Chapter 4.8 Review Acid-Base Reactions

Acid-Base Reactions Reminder: Arrhenius (irrelevant) acids/bases Brønsted-Lowry acids/bases (protons only): Acids are proton donors, bases are proton acceptors Acid-Base Reactions are called neutralization reactions because the acid/base becomes neutralized by the base/acid added to it. *OH- will react with both strong and weak acids acid + base salt + water

Example What volume of a 0.100 M HCl solution is needed to neutralize 25.0 mL of 0.350 M NaOH? Write out reaction: HCl + NaOH --> NaCl + H2O 0.250L X 0.350mol NaOH X 1mol HCl X __1L HCl_ 1 L 1mol NaOH 0.100 mol HCl Solve for = 0.0875L of hydrochloric acid needed

Titrations! If we know the concentration and amount of either the acid or base (titrant in the buret), we can determine the concentration of the other (base or acid) by adding the titrant until the reaction is neutralized (equivalence point)

Titration Setup An indicator is added to the solution to be analyzed (usually phenolpthalein is added to the acid). It will indicate when the solution is one drop beyond a specific pH (phenolpthalein is 7). This is called the endpoint. Endpoint is where the color changes vs. equivalence point, where the number of moles of acid = moles of base Video

Titration Steps Record initial volume of the known concentration of base/acid in buret Record amount (usually mL) of unknown concentration acid/base in beaker Add a few drops of indicator to beaker Add titrant until the indicator has just permanently changed color Record the final volume of the known concentration of base/acid in buret You will now have the information needed to calculate the concentration of the unknown

Example Use the following data to calculate the concentration of the HCl solution: HCl in beaker with indicator: 10.4mL Initial buret reading: 3.5mL 0.100M NaOH Final buret reading (pink): 15.4mL 0.100M NaOH **write out the reaction first!! Answer: 0.114M HCl

Book Example More complicated problem on page 159 TIP pg. 160: The first step in the analysis of a complex solution is to write down the components and focus on the chemistry of each one. When a strong electrolyte is present, write it as separated ions.