Help b/c i can't use my T-89+ on the DAT! lol

[lovedana16]

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I am wondering if anyone has any math tricks for the Gen Chem protion of the DAT. Like almost everyone I always had my T-89+ next to me in every class and test. I can not fugure out how to find the -log for pH's, excpecially when there is somehting like 5.37 x 10^-36 ... 😕

Also when finding Ksp, every slightly soluable salt of general formula MX3 will have a Ksp=27x^4, where X is the molar solubility. For MX2 Ksp=27x^3.

So I have a question in my Kaplan practice test that game me the Ksp of X(OH)2 = 4x10^-18 and you are looking for how many moles of hydrochloric acid must be added to neutralize a one liter of the X(OH)2. Kaplan gives me the answer and how to do it. The problem is the last step, you have to take the 3rd root of 4x10^-18 ... the answer is 1x10-6.. any help on tricks for this stuff or for "powers" or "roots".. ewww

Thanks, Holly Jo

 

[msavaya]

I am wondering if anyone has any math tricks for the Gen Chem protion of the DAT. Like almost everyone I always had my T-89+ next to me in every class and test. I can not fugure out how to find the -log for pH's, excpecially when there is somehting like 5.37 x 10^-36 ... 😕

Also when finding Ksp, every slightly soluable salt of general formula MX3 will have a Ksp=27x^4, where X is the molar solubility. For MX2 Ksp=27x^3.

So I have a question in my Kaplan practice test that game me the Ksp of X(OH)2 = 4x10^-18 and you are looking for how many moles of hydrochloric acid must be added to neutralize a one liter of the X(OH)2. Kaplan gives me the answer and how to do it. The problem is the last step, you have to take the 3rd root of 4x10^-18 ... the answer is 1x10-6.. any help on tricks for this stuff or for "powers" or "roots".. ewww

Thanks, Holly Jo

Hey Holly...

To answer your first question, when given -log of something....like your example, -log 5.37 x 10^-36, since 5.37 is greater than 1, the answer is going to be something a little less that 36, like 35.4ish... This is because -log 1x10^n = n...., so anytime its greater than 1, n will be a little less, and if its less than 1, n will be a little higher... get it? If not, i'll try to re-explain.

 

[mcdds75]

I had a similar question with -log also, and I guess this clears it up? So, I had a post on destroyer Gchem#81, why is 9x10^-7=x^2 = -log 9.5 x 10^-4 = 3.1 or 3? I don't understand the math to get from the first -log all the way to 3?

Thanks!!

 

[artanis]

Hey Guys.

I think that people did a relatively good job explaining but it still takes some trial and error to see it. This is what i suggest both of you do.

Write this down in the middle of the page.

-log(3x10^-7)=
-log(2x10^-7) =
-log(1x10^-7) = 7
-log(0.9x10^-7) =
-log(0.5x10^7) =

Do that.

Then do it with this.

-log(3x10^-3) =
""
""
""
-log(0.5x10^-3) =

Then you should see the pattern.

 

[Mamona]

I explained to someone in this treat hope it helps

http://forums.studentdoctor.net/showthread.php?p=6990226#post6990226

 

[mcdds75]

Thanks guys, I got the -log down and understand, but why does 9x10^-7=x^2 change to 90x10^-8 = x^2 to find pOH? The answer continues with the square root= 9.5 x 10^-4

 

[lovedana16]

Thank ya'll ... anyone got and easy tricks for powers?? the always make me nervous and a tad confused! ... lol