilute
• Molarity
• Percent concentration
• Mass/Volume Percent

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Molarity

• Molarity is an expression of the concentration of
  a solution in moles of solute per liter of
  solution.

Remember
A solute is a solution component that is
dissolved in a solvent.
The solvent is the solution component) in which
one or more solutes are dissolved to form the
solution
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Molarity Example

• Calculate the molarity of a solution made by
  dissolving 0.165 moles of sodium sulfate (Na2SO4)
  in enough water to form 0.500 L of solution

Read as 0.330 molar sodium sulfate
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Molarity Example (2)

• Calculate the molarity of a solution made by
  dissolving 6.00 moles of Hydrogen Chloride (HCl)
  in enough water to form 2.50 L of solution

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Molarity Examples

• Molarity of 0.00700 mol of Li2CO3 in 10.0 mL of
  solution
• First convert to liters of solution

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Molarity Examples

• 11. Calculate the molarity of each of the
  following solutions.
• a. 8.90 g of H2SO4 in 100.0 mL of solution
• First we need to know how many moles of H2SO4 we
  have
• Find Molar Mass of H2SO4
• H 2 x 1.00794 g/mol 2.016 g/mol
• S 1 x 32.066 g/mol 32.066 g/mol
• O 4 x 15.9994 g/mol 63.998 g/mol
• Molar mass of H2SO4 98.080
  g/mol

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Molarity Examples

• b. 439 g of C6H12O6 in 1.25 L of solution
• First we need to know how many moles of C6H12O6
  we have
• Find Molar Mass of C6H12O6
• C 6 x 12.0107 g/mol 72.0642 g/mol
• H 12 x 1.00794 g/mol 12.0953 g/mol
• O 6 x 15.9994 g/mol 95.9964 g/mol
• Molar mass of C6H12O6
  180.1559 g/mol
• Find moles of C6H12O6

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Molarity Example (continued)
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Molarity Examples

• How many grams of solute are needed to prepare
  each of the following solutions?
• a. 2.00 L of 1.00 M NaOH
• First we need to know the mass of one mole of
  NaOH
• Find Molar Mass of NaOH
• Na 1 x 22.989770 g/mol 22.9898 g/mol
• H 1 x 1.00794 g/mol 1.0079 g/mol
• O 1 x 15.9994 g/mol 15.9994 g/mol
• Molar mass of NaOH 39.9971 g/mol

Board
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Molarity Examples

• What volume of 6.00 M NaOH is required to contain
  1.25 mol of NaOH?

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Percent Concentrations

• Sometimes it is more convenient to express
  concentrations by percentages
• Percent by Volume
• Percent by mass

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Percent Composition Examples

• What is the percent by volume of a solution made
  by dissolving 235 mL of ethanol in enough water
  to make exactly 500 mL of solution?

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Volume Percentage Example

• Describe how to make 775 mL of a 40.0 by volume
  solution of acetic acid.
• Solve for Volume of solute
• Volume of solute ( by volume) x (Volume of
  solution)
• 
  100
• Volume of solute (40.0 soln) x (775 mL soln)
• 
  100
• Volume of solute 310 mL of acetic actic
• Take 310 mL of acetic acid and add enough water
  to make 775 mL of solution

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Volumetric Glassware

• Glassware designed for precisely making specific
  concentrations of solutions

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Mass Percentage Example

• What is the percent by mass of a solution of 25.0
  g of NaCl dissolved in 475 g (475 mL) of water?.
• First find total mass of solution
• mass of solution 25.0 g of NaCl 475
  g of water
• 500. g

5.00 NaCl solution
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Mass Percentage Example

• Describe how to prepare 275 g of an aqueous
  solution that is 5.50 glucose by mass.
• Solve for mass of solute
• Mass of solute ( by mass) x (Mass of solution)
• 
  100
• Mass of solute (5.50(mass) soln of glucose) x
  (275 g of soln)
• 
  100
• Mass of solute 15.1 g of glucose
• Mass of solvent needed Mass of solution Mass
  of solute
• 275 g 15.1 g 260 g of water
• Take 15.1 g of glucose and dissolve in 260 g of
  water

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Mass/Volume Percent

• Mass/volume percent is an expression of
  concentration in which the mass of the solute is
  divided by the volume of the solution and that
  quotient multiplied by 100.
• Used in medicine

In medical applications mg/dL
milligrams/deciliter is commonly used
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Mass/Volume Percent

• For dilute aqueous solutions
• Mass/Volume percent is close to Mass/Mass percent
• This is because the density of a dilute aqueous
  solution is approximately 1 g/mL

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Extremely Dilute solutions

• For extremely dilute solutions
• Concentrations expressed as
• Parts per million (ppm)
• Parts per Billion (ppm)
• Parts per trillion (ppt)
• 1 ppm is 1 mg/L

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Saturation Solubilities

• Curve gives maximum amount of solute dissolved at
  given temperature
• Most solubilities of ionic solids increase with
  Temperature