In-Depth Notes on Purity, Formulations, and Chromatography
Pure Substances
- Definition: A pure substance contains only one compound or element.
- Everyday Definition: A substance with nothing added to it (e.g., pure milk).
Determining Purity
- Boiling Point:
- A pure substance has a specific boiling point.
- Impurities decrease boiling point and widen boiling range.
- Melting Point:
- A pure substance has a specific melting point.
- Impurities increase melting point and widen melting range.
- Comparison with Data Book:
- Recorded melting/boiling points are compared with standard values.
- Closer values indicate greater purity.
- Definition: Mixtures designed for specific uses by mixing components in precise quantities.
- Applications: Found in various products, such as:
- Paints
- Fuels
- Cleaning products
- Cosmetics
- Fertilizers
- Foods
- Purpose: Ensures formulations have the correct properties for intended use.
Chromatography
- Definition: Technique that separates substances in a mixture, allowing identification of constituent substances.
- Key Components:
- Stationary Phase: Part where molecules cannot move.
- Mobile Phase: Part where molecules can move (e.g., solvent such as water or ethanol).
- Example: In paper chromatography, the solvent moves up the paper carrying the substances in the mixture.
- Solubility: More soluble chemicals spend more time in the solvent, traveling further up the paper.
Paper Chromatography
- Observation: Pure compounds produce a single spot in all solvents.
- Rf Values:
- Formula: Rf = (distance moved by substance) / (distance moved by solvent).
- Chromatogram: The visual representation showing the separate spots of compounds in a mixture, dependent on used solvent.
- Rf Value Variation: Different compounds have different Rf values in various solvents, indicating distinct separation in chromatograms.