Thursday, May 12 th : “A” Day Agenda  Check lab write-ups  Lab Discussion  Lab: “Titration of an Acid and a Base”  Lab will be due today… Next time… Chapter 15 Review

Lab: “Titration of an Acid and a Base”  The purpose of this lab is to determine the normality of an unknown concentration of sodium hydroxide, NaOH.  For an acid or a base that dissociates in a 1:1 ratio, the normality is equal to the molarity. NaOH Na + + OH – HCl + H 2 O H 3 O + + Cl -

Lab: “Titration of an Acid and a Base”  After the titration, the normality of the base will be calculated using the following formula: Normality (B) Volume (B) = Normality (A) Volume (A)  Rearrange to solve for the normality (B) : Normality (B) = Normality (A) Volume (A) Volume (B)

Lab: “Titration of an Acid and a Base”  Calculation #4: Absolute error: E a = average Normality (B) – accepted value  Calculation #5: Percentage error: E r = E a X 100% accepted value

Lab: “Titration of an Acid and a Base” 1.Which acid and base will you be using? HCl and NaOH 2.Are these strong or weak? Strong

Lab: “Titration of an Acid and a Base” 3. Which is the titrant? HCl A titrant is a solution of known concentration that is used to titrate a solution of unknown concentration.

Lab: “Titration of an Acid and a Base” 4.What indicator will you be using? Phenolphthalien 5.What color is it in a basic solution? Pink

Lab Hints  Practice controlling the stopper with just water – you need enough control so that the buret can delivery 1 drop.  Try to do a total of 3 trials.  You DO NOT have to refill the burets each time. Simply record the starting and ending volume each time to get the total amount of acid/base added.  If you overshoot the end point, don’t worry. Simply add more acid or base and retitrate until only 1 drop changes the color.

Safety Guidelines  Both acids and bases are corrosive – safety goggles, aprons, and appropriate shoes must be worn.  Be sure to lower the burets to eye level before filling them.

Lab: “Titration of an Acid and a Base”  You should have time to do 3 trials and complete the calculations today so the lab will be due at the end of the class period.  Be sure to update your table of contents… Be safe and have…