If a solution is at pH 4, how many hydrogen ions are present in a final solution ending up at pH 7? How many hydroxyl ions are present in the final solution?

Question

Can someone answer this question for me 

Answer 1

At pH = 4, the hydrogen ion concentration is 10^-4 M. At pH of 7, the hydrogen ion concentration is 10^-7 M. You can’t calculate the number of hydrogen ions without knowing the volume of the solution. Same goes with the number of hydroxyl ions. You need to know the volume.