 # Acid-Base Stoichiometry

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Acid-Base Stoichiometry

Acid-Base Stoichiometry
An important application of neutralization reactions is finding the concentration of an unknown solution TITRATION: is a way to determine the concentration of an unknown solution using a different solution of a known concentration During a titration, a measured volume of a standardized solution called the titrant

Acid-Base Stoichiometry
Titrant: is gradually added to a flask containing a measured volume of a solution of unknown concentration Burette is a calibrated tube use to deliver variable known volumes of a liquid during a titration

Acid-Base Stoichiometry
The point during an acid-base titration when neutralization is complete is called the Equivalence point At this point, the amount of acid & base added to the flask exactly match their mole ratio in the chemical equation stoichiometrically equal sudden change in pH or colour of acid-base indicator

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 pH NOTE! The endpoint and Equivalence point are NOT the same.

Method of Titration equal concentration acid = alkali

Method of Titration - Not the same concentration
- concentration= strong acid - To determine how to neutralize the acid we use a method called titration Strong acid = alkali

Step1: add the know volume to a alkali into flask using a pipette
Step2: add a dew drops of indicators Step3: pour some acid into the burette & record the reading Step4: open the tap, add a small amount of acid and swirl the flask to mix Step 5: Add acid until the solution is neutral (colour change) Step 6 Repeat (3x)

Calculations Several 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. Trial 1 2 3 Final burette volume reading (mL) 12.52 24.98 37.62 Initial burette volume reading (mL) 0.10 25.10 Volume of base(titrant) added (mL) 12.42 12.46

Given : V= 10.00mL C= 0.100mol/L Required: Concentration of acid C= n V

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 base VNaOH = 12.42mL mL mL 3 VNaOH = mL

Step #2: Convert the given volumes to litres
VNaOH = mL x L = L 1000mL VH2SO4 = 10.00mL x L = L 1000mL

Step #3: Write a balanced equation for this reaction, listing the given values, required values, molar masses, amount of concentration 2NaOH(aq) + H2SO4(aq) ---> 2H2O(l) + Na2SO4(aq) V= L V= L C= 0.100M C=???

Step #Use the concentration equation to determine the amount of the substance whose volume & concentration are given 2NaOH(aq) + H2SO4(aq) ---> 2H2O(l) + Na2SO4(aq) V= L V= L C= 0.100M C=??? n= C x V = 0.100mol/L x L n= x 10-3mol

Step 5: Use the amount of the substance to determine in step #4 & the mole ration in the balanced equation to determine the moles 2NaOH(aq) + H2SO4(aq) ---> 2H2O(l) + Na2SO4(aq) V= L V= L C= 0.100M C=??? = x 10-3mol 1 mol H2SO4 x 2 mol NaOH = x 10-4 molH2SO4

Step 6: Use the amount of the required to determine concentration
2NaOH(aq) + H2SO4(aq) ---> 2H2O(l) + Na2SO4(aq) V= L C= 6.235 x 10-4 molH2SO4 0.0100L C= mol/L

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