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- May 22, 2017
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hey guys. After watching Chads videos, his method for calculating ph,poh,h+,oh- is just too complicated and takes really long. w/ the anxiety of the exam I'm afraid its too easy for me to mess up. after hunting around through some mcat threads i was able to find a method. This method worked for every single one of the chads videos quiz questions. I want to share this method with you and would like if someone can confirm if i am safe with using this method on the real test. maybe @orgoman22 would know?? It honestly is the best way that works form, and i would hate if it was a false way of doing things..
#1. If [H+] = 6.4x10-8M, what is the pH of the solution?
- 6.8
- 8.3
- 7.2
- 7.8
Method:
- Take the power and subtract 1 (8-1) = 7. __
- Take the front number and subtract 10. 10-6.4= 3.6
- pH ~ 7.36
- closest answer is 7.2 and thats the winner.
#2: If [OH-] = 6.0 x 10-10M, what is the pH of the solution?- 4.1
- 4.8
- 5.2
- 8.8
Method:
- Take the power and subtract 1 (10-11) = 9. __
- Take the front number and subtract 10. 10-6= 4
- pOH ~ 9.4
- pH+pOH=14 --> pH= 4.6; Closest answer is 4.8 and thats the winner
#3. Reverse style problem: If the pH is 3.2, what is the [H+] of the solution?
- 2.1x10-3M
- 8.9x10-3M
- 6.3x10-4M
- 8.9x10-5M
Method:
- Take 3 and +1 (instead of subtracting 1 like before) = a power of 4
- In this case only one power of 4 answer. thats the winner.
#4. If the pOH is 9.1, what is the [OH-] of the solution?
- 6.9x10-9M
- 8.6x10-8M
- 1.6x10-10M
- 7.9x10-10M
Method:
- 9+1 = 10. 10 is the power
- 10- second decimal place= 9 l closest one is 7.9
This is really a sloppy method but it works for me and i got all answers right. if its too risky, or if its not accurate enough someone let me know.
- 2.1x10-3M
- 4.1