A **diprotic acid** is an acid that can donate two hydronium ions (H^{+}).

Since a diprotic acid has two acidic hydrogens it would have 2 equilibrium equations.

**Concept:** Diprotic Acids

The diprotic bases would also have 2 equilibrium equations.

**Concept:** Diprotic Acids

**Concept:** As a result of these equations for diprotic acids and bases the relationship between K_{a} and K_{b} can be established.

**Example:** Sulfurous acid, H_{2}SO_{3}, represents a diprotic acid with a K_{a1} = 1.6 x 10** ^{-2}** and K

**Example:** Determine the pH of 0.115 M Na_{2}S. Hydrosulfuric acid, H_{2}S, contains K_{a1} = 1.0 x 10** ^{-7}** and K

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A 4.00-g quantity of a diprotic acid was dissolved in water and made up to exactly 3.00 x 10^{2} mL. Calculate the molar mass of the acid if 25.0 mL of this solution required 11.6 mL of 1.00 M KOH for neutralization. Assume that both protons of the acid were titrated.

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Complete the K_{a2} expression for H_{2}CO_{3} in an aqueous solution.

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What is the pH of a 0.310 M solution of H2SO4? Ka2 = 1.20 x 10^-2

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Complete the K_{a2} expression for H_{2}CO_{3} in an aqueous solution. K_{a2 }= 4.69 x 10^{-11}

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Write chemical equations and corresponding equilibrium expressions for each of the two ionization steps of carbonic acid.

Express as chemical equation; identify all phases.

a. Write chemical equations for first ionization step of carbonic acid.

b. Write chemical equations for second ionization step of carbonic acid.

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Write the equation for the reaction associated with:

The K_{a2} of sulfuric acid (H_{2}SO_{4}).

The K_{b2} of carbonate in water (CO_{3}^{2-})

Explain in your own words why you do not need a K-value to calculate the dissociation of a strong acid?

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For the diprotic weak acid H_{2}A, K_{a}1 = 3.1 X 10^{-6} and K_{a}2 = 5.1 X 10^{-9}. What is the pH of a 0.0500 M solution of H_{2}A? What are the equilibrium concentrations of H_{2}A and A^{2-} in this solution?

pH = ?

H_{2}A = ?

A_{2}- = ?

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Write the chemical equation for the reaction of carbonic acid (H _{2}CO_{3}) with water.

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Calculate the equilibrium concentration of C_{2}O_{4}^{2−} in a 0.20 *M* solution of oxalic acid.

Express your answer to two significant figures and include the appropriate units.

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The *pKa*'s for carbonic acid and bicarbonate at 37°C are 3.83 and 10.25, respectively. Write the equation for each of these equilibria.

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H_{2}CO_{3} is a diprotic acid. The pKa for H_{2}CO_{3} is 6.35 and the pKa for HCO_{3}^{- }= 10.33. At pH = 9.0, what is the approximate relative quantities of H_{2}CO_{3}, HCO_{3}^{-}, and CO_{3}^{2-}?

a. 1 H_{2}CO_{3}, 10 HCO_{3}^{-}, and 1 CO_{3}^{2-}

b. Negligible H_{2}CO_{3}, 95 HCO_{3}^{-}, and 5 CO_{3}^{2-}

c. 1 H_{2}CO_{3}, 90 HCO_{3}^{-}, and 10 CO_{3}^{2-}

d. Negligible H_{2}CO_{3}, 75 HCO_{3}^{-}, and 25 CO_{3}^{2-}

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Calculate the concentration of H^{+} ions in a 0.010 M aqueous solution of sulfuric acid.

Express your answer to three decimal places and include the appropriate units.

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Identify the weak diprotic acid.

A) CH_{3}COOH

B) HCOOH

C) H_{3}PO_{4}

D) H_{2}SO_{4}

E) H_{2}CO_{3}

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Ascorbic acid, H_{2}C_{6}H_{6}O_{6}, is a common diprotic acid with a K_{a1} = 8.0 x 10 ^{-5} and K_{a2} = 1.6 x 10 ^{-12}.

a. What are the three forms of the diprotic acid?

b. What is the principal species at pH = 2.00?

c. What is the principal species at pH = 6.10?

d. What is the principal species at 13.80?

e. What is the second most prominent species at pH = 8.10?

f. At what pH is [H_{2}C_{6}H_{6}O_{6}] = [HC_{6}H_{6}O_{6} ** ^{-}** ]?

g. At what pH is [HC_{6}H_{6}O_{6} ** ^{-}** ] = [C

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Identify the weak diprotic acid.

A) CH_{3}COOH

B) HCOOH

C) H_{3}PO_{4}

D) H_{2}SO_{4}

E) H_{2}CO_{3}

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Calculate the pH of a 0.080 M carbonic acid solution, H _{2}CO_{3}(aq), that has the stepwise dissociation constants K_{a1} = 4.3 × 10 ^{-7 }and K_{a2} = 5.6 × 10 ^{-11}.

A) 1.10

B) 3.73

C) 6.37

D) 10.25

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