Solution Stoichiometry

1

• Solution Stoichiometry

2

• Solution Stoichiometry

3
Solution Concentration

• Relative amounts of solute and solvent.

• solute substance dissolved.
• solvent substance doing the dissolving.

There are several concentration units. Most
important to chemists Molarity
4
Molarity

Molarity

• V of solution not solvent.

M mol/L

• Shorthand NaOH 1.00 M

Brackets represent molarity of
5
Molarity

• Calculate the molarity of sodium sulfate in a
  solution that contains 36.0 g of Na2SO4 in 750.0
  mL of solution.

0.2534 mol
Unit change! mL ? L
Na2SO4 0.338 mol/L 0.338 M
6

• Solution Concentration Molarity
• What is the concentration of a solution made by
  dissolving 23.5 g NiCl2 into a volume of 250 mL?

7
Molarity

• 6.37 g of Al(NO3)3 are dissolved to make a 250.
  mL aqueous solution. Calculate (a) Al(NO3)3
  (b) Al3 and NO3-.

(a) Al(NO3)3 molar mass 26.98 3(14.00)
9(16.00)
8
Solution Preparation

• Solutions are prepared either by
• Diluting a more concentrated solution.
• or
• Dissolving a measured amount of solute and
  diluting to a fixed volume.

9

• Preparing Solutions Direct Addition
• How many grams of NiCl2 would you use to prepare
  100 mL of a 0.300 M solution?

10
Solution Preparation by Dilution

• MconcVconc MdilVdil

Example Commercial concentrated sulfuric acid is
17.8 M. If 75.0 mL of this acid is diluted to
1.00 L, what is the final concentration of the
acid?
Mconc 17.8 M Vconc 75.0 mL Mdil ? Vdil
1000. mL
1.34 M
11

• Preparing Solutions Dilution from a concentrated
  (stock) solution
• How many mL of a 2.60 M NiCl2 solution would you
  use to prepare 100 mL of a 0.300 M solution?

12
Solution Preparation from Pure Solute

• Prepare a 0.5000 M solution of potassium
  permanganate in a 250.0 mL volumetric flask.

Mass of KMnO4 required nKMnO4 KMnO4 x V
0.5000 M x 0.2500 L (M mol/L)
0.1250 mol
mKMnO4 0.1250 mol x 158.03 g/mol
19.75 g
13
Solution Preparation from Pure Solute

• Weigh exactly 19.75 g of pure KMnO4
• Transfer it to a volumetric flask.

• Rinse all the solid from the weighing dish into
  the flask.
• Fill the flask ? full.
• Swirl to dissolve the solid.

• Fill the flask to the mark on the neck.
• Shake to thoroughly mix.

14
Aqueous Solution Titrations
Buret volumetric glassware used for titrations.
Titrant Base of known concentration
Slowly add standard solution. End point
indicator changes color. Determine Vtitrant
added.
Unknown acid phenolphthalein (colorless in
acid)
turns pink in base
15

• Titrations This weeks lab
• Part 1. Standardizing a solution of base
• 23.8 mL of NaOH solution is used to neutralize
  1.020 g H2C2O4-2H2O. What is the concentration of
  the NaOH solution?

16

• Titrations This weeks lab
• Part 2. Determining the molar mass of an acid
• 35.2 mL of the same NaOH solution is used to
  neutralize 1.265 g of an unknown diprotic acid.
  What is the molar mass of the acid?

17
(No Transcript)
18
Molarity Reactions in Aqueous Solution

• nA A x V
• product nproduct / (total volume).

19
Molarity Reactions in Aqueous Solution

• What volume, in mL, of 0.0875 M H2SO4 is required
  to neutralize 25.0 mL of 0.234 M NaOH?

H2SO4(aq) 2 NaOH(aq) ? Na2SO4(aq) 2 H2O(l)
2.925 x 10-3 mol
20
Molarity Reactions in Aqueous Solution
H2SO4(aq) 2 NaOH(aq) ? Na2SO4(aq) 2 H2O(l)

• 0.002925 mol 0.00585 mol
• V? 25.0 mL

Vacid 0.0334 L 33.4 mL
21
Molarity Reactions in Aqueous Solution

• A 4.554 g mixture of oxalic acid, H2C2O4 and NaCl
  was neutralized by 29.58 mL of 0.550M NaOH. What
  was the weight of oxalic acid in the mixture?

H2C2O4(aq) 2 NaOH(aq) ? Na2C2O4(aq) 2 H2O(l)
nNaOH 0.02958 L x 0.550 mol/L 0.01627 mol

• 1 H2C2O4 2 NaOH

nacid 0.01627 mol NaOH 8.135
x10-3 mol
22
Molarity Reactions in Aqueous Solution
A 4.554 g H2C2O4 / NaCl mixture Wt of oxalic
acid in the mixture?
Mass of acid consumed, macid 8.135 x10-3 mol
x (90.04 g/mol acid) 0.7324 g
16.08
23
Molarity Reactions in Aqueous Solution
25.0 mL of 0.234 M FeCl3 and 50.0 mL of 0.453 M
NaOH are mixed. Which reactant is limiting? How
many moles of Fe(OH)3 will form?
FeCl3(aq) 3 NaOH(aq) ? 3 NaCl (aq) Fe(OH)3(s)
nFeCl3 0.0250 L x 0.234 mol/L 0.005850 mol

• nNaOH 0.0500 L x 0.453 mol/L 0.02265 mol

24
Molarity Reactions in Aqueous Solution
FeCl3(aq) 3 NaOH(aq) ? 3 NaCl (aq) Fe(OH)3(s)
0.005850 mol 0.01925 mol
nFe(OH)3 ?
FeCl3 is limiting 0.00585 mol Fe(OH)3 produced.
25
Aqueous Solution Titrations

• Titration volume-based method used to determine
  an unknown concentration.

• A standard solution (known concentration) is
  added to a solution of unknown concentration.
• Monitor the volume added.
• Add until equivalence is reached
  stoichiometrically equal moles of reactants
  added.
• An indicator monitors the end point.

Often used to determine acid or base
concentrations.