In: Chemistry
Which of the following aqueous solutions are good buffer
systems?
.
a. 0.15 M sodium hydroxide + 0.29 M sodium bromide .
b. 0.31 M hydrofluoric acid + 0.20 M potassium fluoride .
c. 0.27 M nitric acid + 0.24 M potassium nitrate .
d. 0.16 M hydrocyanic acid + 0.18 M potassium cyanide .
e. 0.31 M ammonium nitrate + 0.30 M ammonia .
b.How many moles of sodium hydroxide would have
to be added to 250 mL of a 0.406
M acetic acid solution, in order to prepare a
buffer with a pH of 4.600?
moles
Acid buffer solution : It is a mixture of weak acid and its salt with strong base
HF + KF
CH3COOH + CH3COONa
HCN + NaCN
Basic buffer solution : It is a mixture of weak base and it's salt with strong acid
NH3 + NH4Cl
NH3 + NH4NO3
b. 0.31 M hydrofluoric acid + 0.20 M potassium fluoride .
d. 0.16 M hydrocyanic acid + 0.18 M potassium cyanide .
e. 0.31 M ammonium nitrate + 0.30 M ammonia .
b.
no of moles of CH3COOH = molarity * volume in L
= 0.406*0.25 = 0.1015 moles
----- CH3COOH(aq) + NaOH(aq) --------------> CH3COONa(aq) + H2O(l)
I -------- 0.1015 --------- x ---------------------- 0
C------- -x ------------- -x ----------------------- +x
E ------ 0.1015-x ------- 0 ------------------------------ +x
Pka = 4.74
PH = 4.6
PH = Pka + log[CH3COONa]/[CH3COOH]
4.6 = 4.74 + logx/(0.1015-x)
logx/(0.1015-x) = 4.6-4.74
logx/(0.1015-x) = -0.14
x/(0.1015-x) = 0.7244
x = 0.7244*(0.1015-x)
x = 0.0426
The no of moles of NaOH = x = 0.0426 moles >>>>answer