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Find the H3O+ and OH- from pH 7.65 and determine pH of .001 M stronitium hydroxide.

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mpumpkin | (Level 1) Valedictorian

Posted April 12, 2013 at 10:30 AM via web

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Find the H3O+ and OH- from pH 7.65 and determine pH of .001 M stronitium hydroxide.

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jerichorayel | College Teacher | (Level 1) Senior Educator

Posted April 12, 2013 at 2:30 PM (Answer #1)

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The pH system is used to measure the degree of acidity of any acids ar bases. It can be solved using this expression:

`pH = -log [H^+]`

For the measure of hydroxide we use the pOH which is pretty similar with the above expression:

`pOH = -log [OH^-]`

the relationship of pH and pOH is:

`pH + pOH = 14`

If the pH or pOH is given instead the concentration, we can arrange the expressions as:

`pH = -log [H^+]`

`[H^+] = 10^(-pH)`

AND

`pOH = -log [OH^-]`

`[OH^-] = 10^(-pOH)`

----------------------------------------------------

For pH 7.65:

`pH + pOH = 14`

`pOH = 14- 7.65`

`pOH = 6.35`

 

`[H^+] = 10^(-pH)`

`[H^+] = 10^(-7.65)`

`[H^+] = 2.24x10^-8`

 

`[OH^-] = 10^(-pOH)`

`[OH^-] = 10^(-6.35)`

`[OH^-] = 4.47x10^-7`

 

For 0.001 strontium hydroxide, `Sr(OH)_2`

Since it is a base, we should measure the pOH first. There are two OH- ions in the compounds so the [OH-] would be:

`[OH^-] = 0.001 * 2 = 0.002`

`pOH = -log [OH^-]`

`pOH = -log [0.002]`

`pOH = 2.70`

 

`pH = 14-2.70`

`pH = 11.30`

 

Sources:

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