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CHEM 104
LAB 3
Notebook
Exp
erim
ent
Title: Titration and Titration Curves
Purpose: To perform neutralization titration analyzes to determine the
unknown concentration of a substance as well as the percentage of acid or
base in solution.
Procedure:
Titration #1: Standardization of NaOH
Titrate basic solution of NaOH diluted with water and a phenolphthalein
indicator against weak acid Potassium Hydrogen Phthalate.
Titration #2: Strong Acid/Strong Base
Titrate acidic solution of HCl diluted with water and a bromothymol blue
indicator against standardized NaOH (which was standardized from first
titration = 0.130M NaOH)
Titration #3: Weak Acid/Strong Base
Analysis Vinegar (Weak acid – acetic acid) titrated against NaOH with the
use of phenolphthalein indicator. Determine % of acetic acid in Vinegar.
Titration #4: Strong Acid/Weak Base
Analysis of household ammonia (weak base – 2-10% ammonia solution)
diluted with water and a methyl orange indicator titrated against
standardized HCl.
Titration #5: Back-titration
Grind antacid tablet into powder, dilute with water and bromophenol blue
indicator. Add excess standardized HCl to solution. Boil to evaporate carbonic
acid product to leave only excess hydrochloric acid. Back-titrate with a
standardized NaOH (base).
Titration #6: Titration Curve
Titrate weak acid (acetic acid) with strong base (NaOH). A volume of 35.0 mL
of standard NaOH (0.107M) was added to 25.00 mL of 0.108 M HC2H3O2 in
various increments of 1.0mL during the beginning and end of the titration
and at 0.5 mL or smaller during the middle of the titration. The pH was
recorded at each NaOH addition and a plot of pH versus volume was
constructed to yield a titration curve.
Data/Results/
Calculations:
Titration #1:
KHC8H4O4 + NaOH -> NaKC8H4O4 + H2O
Standardization of NaOH
Data Table:
Mass of KHC8H4O4 0.51g MW = 204.
Volume of NaOH 19.2 mL (to endpoint)
Calculation of NaOH Molarity:
MNaOH = (0.51g/204.2g/mol) / (19.2 mL/1000mL/L) = 0.130 M
Titration #2:
HCl + NaOH -> NaCl +H2O
Standardization of HCl
Data Table:
Volume of HCl 25.0 0 mL
Volume of NaOH 21. 9 mL 0.130M
Calculation of HCl Molarity:
M
HCl
x (25.00mL HCl/1000mL/L) x (1mol HCl/1mol NaOH) = 0.130M NaOH x
(21.9mL NaOH/1000mL/L)
M
HCl
= 0.114 M
Titration #3:
HC
2
H
3
O
2
H
3
O
2
+ H
2
O
Data Table:
Mass of vinegar 3.09g MW =
Volume of NaOH 19.7mL 0.130 M
Calculation of % ammonia in household ammonia:
% NH 3 =((25.2mL/1000mL/L) x 0.106 M HCl x 17.034 g/mol NH 3 )/2.0693g NH 3 x 100 =
Titration #
CaCO 3
H
2
CO
3
H
2
CO
3
-> H
2
O +
CO
2
(For this experiment, HCl was prepared and standardized as 0.106 M
HCl, and NaOH as 0.107 M NaOH)
Data Table:
Mass of antacid 0.2148g MW =
Volume of HCl 25.00mL 0.106M
Volume of NaOH 3.9mL 0.107M
Excess HCl added = .106 x (25.00 mL/1000mL/L) =
0.00265 Moles of Base = 0.107 x (3.9mL/1000mL/L) =
HCl to neutralize CaCO3 = 0.00265 - 0.0004173 = 0.
moles Moles CaCO 3
= 0.0022327 mol/2mol HCL = 0.
moles
g CaCO 3
= 0.00111635 moles x 100.09g/mol = 0.1117g
% CaCO 3
= (0.1117g CaCO 3
/0.2148g sample) x 100 = 52.0%
Titration #
From the data and the titration curve, it can be seen that the endpoint occurred at ~8.39.
The indicator chosen must undergo a color change around this pH. The best indicator for
this use is phenolphthalein, which undergoes a color change at pH 8.0-9.6.
Ka Calculation
From the titration curve at the half-neutralization volume (12.5mL), the corresponding pH
is equal to the pKa, from which the Ka of the weak acid can be determined.
pKa = - log Ka = 4.
log Ka = - 4.
taking the antilog of both sides: antilog (log Ka) = antilog (- 4.60)
Ka = 2.51 x 10
-
Conclusions:
Performing neutralization titration analyses allowed us to determine the unknown
concentration of a substance as well as the % of acid or base in solution. Using measured
additions of known concentration of a substance to get to an endpoint of neutralization, we
were also able to plot a titration curve and calculate Ka with the experimental data.
Notes:
- Phenolphthalein indicator: changes from colorless to pink; color change is at pH 8.
- Bromothymol Blue indicator: changes from yellow to blue; color change is at pH 6.
- Methyl Orange indicator: orange at neutral, added to ammonia (basic)
solution = yellow, color change is at pH 3.1-4.4.
