Your Partner\'s Name Determination of Acetic Acid in Vinegar Post-lab 1 The foll

Question

Your Partner's Name Determination of Acetic Acid in Vinegar Post-lab 1 The following errors were made during the standardization of sodium hydroxide. How would the calculated value of molarity compare to the actual molarity? The KHP mass was misrecorded as 0.6265 g rather than 0.6655 g. Increased Decreased Unchan The NaOH ran down the outside of the burette during filling and some went into the Erlenmeyer flask. Increased Decreased Unchang An air bubble in the tip of the burette comes out during the titration. IncreasedDecreased Unchange The KHP contains a contaminant that does not react with the sodium hydroxide. Increased Decreased Unchange The burette leaked sodium hydroxide during the titration but the leakage did not fall into the Erlenmeyer flask. Increased Decreased Unchange Instead of using 25 mL to dissolve the KHP a student used 30 mL Decreased Unchange Increased 2· The following errors were made during the titration of the vinegar. How would the calculated value of molarity of the vinegar compare to the actual molarity? The molarity of the NaOH had erroneously been determined to be higher than it really was Increased Decreased Unchanged Using a volumetric pipette to deliver the vinegar, a student used the pipette bulb to blow out the last little bit of vinegar from the tip into the Erlenmeyer IncreasedDecreased Unchanged flask A student added 40-mL of water to the vinegar in the Erlenmeyer flask rather than the 25 mL recom Increased Decreased Unchanged mended Determination of Acetic Acid in Vinegar -109

Explanation / Answer

1) KHP is the primary standard reagent used to standardize NaOH.If it's lower mass is recorded then you get lower concentration of KHP.
mol KHP=mass KHP /molar mass KHP
concentration KHP=mol KHP/volume of solution prepared
As KHP and NaOH reacts in 1:1 molar ratio,you get a lower mol of NaOH and thus an erroneously low concentration of NaOH
concentration of NaOH=mol NaOH/molar mass
Eventually, you calculate molarity of acetic acid (M1)using the calculated molarity (concentration) of NaOH.
M1*V1(mol NaOH)=M2*V2 (mol acetic acid),V1=volume of NaOH(titrant),V2=volume of acetic acid
Thus, a lower or decreased value of molarity of acetic acid is calculated out.

2)As some NaOH ran into the erlenmeyer flask,you get a lower volume of titrant to titrate acetic acid than actual.Thus ,a lower value of mol NaOH,which ultimately gives a lower or decreased value of mol acetic acid or molarity of acetic acid.
M1*V1(mol NaOH)=M2*V2 (mol acetic acid),V1=volume of NaOH(titrant),V2=volume of acetic acid

3)If an air bubble is there in the burette, you measure a higher volume of titrant used to titrate acetic acid.The volume of air bubble is deducted from the volume of NaOH.

Thus ,a higher value of mol NaOH,which ultimately gives an increased value of mol acetic acid or molarity of acetic acid.
M1*V1(mol NaOH)=M2*V2 (mol acetic acid),V1=volume of NaOH(titrant),V2=volume of acetic acid

4)KHP is the primary standard reagent used to standardize NaOH.If it is mixed with a contaminant then actual mass of KHP is less than measured value.Thus,a higher mass is recorded giving you get higher concentration of KHP.
mol KHP=mass KHP /molar mass KHP
concentration KHP=mol KHP/volume of solution prepared
As KHP and NaOH reacts in 1:1 molar ratio,you get a higher mol of NaOH and thus an erroneously high concentration of NaOH
concentration of NaOH=mol NaOH/molar mass
Eventually, you calculate molarity of acetic acid (M1)using the calculated molarity (concentration) of NaOH.
M1*V1(mol NaOH)=M2*V2 (mol acetic acid),V1=volume of NaOH(titrant),V2=volume of acetic acid
Thus, a higher or increased value of molarity of acetic acid is calculated out.

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