ChemistryPracticalExam-notes.md

Chemistry Practical Exam Summary

Contents

• Equilibrium
• Boiling point increase
• Electrolysis
• Protein test
• Titration
• Ksp
• Tf
• ∆H

1. Equilibrium

Goals

1. Prove the reversibility of a reaction
2. Show how temperature affects a reaction's equilibrium

Tools and Materials

Substance	Concentration	Amount
K2CrO4	0.1 M	as needed
CH3COOH	0.1 M	as needed
NaOH	0.1 M	as needed
NaCl	-	5 gr
CuSO4	0.1M	100 ml
Frozen H2O	-	a bucket

Item	Quantity
Test tube	3
Test tube rack	1
Graduated cylinder (100 ml)	1
Beaker (250 ml)	1
Spatula	1
Stirring rod	1
Digital scale	1
Lighter	1
Bunsen burner	1
Tripod	1
Mesh	1

Procedure

1. Proving the reversibility of reactions
   • Measure 5 ml of K₂CrO₄ into a test tube
   • Measure another 5 ml into another tube for control
   • Slowly add CH₃COOH into one of the test tubes
   • Observe the color difference between the tubes
   • Slowly add NaOH into the same test tube
   • Observe the color revert back to the original
2. Showing how temperature affects equilibrium point
   • Measure 5 gr of NaCl into a beaker
   • Pour 100 ml of CuSO₄ into the beaker
   • Stir
   • Pour a bit into a clean test tube for control
   • Heat up the beaker (make sure no water evaporates)
   • Observe color change
   • Cool down the beaker
   • Observe the color revert

Equations

1. Reaction reversibility
   • CrO₄^2- + H⁺ ⇋ Cr₂O₇^2- + H₂O
   • When adding CH₃COOH
     • CH₃COOH → CH₃COO^- + H⁺
   • When adding NaOH
     • NaOH → Na⁺ + OH^-
     • H⁺ + OH^- → H₂O
2. Effects of temperature
   • [Cu(H₂O)₆]²⁺ + 4Cl^- ⇋ [CuCl₄]^2- + 6H₂O; ∆H = +

2. Boiling point increase

Goals

1. To observe the rise in boiling point on electrolytes and non-electrolytes when compared with water

Tools and Materials

Substance	Concentration	Amount
Distilled water	-	50 ml
NaCl solution	0.01 M	50 ml
Urea solution	0.01 M	50 ml
Sucrose solution	0.01 M	50 ml

Item	Quantity
Lighter	1
Bunsen burner	2
Tripod	2
Mesh	2
Thermometer	2
Wooden clamp	2
Graduated cylinder (100 ml)	2
Beaker (250 ml)	2
Beaker (200 ml)	1

Procedure

For each sample to be tested:

• Pour roughly 50 ml of the sample into a 200 ml beaker
• Transfer to a graduated cylinder, then add or remove the sample until it is exactly 50 ml
• Transfer to a 250 ml beaker
• Place the beaker on a heater, and use the wooden clamp to hold the thermometer in place
• Note down the highest temperature

3. Electrolysis

Goals

1. To be able to write and determine electrolytic reactions in the anode and cathode
2. To be able to discern between inert and non-inert electrodes

Tools and Materials

Substance	Concentration	Amount
CuSO4	0.5 M	as needed
KI	0.5 M	as needed
Phenolphthalein	-	as needed
Amilum	-	as needed

Item	Quantity
Clamps, stands, and support	1
U-tube	1
Carbon electrode	2
Battery (9 volts)	1
Wires with alligator clips	2
Test tubes	4
Test tube rack	1
Digital scale	1
Pipette	4
Beaker (100 ml)	2
Litmus paper (blue)	1 pack
Litmus paper (red)	1 pack

Procedure

1. First experiment

   • Connect battery to carbon electrodes via alligator wires
   • Clamp U-tube in place, both openings facing upwards
   • Pour KI into a beaker
   • Transfer into the U-tube until about half full
   • Place the electrodes in both openings of the U-tube
   • Observe as yellow Iodine is produced in the anode and Hydrogen gas in the cathode
   • Sample some of the yellow Iodine into 2 test tubes
   • Add 3 drops of Amilum into one of the tubes, and 3 drops of PP into the other
   • Repeat the sampling and testing procedure with the liquid in the cathode side
   • Observe the change in colors

2. Second experiment

   • Wash all equipment clean
   • Note down the weights of both carbon electrodes
   • Repeat the procedures in the first experiment, but with CuSO₄ instead
   • For the testing procedure, use the blue and red litmus papers instead
   • Weigh the electrodes afterwards and note down the difference

Equations

1. First experiment
   • Anode: 2I^- → I₂ + 2e^-
   • Cathode: 2H₂O + 2e^- → 2OH^- + H₂
2. Second experiment
   • Anode: 2H₂O → 4H⁺ + O₂ + 4e^-
   • Cathode: Cu²⁺ + 2e^- → Cu

