Titration Pre-labTitration Pre-lab

What is titration?What is titration?

Method to determine the Method to determine the concentration of one concentration of one solution based on its rxn solution based on its rxn with a known solution with a known solution (titration standard)(titration standard)

It determines the unknown It determines the unknown molarity of a given solutionmolarity of a given solution

The ProcessThe ProcessYou have the followingYou have the following

– 50 ml Unknown solution (acid or 50 ml Unknown solution (acid or base) base)

–Known solution (acid or base)Known solution (acid or base)If you have an unknown acid you If you have an unknown acid you will need the known base and vice will need the known base and vice versaversa

–An indicator (phenolphthalein or An indicator (phenolphthalein or methyl orange) to show a change methyl orange) to show a change in pHin pH

The processThe processThe lab process: The lab process:

–Pour 1/3 of the unknown Pour 1/3 of the unknown (~16.7 ml) into the (~16.7 ml) into the Erlenmeyer flask. Be sure to Erlenmeyer flask. Be sure to record the exact amount in record the exact amount in your data tableyour data table

– If you have an unknown acid If you have an unknown acid put the flask underneath the put the flask underneath the base buret.base buret.

The ProcessThe Process

–Add 3 drops of indicatorAdd 3 drops of indicatorPhenolphthalein is Phenolphthalein is colorless in acids and pink colorless in acids and pink in bases at about a pH 8.2 in bases at about a pH 8.2

Methyl orange is red in Methyl orange is red in acids and turns yellow at acids and turns yellow at about 4.4about 4.4

The ProcessThe ProcessCheck your buret of the Check your buret of the

standard you are using. Be standard you are using. Be sure it is the opposite of the sure it is the opposite of the unknown, and that it is unknown, and that it is reasonably full. Be sure there reasonably full. Be sure there are no air bubbles in the tipare no air bubbles in the tip

Take the initial reading of the Take the initial reading of the buret and record it. Read to buret and record it. Read to the nearest 100the nearest 100thth of a ml of a ml

The ProcessThe ProcessHave 1 person constantly swirling Have 1 person constantly swirling

the flaskthe flaskThe other person should The other person should slowlyslowly

add small amounts of standard add small amounts of standard solutionsolution

When the unknown solution When the unknown solution appears to be close to changing appears to be close to changing colors slow down and add colors slow down and add 11 drop drop at a time until the color stays (end at a time until the color stays (end point)point)

The ProcessThe ProcessIf the color of the end point If the color of the end point is a deep color you added is a deep color you added too much. The end point too much. The end point should be a light, barely a should be a light, barely a change in color.change in color.

Record the final buret Record the final buret reading and the color in the reading and the color in the data tabledata table

The ProcessThe Process

Rinse the flask with tap Rinse the flask with tap water thoroughly and repeat water thoroughly and repeat this 2 more times.this 2 more times.

Thoroughly clean and dry all Thoroughly clean and dry all equipment. Leave unused equipment. Leave unused standard solution in the standard solution in the buretsburets

The CalculationsThe CalculationsCalculate the molarity for each Calculate the molarity for each trial using Mtrial using M11VV11 = M = M22VV22

MM11 = molarity of acid = molarity of acidVV11 = volume of acid = volume of acidMM22 = molarity of base = molarity of baseVV22 = volume of base = volume of baseFind the average of the 3 trialsFind the average of the 3 trials