Please help!!! I need the answers ASAP I have 40 mins to pass this
A 0.800 M solution of NH3 is prepared and is in equilibrium with its ions.
a.) What is the hydroxide ion concentration of the solution? Ammonia has a Kb of 1.75x10 − 5
b.) What is the pH of the solution? Ammonia has a Kb of 1.75x10−5.
c.) What is the percent of ionization? Ammonia has a Kb of 1.75x10−5.
d.) Is the assumption valid (using the 5% rule)? Ammonia has a Kb of 1.75x10−5.
What is the pH of a solution if the given is [OH−] = 4.5x10−4M?
choices:
9.10
7.52
10.65
3.35
To solve these questions, you'll need to use some basic chemistry principles and formulas. I'll explain how to find the answer to each question step by step.
a.) The concentration of hydroxide ions (OH-) can be found using the Kb value of ammonia. The balanced equation for the reaction is:
NH3 + H2O ⇌ NH4+ + OH-
Under equilibrium conditions, the concentration of NH4+ and OH- are equal. Let's assume the concentration of OH- is x.
Using the Kb expression for ammonia:
Kb = [NH4+][OH-] / [NH3]
Since the initial concentration of ammonia is 0.800 M, and the concentration of NH4+ and OH- at equilibrium are both x, we can write:
Kb = x * x / (0.800 - x)
Now we can solve for x. Plugging in the values:
1.75x10^-5 = x^2 / (0.800 - x)
Solving this quadratic equation will give you the value of x, which represents the hydroxide ion concentration.
b.) To find the pH of the solution, we need to determine the concentration of hydrogen ions (H+). Since the solution is in equilibrium, we can assume that the concentration of NH3 is still 0.800 M. The equation for the dissociation of water is:
H2O ⇌ H+ + OH-
Since the concentration of OH- is known from part a, we can use the equation:
[H+] * [OH-] = 1.0x10^-14
Solving for [H+], you can find its concentration. Then you can use the formula pH = -log[H+] to calculate the pH.
c.) The percent ionization can be calculated by dividing the concentration of the ions at equilibrium (x) by the initial concentration of ammonia (0.800 M), and then multiplying by 100 to get the percentage.
d.) The assumption of using the 5% rule in this context refers to the extent of ionization. If the percent ionization is less than 5%, it is considered safe to use the assumption that the concentration of the ions at equilibrium is approximately equal to zero. Otherwise, the assumption is not valid.
For the question about the pH of a solution with [OH-] = 4.5x10^-4 M, you can use the equation:
pH = 14 - pOH
Since [OH-] is given, pOH can be calculated as -log[OH-]. Subtracting pOH from 14 will give you the pH value.
Using these explanations, you can now solve the problems and find the correct answer from the given choices.