Topic 9 - Separate Chemistry 2 Flashcards
Why must the test for any ion be unique?
There are several different tests to detect and identify the ions in compounds. It is important that the test for any ion is unique. The results of a test must let you determine which ion is present, rather than being uncertain about which ion it is.
How do you test for cation?
flame test or sodium hydroxide test
How do you conduct a flame test?
- dip a clean wire loop into a solid sample of the compound being tested 2. put the loop into the edge of the blue flame from a Bunsen burner 3. observe and record the flame colour produced
How do you test for metal cation using sodium hydroxide?
- You add a few drops of sodium hydroxide solution to a solution of your mystery compound 2. If a hydroxide precipitate forms, you can use its colour to tell which metal ion was in the compound.
What colour is the precipitate when these metal ions are present? A - Aluminium B - Calcium C - Copper D - Iron (II) E - Iron (III)
A - Al^3+ - White at first then colourless B - Ca^2+ - White C - Cu^2+ - Blue D - Fe^2+ - Green E - Fe^3+ - Brown
How do you work out whether a substance contains ammonium ions?
- Add some sodium hydroxide solution to a solution of the mystery compound. 2. Now heat it gently 3. If ammonia gas is given off then, it means there are ammonium ions in the mystery substance 4. Test for ammonia gas by holding a piece of damp red litmus paper. 5. If the red litmus paper turns blue, ammonia gas is present
What colour would you get for testing these ions with a flame? A - Lithium B - Sodium C - Potassium D - Calcium E - Copper
A - Li+ - red B - Na+ - yellow C - K+ - lilac D - Ca^2+ - orange-red E - Cu^2+ - blue-green
How do you test for halide ions?
- add a few drops of dilute nitric acid to the sample 2. add a few drops of dilute silver nitrate solution 3. Observe and record the colour of any precipitate that forms. Chloride - Cl- - White Bromide - Br- - Cream Iodide - I- - Yellow
How do you test for carbonate ions?
Carbonate ions, CO32- are detected using a dilute acid. Bubbles are given off when an acid, usually dilute hydrochloric acid, is added to the test compound. The bubbles are caused by carbon dioxide. Limewater is used to confirm that the gas is carbon dioxide. It turns milky when carbon dioxide is bubbled through it. The test for carbonate ions works whatever acid is added.
How do you test for sulfate ions?
Barium ions react with sulfate ions, SO42- to form insoluble white barium sulfate: Ba2+(aq) + SO42-(aq) → BaSO4(s) To test for sulfate ions in solution: 1. add a few drops of dilute hydrochloric to the sample 2. add a few drops of dilute barium chloride solution 3. A white precipitate forms if sulfate ions are present.
What is flame photometry?
It is an instrumental method that allows you to identify ions in a dilute solution. In the flame photometer, the coloured light from a vaporised sample can be split to produce an emission spectrum. The different lines in an emission spectrum look like a coloured barcode. Each metal ion produces a unique emission spectrum. The metal present in a sample is identified by comparing its spectrum with reference spectra. These are emission spectra from known metal ions. If two spectra match, they must be from the same metal ion.
What is the advantages of using instrumental analysis (tests that use machines)?
- Very sensitive - they can detect even the tiniest amounts of substances - Very fast and tests can be automated - Very accurate - don’t involve human error
How do you identify the ions in unknown salts, using the tests for the specified positive and negative ions?
- Carry out one or more tests (Flame test, Hydroxide precipitate test, Ammonium test, Halide ion test, Sulfate ion test and Carbonate ion test) on each salt. You may need to dissolve a sample of salt in a little distilled water if you are given solids, rather than solutions. 2. Record your observations carefully. Repeat any tests that do not get clear results.
What is the formula of the first first four alkanes?
Methane - CH4 Ethane - C2H6 Propane - C3H8 Butane - C4H10
Draw the structure of the first four alkanes
Why are the alkanes saturated hydrocarbons?
All the atoms have formed bonds with as many other atoms as they can.
What are the formulas of 3 alkenes?
Ethene - C2H4 Propene - C3H6 Butene - C4H8
Draw out the structures of the three alkenes (Butene1 and Butene2)
Why are alkenes unsaturated?
This is because they can make more bonds - the double bond can open up, allowing the two carbon atoms to bond with other atoms
What happens in the reaction of bromine with ethene?
The two Br atoms join with the ethene so each carbon atom is joined to 1 bromine atom and 2 hydrogen atom.
How is bromine water used to distinguish between alkenes and alkanes?
An orange-brown solution of bromine dissolved in water, called bromine water, is used to distinguish between alkanes and alkenes: - there is no change when bromine water is mixed with an alkane - the bromine water becomes colourless when it is mixed with an alkene
Describe complete combustion for alkanes and alkenes.
The complete combustion of alkanes and alkenes involves the oxidation of hydrocarbons. Carbon dioxide and water are produced. For example: Ethane + oxygen → carbon dioxide + water C2H6(g) + 3½O2(g) → 2CO2(g) + 3H2O(l) Ethene + oxygen → carbon dioxide + water C2H4(g) + 3O2(g) → 2CO2(g) + 2H2O(l) Notice that more molecules of oxygen are needed to balance the equation for ethane, because the alkane contains more hydrogen atoms which need to be oxidised to form water molecules
What is a polymer?
Substance of high average relative molecular mass made by joining up lots of small repeating units called monomers.
What is addition polymerisation?
Lots of unsaturated monomer molecules can open up and join together to form polymer chains. Ethene (C2H4) becomes poly(ethene) - (C2H4)small n Draw in structure form
How do get from the displayed formula of the polymer to the displayed formula of the monomer?
Draw out the repeating bit of the polymer, get rid of the two bonds going out through the brackets and put a double bond between the carbons. Don forget the n or the number of repeating units on the bottom right.
How are the properties of poly(ethene) related to its use?
Flexible, electrical insulator and cheap - Plastic bags, bottles and wire insulation
How are the properties of poly(propene) related to its use?
Flexible, strong, tough, moldable - crates, furniture, ropes
How are the properties of poly(chloroethene) or PVC related to its use?
Tough, cheap - water pipes, window frames