Question

Determine the [OH ], pH, and pOH of a solution with a [H+] of 2.7 x 10-6 M at 25 °C. [OH^] = pH = рон = Determine the (H+), pH, and pOH of a solution with an [OHof 6.5 x 10-9 M at 25 °C. [H+] = pH = pOH = Determine the (H+), OH), and pOH of a solution with a pH of 1.86 at 25 °C. [1*= M (OH) = M pOH = Determine the H , OH ), and pH of a solution with a pOH of 10.20 at 25 °C. [+] = [OH ) = pH =

Answer 1

pH is measured for acids and is a negative logarithm of [H+] concentration.

Similarly , pOH is measured for bases & is a negative logarithm of [OH​​​​​-​] concentration.

pH scale has been given by Sorensen & extends values from 0 to 14. That means no solution or a solvent can have pH/pOH values less than '0' or greater than '14'.

Therefore , we write as pH + pOH = 14

Temperature given in all the questions is 25°C , which is room temperature .. so nothing to worry about.

Solution

1) pH = log 1/ [H+]

As given [H +] = 2.7× 10-6

pH = log 1/ 2.7×10 -6

= log 106 / 2.7

= 6 log 10 - log 2.7

= 6×1 - 0.43 { log 10=1 & log 2.7 = 0.43 }

= 6- 0.43

= 5.57

Therefore pH = 5.57.

Note : In logarithms , there are formulae

log m​​​​​​n​​​= n log m

&. log m/n = log m - log n.

To find out pOH , let's lee this simple formula

pH + pOH = 14

Substituting pH , we have

5.57+ pOH = 14

pOH = 14- 5.57

pOH = 8.43

Now , to find out [ OH -] , let's use the formula

pOH = log 1/[ OH -]

(or) [OH -] = 10 -pOH

Upon substituting pOH as 8.43 , we have

[OH -] = 10 -8.43

= 3.7153

2 ) Given [OH​​​​​-​​​​] = 6.5× 10-9

First , let's find out pOH

pOH = log 1/ [OH​​​​​- ]

= log 1/ 6.5× 10-9

= log 109 - log 6.5

= 9 log 10 - log 6.5

= 9- 0.81

POH = 8.19

Now as we know

pH + pOH = 14

Therefore ,

pH + 8.19 = 14

pH = 14-8.19

pH = 5.81

Finally ,

[ H+] = 10 -pH​

= 10 - 5.81

= 1.548

3) Given pH = 1.86

& We know

pH+ pOH = 14

1.86 + pOH = 14 .

pOH = 14- 1.86

= 5.81

& Then , [ H+] = 10-pH

[ H+ ] = 10 - 1.86

= 0.0138

[OH​​​​​-​] = 10 - pOH

= 10 - 12.14

= 7.244

4) Given pOH = 10.20

pH + pOH = 14

pH = 14- pOH

= 14- 10.20

= 3.8

& [ H+ ] = 10 - pH

= 10 - 3.8

= 0.00015

= 1.5× 10 -4

[ OH - ] = 10 - pOH

  = 10 - 10.20

= 6.309