Chapter 8 - Reactivity trends Flashcards
What are the group 2 elements called?
Alkali earth metals
List 3 properties of group 2 metals?
- High melting and boiling points
- Low density metals
- Form colourless (white) compounds
What kind of agents are group 2 metals?
Reducing agents
What are reducing agents?
A species that donates electrons to another species. therefore reducing that species - and getting oxidised itself.
How does reactivity change down group 2?
Increases
Why does reactivity increase down group 2?
Atomic radius increases as number of electron shells increases, increasing shielding which decreases nuclear attraction, even though nuclear charge increases - which is outweighed by increased shielding. This means that elements are more reactive as it’s easier to lose an electron from outer shell.
What is the product of reaction between group 2 metal and oxygen? Give the symbol equation.
Metal oxide of M 2+ and O 2- ions
2Ca(s) +O2 -> 2CaO(s)
What is produced when a group 2 metal reacts with water?
Give the symbol equation
Alkaline hydroxide with M(OH)2 formula, and hydrogen gas.
Ca(s) +H2O -> Ca(OH)2 (aq) +H2(g)
What is produced when a metal reacts with a dilute acid?
Salt and hydrogen gas
What is produced when a group 2 oxide reacts with water?
Give symbol equation
Alkaline solution of metal hydroxide and releases hydroxide ions.
MgO(s) + 2H2O(l) -> Mg(OH)2
What is formed when a group 2 carbonate reacts with dilute acid?
Salt + water + carbon dioxide
What is the trend of solubility down group 2?
Increases down the group
Why are group 2 hydroxides more alkaline as you go down the group?
Solubility of hydroxides in water increases down the group, so resulting solutions contain more OH- (aq) ions are more alkaline.
Given that most group 2 oxides, hydroxides and carbonates are soluble in water, what are they besides bases?
Alkalis
What is the use of calcium hydroxide in agriculture?
Ca(OH)2 is added to acidic soils to neutralise them as its alkaline. This forms neutral water.
Ca(OH)2 (s) + 2H+ (aq) -> Ca 2+ (aq) + H2O (l)
How does a group 2 metal react with oxygen?
Reacts vigorously
What are the uses of group 2 compounds in medicine?
Group 2 bases often used as antiacids in treating acid indegestion - indegestion tablets. They neutralise stomach (hydrochloric) acid.
Mg(OH)2 + 2HCl -> MgCl2 +H2O
CaCO3 + 2HCl -> CaCl2 +H2O +CO2
How does the ease of thermal decomposition of group 2 carbonates change down the group?
Decreases
What is the name given to the group 7 elements?
The halogens
What is the trend in boiling point down group 7?
Increases
Explain the trend of boiling point down group 7
More electrons means stronger London forces and therefore more energy is required to break the intermolecular forces, and so boiling point increases.
What is the trend of reactivity down group 7?
Decreases down the group
Explain the trend of reactivity down group 7
Tendency to gain electron decreases as atomic radius increases due to more electron shells - so shielding increases and therefore less nuclear attraction to capture electron.
What do more reactive halogens do to less reactive halide ions?
Displace them in a solution
What can halogen - halide displacement be used to identify?
Which halide is present in a solution and therefore which one is more reactive
What colour is fluorine at room temperature?
Yellow (gas)
What colour is chlorine at room temperature?
Green/yellow (gas)
What colour is bromine at room temperature?
Reddish brown (liquid)
What colour is iodine at room temperature?
Silvery black (solid)
What colour is astatine at room temperature?
Black (solid)
What is a disproportionation reaction?
Redox reaction where the same element is both oxidised and reduction
Why is chlorine used in water treatment?
Chlorine kills water-bourne pathogens that would otherwise cause diseases such as typhoid or cholera?
Give the equation for reaction between chlorine and water. Include oxidation states.
Cl2 (aq) + H20 (l) -> HClO (aq) +HCl (aq)
0. +1 -2. +1+1-2. +1-2
Cl - 0 -> +1 and 0 -> -1
So this is a disproportionation reaction.
Give the equation for reaction of chlorine with cold, dilute aqueous sodium hydroxide. Include oxidation states.
