Calculating pH and Ionization of Aspirin Solutions

In summary, the conversation discusses the pH and percent ionisation of a 0.2M solution of aspirin at 25 degrees Celsius with a Ka of 3.0 x 10^-4. It also explains the effect of adding 0.01M hydrochloric acid to the solution and provides steps for calculating the resulting pH and percent ionisation. The formula pH=-log[H+] is used to find the pH, while the formula [H+]=√(Ka*c) is used to find the H+ concentration. The percentage ionisation is determined using the formula √(Ka/c). The common ion effect is also explained.
  • #1
sci0x
83
5
Question: Aspirin is a weak acid.

(a) Calculate pH of 0.2M solution of aspirin at 25 degrees celsius (Ka = 3.0 x 10^-4 at 25 degrees celcius).

(b) Determine the percent ionisation

(c) Explain qualitatively the effect of adding 0.01M hydrochloric acid to the aspirin solution.

(d) Calculate the pH of the resulting solution

(e) Determine the percent ionisation of the aspirin under these conditions
 
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  • #2
hmmm
well formula goes.. pH=-log[H+]
am not sure what about aspirine...i am is Ka also meant as concentration of H+ ??
if yes ...then

pH=-log[H+]
pH=-log(3.0 x 10^-4)=3.5228

and it is acid...but wouldn't say that weak
 
  • #3
Sci0x : Please read the forum guidelines for getting help with schoolwork. See my signature.
 
  • #4
here is the most effective way with which u must proceed---

1) the conc is given as .2 M and ka is given so find the [tex]H^+[/tex] conc using the formula [tex][H^+] = \sqrt{K_a * c}[/tex]
2) percentage ionisation is given by the formula [tex]\sqrt{\frac{k_a}{c}}[/tex]
3)Explain common ion effect
4) due to addition of hydrochloric acid the conc of H+ will now be 0.01 + the conc of H+ u got in the 1st question
5) repeate the 2 question but now with the new conc of H+ note use formula [tex]\frac{[H^+]}{c}[/tex]
 

1. How do you calculate the pH of an aspirin solution?

To calculate the pH of an aspirin solution, you will need to know the concentration of the solution and the ionization constant of aspirin. The pH can be calculated using the Henderson-Hasselbalch equation: pH = pKa + log([A-]/[HA]), where pKa is the ionization constant, [A-] is the concentration of the deprotonated form of aspirin, and [HA] is the concentration of the protonated form of aspirin.

2. What is the ionization constant of aspirin?

The ionization constant of aspirin, also known as its acid dissociation constant (Ka), is a measure of how easily aspirin dissociates into its ions in a solution. The value of Ka for aspirin is approximately 3.5 x 10^-4 at room temperature.

3. How does the concentration of aspirin affect the pH of a solution?

The concentration of aspirin affects the pH of a solution because it determines the amount of protonated and deprotonated forms of aspirin present. As the concentration of aspirin increases, the pH of the solution will decrease (become more acidic) because there will be more [HA] and less [A-] in the Henderson-Hasselbalch equation.

4. What factors can influence the ionization of aspirin in a solution?

The ionization of aspirin in a solution can be influenced by factors such as temperature, pH, and the presence of other ions or molecules. For example, at higher temperatures, aspirin may ionize more readily, leading to a decrease in pH. In addition, if the solution is more acidic, the protonated form of aspirin will be favored, resulting in a lower pH.

5. Can the pH of an aspirin solution be adjusted?

Yes, the pH of an aspirin solution can be adjusted by adding a strong acid or base. Adding a strong acid will decrease the pH, while adding a strong base will increase the pH. However, it is important to note that changing the pH of an aspirin solution may also affect its stability and effectiveness, so it should only be done with caution and under the guidance of a trained professional.

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