Can someone please explain the following processes to me: Calculate a theoretica
ID: 811082 • Letter: C
Question
Can someone please explain the following processes to me:
Calculate a theoretical pH value for a solution.
(i.e. your solution is derived from the following lab work: Obtain 5.00 mL of the 0.10 M HCl solution in a 10-mL graduated cylinder and add it to a 50-mL graduated cylinder. After adding enough H2O to have a total volume of 50.00 mL, mix thoroughly and measure the pH of this 0.010 M solution of HCl.)
Calculate an experimental [H+] based upon your measured pH.
(I am pretty sure this is just [H+]=10-pH but I wanted to check
Explanation / Answer
1) 5mL of 0.1 M HCl has 0.1*5/1000=5x10^-4 moles HCl.
After diluting it to 50mL the [HCl] = (5x10^-4/50)*1000 = 0.01M and hence the pH is 2.0.
2) Acetic acid is a weak acid. It dissociates only partly, unlike an aqueous solution of HCl. For HCl solution, if you measure pH of 1.0 M and 0.1M solution it would read 0 and 1 respectively. But, this is not the case with acetic acid. For acetic acid the pH of the solution depends on its dissociation constant, Ka.
theequilibrium reaction is:
CH3COOH <--------> H+ + CH3COO-
Ka = [acetate][H+]/[acetic acid]
Therefore, a 1.0M and a 0.1M acetic acid solution may show a same pH.