Chemical Analysis Flashcards
How do you test for hydrogen? What is the positive test?
Place a lit splint over a test tube of gas. Positive test: the hydrogen burns rapidly and makes a ‘squeaky pop’ sound.
How do you test for oxygen? What is the positive test?
Insert a glowing splint into a test tube. Positive test: the glowing splint relights.
How do you test for carbon dioxide? What is the positive test?
Bubble the gas through limewater. Positive test: the limewater turns milky/cloudy.
How do you test for chlorine? What is the positive test?
Hold a piece of damp blue litmus paper over the test tube. Positive test: the litmus paper is bleached and turns white.
How do you test positive ions?
There are two methods:
- Flame test
- Sodium hydroxide test
How do you test for Na+?
Flame test: Yellow.
How do you test for Ca2+?
Flame test: Orange/Red.
Sodium hydroxide: White precipitate.
How do you test for Li+?
Flame test: Crimson.
How do you test for K+?
Flame test: Lilac/Violet.
How do you test for Mg2+?
Sodium hydroxide: White precipitate.
How do you test for Cu2+?
Flame test: Green.
Sodium hydroxide: Blue precipitate.
How do you test for Fe2+?
Sodium hydroxide: Green precipitate.
How do you test for Fe3+?
Sodium hydroxide: Brown/Red precipitate.
How do you test for Al3+?
Sodium hydroxide: White precipitate.
How do you test for negative ions?
There are three ways:
- For carbonates: Add dilute hydrochloric acid to see if it fizzes. Then test it with limewater. If it fizzes with the acid and turns limewater cloudy, carbonate ions are present.
- For halides: Add dilute nitric acid and silver nitrate solution. A precipitate is formed when halide ions are present.
- For sulfates: Add dilute hydrochloric acid and barium chloride solution. A white precipitate forms if sulfate ions are present.
How do you test for Cl-?
Nitric acid + silver nitrate: Cloudy/White precipitate.
How do you test for SO4, 2-?
Nitric acid + silver nitrate: Cloudy/Milky precipitate.
How do you test for F-?
Nitric acid + silver nitrate: No precipitate.
How do you test for I-?
Nitric acid + silver nitrate: Yellow precipitate.
How do you test for Br-?
Nitric acid + silver nitrate: Creamy precipitate.
How do you test for CO3, 2-?
HCl + Limewater: A fizz in acid and cloudy limewater.
What is flame emission spectroscopy?
It is an instrumental analysis method which is used to analyse samples from metal ions. When the sample is heated in a flame, the light produced is analysed. Each metal ion has its own characteristic pattern, called its line spectrum. You can identify the metal ions present through this.
How does flame emission spectroscopy work?
Low energy shell electrons gain energy and move to the outer shells. Here, they then lose energy and move back again. Light is emitted through this.
How do you work out the rf value on a chromatography?
Distance moved by substance / Distance moved by solvent
OR
Small number / big number
How do you test if a substance is pure?
By analysing it’s boiling point. If it has one boiling point, it is pure. If it has multiple, it means it is made up for more than one compound.
How is the solvent front distance measured?
From the bottom of the paper to the solvent front.
What is the solvent in chromatography?
Water.
What does a substance higher up the paper in chromatography mean?
It is more soluble.
