Topic 8 - Chemical analysis: Flashcards
A pure substance:
A single element or commpund, not mixed with any other substance.
- They melt and boil at specific temperatures
- The mp and bp of the pure substances can be used to distinguish them from mixtures
Test for hydrogen:
- Use a burning splint
- A squeaky pop can be heard
Test for oxygen:
- Use a glowing splint
- The splint should relight
Test for carbon dioxide:
- Bubble the gas through limewater
- Turns milky 🥛
Test for chlorine:
- Use damp litmus paper
- Litmus paper becomes bleached and turns white
Flame test colours (used to identify metal ions):
🟥 Lithium-crimson
🟨 Sodium- yellow
🟪 Potassium- lilac
🟧 Calcium- orange
🟩 Copper- green
Leave crimson soap yellow potatoes lilac curd orange AND copper green.
Formulation:
A mixture that has been designed as a useful product
Rf value:
Rf value= Distance moved by substance/Distance moved by solvent
Chromatography:
Purpose- to separate mixtures
- The more soluble a substance is, the further up the paper it travels
Sample containing a mixture of ions:
Flame colours are masked (you cannot see them)
Metal hydroxides (reaction with NaOH):
- Aluminium, calcium and magnesium all form a white precipitate with NaOH
- Only aluminium’s precipitate dissolves with excess NaOH
- Copper (II) produces a blue precipitate 🟦
- Iron (II) produces a green precipitate 🟩
- Iron (III) produces a brown percipitate 🟫
Carbonates:
- Carbonates react with dilute acids to create carbon dioxide
- The gas is bubbled through limewater, if carbon dioxide is present, the limewater turns cloudy ☁
Test for halides:
-
First add nitric acid, followed by silver nitrate solution
Chloride- white precipitate
Bromide- cream precipitate
Iodine- yellow precipitate - Cats with brains can ideally yodel
Test for sulfates:
- First add dilute hydrochloric acid, followed by barium chloride soloution
- A white precipitate will form when sullfate ions are present
Instrumental methods:
- Elements and compounds can be detected using instrumental methods
- Thety are accurate, sensetive and rapid- making them advantageous compared to chemical tests
Flame emission spectroscopy:
- An example of an instrumental method- used to analyse metal ions in a solution
- A sample is put into a flame- the light given out is passed through spectroscope
- The output is a line spectrum- can be analysed to identify the metal ions in the solution and measure their concentrations
Method for chromatoography:
Method
* Draw (pencil) start line on chromatography paper
* Place spot of food colouring on start line
* Place solvent in beaker
* Place chromatography paper in beaker / container
* So (chromatography) paper is in solvent, but solvent is below start line
* Use a lid
* Wait for solvent to travel up the chromatography paper (until
near top)
* Mark solvent front
* Dry the (chromatography) paper
Measurements
* Measure distance between start line and centre of spot
* Use of measurements to determine Rf value
