Molarity, pH, and Stoichiometry of

SolutionsChapter 5 part 4

Solution Concentration

• Molarity (M) = mol of solute Liters of

solution

• To make 1.0 M NaCl, dissolve 58.4 g of NaCl in enough water to give a total solution volume 1.0L

SHORTCUT!

mol

M L

Problem1

• If 25.3 g of Na2CO3 is dissolved in water to make 250. mL of solution. Calculate the molarity of 1) Na2CO3 2) Na+ 3) CO3

2-

Problem2

• How many moles of CaCl2 are in 5.00 mL of a 2.00 M CaCl2 solution?

• How many moles of Cl- in this volume?

Dilution

• Adding solvent lowers the solution’s concentration

• M1V1=M2V2

• What vol. of a 0.20 M NaCl is needed to make 500 mL of 0.0010 M NaCl.

pH

• logarithmic scale• pH = -log [H+] [ ] = M

• [H+] = 10-pH

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pH Problems• Lemon juice has [H+]= 0.0032 M, what is the pH?

• Sea water has a pH of 8.30, what is the concentration of hydrogen ions?

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Stoichiometry of Aq Rxn

• What volume of 2.50 M HCl is required to completely react 11.8 g of Zn?

• Zn + 2 HCl --> ZnCl2 + H2

Practice

• 75.0 mL of 0.350 M HCl reacts with an excess of Na2CO3. What volume of CO2 is produced at STP?

2HCl + Na2CO3 --> 2NaCl + H2O+CO2

Titration

• Chemical analysis used to determine the concentration of a solution or the molar mass of a compound.

• MaVa = MbVb

• Molesacid = Molesbase

Titration (Acid/Base)

• An indicator, dye that changes color, is used to mark when the reaction is complete.

• At the equivalence point, there is an equal amount of acid (H+) and base (OH-)– pH = 7 w/ strong acids & bases

Titration

• A 0.263 g sample of Na2CO3 requires 28.35 mL of HCl to reach the equivalence point. What is the molarity of HCl?

2HCl + Na2CO3 --> 2NaCl + H2O+CO2