Cl2 (aq) +2NaOH (aq) -> NaClO (aq) + NaCl (aq) + H2O (l
0. +1 -2+1. +1+1-2 +1 -2 +1-2
Cl - 0 -> +1 and 0 -> -1
So this is a disproportionation reaction
Why is NaClO used in bleach and not HClO?
Higher concentration of chorine in NaClO due to the low solubility of chlorine in water
What are the risks of using chlorine?
- Forms THMs when mixed with organic matter in water which is carcinogenic - causes cancer.
- Doesn’t kill all bacteria e.eg Ecoli causing bacteria found.
- Toxic, poisonous gas
What is qualitative analysis?
- Relying on simple observations rather measurements. Can be carried out quickly on a test - tube scale.
e. g. bubbles, precipitates, colour changes.
If you were asked to analyse an unknown inorganic compound, what order would you test for anions?
- ). Carbonate test (CO3 2-)
- ) Sulphate test (SO4 2-)
- ) Halide test (Cl-, Br-, I-)
Describe the process of a carbonate test
- ) Add dilute nitric acid to solid or solution in a test tube.
- ) If you see bubbles, the unknown could be a carbonate.
- ) To prove that the gas is carbon dioxide, bubble it through limewater ( Ca(OH)2), and a white precipitate of calcium carbonate would form.
Give an example equation for a carbonate test if sodium carbonate is the carbonate ion
Na2CO3 (aq) + 2HNO3 (aq) -> 2NaNO3 (aq) + CO2(g) + H2O (l)
Describe process of a sulphate test
- ) Add aqueous Barium chloride or barium nitrate to solution with corresponding hydrochloric acid or nitric acid.
- ) If white precipitate of BaSO4 is formed, then the sulphate ion is present
Write the ionic equation for the sulphate ion test
Ba2+(aq) + SO4 2- (aq) -> BaSO4 (s)
Describe the process of the halide test
- ) Add aqueous silver nitrate (AgNO3) to a aqueous solution of a halide.
- ) The colour of silver halide is different for chloride (white), bromide (cream) and iodide (yellow).
- ) If colours are too hard to make out, dilute aqueous ammonia, and the concentrated aqueous ammonia are added to test solubility of solution. Chloride is soluble in dilute NH3, bromide is soluble in concentrated NH3 and iodide is insoluble in both.
What colour precipitates do the 3 halide ions form when reacted with silver nitrate?
Chloride - white
bromide - cream
iodide - yellow
Why is the carbonate test first, sulphate second and halide test last?
- Sulphates and halides don’t produce bubbles with dilute acid
- Barium carbonate is also white and insoluble in water, so would test positive for sulphate ion in a test.
- Silver carbonate and silver sulphate are both insoluble in water and will form precipitates.
Describe the process for testing for ammonium ions (cation).
- ) Aqueous sodium hydroxide, NaOH, is added to solution
- ) Ammonia gas produced if ion is present.
- ) Mixture warmed and ammonia gas released - very soluble in water.
- ) Gas will turn moist litmus paper blue - as it’s alkaline.
What colour solutions are formed when chlorine reacts with bromine and iodide solutions?
Bromide solution - yellow/orange (bromine colour) solution. Chlorine displaces/reduces
Iodide solution - yellow/brown solution (iodine colour). Chlorine displaces/reduces.
What colour solutions are formed when bromine reacts with chloride and iodide solutions?
Chloride - yellow/orange solution. No reaction
Iodide - yellow/brown (iodine colour) solution
What colour solutions are formed when iodine reacts with chloride and bromide solutions?
Chloride - yellow/brown solution. No reaction
Bromide - yellow/brown solution. No reaction
What observations are made when group 2 chloride solutions react with H2SO4?
MgSO4 - No reaction - soluble
CaSO4 - no reaction - soluble
SrSO4 - faint white precipitate - slightly soluble
BaSO4 - thick white precipitate - insoluble
Solubility of group 2 sulphates decreases down the group
What observations are made when group 2 chloride solutions react with NaOH?
Mg(OH)2 - thick white precipitate - insoluble
Ca(OH)2 - faint white precipitate - slightly soluble
Sr(OH)2 - No reaction - soluble
Ba(OH)2 - no reaction - soluble
solubility of group 2 hydroxides increases down the group.
