a. Determine the percent ionization for a 1.00M phosphoric acid solution at 25.0 oC given the following (assume the small x approximation is valid)
H3PO4(aq) H2PO4(aq)H+(aq)
ΔGf (kJ/mol) -1142.6| -1130.2 | 0
b. Assuming ΔGf does not change with temperature, determine the percent ionization at 50.0 oC.
I assume you are to determine Ka from dGf values. Can you do that? What is Ka?
For b. dG = -RTlnK. Plug in R, T, dG and solve for K.
If you have the K values I can show you how to obtain % ionization.
DrBob222...I would assume if people KNEW how to answer a question they would NOT have to seek help on this site.
always
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To determine the percent ionization for a phosphoric acid solution, we need to calculate the concentration of H+ ions and then divide it by the initial concentration of phosphoric acid. The percent ionization is the ratio of the concentration of H+ ions to the concentration of H3PO4, multiplied by 100.
Let's start with part a:
1. Identify the balanced chemical equation for the ionization of phosphoric acid:
H3PO4(aq) ⇌ H2PO4-(aq) + H+(aq)
2. Determine the initial concentrations:
Initial concentration of H3PO4 = 1.00 M (given)
3. Set up an ICE (Initial, Change, Equilibrium) table:
| | H3PO4(aq) | H2PO4-(aq) | H+(aq) |
|-----------|------------|------------|------------|
| Initial | 1.00 M | 0 M | 0 M |
| Change | -x | +x | +x |
| Equilibrium | 1.00-x M | x M | x M |
4. Write the equilibrium expression:
Ka = [H2PO4-][H+]/[H3PO4]
5. Plug in the equilibrium concentrations into the equilibrium expression:
Ka = x * (x) / (1.00 - x)
6. Assuming the small x approximation is valid, you can ignore x in the denominator:
Ka = x^2 / (1.00 - x)
7. Look up the Ka value for phosphoric acid (H3PO4) at 25.0°C. The Ka value is a measure of the acid's strength and indicates the degree of ionization.
Once you have the Ka value, you can solve the above equation to find x, which represents the concentration of H+ ions at equilibrium.
8. Calculate the percent ionization:
[% Ionization] = (H+ concentration / H3PO4 concentration) * 100
= (x / 1.00) * 100
Now, moving on to part b:
Assuming ΔGf (standard free energy change) does not change with temperature, we can assume the equilibrium constant (Ka) remains the same at different temperatures.
To determine the percent ionization at 50.0°C, you can follow the same procedure as in part a. However, you need to use the equilibrium constant and the temperature of 50.0°C to calculate the new value of x. After finding the new value of x, you can calculate the percent ionization using the same equation as in part a.
Remember to adjust the temperatures to Kelvin (50.0°C + 273.15 = 323.15 K) before calculating the new value of x.
I hope this helps! Let me know if you have further questions.