Dilutions, Solution Stoichiometry and

Titrations

Copyright © 2008 Pearson Prentice Hall, Inc. Chapter 1/1

Copyright © 2008 Pearson Prentice Hall, Inc. Chapter 3/2

Diluting Concentrated Solutions

dilute solutionconcentrated solution + solvent

Mi Vi = Mf Vf

finalinitial

Since the number of moles of solute remains constant, all that changes is the volume of solution by adding more solvent.

Copyright © 2008 Pearson Prentice Hall, Inc. Chapter 3/6

Diluting Concentrated Solutions

Add 6.94 mL 18.0 M sulfuric acid to enough water to make 250.0 mL of 0.500 M solution.

Mi = 18.0 M Mf = 0.500 M

Vi = ? mL Vf = 250.0 mL

= 6.94 mL18.0 M

250.0 mLVi = Mi

Mf Vf 0.500 M=

Sulfuric acid is normally purchased at a concentration of 18.0 M. How would you prepare 250.0 mL of 0.500 M aqueous H2SO4?

x

Why?

Copyright © 2008 Pearson Prentice Hall, Inc. Chapter 3/11

Solution Stoichiometry

aA + bB cC + dD

Moles ofA

Volume ofSolution of A

Moles ofB

Volume ofSolution of B

Mole Ratio Between A

and B (Coefficients)

Molar Mass of B

Molarity of A

Copyright © 2008 Pearson Prentice Hall, Inc. Chapter 3/12

Solution Stoichiometry

H2SO4(aq) + 2NaOH(aq) Na2SO4(aq) + 2H2O(l)

What volume of 0.250 M H2SO4 is needed to react with 50.0 mL of 0.100 M NaOH?

Moles ofH2SO4

Volume ofSolution of H2SO4

Moles ofNaOH

Volume ofSolution of NaOH

Mole Ratio Between H2SO4

and NaOH

Molarity of NaOH

Molarity of H2SO4

Copyright © 2008 Pearson Prentice Hall, Inc. Chapter 3/13

Solution Stoichiometry

H2SO4(aq) + 2NaOH(aq) Na2SO4(aq) + 2H2O(l)

2 mol NaOH

1 mol H2SO4

0.250 mol H2SO4

1 L solution

1 L

0.100 mol

1 L

1000 mL

= 0.00500 mol NaOH

Volume of H2SO4 needed:

1000 mL

1 L

10.0 mL solution (0.250 M H2SO4)

0.00500 mol NaOH

50.0 mL NaOH

Moles of NaOH available:

x

x

x

x x

Copyright © 2008 Pearson Prentice Hall, Inc. Chapter 3/25

Titration

How can you tell when the reaction is complete?

HCl(aq) + NaOH(aq) NaCl(aq) + 2H2O(l)

Titration: A procedure for determining the concentration of a solution by allowing a carefully measured volume to react with a solution of another substance (the standard solution) whose concentration is known.

Once the reaction is complete you can calculate the concentration of the unknown solution.

Copyright © 2008 Pearson Prentice Hall, Inc. Chapter 3/26

Titration

unknown concentration solutionErlenmeyerflask

buret standard solution(known concentration)

An indicator is added which changes color once the reaction is complete

Copyright © 2008 Pearson Prentice Hall, Inc. Chapter 3/31

Titration

HCl(aq) + NaOH(aq) NaCl(aq) + 2H2O(l)

48.6 mL of a 0.100 M NaOH solution is needed to react with 20.0 mL of an unknown HCl concentration. What is the concentration of the HCl solution?

Moles ofNaOH

Volume ofSolution of NaOH

Moles ofHCl

Volume ofSolution of HCl

Mole Ratio Between NaOH

and HCl

Molarity of HCl

Molarity of NaOH

Copyright © 2008 Pearson Prentice Hall, Inc. Chapter 3/32

Titration

HCl(aq) + NaOH(aq) NaCl(aq) + 2H2O(l)

20.0 mL solution

0.00486 mol HCl= 0.243 M HCl

Concentration of HCl solution:

Moles of NaOH available:

1 L

0.100 mol= 0.00486 mol NaOH

48.6 mL NaOH

1000 mL

1 L

Moles of HCl reacted:

1 mol NaOH

1 mol HCl= 0.00486 mol HCl

0.00486 mol NaOH

1 L

1000 mL

x

x

x

x

H12 – C3

• 3.19, 3.20, 3.22, 3.87*, 3.89, 3.91*, 3.93*, 3.120*