Acedemic Notes: Experimental Chemistry and Analysis

Stepwise Planning: Involves suggesting a hypothesis, identifying variables (independent, dependent, controlled), choosing apparatus, carrying out tests, and drawing conclusions.
Apparatus Choice: Selection depends on required accuracy. Digital probes (pH, temperature) offer higher resolution than manual indicators or liquid thermometers.
Measuring Volume: For high precision, use volumetric pipettes (fixed volume) or burettes (variable volume). Measuring cylinders are for general use.
Accuracy vs. Precision: Accuracy refers to how close a result is to the true value; precision refers to the consistency of repeated results.
Errors: Random errors are reduced by repetitions and averaging. Systematic errors (like zero errors) require apparatus calibration or adjustment.

Filtration: Separates insoluble solids from liquids (residue stays in paper, filtrate passes through).
Crystallisation: Recovers a soluble solid from a solution by evaporating the solvent.
Simple Distillation: Separates a solvent from a solution (e.g., pure water from seawater).
Fractional Distillation: Separates miscible liquids with close boiling points (e.g., ethanol and water) using a fractionating column.
Magnetic Separation: Used for mixtures containing magnetic metals like iron.
Assessing Purity: Pure substances have sharp, specific melting and boiling points ( $0\,^{\circ}\text{C}$ and $100\,^{\circ}\text{C}$ for water). Impurities lower the melting point and raise the boiling point, often causing melting over a range of temperatures.

Mechanism: Separates substances based on their different solubilities in a solvent and attraction to the paper.
Procedure: Samples are placed on a pencil baseline. The solvent must start below this line. The resulting dried paper is a chromatogram.
Rf Value: A ratio used to identify substances: $R_{f} = \frac{\text{distance moved by substance}}{\text{distance moved by solvent front}}$ .
Locating Agents: Necessary for separating colourless substances (like amino acids) to make them visible under UV light or via chemical reaction.

Cations (Metal Ions):
- Flame Tests: $Li^{+}$ (red), $Na^{+}$ (yellow), $K^{+}$ (lilac), $Ca^{2+}$ (orange-red), $Ba^{2+}$ (light green), $Cu^{2+}$ (blue-green).
- Aqueous Precipitates: Adding $NaOH(aq)$ or $NH_{3}(aq)$ forms characteristic hydroxide precipitates ( $Fe^{2+}$ is green, $Fe^{3+}$ is red-brown, $Cu^{2+}$ is blue).
- Ammonium ( $NH_{4}^{+}$ ): Heating with $NaOH(aq)$ releases ammonia gas.
Anions:
- Carbonate ( $CO_{3}^{2-}$ ): Reaction with acid produces $CO_{2}$ gas (test with limewater).
- Halides ( $Cl^{-}$ , $Br^{-}$ , $I^{-}$ ): Reaction with acidified silver nitrate forms white ( $AgCl$ ), cream ( $AgBr$ ), or yellow ( $AgI$ ) precipitates.
- Sulfate ( $SO_{4}^{2-}$ ): Reaction with acidified barium nitrate forms a white precipitate.
Gases:
- Hydrogen ( $H_{2}$ ): 'Squeaky pop' with a lighted splint.
- Oxygen ( $O_{2}$ ): Relights a glowing splint.
- Carbon Dioxide ( $CO_{2}$ ): Turns limewater cloudy.
- Chlorine ( $Cl_{2}$ ): Bleaches damp litmus paper.
- Ammonia ( $NH_{3}$ ): Turns damp red litmus paper blue.

Purpose: Used to determine the exact concentration of a substance.
Method: An acid is added from a burette to a measured volume of alkali (measured by pipette) until the indicator (e.g., methyl orange) changes colour.
Reliability: Titrations are repeated until 'concordant' results (within $\pm 0.10\,cm^{3}$ ) are achieved.