Calculating pH, pOH, [H+], [OH-] Trick. Someone please confirm if this will work!

[Illstartmydiet2maro]

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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.
  
  

 

[LittleKay]

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.

Why are you doing crazy methods?

Just use this simple method:

6.4x10-8M

1 x 10^-8 (8)

3 x 10^-8 (7.5)

5 x 10^-8 (7.3)

8 x 10^-8 (7.1)

10 x 10^-8 (7)

6.4 is between 5 and 8, roughly in the middle - it’s between 7.1 and 7.3.

Doubt it helps now, but for future viewers. Also you have some wrong answers.