The phenolphthalein will be colorless in the vinegar. As the titration proceeds
ID: 589465 • Letter: T
Question
The phenolphthalein will be colorless in the vinegar. As the titration proceeds and the moles of sodium hydroxide (NaOH) exceed the moles of acetic acid (HC2H302), the indicator will turn pink. This is called the endpoint. Knowing the volume and concentration of NaOH required to completely react with HC2H02, you can calculate the concentration of the HC2H302. Procedure: you may work with ONE other student Obtain a 10-mL transfer pipet and a 50-mL buret. Next obtain your reagents in two separate clean dry beakers: about 30 mL of vinegar and about 90 mL of NaOH. Record the concentration of NaOH on from the bottle. Carefully rinse your buret with tap water, followed by dH2O (de-ionized water). Next rinse the buret with a small amount of NaOH and allow the solution to drain. After the rinsing, carefully fill your buret with NaOH and record the volume.Explanation / Answer
Its a weak acid strong base titration:
Pipette out 10ml of given vinegar(concentration is unknown) solution into a clean conical flask. Add 2 to 3 drops of phenolphthalien indicator.
Fill the standard sodium hydroxide solution into a clean rinsed burette upto the zero mark and note down the initial burette reading. See that the nozzle of the burette is also filled.
Start adding sodium hydroxide from burette dropwise to vinegar solution taken in the flask. Till the solution in the conical flask turns pale pink color, the end point of the titration.
Stop adding sodium hydroxide and note down the final burette reading.
By subtraction of final Burette reading from initial burette reading the total volume of NaOH consumed during the reaction can be known.
Repeat the titration to get a concordant value. Upto minimum 3 trials to get a precise value.
By knowing the volume of NaOH Consumed and concentration of NaOH the concentration of vinegar can be calculated.
Reaction :
CH3COOH + NaOH --------> CH3COO Na + H2O
Calculations: can be done using the formula
a1M1V1(vinegar) = a2M2V2(NaOH) where a1 and a2 are acidity and basicity of base and acid respectively, M1 and M2 are their concentration in molarity, V1 and V2 are their voices respectively.
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