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Solving Antilog MCAT Questions Without A Calculator

June 9, 2014 By Leah4sci 17 Comments

MCAT math tutorial video on anti logsThis video picks up from MCAT Math Part 8 – Logs and Negative Logs showing you how to solve questions where the log value is provided. Instead you're asked to solve for the anti-log value in questions relating to ion concentration and Ka values.

Anti-logs, just like logarithms, are difficult to calculation without a calculator UNLESS you know the tricks and shortcuts to apply. Watch the video below to learn how to tackle these MCAT style questions.

Anti-logs Without A Calculator

(click to watch on YouTube or click for Video Transcript)

MCAT Style Question Covered In This Video:

Chemistry Buffers/Ka Question: Find the ka of an acid whose buffer has a pH of 4.19 in a solution containing equal moles of acid and conjugate base.

<– Watch Previous Video: Logarithms and Negative Logs
–> Watch Next Video: Decimals & Exponents

Need additional MCAT style math practice? Click HERE for my FREE MCAT Math Quiz

This is Video #9 in my MCAT Math Without A Calculator tutorial series. Click HERE for the entire series

Filed Under: MCAT Math Tagged With: mcat, mcat logs, mcat math, medical college admissions test

Comments

  1. Mon says

    September 28, 2018 at 9:56 am

    How did you figure out that the final range was raised to the power of -5?

    Reply
  2. Calvin says

    April 11, 2018 at 11:09 pm

    Hi Leah, thank you for these videos. If you have time, can you please respond to my question regarding the last video at 5:00 min.

    So since you said that .19 is closer to .1 than .3, we got with number closer to 8. However, the calculator number is closer to 5 than it is to 8. Does your shortcut still work here? I know it’s unlikely MCAT will give us numbers this close together, but it does help if we do run into such a problem on the MCAT.

    Reply
  3. Sana Ali says

    March 1, 2018 at 8:22 pm

    Hi Leah!

    I am having a really hard time understanding how you selected 5 and 8 bc I was thinking if 5×10 raised to -x equals 2.3 or .3 & the number is 4.19, then we should be looking at higher numbers such higher than 2.3 since 4.19 is lower than 5. So we should look at 5×10 raised to -3 and 3×10 raised to -3 etx & not go to 8 or 10 since that would lower the exponent vlaue
    Thank you!

    Reply
  4. Greilys Lopez says

    February 17, 2017 at 11:54 am

    Hi Leah, I’m still confused with the exponent 10^5 instead of 10^4. I read the MCAT math sheet but I don’t get it. Did you decide to round it off to 5 because 4.19 is in between 4 and 5?
    Thanks for the videos. They are amazing!!!

    Reply
  5. Amna says

    February 15, 2017 at 1:06 am

    Hey! I looked through the mcat cheat sheet and noticed the x-1= # but in the example I am still unclear how you knew the range was 5*10^-5 and so on right away… Please let me know! Much appreciated:D

    Reply
  6. Malini says

    August 24, 2016 at 2:38 pm

    How did you decide that the answer was # x 10^-5 rather than # x 10^-4? Because the range for the pKa was between 4 and 5, so what made you conclude that the pKa was closer to 5 than to 4?

    Reply
    • Rabbit says

      January 22, 2017 at 1:13 am

      I am also unsure how concluded the answer was 10^-5 and not 10^-4.

      Reply
    • Emily says

      February 11, 2019 at 12:48 pm

      I have the same question. Leah, can you please explain how you knew to pick the number to the -5 power instead of to the -4 power for 4.2? Is it because you always pick the smaller number?

      Reply
  7. michael c says

    July 12, 2016 at 5:57 pm

    I think you may have misspoke… 6.46 is closer to 5 than to 8 🙂 These videos are very helpful!!

    Reply
  8. Remy says

    June 7, 2016 at 9:17 pm

    At 3:48, how did you just concluded that 4.19 will give you a number (#) x 10^-5?

    I know that is what the answer ends up being, but how did you just jump to that?

    Reply
    • Leah4sci says

      June 10, 2016 at 3:13 pm

      See the math cheat sheet

      Reply
  9. Samia Jaffar says

    May 31, 2016 at 5:03 pm

    Hi Leah, I am confused as to what the .1 .3, and .5 values refer to? is that the value of the pKA?

    Reply
    • Leah4sci says

      June 21, 2016 at 10:31 pm

      See the MCAT math cheat sheet

      Reply
  10. Tim says

    May 12, 2016 at 8:20 pm

    I thought I had it, then lost it after some practice. I had a problem where I found the pKa to be 5.4. I tried to estimate it the exponents to be between 5 and 6 but got stuck between the answer choices 4×10^-5 and 4×10^-6. Was I on the right track? and if 4 x 10^x wasnt all the answer choices, Im not sure i would have gotten 4 as my number..

    Reply
  11. shantanu says

    April 28, 2016 at 2:22 am

    what is the value of 10 raised to -0.2????

    Reply
    • Leah4sci says

      May 3, 2016 at 8:49 am

      For the MCAT simply estimate that it’s between 10^0 and 10^-1. That’s between 1 and 0.1

      Reply

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