(6A1X0) Practical
introduction course to
chemistry and chemical
technology
Full Notes!
1
,Contents INDEX Page number
-C1. Report: Acid-Base Titration with Lactic Acid 3
-C2. Report: Determination of the Amount of Quinine in Tonic 13
-C3. Report: Synthesis of Diazo Dyes in a Continuous-flow Microreactor 23
-C4. Lab Safety Exam Theory 37
2
,22/09/2021 Name (Student Number)
Acid-Base Titration with Lactic Acid
Goal and Method: Determining the molarity of sodium hydroxide, the molarity
of lactic acid and the pKa of lactic acid by using titrations.
Reaction Scheme of Sodium Hydroxide and Oxalic Acid:
𝐻2 𝐶2 𝑂4 ⋅ 2𝐻2 𝑂(𝑎𝑞) + 2𝑁𝑎𝑂𝐻(𝑎𝑞) → 𝑁𝑎2 𝐶2 𝑂4 (𝑎𝑞) + 4𝐻2 𝑂(𝑙)
Reaction Scheme of Sodium Hydroxide and Lactic Acid:
𝐶3 𝐻6 𝑂3 (𝑎𝑞) + 𝑁𝑎𝑂𝐻(𝑎𝑞) → 𝑁𝑎𝐶3 𝐻5 𝑂3 (𝑎𝑞) + 𝐻2 𝑂(𝑙)
Reaction Setup to Determine the Molarity of NaOH:
3
,Reaction Setup to Determine the Molarity of Lactic Acid:
Reaction Setup to Determine the pKa of lactic acid:
4
,Used Formulas:
𝑀𝑜𝑙𝑒𝑠 𝑜𝑓 𝑆𝑜𝑙𝑢𝑡𝑒 (1)
𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 =
𝑉𝑜𝑙𝑢𝑚𝑒
Where the moles of solute are given (in moles), the volume (in litres) and
concentration is given in (mol/L).
𝑛
1
𝑥̅ = ∑ 𝑥𝑖 (2)
𝑛
𝑖=1
Where 𝑥̅ = Average, n= number of trials and 𝑥𝑖 = single measurement.
𝑀𝑎𝑠𝑠
𝑀𝑜𝑙𝑒𝑠 = (3)
𝑀𝑜𝑙𝑎𝑟 𝑀𝑎𝑠𝑠
Where moles is given (in moles), mass (in grams) and molar mass (in g/mol).
[𝑎𝑐𝑖𝑑𝑖𝑐 𝑓𝑜𝑟𝑚]
𝑝𝐾𝑎 = 𝑝𝐻 + 𝑙𝑜𝑔 ( ) (4)
[𝑏𝑎𝑠𝑖𝑐 𝑓𝑜𝑟𝑚]
Error Analysis Formulas:
𝑛
∑𝑖=1(𝑥𝑖 − 𝑥̅ )2
𝜎=√ (5)
𝑛−1
Where 𝜎 = standard deviation, n= number of measurements, 𝑥𝑖 = measurement
and 𝑥̅ = Average.
Error Propagation Laws:
𝜎𝑐 𝜎𝑚 2 𝜎𝑀 2 𝜎𝑉 2 (6)
= √( ) + ( ) + ( )
𝐶 𝑚 𝑀 𝑉
Where 𝜎𝑚 = standard deviation for the mass of oxalic acid (in g), 𝜎𝑀 = Standard
deviation for the molar mass of oxalic acid (in g/mol), 𝜎𝑉 = Standard deviation
for the volume of NaOH (in L), 𝜎𝑐 = Standard deviation of the concentration of
NaOH (in mol/L) , m= Average mass of oxalic acid (in Kg), V= Average volume of
NaOH (in L), M= Molar Mass of oxalic acid (in g/mol) and C= Average
Concentration or Molarity of NaOH (in mol/L).
