GCSE Key Topics Revision Flashcards
What is HPLC or Gas-Liquid Chromatography used for?
To separate mixtures of volatile liquids.
What are the advantages of Mass Spectrometry/HPLC ?
Small samples are only required
Results are obtained quick
Gas-Liquid Chromatography and Mass Spectrometry can be combined to separate and identify compounds. This allows chemists to determine exactly what compounds are contained in a sample of an unknown mixture.
What are the disadvantages of Mass Spectrometry/HPLC ?
Equipment expensive
Requires the expertise of trained analytical chemists
Care is taken too observe the necessary health and safety procedures
Test for Cations
Flame Test - Method
Clean a nichrome wire (a nickel-chromium alloy) by dipping it into concentrated hydrochloric acid.
Hold the wire in a hot Bunsen flame. Repeat until the wire does not produce any colour in the flame.
Dip the clean nichrome wire into the concentrated hydrochloric acid again and dip it into a small amount of the unknown solid.
(A small sample of he solid will stick to the wire)
Place the wire in the Bunsen flame
Observe the colour of the flame
Results for the: Test for Cations - Flame Test
Sodium ion - Yellow (persistent)
Potassium ion - Lilac
Calcium ion - Brick red
Barium ion - Apple green
Copper ion - Green/Blue
Test for Cations
Using Sodium Hydroxide Solution - Method
Dissolve a small sample of the solid salt in water
Place approximately 10cm*3 of the solution into a test tube
Add Sodium hydroxide solution drop by drop
Observe the colour of the precipitate if one is produced
For any white precipitate produced, continue to add Sodium hydroxide solution, drop by drop
Observe what happens to the precipitate.
Test for Cations
Using Sodium hydroxide solution - Results
Blue - Copper(II) ion
Green - Iron(II) ion
Red-Brown - Iron(III) ion
White - Magnesium ion
White precipitate that redissolves in excess Sodium hydroxide solution - Aluminium ion or Zinc ion
Test for Anions
Test for Halide ions - Method
Dissolve a small sample of the solid salt in water
Place approximately 10cm*3 of the solution into a test tube
Add four drops of nitric acid
Add silver nitrate solution drop by drop
Observe the colour of the precipitate if one is produced
Test for anions
Test for Halide ions - Results
Colour of precipitate produced
White - Chloride ion
Cream - Bromide ion
Yellow - Iodide ion
Test for anions
Test for Sulfate ions - Method
Dissolve a small sample of the solid salt in water
Place about 10cm*3 of the solution into a test tube
Add barium chloride solution drop by drop
Observe the colour of the precipitate if one is produced
Test for anions
Test for Sulfate ions - Results
Colour of the precipitate
White - Sulfate ions are present
Test for anions
Test for Carbonate ions - Method
Add hydrochloric acid to the solid salt
Collect and test any gas formed with limewater
If the limewater turns milky/cloudy the gas evolved is carbon dioxide and the salt is a carbonate
Factors affecting solubility
Volume of solvent
Temperature of solvent
Stirring the solution (Kinetic Energy)
Increasing the surface area of the solute
Definition - Hydrated
When some solids crystallise from aqueous solution they contain water and are said to be hydrated.
Anhydrous - Definition
When some solids lose their crystal structure and water of crystallisation, they are said to be anhydrous.
Dehydration - Definition
The removal of the elements of water from a compound to form a new compound.
Water of crystallisation
Water that is chemically combined with the solid and forms part of the compound. Water chemically joined in this way is called water of crystallisation.
How can water of crystallisation be removed from the compound?
Heating the hydrated solid to constant mass.
Safety precautions when carrying out experiments with halogen gases.
Safety gloves
Fume cupboard
Safety glasses
What colour will bromine dissolved in water appear in low, medium and high concentrations?
Low = Yellow
Medium = Orange
High = Brown
What colour will iodine dissolved in water appear in low, medium and high concentrations?
Low = Yellow
Medium = Brown
High = Purple?
(Think of iodine solution in biology which will turn blue/black in the presence of starch)
What is Chromatography used for?
To separate mixtures of coloured compounds
Similarities and differences between simple distillation and fractional distillation.
Fractional Distillation
- Used to separate liquids with close boiling points
- Uses a complex apparatus with a fractionating column
- Process has to be repeated several times to get the pure components
- Cannot be used to separate a solvent from a solute
- Used in crude oil refinery
Simple Distillation
- Simple distillation is used to separate liquids with boiling point gaps of at least 50 degrees (apart from water and ethanol = 22°C boiling point gap)
- Uses a simple apparatus with 2 flasks and a condenser (Liebeg condenser)
- Process doesn’t have to be repeated to get the pure components
Can be used to separate a solvent from a solute
Element definition
A substance that consist of only one type of atom
Compound definition
A substance that consists of two or more different elements chemically bonded together
Mixture definition
A mixture consisting of two or more substances not chemically bonded together.
