2-2: Group 2 And Group 7 Elements Flashcards
(43 cards)
Explain the trend in ionisation energy down group 2:
- decreases
- shielding increases, increased atomic radius, weaker attraction to nucleus, less energy needed
How does reactivity with water change down group 2?
- increases
- outer electrons further from nucleus and more shielding
- weaker attraction to nucleus
- electrons lost more easily
State an equation for the reaction of Barium with water and observations
Ba(s) + 2H2O (l) —> Ba(OH)2(aq) + H2(g)
A vigorous effervescence
Write an equation for magnesium with cold water and steam and their observations
- Mg(s) + H2O(g) —> MgO(s) + H2(g)
(Few bubbles) - Mg(s) + H2O(l) —> Mg(OH)2(s) + H2(g)
(White light)
What is the trend in hydroxide (OH-) solubility down group 2?
Increases
- Mg(OH)2 is sparingly soluble
- Ca(OH)2 is slightly soluble
- Sr(OH)2 is fairly soluble
- Ba(OH)2 is very soluble
What is the trend for sulphate (SO42+) solubility down group?
- Decreases
- MgSO4 is very soluble
- CaSO4 is fairly soluble
- SrSO4 is slightly soluble
- BaSO4 is sparingly soluble
Explain the trend in MP down group 2:
- decreases
- sea of delocalised electrons is further from positive charge of the nucleus
- weaker metallic bonds/ forces of attraction which take less energy to weaken
Explain how Mg is used for the extraction of Ti:
- Ti oxide is reacted with a Cl to form TiCl4
- it is then displaced by Mg to form MgCl2 and Ti
- Mg(s) + TiCl4(aq) —> 2MgCl2(aq) + Ti(s)
When reacted in water, what happens to group 2 elements oxidation states?
- oxidised
- 2+ ions
Does beryllium react with water?
No
What does solubility of group 2 compounds depend on?
- the anion (-) in the compound
- generally, single charged ions (OH-) increase in solubility
- whereas doubly charged negative ions (SO42-) decrease in solubility
What are Flue gases?
Gases produced by power stations which are harmful to the environment
How can CaO or CaCO3 be used to remove flue gases (E.g SO2)? Say the equations
- CaCO3(s) + SO2(g)—>CaSO3(s) + CO2(g)
- CaO(s) + SO2(g)—>CaSO3(s)
What is Ca(OH)2 and Mg(OH)2 used for?
- neutralise acidic soil (Ca)
- medicine for indigestion as an antacid (neutralises excess stomach acid) (Mg)- milk of magnesia
What is the use of BaSO4? Why is this safe?
- outline the gut in x-rays
- Ba2+ is toxic, but Barium sulphate is insoluble
Describe the test for sulfate ions and explain why it should be acidified
- add dilute HCl to sample to acidify
- remove risk of false positives caused by carbonates for example (BaCO3), carbonate or sulfate ions are removed
- add BaCl2
- if sulfate ions are present, white precipitate forms
-Ba2+ + SO42- —> BaSO4 (solid precipitate)
Why is Mg(OH)2 sparingly soluble
- only a small amount dissolves in water before equilibrium is reached
- due to strong ionic bonding- H2O cannot break them
What is the trend in BP down group 7?
- increases
- atom size increases, stronger van der waals
Explain the trend in electronegativity down group 7?
- decreases
- more occupied shells, valence further from nucleus
- lower force of attraction which take between nucleus and bonding pair
What do you use to test for halide ions?
- acidified AgNO3
State the colour and standard state of F, Cl, Br, I and the colour of Br and I ‘s aqueous states
- F= pale yellow, gas
- Cl= green, gas (pale green)
- Br= red-brown, liquid (orange when aqueous)
- iodine= grey, solid (brown when aqueous)
Why do halogens become less oxidising down group?
- atoms become larger, more shielding, outer shells get further away
Which halogens will displace which halides?
- halide lower in group 7 that the halogen
- KBr is displaced by Cl2(aq)
How do displacement reactions help to identify halides?
- halide ions are colourless in solution
- once displaces, their colour is visible
- e.g, Br displaced by Cl2 or F2, sol turns from colourless to orange when the halogen is added since KBr is colourless and the halogen isn’t in there yet
