H2O(l)+H2O(l) ⇄ H3O+(aq)+OH−(aq)
At 5.0°C, the value of Kw for the equilibrium shown above is 1.9×10−15 and the value of pKw is 14.73. Which of the following is correct for pure water at this temperature?
A. [H3O+] = √1.9×10^(−15)
B. pH = −log(1.9×10^(−15))
C. 14.73 = [H3O+]eq [OH−]eq
D. pOH = pH+14.73
A is correct.
B. pH = −log(1.9×10^(−15))
C. 14.73 = [H3O+]eq [OH−]eq
D. pOH = pH+14.73
B is incorrect. To be correct it should be pH = - log(H3O+)/
C is incorrect. To be correct it should be 14.73 = pH + pOH or
Kw = (H3O^+)(OH^-)
D is incorrect. To be correct it should be pOH + OH = 14.73 = pKw
Thanks DrBob222!
To determine which statement is correct for pure water at 5.0°C, we need to understand the relationships between the various species involved in the equilibrium and the concept of pH.
First, let's understand the given equilibrium reaction:
H2O(l) + H2O(l) ⇌ H3O+(aq) + OH-(aq)
This equation represents the dissociation of water into hydronium ions (H3O+) and hydroxide ions (OH-) in an aqueous solution.
The value of Kw (the ion product of water) at 5.0°C is given as 1.9×10^(-15). Kw is defined as the product of the concentrations of hydronium and hydroxide ions in a water solution at equilibrium. Mathematically, it can be stated as:
Kw = [H3O+][OH-]
Next, we are given the value of pKw at 5.0°C, which is 14.73. pKw is the negative logarithm of Kw and is related to the pH scale. Mathematically, it can be stated as:
pKw = -log(Kw)
Now, let's evaluate each statement to determine which one is correct:
A. [H3O+] = √1.9×10^(-15)
This statement suggests that the concentration of hydronium ions can be determined by taking the square root of Kw. However, this is not correct. The concentration of hydronium ions cannot be determined solely from Kw. This statement is incorrect.
B. pH = -log(1.9×10^(-15))
pH is a measure of the concentration of hydronium ions in a solution. This statement uses the definition of pKw to calculate pH. Since pKw is given as 14.73, we can substitute this into the equation:
pH = 14.73
This statement is incorrect because it does not provide any information about the concentration of hydronium ions.
C. 14.73 = [H3O+]eq [OH-]eq
This statement suggests that the product of the concentrations of hydronium ions and hydroxide ions will always be equal to 14.73. However, this is not true. The actual value of [H3O+][OH-] can vary depending on the conditions of the solution. This statement is incorrect.
D. pOH = pH + 14.73
pOH is another measure of the concentration of hydroxide ions in a solution. This statement suggests that the relationship between pOH and pH is defined by adding 14.73. However, this is not correct. The correct relationship between pOH and pH is given by the equation:
pOH = 14 - pH
So, the statement is incorrect.
To summarize, none of the given statements are correct for pure water at 5.0°C. The correct statement would be that the concentration of hydronium ions ([H3O+]) and hydroxide ions ([OH-]) in pure water at this temperature can be calculated using the value of Kw, but the exact values cannot be determined solely from the given information.