2 Acid-Base Stoichiometry An important application of neutralization reactions is finding the concentration of an unknown solutionTITRATION: is a way to determine the concentration of an unknown solution using a different solution of a known concentrationDuring a titration, a measured volume of a standardized solution called the titrant
3 Acid-Base Stoichiometry Titrant: is gradually added to a flask containing a measured volume of a solution of unknown concentrationBurette is a calibrated tube use to deliver variable known volumes of a liquid during a titration
4 Acid-Base Stoichiometry The point during an acid-base titration when neutralization is complete is called the Equivalence pointAt this point, the amount of acid & base added to the flask exactly match their mole ratio in the chemical equationstoichiometrically equalsudden change in pH or colour of acid-base indicator
5 Acid-base Stoichiometry Endpoint: the point during which a titration when a sudden change in an observable property of the solution occurs. Usually a change in color of an acid-base indicator or a significant change in pHNOTE! The endpoint and Equivalence point are NOT the same.
6 Method of Titrationequal concentrationacid=alkali
7 Method of Titration - Not the same concentration - concentration= strong acid- To determine how to neutralize the acid we use a method called titrationStrong acid=alkali
9 Step1: add the know volume to a alkali into flask using a pipette Step2: add a dew drops of indicatorsStep3: pour some acid into the burette & record the readingStep4: open the tap, add a small amount of acid and swirl the flask to mixStep 5: Add acid until the solution is neutral (colour change)Step 6 Repeat (3x)
10 CalculationsSeveral 10.00mL samples of sulfuric acid solution of unknown concentration are titrated with a mol/L solution of sodium hydroxide. (Note: the burette contains NaOH). The endpoint was determined using phenolphthalein indicator. The acceptable observations from the titration are summarized below. Use these data to determine the amount concentration of the acid solution.Trial123Final burette volume reading (mL)12.5224.9837.62Initial burette volume reading (mL)0.1025.10Volume of base(titrant) added (mL)12.4212.46
11 Given :V= 10.00mLC= 0.100mol/LRequired:Concentration of acidC= nV
12 Step #1: Calculate the average volume of titrant used Step #1: Calculate the average volume of titrant used. In this example, the titrant is the baseVNaOH = 12.42mL mL mL3VNaOH = mL
13 Step #2: Convert the given volumes to litres VNaOH = mL x L= L1000mLVH2SO4 = 10.00mL x L= L1000mL
14 Step #3: Write a balanced equation for this reaction, listing the given values, required values, molar masses, amount of concentration2NaOH(aq) + H2SO4(aq) ---> 2H2O(l) + Na2SO4(aq)V= LV= LC= 0.100MC=???
15 Step #Use the concentration equation to determine the amount of the substance whose volume & concentration are given2NaOH(aq) + H2SO4(aq) ---> 2H2O(l) + Na2SO4(aq)V= LV= LC= 0.100MC=???n= C x V= 0.100mol/L x Ln= x 10-3mol
16 Step 5: Use the amount of the substance to determine in step #4 & the mole ration in the balanced equation to determine the moles2NaOH(aq) + H2SO4(aq) ---> 2H2O(l) + Na2SO4(aq)V= LV= LC= 0.100MC=???= x 10-3mol1 mol H2SO4x2 mol NaOH= x 10-4 molH2SO4
17 Step 6: Use the amount of the required to determine concentration 2NaOH(aq) + H2SO4(aq) ---> 2H2O(l) + Na2SO4(aq)V= LC=6.235 x 10-4 molH2SO40.0100LC= mol/L
18 Determine Concentration Using a primary Solution A sample of 1.00g of potassium carbonate is dissolved in 100mL water. A titration of this sample requires mL of nitric acid to reach the endpoint. Calculate the amount concentration of the Nitric Acid