Percent Composition of Solutions

I. Percent by mass

Percent by mass =

mass of solute x 100%

mass of solution

 

Example 1 - Calculate the percent by mass of sucrose in a solution made be dissolving 4.00 g of sucrose in 46.0 g of water.

 

 

Example 2 - What mass of a 15.0 % by mass sucrose solution contains 25.0 g of sucrose?

 

 

Example 3 - Low fat milk is labeled 2.0% fat by mass. What is the percent of fat calories in milk? Given: 250 g of milk = 1 cup; 1 cup milk contains 140 Cal; 1 g of fat contains 9 Cal.

 

 

 

 

Percent by volume =

volume of solute x 100%

volume of solution

Example 4 - Wine is labeled as containing 12.5% alcohol by volume. What volume of alcohol is present in 250 mL of wine?

 

Molarity Problems

Example 5 - How many moles of NaOH are present in 50.0 mL of 0.500 M NaOH solution?

 

 

Example 6 - What is the concentration of Ca2+ ions and Cl- ions in 25.0 mL of 0.300 M CaCl2?

 

 

Example 7 - How many moles of Cl- ions are present in 100. mL of 0.300 M CaCl2 solution?

 

 

 

Solution Stoichiometry

I. Reactions involving precipitation of ionic compounds

Example 1 - What mass of sodium chloride must be added to 50.0 mL of 2.00 M Pb(NO3)2 solution to precipitate all of the lead ions?

Balanced net ionic equation:

Plan:

 

 

 

 

 

 

 

 

 

Example 2 - How many mL of 0.100 M BaCl2 solution are needed to react with 100. mL of 0.150 M Pb(NO3)2 solution?

Balanced net ionic equation:

Plan:

 

 

 

 

 

 

 

 

 

Example 3 - What volume of 0.250 M Pb(NO3)2 solution and 0.400 M NaF solution are needed to make 5.60 g of PbF2?

Balanced net ionic equation:

Plan:

 

 

 

 

 

 

 

 

Example 4 - What mass of PbCl2 will precipitate when 100. mL of 2.40 M NaCl is mixed with 200. mL of 0.900 M Pb(NO3)2 solution?

Balanced net ionic equation:

Plan:

 

 

 

 

 

 

 

 

 

 

II. Titrations - Reaction of acids and bases

Net Ionic Equation for the reaction of a strong acid and a strong base:

 

In a titration at neutralization (indicated by an indicator), the number of moles of H+ is equal to the number of moles of OH-.

mol H+ = mol OH-

 

In the book example, 50.00 mL of an acid of unknown molarity is titrated with 0.100 M NaOH solution. Neutralization is reached after the addition of 22.50 mL of base. Determine the molarity of the acid.

 

 

 

 

 

 

Example 1- What volume of 0.250 M NaOH is needed to neutralize 30.0 mL of 0.200 M HCl solution?

 

 

 

 

 

Example 2 - Tums contains solid Ca(OH)2. What mass of Ca(OH)2 is needed to neutralize 100. mL of 0.200 M HCl?

 

Example 3 - What is the molarity of a H2SO4 solution if 25.0 mL of the acid is neutralized by 40.0 mL of 0.200 M NaOH?

Plan:

 

 

 

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