Math on the chem section without a calculator?!

[rickblas]

So I took a online kaplan practice test today (my 2nd practive test) and I soon realized something...How do I deal with the math involved in the chemistry section of the DAT without a calculator. For example one question about Ksp brought me up to the point where:

x^2 = 1 x 10^-5

and it needed me to do the radical expression of (1 x 10^-5) to get the answer which I did NOT remember how to do without a calculator . What shall I do about this?! I tried searching for similar forum posts and didnt really get much from my searches...sorry if this is a silly question I am actually very serious!

Thanks!

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[UCB05]

So I took a online kaplan practice test today (my 2nd practive test) and I soon realized something...How do I deal with the math involved in the chemistry section of the DAT without a calculator. For example one question about Ksp brought me up to the point where:

x^2 = 1 x 10^-5

and it needed me to do the radical expression of (1 x 10^-5) to get the answer which I did NOT remember how to do without a calculator . What shall I do about this?! I tried searching for similar forum posts and didnt really get much from my searches...sorry if this is a silly question I am actually very serious!

Thanks!

roots of large or small base 10 numbers are fairly easy, given the property that sqrt(xy)=sqrt(x)sqrt and that to find the square root of a base 10 power, divide the exponent by 2

When you have 10 raised to an odd power, make it something easier. In this case, notice 1x10^-5 = 10x10^-6

Now you can use that property of exponents: sqrt(10) x sqrt(10^-6) = 3.2ish x 10-3

 

[Zakl]

i think the real dat is pretty fair, they probably won't do that to you, most of the time i don't think there are any hard calculation, again why dat destroyer i believe is kind of ridiculous

 

[nze82]

So I took a online kaplan practice test today (my 2nd practive test) and I soon realized something...How do I deal with the math involved in the chemistry section of the DAT without a calculator. For example one question about Ksp brought me up to the point where:

x^2 = 1 x 10^-5

and it needed me to do the radical expression of (1 x 10^-5) to get the answer which I did NOT remember how to do without a calculator . What shall I do about this?! I tried searching for similar forum posts and didnt really get much from my searches...sorry if this is a silly question I am actually very serious!

Thanks!

My #1 advice to you is to PRACTICE PRACTICE PRACTICE, and when you feel you have no life left in you, PRACTICE SOME MORE!

In most cases, however, you can find the correct answer by eliminating the wrong choices. For example, in most questions, where the answers are stated in a scientific form (K x 10^n). You can eliminate the wrong choice by focusing on K. For example, if you know that:

X^2 = 9 x 10^-5 then X = 3 x Sqrt(10^-5)

Now you can eliminate all the answers that don't start with a 3, and this method usually reveals the correct answer.

 

[rickblas]

ya! a 9 x 10^-5 would be quite easy because radical 9 is obviously 3...but for numbers like 1 and 10 (which i did not know the radical of 10 is 3.2)...it is kind of tricky. Should I waste time memorizing the radicals of some common single digit numbers that are not so easy to radical (i.e. radical of 1, 3, 5, 7)? Is there an easier method? mmmm. and Thanks!

 

[nze82]

ya! a 9 x 10^-5 would be quite easy because radical 9 is obviously 3...but for numbers like 1 and 10 (which i did not know the radical of 10 is 3.2)...it is kind of tricky. Should I waste time memorizing the radicals of some common single digit numbers that are not so easy to radical (i.e. radical of 1, 3, 5, 7)? Is there an easier method? mmmm. and Thanks!

It's not that hard. Like I said. It takes practice.
In case of a number like 10, what are the two numbers below and above 10 that you know the square root of?
9 and 16....So:

9<10<16...So:

Sqrt(9)<Sqrt(10)>Sqrt(16)....So:

3<Sqrt(10)<4

Which means you're looking for a number larger than 3 and smaller than 4. Now go through your answer choices and eliminate the ones that don't satisfy this condition.
If you're trying to come up with an easy method to figure out the EXACT square root of numbers like 10 without a calculator, you're wasting time.

 

[rickblas]

alright! Thanks!!

 

[slm266]

it seemed like half of the gen chem questions had answer choices with the work already set up for you. All you had to do was know how to set it up. If it wasnt set up, it seemed like answer choices were spread out allowing you to approximate values by rounding.

I did know how to do everything w/o a calculator, like going from [H+] concentrations of 3E-3 to pH 2.5 or estimating square roots from numbers in scientific notation.

I agree though. Practice practice practice. It's all pretty straight forward.

 

[bmagee]

it seemed like half of the gen chem questions had answer choices with the work already set up for you. All you had to do was know how to set it up. If it wasnt set up, it seemed like answer choices were spread out allowing you to approximate values by rounding.

I did know how to do everything w/o a calculator, like going from [H+] concentrations of 3E-3 to pH 2.5 or estimating square roots from numbers in scientific notation.

I agree though. Practice practice practice. It's all pretty straight forward.

Hey slm266, how did you manage to calculate the pH value of 2.5 from the conc. of 3E-3 by the way? I tried memorizing as many pH-conc. values as I can, but it's not helping out too much..thanks!