Question

In: Chemistry

How many moles of KF should be added to 0.50 L of a 0.10 M HF...

How many moles of KF should be added to 0.50 L of a 0.10 M HF solution to prepare a buffer with a pH of 2.84?

Expert Solution

Given

HF

Molarity= 0.1

volume =0.5 L

pH buffer = 2.84

Solution:

Lets write reaction for this buffer

HF + KOH -- > KF + H2O

We first calculate concentration of F^- by using Henderson Hasselbalch equation.

The equation :

pH = pka + log([conj. Base]/[weak acid])

here conjugate base is F^- and weak acid is HF

pka = -log ka

ka of HF = 7.2 E-4

pka = -log (7.2E-4)

pka = 3.143

lets plug all the values in Henderson equation

2.84 = 3.143 + log ([F^-] /0.1)

log ([F^-] /0.1) = 2.84 – 3.143

log ([F^-] /0.1) =-0.3026675

Lets take antilog of both side and find the value of [F-]

[F-]= 0.0498117 M

We know [F-] = [KF-] ; KF dissociates fully.

We use molarity and volume in L to calculate the moles of F-

Mol = Molarity x volume in L

n KF= 0.0498117 M x 0.5 L

=0.025 mol

So we need to add 0.025 moles of KF to the solution.

queen_honey_blossom answered 2 years ago

How many mL of 6.0 NaOH must be added to 0.50 L of 0.20 M HNO2...

How many mL of 6.0 NaOH must be added to 0.50 L of 0.20 M HNO2 to prepare a pH = 3.86 buffer?

How many mL (to the nearest mL) of 0.225-M KF solution should be added to 370....

How many mL (to the nearest mL) of 0.225-M KF solution should be added to 370. mL of 0.246-M HF to prepare a pH = 3.90 solution? Please show work, thank you in advance.

How many moles of HCl must be added to 1.0 L of 1.0 M NH3(aq) to...

How many moles of HCl must be added to 1.0 L of 1.0 M NH3(aq) to make a buffer with a pH of 9.00? (pKa of NH4+ =9.25) the answer is 0.64, explain please.

Part A How many moles of HF (Ka=6.8

Part A How many moles of HF (Ka=6.8×10−4) must be added to water to form 0.230...

Part A How many moles of HF (Ka=6.8×10−4) must be added to water to form 0.230 L of solution with a pH of 2.50? Express your answer using two significant figures. n=____mol

How many grams of ammonium chloride, NH4Cl, must be added to 500 ml of 0.10 M...

How many grams of ammonium chloride, NH4Cl, must be added to 500 ml of 0.10 M NH3 solution to give a solution with a pH of 9.0?

Calculate the percent dissociation of HF (Ka= 3.5x10^-4) in (a) 0.050 M HF (b) 0.50 M...

Calculate the percent dissociation of HF (Ka= 3.5x10^-4) in (a) 0.050 M HF (b) 0.50 M HF

When you titrate 100 mL of 0.10 M HF with 0.10 M KOH a) When will...

When you titrate 100 mL of 0.10 M HF with 0.10 M KOH a) When will this titration reach the equivalence point? b) Calculate pH when you add 5 mL of KOH. c) Calculate pH when you add 50 mL of KOH. d) Calculate pH at the equivalence point. e) Calculate pH when you add 101 mL of KOH. (show each step)

How many moles of NH4Cl must be added to 100 mL of 0.1 M NH4OH solution...

How many moles of NH4Cl must be added to 100 mL of 0.1 M NH4OH solution to prevent precipitation of Mn(OH)2 when this solution is added to 100 mL of a 0.002 M solution of MnCl2? Assume no change involume on addition of NH4Cl.

a) How many grams of solid potassium cyanide should be added to 1.00 L of a...

a) How many grams of solid potassium cyanide should be added to 1.00 L of a 0.158 M hydrocyanic acid solution to prepare a buffer with a pH of 8.688 ? b) How many grams of solid ammonium chloride should be added to 2.00 L of a 0.171 M ammonia solution to prepare a buffer with a pH of 9.940 ? c) Design a buffer that has a pH of 7.98 using one of the weak acid/conjugate base systems shown...