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Problem set1. A) What is the pH of a solution with [H+] = 1 x 10-8 M? 8B) Is this solution acidic or basic? Basic2. A) What is the [OH-] of a solution that has an [H+] = 1 x 10-4 M? 10B) Is this solution acidic or basic? Basic3. What is the [OH-] of a solution that has a pH of 2?4. A) The pH of a solution is changed from pH 6 to pH 10. Does this reflect an increase or decrease in [H+]?B) By how much has the [H+] changed?5. A) If a solution at pH 5 undergoes a 1000-fold increase in [H+], what is the resulting pH?B) If a solution at pH 5 undergoes a 1000-fold increase in [OH-], what is the resulting pH?

Sagot :

2. The pH scale is well used in Chemistry to determine if a solution will be considered to be acidic or basic, and this definition is due to the concentration of protons, which you can also see as H+, and Hydroxide ions, which is also OH-, for concentration, it is usually represented with this symbol []. Now to find out what is the pH of a substance, we can use the pH formula, which is:

pH = -log [H+]

For example we have in question number 1

pH = -log [1*10^-8]

pH = 8

Therefore it will be a basic compound, because the pH scale is divided into below 7 and over 7, <7 = acidic, which also means a high concentration of H+.

>7 = basic, which also means a low concentration of H+

But if we make this simple calculation 7+7 we will have 14, which is the higher number from the pH scale, and this thought when it comes to concentration of ions will be describe as:

1*10^-14 = (1*10^-7) * (1*10^-7)

This is also represented by this equation:

Kw = [H+] * [OH-], where Kw is the constant for pure water

So from this math you realize that if we increase H+, we need to decrease OH-, the same goes for OH-, this is why substances are basic or acids

Now into our question

2. A) if the solution has a concentration of H+ = 1*10^-4, this means that the pH is 4, and 14 (higher value) - 4 = 10, therefore the concentration of OH- must be really low, which is 1*10^-10, or simply 10

B) If the solution has a [H+] = 1*10^-4, the pH will be 4, therefore the solution will be acidic

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