Topic 8 - Chemical Analysis Flashcards
What is a pure substance
Something that contains only one compound or element
What will impurities do to the melting and boiling point of a substance
Lower the melting point and increase the boiling point
What will impurities do the melting and boiling ranges of a subatance
It will increase
How can you find whether a substance is pure
Measure its melting and boiling point and compare it to that of the pure substance
What’s a formulation
Mixtures made for a specific purpose by following a formula e.g cleaning products
What’s the mobile phase of paper chromotography
The solvent
Whats the stationary phase of paper chromatography
The paper
In paper chromatography, what does how far a chemical move depend on
Whether it spends more time in the mobile or stationary phase. If it spends more time in the mobile phase it will move more.
What does how much time the molecules spend in each phase depend on
How soluble they are in the solvent and how attracted they are to the paper
What’s the formula for Rf value
Distance travelled by substance (B) ÷ distance travelled by the solvent (A)
How do you find out if a certain substance is in a mixture using paper chromotography
1) run a pure sample of that substance alongside the unknown mixture
2) do this multiple times in different solvents
3) measure Rf values
4) if the Rf value of the pure substance matches one of the Rf values of one of the spots in the mixture in all of the solvents it’s likely the substance is present
What’s the test for chlorine
Use damp litmus paper - chlorine will turn the paper from blue to white
What’s the test for oxygen
A glowing splint - oxygen will cause it to relight
What’s the test for carbon dioxide
Bubbling through limewater (calcium hydroxide) - carbon dioxide will turn it cloudy
What’s the test for hydrogen
Lit splint- hydrogen will make a sqeaky pop
What’s a catbonate
A substance that contains CO3 2- ions
What’s the test for carbonates
Put a sample of the solution in a test tube and then use a dropping pipette to add a couple drops of dilute acid. Then connect the test tube to a test tube filled with limewater. If carbonates are present, carbon dioxide will be released, causing the limewater to go cloudy
What’s the formula for a sulfate ion
SO4 2-
What’s the test for sulfates
Use a dropping pipette to add a couple drops of dilute hydrochloric acid, followed by a couple drops of barium chloride solution to test tube containing th solution - if sulfate ions are present white precipitate will form
What is the test for halides
Add a couple drops of dilute nitric acid (HNO3), followed by a couple drops of a silver nitrate solution (AgNO3) to the solution
What are the results of the halide test
Chloride = white precipitate of silver chloride
Bromide = cream precipitate of silver bromide
Iodide = yellow precipitate of silver iodide
What’s the method for flame tests
1) clean a platinum loop by dipping it into some dilute HCl and then holding it in a blue flame until it burns w/o any colour
2) dip the clean loop into the sample and place it back into the flame
What’s the results of the flame test
Lithium ions = crimson flame
Sodium ions = yellow flame
Potassium ions = lilac flame
Calcium ions = orange - red flame
Copper ions = green flame
What the method for the precipitate test
Add a few drops of sodium hydroxide solution to the mystery compound. If you get a coloured insoluble hydroxide you can often tell what metal is in the compound.
