Calculating [OH-] from an acid and salt.

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In summary, to calculate the [OH-] concentration in a 0.5 M solution of potassium fluoride (KF), we use the fact that KF dissociates into K+ and F- in a 1:1 ratio. Therefore, the [F-] concentration is 0.5 M. Using the Ka value for HF, we can set up an ICE chart to find the [OH-] concentration, noting that F- acts as a Bronsted base in this reaction.
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Homework Statement


Calculate the [OH-] concentration in a 0.5 M solution of potassium fluoride (KF). Ka for
HF is 7.2 × 10−4.

The Attempt at a Solution


I know that KF → K+ + F-, therefore having a 1:1 ratio, [F-] = 0.5M
,but from here I am unsure what to do with the F- concentration.

I know that Ka = ([H+][F-])/[HF] and normally I would set up an ICE chart, but I would have too many variables in this case. (Not knowing the concentration of [HF] as well as the "change")
 
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F- + H2O <-> HF + OH-

Or, to put it differently - F- is a Bronsted base.
 

FAQ: Calculating [OH-] from an acid and salt.

What is the formula for calculating [OH-] from an acid and salt?

The formula for calculating [OH-] from an acid and salt is [OH-] = (Kw/[H3O+]) - [H+], where Kw is the ionization constant of water, [H3O+] is the concentration of hydronium ions from the acid, and [H+] is the concentration of hydrogen ions from the salt.

What is the purpose of calculating [OH-] from an acid and salt?

The purpose of calculating [OH-] from an acid and salt is to determine the concentration of hydroxide ions, which can be used to determine the pH of the solution. This information is important in many scientific and industrial applications.

What factors can affect the accuracy of [OH-] calculations from an acid and salt?

Some factors that can affect the accuracy of [OH-] calculations from an acid and salt include measurement errors, deviations from ideal conditions, and incomplete dissociation of the acid and salt. It is important to carefully control experimental conditions and use accurate measurements to minimize these errors.

How is [OH-] affected by the strength of the acid and salt?

The strength of the acid and salt can affect the concentration of hydroxide ions in a solution. Strong acids and salts will result in a higher concentration of [OH-], while weak acids and salts will result in a lower concentration. This is due to the different dissociation constants of each acid and salt.

Are there any limitations to using the formula for calculating [OH-] from an acid and salt?

Yes, there are some limitations to using this formula. It assumes ideal conditions, such as a constant temperature and complete dissociation of the acid and salt. In reality, these conditions may not be met, resulting in some errors in the calculated [OH-] concentration. Additionally, this formula is only applicable for aqueous solutions and may not work for other types of solvents.

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