Multiple Choice
Rank the following in order of increasing base strength (weakest to strongest).
OI− OCl− OBr−
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17. Acid and Base Equilibrium
The pH Scale
Multiple Choice
Which of the following statement(s) on aqueous solutions is/are correct?
a) aqueous solutions have a pH of 7
b) as concentration of hydronium ion increases, concentration of hydroxide ion decreases
c) solutions of weaker acids generally have a higher pOH then solutions of stronger acids
d) pH of pure water equals to 7 at 35º C.
A
aqueous solutions have a pH of 7
B
as concentration of hydronium ion increases, concentration of hydroxide ion decreases
C
solutions of weaker acids generally have a higher pOH then solutions of stronger acids
D
pH of pure water equals to 7 at 35º C.
Verified step by step guidance1
Understand that an aqueous solution is a solution in which the solvent is water. The pH of an aqueous solution can vary depending on the substances dissolved in it.
Recall the relationship between hydronium ions \( \text{H}_3\text{O}^+ \) and hydroxide ions \( \text{OH}^- \) in water. According to the ion product of water \( K_w \), \( [\text{H}_3\text{O}^+] \times [\text{OH}^-] = 1.0 \times 10^{-14} \) at 25º C. As the concentration of hydronium ions increases, the concentration of hydroxide ions must decrease to maintain this constant.
Consider the strength of acids. Stronger acids dissociate more completely in water, producing more hydronium ions, which results in a lower pH and consequently a lower pOH. Weaker acids dissociate less, resulting in fewer hydronium ions and a higher pOH.
Understand that the pH of pure water is 7 at 25º C, but this value changes with temperature. At 35º C, the ion product of water \( K_w \) increases, causing the pH to be slightly less than 7.
Evaluate each statement based on these principles: (a) is incorrect because not all aqueous solutions have a pH of 7; (b) is correct due to the inverse relationship between hydronium and hydroxide ions; (c) is correct because weaker acids have higher pOH; (d) is incorrect because the pH of pure water is not 7 at 35º C.
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