The conjugate acid of the dihydrogen orthosilicate anion (H₂SiO₄²⁻) is:

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11ecba2d_1216_a0ab_a3bf_537fac96e2d5_MD0008_00 According to the Brønsted-Lowry definitions, an acid is a chemical species capable of donating a proton (H⁺ ion), and a base is a chemical species that can accept a proton. Acids that can donate more than one proton are called polyprotic acids. Such acids donate protons in a stepwise manner and produce more than one ionic species. The conjugate of an acid (or base) is the species that the acid (or base) becomes after losing (or gaining) one proton. A base is converted into its conjugate acid when the base accepts a proton. Likewise, an acid is converted into its conjugate base when the acid donates a proton. Therefore, an acid (or base) and its conjugate have chemical formulas that differ by only one proton. With two acidic protons and two negative charges, the H₂SiO₄²⁻ anion can function as either an acid (proton donor) or a base (proton acceptor). If H₂SiO₄²⁻ acts as a base and accepts a proton, an ion of H₃SiO₄⁻ is formed. Because the newly formed H₃SiO₄⁻ anion has one more available proton to donate compared with H₂SiO₄²⁻, H₃SiO₄⁻ is the conjugate acid of H₂SiO₄²⁻. (Choice A) HSiO₄³⁻ is the conjugate base, rather than the conjugate acid, of H₂SiO₄²⁻. Donation of a proton by H₂SiO₄²⁻ (acting as an acid) forms an ion of HSiO₄³⁻, which has one less acidic proton than H₂SiO₄²⁻. (Choice C) Although the stepwise loss of two protons does produce H₂SiO₄²⁻, the chemical formula H₄SiO₄ differs by more than one proton from H₂SiO₄²⁻. Therefore, H₄SiO₄ is not the conjugate acid of H₂SiO₄²⁻. (Choice D) The hydronium ion (H₃O⁺) forms when an acid donates a proton to a water molecule (H₂O acts as a base). H₃O⁺ differs by more than a proton from H₂SiO₄²⁻ and is not the conjugate acid of H₂SiO₄²⁻. Educational objective: The conjugate of an acid (or base) is the species that the acid (or base) becomes after losing (or gaining) one proton. An acid (or base) and its conjugate have chemical formulas that differ by only one proton.

The Conjugate Acid of the Dihydrogen Orthosilicate Anion (H2SiO42−) Is

The Conjugate Acid of the Dihydrogen Orthosilicate Anion (H₂SiO₄²⁻) Is