Chem - topic 4 Flashcards
What is a common name given to group 2 metals?
Alkaline earth metals
What is the most reactive metal of group 2
Barium
List 3 physical properties of group 2 metals
- high melting and boiling points
- low density metals
- form colourless (white) compounds
Does reactivity increase or decrease down group 2? Why?
- increases
- electrons are lost more easily because larger atomic radius and more shielding
What type of reaction is the reaction between group 2 elements and oxygen
redox
What are the products when group 2 elements react with water
hydroxide and hydrogen gas
Which group 2 element doesn’t react with water
Beryllium
What are the products when a group 2 oxide reacts with a dilute acid
salt and water
What is formed when group 2 oxides react with water
metal hydroxide
What group 2 metal oxide is insoluble in water?
Beryllium oxide
Write an equation for the reaction between Mg(OH)2 and nitric acid
(2) nitric acid + magnesium hydroxide → magnesium nitrate + (2) water
Explain the reasons for the trend of thermal stability in group 1 and 2 carbonates
Group 2 carbonates are more thermally stable as you go down the group this is because the cations get bigger so therefore have less of a polarising effect distorting the carbonate ion less. As C-O bond is not weakened as much it is harder to break down.
Group 1 carbonates do not decompose except for lithium. This is because they don’t have a big enough charge density to polarise the carbonate ion as they only form 1+ ions. However, lithium ion is small enough to have a polarising effect so therefore lithium carbonate can decompose.
Explain the reasons for the trend of thermal stability in group 1 and 2 nitrates
The ease of thermal decomposition decreases down group 2 and this is because down the group the ions get larger and therefore has less charge density = less polarisation of nitrate anion and less weakening of the N-O bond.
Group 1 nitrate do not decompose with the exception of lithium nitrate. Lithium ion is small enough to charge polarisation of the nitrate anion and thus weakening the N-O bond
Flame colours:
Lithium
Sodium
Potassium
Rubidium
Caesium
Magnesium
Calcium
Strontium
Barium
Lithium - red (Le red)
Sodium - yellow (pasta)
Potassium - lilac
Rubidium - red (ruby)
Caesium - blue (like sea)
Magnesium - no colour
Calcium - brick red
Strontium - red
Barium - apple green
How are the colours form the flame test formed
The heat causes the electron to get excited and thus move to a higher energy level but at this higher level the electron is unstable so then moves back down. As it moves from a higher to lower energy level, energy is emitted in the form of visible light energy which is the colour you see
List two properties of halogens
- low melting and boiling points
- exist as diatomic molecules
What is the trend in boiling point down group 7? Why?
Increases down the group
Larger atomic radius as more occupied electron shells
stronger London forces
takes more energy to break
What is the trend in reactivity down group 7? Why?
Reactivity decreases because:
- atomic radius increases
- electron shielding increases
- ability to gain an electron and form 1- ions decreases
Explain the trend of electronegativity down Group 7
Down the group the electronegativity of the elements decreases. This is because the atomic radii increases due to the increasing number of shells so there is reduced nuclear attraction between the outermost electron and the nucleus
What is the trend in oxidising ability down the group? Why?
Decreases down group (Cl strongest, I weakest)
This is because Cl has the fewest occupied electron shells, greatest force of attraction between outer electrons and nucleus and thus is the easiest to gain electrons and be reduced (best oxidising agent)
What is the trend in reducing ability of halides down the group? Why?
Increases down the group (Cl- weakest, I- strongest)
This is because I- has the most occupied electron shell so outer electrons are further from the nucleus, weakest force of attraction between outer electrons and positive charge of nucleus and thus is the easiest to be oxidised and lose electrons (best reducing agent)
Colour of chlorine in water
Pale green
Colour of bromine in water
orange
Colour of iodine in water
brown
Colour of chlorine in cyclohexane
pale green
Colour of bromine in cyclohexane
orange
colour of iodine in cyclohexane
violet
Write the equation for chlorine oxidising bromide ions in water and associated colour change
Cl2 + 2Br- →. 2Cl- + Br2
Yellow solution
Colour change of Cl2 oxidising 2I- in cyclohexane
purple solution
Colour change of Br2 oxidising 2I- in water
Brown solution
What is the equation for the reaction of Cl2 with water?
Cl2 + H2O → HClO + HCl
Why is chlorine added to drinking water
it kills the bacteria in the water and makes it safer to drink
What are the two forms of the chlorate ion?
ClO - is chlorate (I)
ClO3 - is chlorate (V)
What is the equation for forming bleach and conditions
Cold dilute alkali
Cl2 + 2NaOH → NaCl + NaClO + H2O
NaClO is bleach
What do you use to test for halide ions
Acidified AgNO3
In the test for halides, why do we use HNO3 and why instead of HCl
To remove CO3^2-
Adding HCl would add Cl- ions, giving a false positive result
Result and equation for Cl- test
white ppt
Ag+ + Cl- → AgCl
Result and equation for Br- test
Cream ppt
Ag+ + Br- →AgBr
Result and equation for I- test
Yellow ppt
Ag+ + I- →AgI
What happens (+equations) to each of the silver halide precipitates when dilute / conc NH3 are added
AgCl- dissolves in both dilute and conc
AgCl + 2NH3 → [Ag(NH3)2]+ + Cl-
AgBr- only dissolves in conc
AgBr + 2NH3 → [Ag(NH3)2]+ + Br-
AgI- will not dissolve in either
What products are formed when I- reduced H2SO4? Do equations for all 4.
H2SO4 + 2I- →SO4^2- +2HI
H2SO4 + 2H+ + 2I- →SO2 + I2 + 2H2O (SO2 is a choking gas with a pungent odour)
H2SO4 + 6H+ + 6I- → S + 3I2 + 4H2O (S is a yellow solid)
H2SO4 + 8H+ + 8I- → H2S + 4I2 + 4H2O (H2S smells like rotten eggs)
What are the products of Br- and H2SO4
HBr and SO2
How can you test for carbonate ions
Add strong acid to the sample
Collect the gas produced
Pass through lime water
What are the observations for a positive test of carbonate ions
Fizzing
Limewater turns cloudy
How can you test for sulfate ions
Add dilute hydrochloric acid and barium sulphate to the sample
What are the observations for a positive test of sulfate ions
White ppt of barium sulfate is produced
When testing for carbonate, sulfate and halide ions, in which order should the tests be carried out and why?
- Carbonate test
- Sulfate test
- Halide test
Because barium ions forms insoluble precipitate of BaCO3 and silver ions form insoluble precipitate of Ag2SO4
How can you test for ammonium ions
Add sodium hydroxide to the sample and warm it
Test the gas produced with red litmus paper
What are the observations for a positive ammonium ion test
Red litmus paper turns blue
Ammonia has a pungent smell
