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Question

Tell if the pH and pOH of the solution is weak or strong.

pH=3.60

pOH=2.46

pH=2.35

pH=2.07

Answer 1

Hello Linie,

The first aspect about pH to be aware of is that there is a scale from 1-14. A liquid solution that has a low pH is considered to be acidic, so like pH of 2 or 3, whereas a liquid solution with a pH of 12 or 13 is considered to be basic. A pH of 7 is considered to be neutral, not acidic, and not basic. A pH of 7 is right in the middle, anything greater is basic, anything less than 7 is acidic.

There is an important formula where the pH + pOH = 14 so when the pH = 2 the pOH = 12, when the pOH is 6 the pH is 8, etc.

When we get down to the meat of what pH means, it is based on a log scale, and the p is actually a symbol for the negative log of a number and in this case the number is the concentration of hydrogen (H+) ions. For pOH it is the same, except for it is the negative log of hydroxide ions (OH-). A pH of 2 can be re-written as the -log(concentration of H+) = 2, and lets say we want to know the concentration of H+ it would be:

log(concentration of H+) = -2

Concentration of H+ = 10^-2 M (this M is the unit for concentration, typically # moles/Liter of solution)

Concentration is just an amount of "stuff" you are looking at in a certain volume of space

So if we take your examples-

pH = 2.07 --> 10^-2.07 = 8.5x10^-3 M (M = "Molars" = moles of H+ ions in 1 liter of solution)

pH = 2.35 --> 10^-2.35 = 4.4x10^-3 M

pH = 3.60 --> 10^-3.6 = 2.5x10^-4 M

pOH = 2.46 [pH + pOH = 14, so pH = 14 - 2.46 = 11.54] = pH of 11.54 --> 10^-11.54 = 2.9x10^-12 H+ ions (very small number)

So we can see that as the pH is increasing, the number of H+ ions in solution goes down, and the solution becomes less acidic and more basic. The more basic a solution is, there will be a greater amount of OH- ions and a lesser amount of H+ ions in solution.

So a pH of 2.07 is acidic and strongly acidic, pH = 2.35 is still acidic but less acidic than 2.07, pH = 3.60 is still acidic but less acidic than 2.35. A pOH = 2.46 = pH of 11.54 is a decently strong basic solution, and not considered to be acidic.

I hope this helps, please reach out to me with any questions!

Answer 2

pH is a measure of the strength of hydrogen ions in solution. A pH around 7 is considered neutral (think about water). When a substance has a pH higher than 7, it is basic. The higher the pH, the stronger base (and weaker acid) that substance is. A pH below 7 indicates that a substance is acidic. The lower the pH, the stronger acid (and weaker base) that substance is. pH of less than around 3 tends to indicate a strong acid. pOH can be converted to pH by subtracting pOH from 14. You can then compare the values you listed using this scale to determine whether they are strong or weak acids or bases.