Which solution has the highest pH?
A) 50.0 mL 0.0500 M calcium hydroxide, Ca(OH)2 (aq)
B) 50.0 mL 0.0500 M sodium hydroxide, NaOH (aq)
C) 50.0 mL 0.0500 M nitric acid, HNO3 (aq)
D) 50.0 mL 0.0500 M nitrous acid, HNO2 (aq)
Answers
Answered by
3
Ok. So the first step is to identify whether the solution is an acid or a base. That is, wherer it contains the H+ ion (acid) or the OH- ion (base). There are two rules that follow.
For an acid. pH = -log(H+), where log is log base 10 and H+ is the concentration (molarity) of H+ ions in the solution.
For a base. pH = 14 + log(OH-), where log is log base 10 and OH- is the concentration (molatity) of OH- ions in the solution.
Basically, if you have a calculator, you can work this out.
--------------------------------------...
Now, to answer your questions:
a) This is an acid as it contains the H= ions. Now:
pH = -log(H+) = -log(0.05) = 1.3
[Notice how the volume does not affect the pH of the solution]
b) Similarly ph= =log(0.05) = 1.3
c) Now this is a base (contains OH-)
pH = 14 + log(0.05) = 12.7
d) This one is a base but a little tricky. Notice how there is 0.05M of the solution, but there is 2 moles of OH- for every mole of the solution (2 OH- particles for ever calcium hydroxide particle). so (OH-) is in fact 0.1
ph= 14 + log(0.1) = 13
That's the pH calculation. But in actual fact it is not always this way. There is one more thing you need to know.
Nitric acid is a strong acid, so it completely ionises in water. Whilst nitrous acid is a weak acid. Therefore, the nitric acid solution has the LOWEST ph.
Sodium hydroxide and Calcium hydroxide are strong bases so they completely ionisesin solution. Because they ionise at the same rate, and Calcium hydroxide has the higher pH calculated, then Calcium hydroxide in fact has the highest pH.
For an acid. pH = -log(H+), where log is log base 10 and H+ is the concentration (molarity) of H+ ions in the solution.
For a base. pH = 14 + log(OH-), where log is log base 10 and OH- is the concentration (molatity) of OH- ions in the solution.
Basically, if you have a calculator, you can work this out.
--------------------------------------...
Now, to answer your questions:
a) This is an acid as it contains the H= ions. Now:
pH = -log(H+) = -log(0.05) = 1.3
[Notice how the volume does not affect the pH of the solution]
b) Similarly ph= =log(0.05) = 1.3
c) Now this is a base (contains OH-)
pH = 14 + log(0.05) = 12.7
d) This one is a base but a little tricky. Notice how there is 0.05M of the solution, but there is 2 moles of OH- for every mole of the solution (2 OH- particles for ever calcium hydroxide particle). so (OH-) is in fact 0.1
ph= 14 + log(0.1) = 13
That's the pH calculation. But in actual fact it is not always this way. There is one more thing you need to know.
Nitric acid is a strong acid, so it completely ionises in water. Whilst nitrous acid is a weak acid. Therefore, the nitric acid solution has the LOWEST ph.
Sodium hydroxide and Calcium hydroxide are strong bases so they completely ionisesin solution. Because they ionise at the same rate, and Calcium hydroxide has the higher pH calculated, then Calcium hydroxide in fact has the highest pH.
Similar questions