I need help answering this question. It says Mass OF NH4Cl should the student di

Question

I need help answering this question. It says Mass OF NH4Cl should the student dissolve in the NH3 solution that turns into a BUFFER with a ph of 9.76.. You can assume the solution wont change when the NH4CL dissolves. Please show your full work, and answer in 2 significant digits.

A chemistry graduate student is given 300 mL of a 0 40 M ammonia NH3) solution. Ammonia is a weak base with K,-1.8 × 10 NH4Cl should the student dissolve in the NH3 solution to turn it into a buffer with pH 9.76? . What mass of You may assume that the volume of the solution doesn't change when the NH4CI is dissolved in it. Be sure your answer has a unit symbol, and round it to 2 significant digits. x10

Explanation / Answer

Kb = 1.8*10^-5

pKb = - log (Kb)

= - log(1.8*10^-5)

= 4.7447

POH = 14 - pH

= 14 - 9.76

= 4.24

use formula for buffer

pOH = pKb + log ([NH4Cl]/[NH3])

4.24 = 4.7447 + log ([NH4Cl]/[NH3])

log ([NH4Cl]/[NH3]) = -0.5047

[NH4Cl]/[NH3] = 0.3128

[NH4Cl] = 0.1251

volume , V = 300.0 mL

= 0.3 L

number of mol,

n = Molarity * Volume

= 0.1251*0.3

= 3.754*10^-2 mol

Molar mass of NH4Cl,

MM = 1*MM(N) + 4*MM(H) + 1*MM(Cl)

= 1*14.01 + 4*1.008 + 1*35.45

= 53.492 g/mol

mass of NH4Cl,

m = number of mol * molar mass

= 3.754*10^-2 mol * 53.492 g/mol

= 2.008 g

Answer: 2.0 g

Feel free to comment below if you have any doubts

Related Questions

Navigate

• Browse (All)
• Browse I
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.