Question

In: Chemistry

The pH of 0.30 M solution of HCN is 5.20. Calculate the Ka value for HCN.

Expert Solution

Let a be the dissociation of the weak acid,HA
HA <---> H ⁺ + A^-

initial conc. c 0 0

change -ca +ca +ca

Equb. conc. c(1-a) ca ca

Dissociation constant , K_a = ca x ca / ( c(1-a)

= c a² / (1-a)

In the case of weak acids α is very small so 1-a is taken as 1

So K_a = ca²

==> a = √ ( K_a / c )

Given c = concentration = 0.30 M

pH = 5.20

- log[H⁺] = 5.20

[H⁺] = 10^-5.20

= 6.31x10^-6 M

[H⁺] = ca = 6.31x10^-6 M

a = (6.31x10^-6 M ) / 0.30

= 2.10x10^-5

So K_a = ca²

= 0.30 x (2.10x10^-5)²

= 1.33x10^-10

queen_honey_blossom answered 2 years ago

The pH of a 0.10 M HCN solution is 5.20. a. What is [H3O+ ] in...

The pH of a 0.10 M HCN solution is 5.20. a. What is [H3O+ ] in that solution? _______________ M b. What is [CN-]? What is [HCN]? (Where do the H+ and CN - ions come from?) [CN-] = _______________ M; [HCN] = _____________ M c. What is the value of Ka for HCN? What is the value of pKa? Ka = _______________ pKa = _______________

A 0.30 M solution of a salt NaA has pH=9.15. What is the value of Ka...

A 0.30 M solution of a salt NaA has pH=9.15. What is the value of Ka for the parent acid HA?

Calculate the ph of a solution that is 0.30 M in ammonia (NH3) and 0.20 M...

Calculate the ph of a solution that is 0.30 M in ammonia (NH3) and 0.20 M in ammonium chloride. Kb=1.76 x 10^-5 Then calculate the ph if you add 10 mL of 1.0 M HCl to 50 mL of your solution in the problem above.

Calculate the pH of .346 M aqueous solution hydrocyanic acid HCN, Ka=4.0x10^-10 and the equilibrium concentrations...

Calculate the pH of .346 M aqueous solution hydrocyanic acid HCN, Ka=4.0x10^-10 and the equilibrium concentrations of the weak acid and it’s conjugate base pH= HCN equilibrium= CN-= Calculate the pH of a .0169 M aqueous solution of hydro fluoric acid HF, Ka=6.6x10^-4 and the equilibrium concentrations of the weak acid and it’s conjugate base pH= HF equilibrium= F-=

Part A. Calculate the pH of a buffer solution that is 0.250 M in HCN and...

Part A. Calculate the pH of a buffer solution that is 0.250 M in HCN and 0.168 M in KCN. For HCN, Ka = 4.9×10−10 (pKa = 9.31). Part B. Calculate the pH of a buffer solution that is 0.240 M in HC2H3O2 and 0.190 M in NaC2H3O2. (Ka for HC2H3O2 is 1.8×10−5.) Part C. Consider a buffer solution that is 0.50 M in NH3 and 0.20 M in NH4Cl. For ammonia, pKb=4.75. Calculate the pH of 1.0 L of...

Calculate the pH of a solution that is made by mixing 0.80 L of 0.30 M...

Calculate the pH of a solution that is made by mixing 0.80 L of 0.30 M formic acid (HCOOH, Ka=1.77X10-4) and 0.90 L of 0.20 M sodium formate (NaHCOO). [Hint: don’t forget that you are mixing, and so each is diluted upon mixing]

Determine the pH of 0.35M HCN. The Ka of HCN is 6.2e-10 M.

1.Calculate the pH of a buffer solution that is 0.249 M in HCN and 0.175 M...

1.Calculate the pH of a buffer solution that is 0.249 M in HCN and 0.175 M in KCN. For HCN, Ka = 4.9×10−10 (pKa = 9.31). 2.Calculate the pH of a buffer solution that is 0.210 M in HC2H3O2 and 0.200 M in NaC2H3O2. (Ka for HC2H3O2 is 1.8×10−5.) 3.Consider a buffer solution that is 0.50 M in NH3and 0.20 M in NH4Cl. For ammonia, pKb=4.75. Calculate the pH of 1.0 L of the original buffer, upon addition of 0.020...

Calculate the pH of a .003 M solution of NaF, given that the Ka of HF...

Calculate the pH of a .003 M solution of NaF, given that the Ka of HF = 6.8 x 10^-4 at 25 degrees celcius.

Calculate the pH and pOH of a 0.50 M solution of Acetic Acid. The Ka of...

Calculate the pH and pOH of a 0.50 M solution of Acetic Acid. The Ka of HOAc is 1.8 x10-5 [H3O+]/(0.50-0.00095)=1.8x10-5 where did they get the .00095, its said to take that as the second assumption [H3O+]=9.4x10-4 [H3O+]/(0.50-0.00094)=1.85x10-5 [H3O+]=9.4x10-4 (this is said to be the third assumption) Please, please help I really dont understand this, please show all steps and be as descriptive as possible.