dilutions, solution stoichiometry and titrations copyright © 2008 pearson prentice hall,...
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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