At 40.8c the value of kw is 2.92 3 10214. a. calculate the [h1] and [oh2] in pure water at 40.8c. b. what is the ph of pure water at 40.8c? c. if the hydroxide ion concentration in a solution is 0.10 m, what is the ph at 40.8c?

Answer :

(a) The concentration of hydrogen ion and hydroxide ion are, .

(b) The pH of pure water is, 6.78

(c) The pH of solution is, 13

Explanation :

(a) First we have to calculate the concentration of hydrogen ion and hydroxide ion.

As we know that,

In pure water, the concentration of hydrogen ion and hydroxide ion are equal. So, let the concentration of hydroxide ion and hydrogen ion be, 'x'.

The concentration of hydrogen ion and hydroxide ion are, .

(b) Now we have to calculate the pH of pure water.

The pH of pure water is, 6.78

(c) In this, first we have to calculate the pOH when the concentration of hydroxide ion is, 0.10 M.

Now we have to calculate the pH.

The pH of solution is, 13

answer : third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol

explanation :

let us write down the given equations

equation 1 :

equation 2 :

equation 3 :

let us use hess's law to find out which 2 equations can be added to get the third equation.

let us reverse equation 2 and multiply it by 2. the new equation that we get is,

equation 4 :

let us add equation 1 & 4

the above equation is similar to equation 3 but has different value for dhrxn.

therefore third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol