Chemical Waste

• Definition: Unwanted material from chemical reactions or expired products.
• Examples:
  • Unused chemicals (acids, alkalis)
  • Broken glassware, sharp objects
  • Plastics, waste papers, rubbers
  • Poisonous gases

Safe Disposal Methods

1. Normal Waste Bins: For non-recyclable plastics, wood, rubber, dirty papers.
2. Special Controlled Waste Containers: For sharp objects and hazardous items; must be emptied regularly.
3. Draining with Water: For harmless soluble salts and diluted acids/alkalis.
4. Recycling: Unbroken glass, packing waste, paper.
5. Incineration: Burning wastes like syringes, organic solvents, and mineral oils in an incinerator.

Designing Scientific Investigation

• Definition: Systematic process to find answers to problems or observations.

Components of a Scientific Investigation

1. Problem Identification: Asking questions about the natural world (e.g., causes of rusting).
2. Formulation of a Hypothesis: Guessed answer based on knowledge.
3. Experimentation: Series of investigations to test the hypothesis.
4. Observation and Data Collection: Accurate recording of observations and measurements.
5. Interpretation of Data: Explaining observations and trends.
6. Conclusion: Confirmation or rejection of the hypothesis; if rejected, formulate a new one.

Purity of a Substance

• Definition: A material with constant composition and no impurities.

Criteria for Purity

• Tests:
  • Melting Point: A pure substance has a specific melting point; impurities lower it and cause a range.
  • Boiling Point
  • Paper Chromatography

Checking Purity by Melting Point

• Impurities Effect:
  • Lower the melting point.
  • Cause melting over a range of temperatures.

Experiment 1: Melting Point Test

Materials:

• Sample of the substance
• Melting point apparatus or heating plate
• Thermometer
• Capillary tubes (for sample)
• Stopwatch or timer

Procedure:

1. Preparation:
   • Fill a capillary tube with a small amount of the substance to be tested.
   • Insert the capillary tube into the melting point apparatus.
2. Heating:
   • Gradually increase the temperature.
   • Observe the temperature on the thermometer as the sample heats.
3. Observation:
   • Record the temperature at which the substance completely melts.

Observations:

• Record the melting point of the substance.
• Note any color changes or the appearance of impurities during melting.

Conclusion:

• Compare the observed melting point with the known melting point of the pure substance.
• If the melting point is lower or has a broader range than expected, this indicates the presence of impurities.

By Boiling Point

• Definition: A pure substance has a fixed boiling point.
• Effects of Impurities:
  • Raises Boiling Point: More impurities lead to a higher boiling point.
  • Range of Temperatures: Impurities cause boiling over a range rather than at a specific point.

Experiment 2: Boiling Point Test

Materials:

• Sample of the substance
• Boiling point apparatus or heating setup
• Thermometer
• Beaker
• Stopwatch or timer

Procedure:

1. Setup:
   • Place the substance in a beaker and set up the boiling point apparatus.
2. Heating:
   • Gradually heat the substance.
   • Monitor the temperature with the thermometer.
3. Observation:
   • Record the temperature when the substance starts boiling and remains boiling steadily.

Observations:

• Record the boiling point of the substance.
• Note any changes in appearance or formation of bubbles.

Conclusion:

• Compare the observed boiling point with the known boiling point of the pure substance.
• A deviation from the expected boiling point indicates impurities present in the sample.

By Paper Chromatography

• Purpose: Used to separate mixtures of soluble substances (e.g., dyes, inks).
• Phases:
  • Stationary Phase: Solid part (e.g., filter paper).
  • Mobile Phase: Liquid or gas (e.g., solvent).

Procedure:

1. Draw a ‘start line’ near the bottom of chromatography paper.
2. Spot the mixture on the start line.
3. Dip the bottom of the paper in solvent; the solvent travels up.
4. Different components move at different rates.
5. Mark the “solvent front” (the furthest point reached by the solvent).

Interpreting Chromatograms

• Chromatogram: The pattern formed by separated substances.
  • Pure Substance: One spot.
  • Impure Substance: Two or more spots.

Experiment 3: Paper Chromatography

Materials:

• Chromatography paper

• Solvent (e.g., water or ethanol)

• Pencil

• Ruler

• Sample of the substance

• Sample of a pure substance (if available)

Procedure:

1. Preparation:

   • Draw a faint baseline (about 1 cm from the bottom) on the chromatography paper using a pencil.

2. Application:

   • Place a small spot of the substance on the baseline.

   • If available, place a spot of the pure substance next to it for comparison.

3. Development:

   • Dip the bottom of the paper in the solvent, ensuring the spots remain above the solvent level.

   • Allow the solvent to rise and separate the components.

4. Observation:

   • Once the solvent front has moved sufficiently (about 3/4 of the paper), remove it and mark the solvent front.

Observations:

• Note the number of spots and their positions.

• Measure the distance traveled by each spot and the solvent front.

Conclusion:

• Compare the distance traveled by the sample with that of the pure substance.

• A single spot indicates high purity, while multiple spots suggest impurities.

• The position of the spots can also reveal the identity of components in the mixture.

Relative Flow Values (Rf)

• Definition: Ratio of the distance travelled by the substance to the distance travelled by the solvent.

Formula:

Rf=Distance travelled by substance/Distance travelled by solvent

Characteristics:

• Rf values are always less than 1.
• Pure Substance: One Rf value.
• Impure Substance: More than one Rf value.