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Samenvatting Verslag potentiometrie - buffercapaciteit
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Verslag potentiometrie - buffercapaciteit - eerstejaarsstudent chemie te AP Hogeschool, labportofolio semester 2, lab algemene chemie
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1CH – Labportfolio semester 2: Algemene chemieVerslag labo Buffercapaciteit / Wet van Ostwald
Deel I: Buffercapaciteit
Doel: Invloed van de concentratie bepalen op de buffercapaciteit van een buffer.
Gegeven: de buffermengsels:
Buffer nr. Volume (mL) Zuur (geconjugeerd) Volume (mL) Base (geconjugeerd)
1 20 CH3COOH 0,5 M 20 CH3COO- 0,5 M
(Natriumacetaat)
2 20 CH3COOH 0,1 M 20 CH3COO- 0,1 M
3 20 NH4+ 0,5 M (NH4Cl) 20 NH3 0,5 M
4 20 NH4+ 0,1 M (NH4Cl) 20 NH3 0,1 M
Resultaten:
na toevoegen van 3 mL HCl 0,5 M
Mengsel pH voorspeld pH gemeten pH voorspeld pH gemeten ∆pH
nr.
1 4,75 4,73 4,62 4,61 0,12
2 4,75 4,72 4,40 4,42 0,32
3 9,20 9,22 9,10 9,09 0,13
4 9,20 9,19 8,90 8,96 0,23
na toevoegen van 3 mL NaOH 0,5 M
Mengsel pH voorspeld pH gemeten pH voorspeld pH gemeten ∆pH
nr.
1 4,75 4,73 4,88 4,87 -0,14
2 4,75 4,74 5,09 5,11 -0,37
3 9,20 9,21 9,37 9,30 -0,09
4 9,20 9,23 9,58 9,53 -0,30
Vul deze tabel volledig aan.
, 1CH – Labportfolio semester 2: Algemene chemie
Modelberekeningen:
Kies 1 buffermengsel (bv. hetgeen waarvan jij de metingen gedaan hebt) en vul daarvoor
onderstaande vragen in:
Geef de modelberekening voor de pH-voorspelling van de buffer.
Buffer 1: CM (CH3COOH) = 0,25M CM (CH3COO-) = 0,25M
[A− ]
pH = pka + log [HA]
[0,25]
pH = 4,75 + log [0,25]
pH = 4,75
Geef de modelberekening voor de pH-voorspelling na toevoeging van HCl of NaOH.
3mL HCl 0,5M: 0,5 mol / 333,333.. = 0,0015 mol = 1,5 mmol
HCl + CH3COO- CH3COOH
1,5 mmol 10,0 mmol 10,0 mmol
-1,5mmol -1,5mmol +1,5 mmol
/ 8,5 mmol 11,5mmol
[8,15]
pH = 4,75 + log [11,5]
pH = 4,62
Bereken de buffercapaciteit m.b.v. de vergelijking van Henderson-Hasselbach.
1 𝛥𝑛
𝛽= ⋅ 𝛥𝑛 = ?
0,041 𝛥𝑝𝐻
[0,25−x]
3,75 = 4,75 + log [0,25+x]
[0,25−x]
−1 = log [0,25+x]
[0,25−x]
0,1 = [0,25+x]
0,1 . (0,25 + x) = 0,25 – x
0,025 + 0,1x = 0,25 – x
-0,025 = -1,1x
X= 0,20
1 0,20
𝛽= ⋅ = 0,50
0,041 1
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