5
,𝜎𝑐𝑙𝑎𝑐𝑡𝑖𝑐 𝜎𝑉𝐿 2 𝜎𝑉𝑁 2 𝜎𝑐 2 (7)
√
= ( ) +( ) +( )
𝐶𝑙𝑎𝑐𝑡𝑖𝑐 𝑉𝐿 𝑉𝑁 𝐶
Where 𝜎𝑉𝐿 = standard deviation for the volume of lactic acid (in L),
𝜎𝑉𝑁 = Standard deviation for the volume of NaOH (in L), 𝜎𝑐 = Standard
deviation of the concentration or molarity of NaOH (in mol/L), 𝜎𝑐𝑙𝑎𝑐𝑡𝑖𝑐 =
Standard deviation for the concentration or molarity of lactic acid (in L),
𝑉𝐿 = Average volume of lactic acid (in L) , 𝑉𝑁 = Average volume of NaOH (in L),
C= Average Concentration or Molarity of NaOH (in mol/L) and 𝐶𝑙𝑎𝑐𝑡𝑖𝑐 = Average
Concentration or Molarity of Lactic Acid (in mol/L).
General Procedure to Determine the Molarity of Sodium Hydroxide:
Enough oxalic acid (C2H2O4 ⋅ 2H2O) to neutralise 25mL of 0.1M solution of
NaOH was weighed and the exact amount was transferred quantitively to a
conical flask of 300mL. The oxalic acid was then dissolved in demineralized
water and the volume was increased to 50mL using demineralized water.
Three droplets of phenolphthalein indicator were added, and the solution with
NaOH solution was titrated until the colour remained pink for at least 30
seconds. The entire procedure was performed a total of 3 times.
General Procedure to Determine the Molarity of Lactic Acid:
25,00 mL of lactic acid was pipetted, and the amount was transferred
quantitatively to a 300mL Erlenmeyer flask. Demineralized water was added to
the solution until the total solution inside the Erlenmeyer flask had a volume of
50mL. Next, 3 drops of phenolphthalein indicator were added to the solution
and the NaOH solution was titrated from the burette until the colour change
stayed for at least 30 seconds. This procedure was repeated a total of 2 times.
6
,General Procedure to Determine the pKa of Lactic Acid:
First and foremost, the pH meter was calibrated. Then, a 25,00 mL pipette was
used to transfer quantitatively the amount of lactic acid to a 150 mL beaker.
The beaker was placed on a magnetic stirring plate, and the combined
electrodes of the pH-meter were dipped in the lactic acid solution and the
solution was stirred at a low rotation to prevent loss of material.
The lactic acid solution was titrated with the NaOH solution using a burette. In
the beginning, the titrations were done stepwise by adding sequential portions
of 0,5 mL of NaOH solution. When the pH of the solution was near the
equivalence point (pH=5), the titrations were done by adding sequential
portions of 0,1 mL of NaOH solution. Finally, the solution was titrated until the
pH of the solution what higher than its equivalence point, until pH=11 approx.
Used Equipment:
• Analytical Balance
• Conical Flask (300mL)
• Burette
• Burette Clamp
• pH meter
• Pipette (25mL)
• Erlenmeyer flask (300mL)
• Ring stand
• Beaker (150mL)
• Weighing boat
• Finn pipette
• Magnetic stirrer
• Magnetic stirring plate
• Measuring Cylinder (100mL)
7
, Results:
Results of Molarity of NaOH:
The moles of oxalic acid were calculated using formula 3, for the molar mass
the value of (126,065 g/mol). Then, the moles of NaOH were calculated by
multiplying the moles of oxalic acid by 2, as the ratio is 2:1 which can be seen
in the chemical equation. Using the formula (1), the molarity of NaOH was
calculated. Then, using formula (2) the average molarity of NaOH was
calculated.
Results of Molarity of Lactic Acid:
The moles of lactic acid were calculated by using formula (1) and multiplying
the titre volume with the average molarity of NaOH. Then, the molarity of
lactic acid was calculated using again formula (1) and the volume used was
0,025 L. Finally, the average molarity of lactic acid was calculated using formula
(2).
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