Find the pH of each mixture of acids
1) 0.115M in HBr + 0.125M in HCHO2
2) 0.050M in acetic acid + 0.050M in hydrocyanic acid
To find the pH of each mixture of acids, we can use the formula for calculating the pH of a solution. The pH is determined by the concentration of hydronium ions (H3O+), which can be found using the concentration of the acid in the solution.
1) 0.115M HBr + 0.125M HCHO2:
HBr is a strong acid, so it dissociates completely in water to release H3O+ ions.
HCHO2 is a weak acid, so it only partially dissociates in water.
To determine the pH of the mixture, we need to find the concentration of H3O+ ions in the solution.
Step 1: Calculate the concentration of H3O+ ions from HBr:
Since HBr is a strong acid, it will dissociate completely.
Thus, the concentration of H3O+ ions from HBr is equal to the concentration of HBr, which is 0.115M.
Step 2: Calculate the concentration of H3O+ ions from HCHO2:
To determine the concentration of H3O+ ions from HCHO2, we need to consider its acid dissociation constant (Ka) and the concentration of HCHO2.
The Ka of HCHO2 is given as 1.8 x 10^-4.
HCHO2 ⇌ H+ + CHO2-
Let x be the concentration of H+ ions.
Ka = [H+][CHO2-] / [HCHO2]
1.8 x 10^-4 = x * x / (0.125 - x)
Since x is much less than 0.125, we can approximate (0.125 - x) as 0.125.
1.8 x 10^-4 = x^2 / 0.125
x^2 = 0.125 * (1.8 x 10^-4)
x^2 = 0.0225 x 10^-4
x = √(0.0225 x 10^-4)
x = 0.015 x 10^-2
x = 1.5 x 10^-4
Therefore, the concentration of H3O+ ions from HCHO2 is 1.5 x 10^-4 M.
Step 3: Calculate the total concentration of H3O+ ions in the mixture:
To find the total concentration of H3O+ ions, we need to sum up the concentrations from HBr and HCHO2.
Total [H3O+] = [H3O+] from HBr + [H3O+] from HCHO2
Total [H3O+] = 0.115M + 1.5 x 10^-4 M
Total [H3O+] ≈ 0.115M (since 1.5 x 10^-4 M is negligible compared to 0.115M)
Therefore, the pH of the mixture of 0.115M HBr and 0.125M HCHO2 is approximately equal to the pH of a 0.115M HBr solution, which is acidic.
2) 0.050M acetic acid + 0.050M hydrocyanic acid:
Acetic acid (CH3COOH) is a weak acid, and hydrocyanic acid (HCN) is also a weak acid.
To determine the pH of the mixture, we need to find the concentration of H3O+ ions in the solution.
Step 1: Calculate the concentration of H3O+ ions from acetic acid:
Since acetic acid is a weak acid, it only partially dissociates.
The Ka of acetic acid is 1.8 x 10^-5.
CH3COOH ⇌ H+ + CH3COO-
Let x be the concentration of H+ ions.
Ka = [H+][CH3COO-] / [CH3COOH]
1.8 x 10^-5 = x * x / (0.050 - x)
Since x is much less than 0.050, we can approximate (0.050 - x) as 0.050.
1.8 x 10^-5 = x^2 / 0.050
x^2 = 0.050 * (1.8 x 10^-5)
x^2 = 0.0009 x 10^-5
x = √(0.0009 x 10^-5)
x = 0.03 x 10^-3
x = 3 x 10^-5
Therefore, the concentration of H3O+ ions from acetic acid is 3 x 10^-5 M.
Step 2: Calculate the concentration of H3O+ ions from hydrocyanic acid:
Since hydrocyanic acid is also a weak acid, it only partially dissociates.
However, to simplify the calculation, we will assume that it dissociates completely to form H+ ions.
Therefore, the concentration of H3O+ ions from hydrocyanic acid is equal to the concentration of hydrocyanic acid, which is 0.050M.
Step 3: Calculate the total concentration of H3O+ ions in the mixture:
To find the total concentration of H3O+ ions, we need to sum up the concentrations from acetic acid and hydrocyanic acid.
Total [H3O+] = [H3O+] from acetic acid + [H3O+] from hydrocyanic acid
Total [H3O+] = 3 x 10^-5 M + 0.050M
Total [H3O+] ≈ 0.050M (since 3 x 10^-5 M is negligible compared to 0.050M)
Therefore, the pH of the mixture of 0.050M acetic acid and 0.050M hydrocyanic acid is approximately equal to the pH of a 0.050M hydrocyanic acid solution, which is acidic.
To find the pH of each mixture of acids, you need to understand the concept of acid dissociation and the relationship between concentration and pH.
The pH of a solution is a measure of its acidity or basicity. It is defined as the negative logarithm (base 10) of the concentration of hydrogen ions, H+.
1) For the first mixture of acids, HBr (hydrobromic acid) and HCHO2 (formic acid), you need to determine the concentration of H+ ions.
HBr is a strong acid that dissociates completely in water, so the concentration of H+ ions is equal to the concentration of HBr, which is 0.115M.
HCHO2 is a weak acid that does not dissociate completely, so you need to consider its dissociation constant (Ka) to determine the concentration of H+ ions. The Ka for formic acid is 1.8 x 10^-4. Start by assuming the concentration of H+ ions from HCHO2 is x. Then, the concentration of HCHO2 is given as 0.125M.
HCHO2 ⇌ H+ + CHO2-
Using the equilibrium expression for Ka:
Ka = [H+][CHO2-] / [HCHO2]
1.8 x 10^-4 = x * 0.125M / (0.125M - x)
Solving this equation will give you the value of x, which represents the concentration of H+ ions from HCHO2.
Once you have the concentrations of H+ ions from HBr and HCHO2, you can calculate the total concentration of H+ ions in the mixture. Then, take the negative logarithm (base 10) of this concentration to find the pH of the mixture.
2) For the second mixture of acids, acetic acid and hydrocyanic acid, the process is similar.
Acetic acid, CH3COOH, is a weak acid. The Ka value for acetic acid is 1.8 x 10^-5. The concentration of acetic acid is given as 0.050M. Follow the same steps as in the first example to calculate the concentration of H+ ions from acetic acid using the given Ka value.
Hydrocyanic acid, HCN, is also a weak acid. Its Ka value is 4.9 x 10^-10. The concentration of hydrocyanic acid is also given as 0.050M. Apply the same procedure to calculate the concentration of H+ ions from hydrocyanic acid.
Once you have the concentrations of H+ ions from both acids, calculate the total concentration of H+ ions in the mixture and determine the pH using the negative logarithm (base 10) of this concentration.
1) HBr is a strong acid meaning it ionizes 100% so H^+ from HBr is 0.115M. To this can be added the H^+ from HCHO2 but remember that the strong acid is a common ion to the HCHO2 so the ionization of HCHO2 will be suppressed.
It may be suppressed so much that the amount HT+ added is not significant but you will need to calculate it to know.
2) This is done the same way; however, both are weak acids. Caculate H^+ from acetic acid (the stronger one) and proceed as in 1 above.
Post your work if you get stuck.