They can be easily separated by, for example iron and sulfur, salt and sand.
Distillation definition
A process that can be used to separate a pure liquid from a mixture of liquids.
In Mass Spectrometry, all of the atoms and molecules are measured relative to ________________________.
Answer: one twelfth the mass of a Carbon-12 atom,
12
6 C
By carefully interpreting the data from mass spectrometry we can see that it is possible to deduce ____________________________.
Answer:
- The relative atomic masses of elements
- The number of isotopes an element contains
- The relative molecular masses of compounds and molecules
Molecule definition
Two or more atoms covalently bonded
Copper(II) Oxide is the colour …..
Black
Copper(II) Carbonate is ….
Green
Hydrated Copper(II) Sulfate is ….
Blue
Most Copper Salts are ____ in solution.
Blue
Group 1 Compounds
Group 2 Compounds
Aluminium Compounds
Zinc Compounds
Colour = ?
Solution Colour = ?
Colour = White
Solution = Colourless
Why is it that some alloys are harder than the pure metal they contain?
Alloys contain atoms of different sizes which distorts the regular arrangement of atoms. This makes it more difficult for the layers to slide easily over each other.
Uses of Aluminium
Overhead electrical wiring
Alloys for aircraft
Uses of Copper
Electrical wiring
Plumbing
Brass (Alloy)
Coinage
Uses of Iron
Bridges
Infrastructure
Uses of Magnesium
Flares
High strength alloys for aircraft
Chemical reactions use up _________ and produce new substances called ________.
Answers:
Reactants
Products
John Newland proposed the Law of Octaves but his work was rejected by other scientists. Why?
- His classification assumed that all of the elements had been discovered, even though a number of new elements had been recognised a few years prior to his publication
He grouped some elements together which were not alike, e.g Manganese + Nitrogen, Phosphorus + Arsenic, Copper + [Lithium + Sodium + Potassium + Rubidium]
He placed two elements together, Cobalt and Nickel
Dmitri Mendeleev created the ‘Periodic Table’ in 1869. What features did his arrangement and classification of elements include?
He arranged elements in order of increasing relative atomic mass.
He placed elements with similar properties in the same vertical columns (Groups).
He left gaps - For undiscovered elements, helped keep his elements in their proper groups and allowed him to predict elements with unexpected accuracy (e.g Gallium and Germanium).
Mendeleev’s Periodic Table of 1869 differs from today’s Modern Periodic Table of elements. In what ways?
Mendeleev = Increasing atomic mass Today = Atomic number
Group 8/0 Noble Gases added
Transition metals added in between group 2 and 3
Some groups have been given common names
Clear distinction between metals and non-metals thanks to a solid black line starting at group 3 separating the elements
Fluorine
Colour and state at 25°C
Yellow
Gas
Chlorine
Colour and State at 25°C
Green
Gas
Bromine
Colour and state at 25°C
Brown
Liquid
Iodine
Colour and state at 25°C
Purple/Dark grey
Solid
Astatine
Colour and state at 25°C
Black
Solid
The darkness in colour and appearance of the group 7 elements _________ as you go down the group.
Increases
The melting and boiling points of the Group 7 halogen elements _________ as you move down the group.
Increases
Fluorine has the lowest melting and boiling point.
Acid + Alkali = ?
Salt + Water
What is concentration measured in?
mol/dm3️⃣
Give an example of a strong acid
Hydrochloric acid
Sulfuric acid
Nitric acid
Give an example of a strong alkali
Sodium hydroxide
Potassium hydroxide
Give an example of a weak acid
Ethanoic acid
Carbonic acid
Give an example of a weak alkali
Ammonia
Pure hydrogen burns with a squeaky pop and can be tested by placing a lighted splint into a test tube containing Hydrogen gas. The combustion of hydrogen gas in the air (With oxygen) produces a pop. Recall the balanced symbol equation.
2H2️⃣ + O2️⃣ –> 2H2️⃣O
Give the chemical name for limewater
Calcium hydroxide solution
To test for Cations, one may use Sodium hydroxide solution. Magnesium ions, Zinc ions and Aluminium ions all form white precipitates in this test. When excess Sodium hydroxide solution is added, the Magnesium precipitate does not dissolve, leaving only Zinc and Aluminium. What alkali could be used to prove that Zinc ions are present, increasing the validity of the test?
Ammonium hydroxide solution
If Zinc ions are present a white precipitate will form (Zinc hydroxide) which will, unlike Aluminium, will dissolve in excess Ammonium hydroxide solution.
