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pKa to pH calculator

pKa to pH calculator

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Convert From:

Buffer Type

Ka

Acid Concentration

 

Salt Concentration

 

pH

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The pKa to pH calculator measures the pH of a buffer solution by using the pKa concentration. The buffer solution can be acidic or buffer in nature and has various pH values.

What is Buffer Solution?

“A buffer is a water-based solution containing a mixture of a weak acid and its conjugate base.”

The buffer solution resists changing its hydrogen(H⁺) ions concentration or (pH) when we add the acid or base to the buffer solution. The buffer solutions are used in preservatives, drugs, electroplating, and printing.
It is essential to calculate pH of buffer solution exactly for maintaining the quality of our products.

Types of buffer solution:

There are two types of buffer solutions:

Acidic buffer Solution:

The acidic buffer solution can be prepared by mixing up a weak acid and its salt. An acidic buffer solution needs a specific pH.

For example, the acetic acid and sodium acetate(CH3COONa) buffer solution pH should be 4.74. For maintaining a precise pH level, a buffer calculator is handy in achieving the precise pH of the solution. Calculate the ph of a buffer solution before preparing an acidic buffer solution.
There are some characteristics of the Acidic buffer Solution:

  • pH Acidic buffer Solution is less than 7
  • Acidic buffer Solution has weak acid and salt.

Basic Buffer Solution: 

The Basic buffer solution can be prepared by mixing up a weak base and its salt. The basic buffer of ammonium hydroxide (NH4OH) has a pH of 9.25. The pH of ammonium hydroxide (NH4OH) should be maintained for an alkaline basic solution, it can be quite helpful to use a pka to ph calculator  to find the pH of the Basic buffer solution.

  • The pH of a Basic buffer solution is greater than 7
  • A basic buffer solution has a weak base and a salt of the weak base.

How to Calculate the pH of a Buffer Solution?

For calculating the pH of a buffer, consider a weak acid(HA) and its salt (KA) with a strong base (KOH).
The weak acid HA ionizes readily and the equilibrium equation can be written as
HA + H2O ⇋ H+ + A−
Acid Dissociation Constant = Ka = [H+] [A–]/HA
Take the negative log of the LHS and RHS side of the equation:
-log Ka= -log[H+]-log([A+]/[HA])
We know that pH=-log[H+] and pKa=-log Ka
pKa = pH – log([Salt]/[Acid])
pH of buffer solution = pKa + ([salt]/[acid])

How to calculate pH of buffer solution of Alkali?
You just have to change the ph to pOH and ka to Kb for alkaline buffer solution.
pOH of a basic buffer = pKb + log ([salt]/[base])

We need specific pH values for an acidic or a basic buffer solution. You can find the appropriate pH value of an acidic or a basic buffer solution by pKa calculator.

Buffer Solution Calculations Table:

The buffer solution calculations of various solutions is given below:

Buffer Solution pKa (25°C)
Sulfonate 1.8
Aspartic acid 2.1, 3.9, 9.8
Phosphate 2.1, 7.2, 12.3
Chloroacetate 2.9
Sulfonate 1.8
Citrate 3.1, 4.8, 6.4
Gluconic acid 3.6
Lactate 3.9
Acetate 4.8
Carbonate 6.4
Ammonia 9.2

Practical Example:

Find the pKa of an acid having 4.75 pH and a 0.1Molar concentration solution.

Sol:

Now we know that:

pH = pKa + log([A]/[HA])

The pKa to pH calculator use this formula to get the solution:

pH = 4.75 + log10 (0.1)

pH = 4.75 + (−1) 

pKa= 3.75

How to use the pKa to pH Calculator?

For maintaining the precise and accurate pH of the buffer solution follow the steps

Input:

  • Select the buffer type
  • Enter the pKa
  • Enter Acid or base concentration
  • Enter Relative salt concentration 
  • Hit the Calculate Button.

Output:

  • pKA and pH values of buffer solution 

References:

From the source of Wikipedia: Buffer solution, Principles of buffering

From the source of chem.libretexts.org: Introduction to Buffers, What is a buffer