Question

How many grams of solid **ammonium**
**bromide** should be added to **0.500**
L of a **0.164** M **ammonia** solution
to prepare a buffer with a pH of **8.640**
?

grams **ammonium** **bromide**
= g.

Answer #1

Kb = 1.8*10^-5

pKb = - log (Kb)

= - log(1.8*10^-5)

= 4.7447

POH = 14 - pH

= 14 - 8.64

= 5.36

use formula for buffer

pOH = pKb + log ([NH4Br]/[NH3])

5.359999999999999 = 4.7447 + log ([NH4Br]/[NH3])

log ([NH4Br]/[NH3]) = 0.6153

[NH4Br]/[NH3] = 4.1236

[NH4Br]/0.164 = 4.1236

[NH4Br] = 0.6763

volume , V = 0.5 L

we have below equation to be used:

number of mol,

n = Molarity * Volume

= 0.6763*0.5

= 0.3381 mol

Molar mass of NH4Br = 1*MM(N) + 4*MM(H) + 1*MM(Br)

= 1*14.01 + 4*1.008 + 1*79.9

= 97.942 g/mol

we have below equation to be used:

mass of NH4Br,

m = number of mol * molar mass

= 0.3381 mol * 97.942 g/mol

= 33.1 g

Answer: 33.1 g

PART A
How many grams of solid sodium
cyanide should be added to 0.500
L of a 0.135 M hydrocyanic acid
solution to prepare a buffer with a pH of 8.597
?
grams sodium cyanide = _________
g.
PART B
How many grams of solid potassium
fluoride should be added to 0.500
L of a 8.48×10-2M hydrofluoric
acid solution to prepare a buffer with a pH
of3.807 ?
grams potassium fluoride =
________ g.
PART C
How many grams of...

Part A: How many grams of solid ammonium
chloride should be added to 1.50
L of a 5.46×10-2 M
ammonia solution to prepare a buffer with a pH of
8.630?
Part B: How many grams of solid potassium
nitrite should be added to 2.00 L
of a 0.255 M nitrous acid
solution to prepare a buffer with a pH of
2.353?

How many grams of solid sodium fluoride should be added to 0.500
L of a 0.248 M hydrofluoric acid solution to prepare a buffer with
a pH of 3.988 ? grams sodium fluoride = g.

How many grams of solid sodium fluoride should be added to 0.500
L of a 0.241 M hydrofluoric acid solution to prepare a buffer with
a pH of 3.720 ?

How many grams of dry NH4Cl need to be added to 2.20 L of a
0.500 M solution of ammonia, NH3, to prepare a buffer
solution that has a pH of 8.62? Kb for ammonia is
1.8×10−5.

How many grams of dry NH4Cl need to be added to 2.50 L of a
0.500 M solution of ammonia, NH3, to prepare a buffer solution that
has a pH of 8.69? Kb for ammonia is 1.8×10−5?

How many grams of solid potassium cyanide should be added to
1.00 L of a 0.239 M hydrocyanic acid solution to prepare a buffer
with a pH of 10.174 ?
grams potassium cyanide=

How many grams of dry NH4Cl need to be added to 1.80 L of a
0.400 M solution of ammonia, NH3, to prepare a buffer solution that
has a pH of 8.83? Kb for ammonia is 1.8×10−5.

How many grams of dry NH4Cl need to be added to 2.00 L of a
0.300 M solution of ammonia, NH3, to prepare a buffer solution that
has a pH of 8.64? Kb for ammonia is 1.8×10−5.

How many grams of dry NH4Cl need to be added to 2.10 L of a
0.700 M solution of ammonia, NH3, to prepare a buffer
solution that has a pH of 8.57? Kb for ammonia is
1.8×10−5.

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