Chemical Analysis Flashcards
What is test for chlorine?
Chlorine bleaches damp litmus paper = turns it white
If you use blue litmus paper (when testing for chlorine), why might it turn red for a moment?
Because solution of chlorine is acidic
What smell does chlorine have?
Has characteristic sharp, choking smell
What is test for hydrogen?
Burning splint at open end of test tube containing hydrogen = get “squeaky pop”
Where does the noise come from when testing for hydrogen?
Comes from hydrogen burning quickly in oxygen in air to form water
What is the test for oxygen?
Glowing splint inside test tube containing oxygen = oxygen will relight growling splint
What is the test for carbon dioxide?
Bubbling carbon dioxide though limewater = solution turns cloudy
What is test for ammonia?
- Makes damp red litmus paper turn blue
- Forms a white smoke of ammonium chloride when hydrogen chloride gas (from concentrated hydrochloric acid) is held near it
What is the test for sulfate ions?
- Use dropping pipette to add a couple drops of dilute hydrochloric acid (HCl)
- Followed by couple drops of barium chloride solution (BaCl2) to test tube containing mystery solution
- If sulfate ions are present = white precipitate of barium sulfate will form
What is the test carbonate ions?
- Using a dropping pipette to add few drops of dilute acid to test tube containing mystery substance
- Then connect test tube to test tube containing limewater
- If carbonate ions are present = reaction with acid will release CO2 = turns limewater cloudy when it bubbles through
- Turns cloudy white bc carbon dioxide produces = a white precipitate
What is the test for halide ions (Cl-, Br-, I-)?
- Add couple drops of dilute nitric acid (HNO3)
- Followed by couple drops of silver nitrate solution (AgNO3) to mystery solution
In the test for halide ions, what does chloride give?
White precipitate of silver chloride
In the test for halide ions, what does bromide give?
Cream precipitate of silver bromide
In the test for halide ions, what does iodide give?
Yellow predicate of silver iodide
How can you test for metal ions?
By heating your substance and seeing whether the flame turns a distinctive colour → use these colours to detect & identify different ions
Describe the method for testing for metal ions
- Clean nichrome or platinum wire loop by rubbing with fine emery paper
- Hold it in blue flame Bunsen burner
- Flame might change colour but once it’s blue again = loop is clean
- Dip loop into sample you want to test & put back in flame
- Record colour of flame
Why does the method for testing for metal ions only work for samples that contain a single metal ion?
If sample tested contains a mixture of metal ions = flame colours of some ions may be hidden by colours of others
What colour flame do lithium ions produce?
Crimson
What colour flame do sodium ions produce?
Yellow
What colour flame do potassium ions produce?
Lilac
What colour flame do calcium ions produce?
Orange-Red
Many metal hydroxides are…
Insoluble and precipitate out of solution when formed
What is the test for (some) metals?
- Add few drops of sodium hydroxide solution to a solution of your mystery compound
- If you get a coloured precipitate (insoluble hydroxide) = can tell which metal was in the compound
What is the colour of the precipitate that calcium ions forms?
White
What is the colour of the precipitate that copper(II) ions forms?
Blue
What is the colour of the precipitate that iron(II) ions forms?
Green
What is the colour of the precipitate that iron(III) ions forms?
Brown
What is the colour of the precipitate that aluminium ions forms?
White at first. But then redissolves in excess NaOH to form a colourless solution.
What is the colour of the precipitate that magnesium ions forms?
White
What colour flame do barium ions produce?
Green
What is a pure substance?
Substance that contains only one compound or element throughout
A chemically pure substance will melt or boil at a…
specific temperature
How can you test the purity of sample?
By measuring its melting/boiling point & comparing it with melting/boiling point of pure substance
The purer the sample, the…
closer its melting/boiling point is to the actual melting/boiling point (of the pure substance)
What will impurities in sample do to the melting point? (name 2 things)
- Lower the melting point
- Increase melting range of substance
What will impurities in sample do to the boiling point? (name 2 things)
- Increase the boiling point
- Sample boils at range of temperatures
What are formulations?
Useful mixtures with a precise purpose that are made by following a ‘formula’ (i.e. a recipe)
In a formulation, what is each component and what do they do (and why)?
Each component: measured quantity & contributes to properties → to meets its required function
Name 3 products that formulations are found in
- Cosmetics
- Cleaning products
- Fuels
- Metal Alloys
- Drugs
- Fertilisers
Explain how paint is a formulation
It’s composed of pigments, solvents, binders, additives, etc
Depending on purpose of paint = chemicals used and their amounts will be changed so paint produced is right for the job
What is chromatography?
(Analytical) method used to separate substances in a mixture (based on their solubilities) & then used to identify substances
Name the 2 phases in chromatography
- Mobile Phase
- Stationary Phase
A mobile phase is where…
Where molecules can move
A stationary phase is where…
where molecules can’t move
Where does the mobile phase take place?
Always in liquid or gas
Where does the stationary phase take place?
Solid or really thick liquid
During chromatography, what do substances in a sample do constantly?
Constantly move between mobile and stationary phrases
What is formed when substances in a sample constantly move between mobile and stationary phases?
Equilibrium (formed between 2 phases)
When the mobile phase moves through stationary phase, what happens?
Anything dissolved in mobile phase moves with it
How quickly a chemical moves between the 2 phases depends on…
how it’s ‘distributed’ i.e. whether it spends more time in mobile phase or stationary phase
What happens to chemicals that spend more time in mobile phase than stationary phase?
They will move further through the stationary phase
When do components in mixture normally separate?
Through stationary phase BUT only if all components spend different amounts of time in mobile phase
Why may the number of spots change in different solvents?
Bc the distribution of a chemical may change depending on solvent
How do you know a substance is pure in chromatography?
When it forms one spot in any solvent
Why does a pure substance only form one spot in chromatography?
Bc there’s only one substance in sample
How do you work out a Rf value?
Distance travelled by substance (B)
Distance travelled by solvent (A)
In paper chromatography, what is the stationary phase?
The chromatography paper (filter paper)
In paper chromatography, what is the mobile phase?
Solvent
In paper chromatography, the amount of time molecules spend in each phase depends on what? (name 2 things)
- How souble they are in a solvent
- How attracted they are to the paper
Why will molecules with a higher solubility in a solvent be carried further up the paper?
They’re more attracted to the mobile stage/solvent (i.e. spend more time in the mobile phase)
Why will molecules with a low solubility (in a solvent) travel not very far up the paper?
They’re more attracted to the stationary stage/paper (i.e. spend more time in the stationary phase)
In chromatography, what does separation depend on?
Amount of time substances spend in mobile and stationary phase
