C8-Chemical Analysis Flashcards
What are pure substances?
Compounds or elements that contain only one substance
How can we test if a substance is pure?
The melting and boiling points of an elements are at specific temperatures
What is a formulation?
A mixture that has been designed to produce a useful product
Why do some substances move further along a chromatogram than others?
They have a stronger force of attraction between itself and the mobile phase relative to the stationary phase.
What does Rf stand for?
Retention factor
How do you calculate Rf values?
Distance travelled by substrate/distance travelled by solvent
What tube is used to drop substances onto chromotography paper?
Capillary
How is hydrogen gas tested and what is the positive result?
- Holding a lit splint at the open end
- A squeaky ‘pop’ sound
How is oxygen gas tested and what is the positive result?
- Insert glowing splint into flask (made from blowing out splint)
- The splint relights
How is carbon dioxide gas tested and what is the positive result?-2 methods
- Bubble carbon dioxide through limewater using a delivery tube
- Limewater turns cloudy
or - Hold a lit splint at open end
- Splint extinguishes
How is chlorine gas tested and what is the positive result?
- Hold damp blue litmus paper at top of boiling tube
- Damp blue litmus paper turns red then white (bleaches)
How is a metal flame test carried out?
- A nichrome wire loop should be dipped in concentrated hydrochloric acid, heated and dipped in acid again before dipping it into the metal compound that is being tested
- The loop us then held over the roaring blue flame of a Bunsen burner
What colour does the flame test for lithium produce?
Crimson
What colour does the flame test for sodium produce?
Yellow
What colour does the flame test for potassium produce?
Lilac
What colour does the flame test for calcium produce?
Orange-red
What colour does the flame test for copper produce?
Green
When a metal ion is combined with sodium hydroxide what is formed?
A precipitate
What colour precipitate is formed when adding sodium hydroxide to copper (II) ions?
Blue
What colour precipitate is formed when adding sodium hydroxide to iron (II) ions?
Green
What colour precipitate is formed when adding sodium hydroxide to iron (III) ions?
Brown
What colour precipitate is formed when adding sodium hydroxide to Al³⁺ ions?
White
What colour precipitate is formed when adding sodium hydroxide to Ca²⁺ ions?
White
What colour precipitate is formed when adding sodium hydroxide to Mg²⁺ ions?
White
How can we tell apart aluminium ions from magnesium or calcium irons?
Aluminium ions dissolve
How can we tell apart calcium ions from magnesium ions
Calcium ions produce an orange-red flame when burnt. Magnesium ions dont produce a flame when burnt.
What are the tests for carbonates?
Add a dilute acid to a carbonate and it produces carbon dioxide gas (effervesced)-turns limewater milky
What is the test for sulfates?
Add dilute hydrochloric acid then barium chloride solution-a white precipitate tells you sulfate ions are present
How do you test for halides?
Add dilute nitric acid then silver nitrate solution
What Colour precipitates do chloride, bromide and iodide ions form?
- White
- Cream
- Yellow
What are benefits of modern instrumental methods?
- Highly accurate and sensitive
- Quicker
- Enable very small samples to be analysed
What are the disadvantages of using instrumental methods?
- Expensive
- Requires specialist training
- Gives results that can only be interpreted by comparison with data from known substances
How does flame emission spectroscopy work?
- Sample is heated in a flame
- This energy causes electrons to jump into higher shells
- When the electrons fall back down, the energy is released as light energy
- In a spectrosope, the wavelengths are analysed to produce a line spectrum
- This is compared to data base values
