Neutralization Reactions Acids and bases are neutralized as they react with one another. Often called “titration” Reactants: Acid and a base Products: Water and a salt Example: HCl neutralizes KOH HCl + KOH --> H2O + KCl

Titration (Neutralization) Reactions in the Lab The image shows a flask containing an unknown concentration acid and a buret of known concentration base. The buret is marked in mL, so you can monitor the amount of base that you are adding to the acid. An indicator has been added to the acid so that a color change will occur when the acid’s pH reaches 7. This will signal that the neutralization reaction is complete. Simple stoichiometry can then be done to calculate the unknown concentration of the acid.

Calculating the Unknown Concentration A volume of 9.0 mL of 0.70M NH4OH neutralizes a 35 mL sample of HClO4 solution. What is the concentration of HClO4? NH4OH + HClO4  H2O + NH4ClO4 Use the Molarity equation with 9.0 mL and 0.7 M to calculate 0.0063 moles of NH4OH. Convert to moles of HClO4: 0.0063 mol NH4OH 1mol HClO4 = 0.0063 mol HClO4 1 mol NH4OH Finally, use the Molarity equation with 0.0063 mol HClO4 and 35 mL to calculate the concentration of HClO4. 0.18 M HClO4

Notice the subtle differences in color of the solutions in the photo. Tricky Titrations Notice the subtle differences in color of the solutions in the photo. Add more STOP! START OVER In the titration set-up, you see that you’ll be adding the known into the unknown. You are looking for a color change in the flask to tell you when to STOP adding the known. If you add just ONE DROP too much, then you’ll have to begin your experiment over again as you’ll have passed the neutralization point.

Calculating the Volume of the Known In order to avoid having to start over, you can calculate the theoretical volume of known to allow to drop from the buret into the flask. Example: pg. 591 #43 A 100.0mL sample of 0.50M HCl is titrated with 0.10M NaOH. What volume of the NaOH is required to reach the endpoint of the titration? HCl + NaOH  H2O + NaCl Use the Molarity equation with 100 mL and 0.50 M HCl to calculate 0.05 moles HCl. Convert moles HCl to moles NaOH. 0.05 moles HCl 1 mole NaOH = 0.05 moles NaOH 1 mole HCl Use the Molarity equation with 0.05 moles NaOH and 0.1 M NaOH to calculate 0.5 Liters.

Individual Practice Calculating Concentration of the unknown Let’s look at the 19-3 Practice Problems in your practice packet. We’ve already answered #2 together a few moments ago. Solve the odd problems. We’ll use the iRespond remotes to check your answers.

Application Level Question #1 F Multiple Choice iRespond Question Application Level Question #1 19-3 PP #1 A volume of 30.mL of 0.25M HCl neutralizes a 50.mL sample of KOH solution. What is the concentration of KOH? A.) 0.15 M B.) 1.5 M C.) 0.000375 M D.) 0.015 M E.)

F Multiple Choice iRespond Question Application Level Question #2 19-3 PP #3 A volume of 90mL of 0.2M HBr neutralizes a 60mL sample of NaOH solution. What is the concentration of the NaOH solution? A.) 0.3 M NaOH B.) 37.0 M NaOH C.) 0.03 M NaOH D.) 3.7 M NaOH E.)

F Multiple Choice iRespond Question Application Level Question #3 19-3 PP #5 A volume of 46mL of 0.40M NaOH neutralizes an 80.mL sample of HCN solution. What is the concentration of HCN? A.) 2.3 M HCN B.) 0.23 M HCN C.) 108.7 M HCN D.) 10.9 M HCN E.)

Application Level Question #4 F Multiple Choice iRespond Question Application Level Question #4 19-3 PP #7 A volume of 20.mL of 0.25M Al(OH)3 neutralizes a 75mL sample of H2SO4 solution. What is the concentration of H2SO4? A.) 0.7 M Al(OH)3 B.) 0.07 M Al(OH)3 C.) 1 M Al(OH)3 D.) 0.1 M Al(OH)3 E.)

Application Level Question #5 F Multiple Choice iRespond Question Application Level Question #5 19-3 PP #9 A volume of 10.mL of 0.75M NaOH neutralizes a 30.mL sample of HClO solution. What is the concentration of HClO? A.) 0.25M HClO B.) 2.5M HClO C.) 25M HClO D.) 0.025M HClO E.)

More advanced 300-mL of HBr solution reacts with 550-mL of Mg(OH)2 solution.  If the pH of the base is 12.9, what molarity of the acid is needed to react with the base?

Who is coming for make-ups? As you come in, The Materials: Paper, pencil, calculator Practice packet The Plan: Review the Solutions Unit Test Take the Titrations Quiz Complete the Virtual Titrations Lab The Assessments: Cumulative Quiz 9 (Solutions) – TOMORROW Unit 10 Acid/Base Test – Thursday Cumulative Quiz 10 (Acid/Base) - Tuesday

Individual Assignment Acid-Base Titration Simulation Follow the instructions on the page. There is an UNDERSCORE in the address. The order of the directions is significant. Don’t skip steps or work out of order. Complete the data table on the back of the page as you go. (NOTE: The website will give each student different numbers so don’t copy someone else!) http://www.chem.iastate.edu/group/Greenb owe/sections/projectfolder/flashfiles/stoichi ometry/acid_base.html