What is the Ka of NaH2PO4?

Last updated on May 9th, 2023 at 02:47 pm

The Ka of NaH2PO4 is a measure of its acid strength. It tells us how effectively NaH2PO4 can donate H+ ions to a solution. Knowing the Ka value helps us to understand the behavior of NaH2PO4 in acidic or basic solutions.

  • The Ka of NaH2PO4 depends on the pH of the solution
  • At higher pH values, NaH2PO4 behaves as a weak acid and has a Ka value of around 6.2 x 10^-8
  • At lower pH values, NaH2PO4 behaves as a buffer and has a Ka value around 1.2 x 10^-2
  • The pKa of NaH2PO4 is 7.20
  • The Ka value can be calculated using the formula Ka = [H+][H2PO4-]/[H3PO4]
  • NaH2PO4 is commonly used in the food industry as a food additive and as a pH buffer in laboratories
  • It is important to consider the Ka value when using NaH2PO4 in any application that involves changing the acidity of a solution

  • Pro Tips:
    1. Understand the concept of acid dissociation: Before solving for the Ka of NaH2PO4, it is essential to understand the concept of acid dissociation, i.e. how an acid dissociates in water to produce hydronium ions and anions.

    2. Write the balanced equation: The next step is to write the balanced equation for the dissociation of NaH2PO4 in water. This equation will help you determine the concentration of hydronium and anions in the solution.

    3. Set up the equilibrium expression: Once you have the balanced equation, set up the equilibrium expression for the reaction. This expression represents the Ka of the acid and helps you solve for its value.

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    4. Calculate the concentrations: To solve for the Ka of NaH2PO4, you need to know the concentrations of the reactants and products in the solution. Use the balanced equation and stoichiometry to determine these values.

    5. Solve for Ka: Once you have the equilibrium concentrations and the equilibrium expression, you can solve for the Ka of NaH2PO4 by plugging in the values. Simplify the expression to obtain the final result.

    Understanding Ka: Calculating Ka for NaH2PO4

    Understanding Acid-Base Equilibria

    Acid-base equilibria refer to the balance between acidic and basic properties of a chemical compound. A compound’s acidity or, in rare cases, basicity, is determined by its ability to donate or accept protons. A simpler way to refer to this is as an acid or base. The strength of an acid or base is a critical factor to consider in chemical reactions.

    An Overview of Ka

    Ka is the acid dissociation constant or the measure of the strength of an acid in a solution. It is used to describe the degree to which an acid dissociates into its component ions in water. When an acid dissociates, it loses a proton and forms a conjugate base, which is involved in further reactions with other compounds. Ka is an important concept in chemistry as it determines the acidity of a solution.

    Definition of NaH2PO4

    Sodium dihydrogen phosphate, also known as NaH2PO4, is an ionic compound commonly used in the food industry as a leavening agent. It is a white, crystalline powder that is easily soluble in water, and it dissociates into ions when placed in an aqueous solution.

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    Calculation of Ka for NaH2PO4

    To calculate the Ka for NaH2PO4, we need to know the equilibrium equation for the dissociation of the acid in water:

    H2PO4- + H2O ⇌ H3O+ + HPO42-

    The Ka expression for NaH2PO4 can be derived as follows:

    Ka = [H3O+][HPO42-]/[H2PO4-]

    To solve for Ka, we need to know the concentrations of the ions in our solution. This can be done by measuring the pH of the solution and using the equation of the dissociation constant. Once we have determined the pH, we can plug in the values to get the Ka.


    Suppose a 0.1 M NaH2PO4 solution is prepared, and its pH is measured at 7.3. Using the equation, we can determine the concentration of each ion:
    [H3O+] = 10^(-7.3) = 5.01 × 10^(-8) M
    [HPO42-] = [H2PO4-] = 0.1 M (initial concentration)

    Substituting the values into the Ka expression, we get:
    Ka = 4.76 × 10^(-13)

    Factors Affecting Ka Value

    There are various factors that could affect the value of Ka for a chemical compound. These include:

    • Temperature: higher temperatures usually result in higher Ka values as the reaction rate is faster with more energy
    • Concentration of reactants: higher concentrations of reactants favor the formation of the products and hence lead to higher Ka values
    • Catalysts: the presence of catalysts may increase the rate of the reaction, leading to higher Ka values

    Importance of Ka in Chemical Reactions

    The value of Ka is important in determining the strength of acids and bases and in understanding how they react with other chemical compounds. It helps to predict how well an acid will donate a proton in a solution and how strong the conjugate base will be. It also determines the pH of a solution, which can have a significant effect on chemical reactions. In summary, understanding Ka is essential in predicting and interpreting various chemical reactions in the laboratory or real-world applications.

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