[H+] and [OH-] Relationship
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Water
- Sometimes water collides with another water molecule with enough force to transfer hydrogen.
- The result is a hydroxide ion (OH-) that is a base and hydronium ion (H3O+), which is an acid.
- This is known as self-ionization of water.
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Neutral
- In pure water at 25oC the concentration of [H+] and the concentration of [OH-] are each only 1.0 x 10-7 M.
- what this means is the concentration of [H+] and [OH-] are equal and is described as a neutral solution
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Water constant
- In most cases [H+] and [OH-] are interdependent meaning that when [H+] increases [OH-] decreases and vis versa.
- For aqueous solutions, the product of hydrogen ion concentration and hydroxide ion concentration equals 1.0 x 10-14
- [H+] x [OH-] = 1.0 x 10-14
- The product of the concentrations of the hydrogen ions and the hydroxide ions in water is called the ion-product constant for water (Kw)
- Kw = [H+] x [OH-] = 1.0 x 10-14
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Acids and Bases Numerically
- Not all solutions are neutral, when this happens the hydrogen ion concentration is greater than the hydroxide ion concentration and is known as an acidic solution. Which means that [H+] is greater than 1.0 x 10-7 M
- A base is a solution with a larger hydroxide ion concentration than the hydrogen ion concentration. Which means that [H+] is less than 1.0 x 10-7 M. Basic solutions are known as alkaline solutions.
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Example Prob(Copy all)
- Ex prob
- If the [H+] is 1.0 x 10-5 M, is this solution acidic, basic, or neutral? What is the [OH-] of this solution?
- If the concentration of [H+] is more than 1.0 x 10-7 then it is an acidic solution
- To determine the [OH-] use the Kw information and substitute the knowns.
- Kw = [H+] x [OH-] = 1.0 x 10-14
- We know Kw = 1.0 x 10-14 and [H+] = 1.0 x 10-5 so rearrange for [OH-] and solve
- Kw= [OH-] so 1.0 x 10-14 = 1.0 x 10-9 M
- [H+] 1.0 x 10-5 M
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