This 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

**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**

Mon says

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

Calvin says

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.

Sana Ali says

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!

Greilys Lopez says

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!!!

Amna says

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

Malini says

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?

Rabbit says

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

Emily says

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?

michael c says

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

Remy says

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?

Leah4sci says

See the math cheat sheet

Samia Jaffar says

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

Leah4sci says

See the MCAT math cheat sheet

Tim says

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..

shantanu says

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

Leah4sci says

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