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APChem

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If an air bubble passes unnoticed through the tip of a buret during a titration (where a weak nonvolatile acid HA is the analyte) , the calculated molar mass of HA would be too high, too low, or not affected?

I thought it would be too high, since an air bubble in the buret means that the volume of base(titrant)is actually less than it should be; since the amount of base reacting with the acid(anlyte) is less , the amount of acid that is needed to react is also less....so it would seem that if the necessary amount of acid needed to react is small, then the molar mass of that acid should be large...so the calculated molar mass of HA would be too high.....

Does this sound right?



THank you!!!!

  • APChem - ,

    I thought it would be too high, since an air bubble in the buret means that the volume of base(titrant)is actually less than it should be; since the amount of base reacting with the acid(anlyte) is less You are ok to here, the amount of acid that is needed to react is also less...you are right that the air bubble takes up space, but since it goes through the buret unnoticed (actually it makes no difference whether you notice it or not), then it takes the same amount of base (after all, the indicator you used doesn't know there was an air bubble there--it just knows when enough titrant has been added. Therefore, the indicator will turn at the right place; however, the buret will read too high because of the air bubble. Since the molar mass is determined from mLbase x Mbase x molar mass acid = grams acid, we can rearrange to molarmass = grams/mL x M. The denominator will be too large making the calculated molar mass too low. Check my thinking.so it would seem that if the necessary amount of acid needed to react is small, then the molar mass of that acid should be large...so the calculated molar mass of HA would be too high.....
    The above in a nutshell: The acid will use the same amount of base it would normally use but the buret will read higher than it should because of the air bubble, mL too high in the denominator makes the fraction too large.

  • APChem--correction - ,

    No, I goofed in the last sentence. The acid will use the same amount ........ ml too high in the denominator makes the fraction too SMALL and the calculated molar mass will be too low.

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