if you have taken the dat....

[babyblue3b]

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to anyone who took the DAT, will i need to know how to calculate -log of something...for example i was doing chads quiz and i was given Ka and needed to get pKa...do i need to do this on DAT considering no calculator?? what is the formula to do so?

 

[IdahoDoc]

to anyone who took the DAT, will i need to know how to calculate -log of something...for example i was doing chads quiz and i was given Ka and needed to get pKa...do i need to do this on DAT considering no calculator?? what is the formula to do so?

What i did was just memorize the values and went over them again and again it really isn't too bad. here are the numbers i used.

2 = .69
3 = .52
4 = .39
5 = .3
6 = .22
7 = .15
8 = .09
9 = .04


So the example is 3.0*10^-12 to take the -log of that value you add 1 to the exponent and that becomes your whole number so in this case it is 11 then the 3.0 is the decimal portion so look at the chart and 3 has a value of .52 so the -log of 3.0*10^-12 would be about 11.52


If your value is 1.0 *10 to the any power then the -log is just the value of exponent as a whole number.

When you have values like 3.4*10^-12 then what i would do is add 1 to the exponent to get the whole value of 11 and then i would look at what two whole numbers my values is between in this case it is 3 and 4 and the values of 3 and 4 are .52 and .39 then we have to guess a bit and see that the value is slight closer to 3 and so pick a value that is slightly closer to our value for 3 but pretty close to the middle so i would guess around .47 and our whole value would be close to 11.47 ( i didn't actually do it with a calculator so it might be slightly off.) This will get you close enough to be able to tell the correct answer. If you have another question let me know. Hope this helps.

 

[LuckMC11]

wow thats amazing idahodoc!!

 

[CANgnome]

I just think:

if it is like, 3.33 x 10^-10

I think to myself, well its log is 10 if it is just 1.00. But 3.33 is obviously a bit larger, so log 3.33e-10 would be between log 1e-10 and log 1e-9, which is about 9.5, which it is.

 

[2PacClone23]

Idahodoc, that REALLY helped.


*puts this in the memorize folder of this DAT study materials*

 

[IdahoDoc]

Idahodoc, that REALLY helped.


*puts this in the memorize folder of this DAT study materials*

Not a problem guys glad i could help. Like I said it is not full proof but it will get you dang close the actual pH value. But do expect to get very very weird looks from people when you say you can do -log functions in your head.😀