Which one of the following statements is not true?a)The conjugate bas...
Explanation:
The correct statement is option C, the pH of 1 × 10–8 M HCl is 8. Let's analyze each statement to understand why this is the incorrect statement.
a) The conjugate base of H2PO4– is HPO42–.
This statement is true. When H2PO4– donates a proton, it forms its conjugate base HPO42– by losing one hydrogen ion (H+). The chemical equation for this dissociation is:
H2PO4– ⇌ H+ + HPO42–
b) pH + pOH = 14 for all aqueous solutions.
This statement is true. In any aqueous solution, the pH and pOH values are inversely related and their sum is always equal to 14. pH measures the concentration of H+ ions, while pOH measures the concentration of OH– ions. The relationship between pH, pOH, and the concentration of H+ and OH– ions is given by the equation:
pH + pOH = 14
c) The pH of 1 × 10–8 M HCl is 8.
This statement is false. HCl is a strong acid that completely dissociates in water to form H+ ions. Therefore, the concentration of H+ ions in a 1 × 10–8 M HCl solution is 1 × 10–8 M. Taking the negative logarithm (base 10) of this concentration gives us the pH value:
pH = -log[H+]
pH = -log[1 × 10–8]
pH = -(-8) = 8
Therefore, the correct pH value for a 1 × 10–8 M HCl solution is 8, not 14 as stated in option C.
d) 96,500 coulombs of electricity when passed through a CuSO4 solution deposits 1 gram equivalent of copper at the cathode.
This statement is true. Faraday's Law of Electrolysis states that the amount of substance deposited at an electrode is directly proportional to the quantity of electricity passed through the electrolyte. The proportionality constant is known as the Faraday constant and is equal to 96,500 coulombs (C) per mole of electrons. Therefore, when 96,500 coulombs of electricity is passed through a CuSO4 solution, it deposits 1 gram equivalent of copper at the cathode.