Chemical analysis

"What is a formulation?"

"A mixture designed as a useful product, with carefully measured components to give the required properties (e.g. foods, medicines, sunscreens, paints, alloys)."

"What does 'pure' mean in science vs everyday use?"

"Scientific: a single element or compound not mixed with others. Everyday: substance with nothing added, in its natural state (e.g. pure milk)."

"How can melting/boiling points be used to check purity?"

"Pure substances have fixed melting/boiling points; mixtures melt/boil over a range of temperatures."

"What are the two phases in paper chromatography?"

"Stationary phase = paper; Mobile phase = solvent."

"How does chromatography separate substances?"

"Different substances travel at different speeds depending on solubility; more soluble substances travel further."

"What is the formula for Rf value?"

"Rf = distance moved by substance ÷ distance moved by solvent."

"How can chromatography show if a substance is pure?"

"Pure substances produce a single spot in all solvents; mixtures produce multiple spots."

"What are locating agents in chromatography?"

"Chemicals (e.g. ninhydrin, iodine) or UV light used to reveal colourless spots."

"What is filtration used for?"

"Separating an insoluble solid (precipitate) from a liquid."

"What is crystallisation used for?"

"Separating a soluble solid (e.g. salt) from a solution by evaporating solvent, cooling, and forming crystals."

"What is simple distillation used for?"

"Separating a solvent from a solution, e.g. pure water from salt solution."

"What is fractional distillation used for?"

"Separating a mixture of liquids with different boiling points (e.g. crude oil fractions)."

"What is sacrificial protection?"

"Coating a metal with a more reactive one (e.g. zinc galvanising iron) so the coating corrodes first."

"What is representative sampling in qualitative analysis?"

"Taking samples that reflect the whole material so variations are identified."

"What are the flame test colours for lithium

sodium, potassium, calcium, and copper?","Lithium = crimson; Sodium = yellow; Potassium = lilac; Calcium = orange-red; Copper = green."

"How do you carry out a flame test?"

"Place sample on a spatula in a Bunsen flame and observe the flame colour."

"What are the sodium hydroxide test results for metal ions?"

"Calcium = white ppt (no change in excess); Copper(II) = blue ppt; Iron(II) = green ppt; Iron(III) = orange-brown ppt; Zinc = white ppt (dissolves in excess)."

"How are carbonate ions tested for?"

"Add dilute acid → fizzing as CO₂ forms; CO₂ turns limewater cloudy."

"How are halide ions tested for?"

"Add dilute nitric acid then silver nitrate: Chloride = white ppt, Bromide = cream ppt, Iodide = yellow ppt."

"How are sulfate ions tested for?"

"Add dilute HCl then barium chloride (or nitrate): White ppt forms if sulfate present."

"What is emission spectroscopy used for?"

"To identify elements from light spectra; different elements give characteristic line patterns."

"What are the advantages of instrumental methods of analysis?"

"Accurate, sensitive, rapid."

"What is the difference between qualitative and quantitative analysis?"

"Qualitative = identifies substances; Quantitative = measures amounts."

"What is the formula for concentration in g/dm³?"

"Concentration (g/dm³) = mass of solute (g) ÷ volume (dm³)."

"What is the formula for concentration in mol/dm³?"

"Concentration (mol/dm³) = moles of solute ÷ volume (dm³)."

"What is neutralisation?"

"Acid + alkali → salt + water."

"Which salts do common acids produce?"

"HCl → chlorides, HNO₃ → nitrates, H₂SO₄ → sulfates."

"What ions do acids and alkalis release in solution?"

"Acids → H⁺ ions; Alkalis → OH⁻ ions."

"What is the ionic equation for neutralisation?"

"H⁺(aq) + OH⁻(aq) → H₂O(l)."

"What is the method for a titration?"

"Add acid to burette; measure alkali in conical flask with indicator; add acid until end point; record titre; repeat to get concordant results."

"How do you judge titration data quality?"

"Check for repeat trials and concordant titres (close agreement, excluding anomalies)."

"How are titration results used to find unknown concentrations?"

"1. Calculate moles of known solution. 2. Use balanced equation to find moles of unknown. 3. Calculate concentration = moles ÷ volume."