Question

Complete the following table. (All solutions are at 25 °C.) 

Answer 1

In order to solve this question, we can use the following formula:

Here, the value of pKw is 14 at room temperature and 1 bar of pressure, and pH and pOH are as follows:

Using these formulae and the given values, we can ascertain all the unknowns in the given table:

For the First row:

The concentration of H3O+ ion is given, 3.5 X 10-3

From this value, we can ascertain the pH for the first row, pH1

From this we can ascertain the concentration of OH- ion:

Now, using the relation between pOH and concentration of OH-, we can arrive at the following equation:

Now, since the concentration of H3O+ ions is more than the concentration of OH- ions, and the pH is less than 7, the solution is acidic.

For the second row:

The concentration of OH- ions is given, 3.8 X 10-7

From this value, we can ascertain the pOH for the first row, pOH

From this, we can ascertain the concentration of H3O+ ions:

Now, using the relation between pH and concentration of H3O+ ions, we can arrive at the following equation:

Now, since the concentration of H3O+ ions is less than the concentration of OH- ions, and the pH is more than 7, the solution is basic.

For the third row:

The concentration of H3O+ ion is given, 1.8 X 10-9

From this value, we can ascertain the pH for the first row, pH1

From this we can ascertain the concentration of OH- ion:

Now, using the relation between pOH and concentration of OH-, we can arrive at the following equation:

Now, since the concentration of H3O+ ions is less than the concentration of OH- ions, pH is more than 7, the solution is basic.

For the fourth row:

The pH is given, 7.15, from this we can say that the solution is basic because the pH is more than 7.

From this, we can ascertain the concentration of H3O+ ions,

From the given value of pH, we can ascertain the value of OH- ions:

Now, using the relation between pOH and concentration of OH-, we can arrive at the following equation:

Now, since the concentration of H3O+ ions is less than the concentration of OH- ions, pH is more than 7, the solution is basic.

So, the completed box would be as follows:

[H3O+]	[OH-]	pH	Acidic or Basic
3.5 X 10-3	2.88 X 10-12	2.46	Acidic
2.63 X 10-8	3.8 X 10-7	7.58	Basic
1.8 X 10-9	5.50 X 10-6	8.74	Basic
7.08 X10-8	1.41 X 10-7	7.15	Basic