4. Protein test

Goals

1. To determine whether a given sample contains proteins, benzene bonds, or sulfur

Tools and Materials

Substance	Concentration	Amount
NaOH	6 M	as needed
NaOH	0.1 M	as needed
CuSO4	1%	as needed
HNO3	1.67 M	as needed
Lead (II) Acetate	-	as needed
CH3COOH	3M	as needed

Item	Quantity
Beaker (250 ml)	2
Beaker (500 ml) [for egg]	1
Filter paper	number of samples
Test tubes	number of samples
Test tube rack	1
Pipette	3
Lighter	1
Bunsen burner	1
Tripod	1
Mesh	1
Wooden clamp	1

Procedure

1. Biuret test
   • Add 3 drops of CuSO₄ (1%) into the sample and mix
   • Add 3 drops of NaOH (0.1 M) into the sample and mix
   • If the sample turns purple, it contains proteins
2. Xanthoproteic test
   • Add a bit of HNO₃ (1.67 M) into the sample
   • Heat up the test tube
   • Slowly add NaOH (6 M)
   • If the sample turns orange, it contains a benzene bond / aromatic amino acid
3. Lead (II) acetate test
   • Add a bit of NaOH (6 M) into the sample and mix
   • Add a bit of CH₃COOH into the sample and mix
   • Cover the test tube's opening with a filter paper and clamp it in place
   • Drop some Lead (II) Acetate onto the filter paper
   • Heat up the test tube
   • If the filter paper turns black, the sample contains sulfur

5. Titration

Tools and Materials

Substance	Concentration	Amount
Phenolphthalein	-	1 bottle
NaOH	0.1 M	as needed
HCl	To be found
CH3COOH	25%
Distilled water	-	as needed

Item	Quantity
Double clamp	1
Stand	1
Biuret	1
Funnel	1
Test tubes	3
Test tube rack	1
Volumetric pipette (10 ml)	2
Erlenmeyer flask (250 ml)	4
Volumetric flask (100 ml)	1
Pipette pump	1
Beaker (250 ml)	1

General Procedure

• Measure the volume of analyte (the substance to be tested) and note it down
• Transfer the analyte to an Erlenmeyer flask
• Secure the biuret on the stand with a double clamp
• Fill the biuret with the titrant (NaOH if analyte is HCl) up to the zero point
  • If it overflows, place a container under the biuret and open the tap to let some of the titrant out
• Add some indicator (PP) into the analyte
• Place analyte underneath the biuret
• Slowly let the titrant flow into the analyte, while also swirling the flask to make sure it's mixed well
• Close the biuret tap once the whole analyte starts to turn faint purple
  • If it's dark purple then you've messed up
• Record the amount of titrant in the biuret
• Use M₁V₁ = M₂V₂ to solve for the analyte molarity

6. Ksp

You have 3 samples, namely

• B₁ = H₂O
• B₂ = NaOH (0.025 M)
• B₃ = NaOH (0.05 M)

Add 2 grams of Ca(OH)₂ to each of the samples. Stir them well and wait until everything settles.

From each sample, take 3 test tubes of 25 drops each, and add 1 drop of PP to each test tube.

Perform titration on each test tube:

• Add HCl (0.1 M) drop by drop until the solution turns colorless
• Record the number of drops and average them over the 3 test tubes for each sample
• Multiply the average number of drops by 0.05 ml to get the volume of HCl used
• Use M₁V₁ = M₂V₂ to solve for the volume of NaOH

Then do this little magic trick:

• First sample (B₁)
  • Ca(OH)₂ → Ca²⁺ + 2OH^-
  • Q₁ = [Ca²⁺][OH^-]²
• Second sample (B₂)
  • Use M_B2 = [Ca(OH)₂] + [NaOH] to find the concentration of Ca(OH)₂
  • Ca(OH)₂ → Ca⁺ + 2OH^-
  • Q₂ = [Ca⁺][OH^-]²
    • Note: also include the concentration of OH^- from the NaOH (0.025 M)
• Third sample (B₃)
  • Use M_B3 = [Ca(OH)₂] + [NaOH] to find the concentration of Ca(OH)₂
  • Ca(OH)₂ → Ca⁺ + 2OH^-
  • Q₃ = [Ca⁺][OH^-]²
    • Note: also include the concentration of OH^- from the NaOH (0.05 M)

7. Tf

Probably like Boiling point increase.

8. ∆H

Measure the temperature change and use the formula: ∆H = mc∆T

Some experiments that you will do:

1. Exothermic reactions
   • H₂O + NaOH
   • HCl + Mg
2. Endothermic reactions
   • NH₄Cl + Ba(OH)₂
   • Heating up CuSO₄ hydrate crystal