Chad's Ksp problems...

[Avery07]

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I'm working on Chad's Ksp problems (ch 5) and the math seems impossibly difficult.. I understand how to set everything up but just can't figure these numbers out.

Example:

x^4 = (3.0x10^-19)/27

x^4 = 0.11 x 10^-19 = 1.1x10^-20 (I'm ok with this)

x = (1.1 x 10^-20)^1/4

x = ~ 1.0 x 10^-5


Yeah.. not going to be able to crank that out on the DAT. So does the math ever get this tough for gen chem stuff? Or is this even tough for most of you??

 

[Baylor2011]

It's just knowing how to do math w/ scientific notation, which makes huge numbers LOTTSS easier. First, which part of that math do you not get?

 

[Avery07]

It's just knowing how to do math w/ scientific notation, which makes huge numbers LOTTSS easier. First, which part of that math do you not get?

It's mainly that first step..

 

[Baylor2011]

x^4 = (3.0x10^-19)/27

ok rewrite it as: 3.0 x 10^-19 / 2.7 x 10^1

3.0 / 2.7 is about 1.1 and -19 - 1 is -20 so 1.1 x 10^-20

Being able to manipulate numbers in scientific notation makes the math alot easier, chad's practice sheets are great for that

 

[Avery07]

x^4 = (3.0x10^-19)/27

ok rewrite it as: 3.0 x 10^-19 / 2.7 x 10^1

3.0 / 2.7 is about 1.1 and -19 - 1 is -20 so 1.1 x 10^-20

Being able to manipulate numbers in scientific notation makes the math alot easier, chad's practice sheets are great for that

Ahh... got it. Thanks so much.

 

[shiftypoptart]

working with scientific notation I all learned all from chads videos and will be extremely helpful moreso in the QR section of the test. Make sure you know how to add, subtract, divide, multiply, squareroot and square with scientific notation and you will definitely have an upperhand on the Math portion moreso than the chem. In the real thing calculations will never be difficult as to want a specific number, Its kinda you got 4x^3 with a molar solubility of 4E-13 so an answer choice would be 4(4E-13)^3 (these are just random #s for an example).

 

[IBelieve]

I have similar problem... not knowing the trick to solve for Ksp/Ka/Kb problems... because of all the square roots and stuff.. can someone please help me with this question.
Find the pH of 0.04M NaCN soln. Given: Ka of HCN is 5.0x10^-10

so I have x^2/2=5.0x10^-10
x^2=12.0X10^-10
x=.........???? HELP PLEASE!!!!

 

[Baylor2011]

so I have x^2/2=5.0x10^-10
x^2=12.0X10^-10
x=.........???? HELP PLEASE!!!!

square root of 12: split it up into 3 x 4..so sqr root of 4 is 2. sqr root of 3 has to be in between 1 and 2...more toward 2 since 1.5^2 is 2.25 - just guess at it..say 1.7. 2 X 1.7 = 3.4

sqr root of 10^-10. All this means is divide the exponent by 2, which brings it to 10^-5

3.4 x 10^-5 - ish.

 

[IBelieve]

Thank you Baylor... but I think I did the problem wrong.. lol... I should not have divided by 2... I should have divided by 0.04... I think..