(I) Topic 8 & 9 - Periodicity & Group 2
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Describe and Explain: The melting and boiling point trend across period 3
• Increases between Na & Si due to metallic bonding, which gets stronger as ions get larger and there are more delocalised electrons. • Si is giant covalent - peak of mps & bps. • Decreases when reaching P as simple molecular - weak intermolecular forces. This decreases till Ar as atoms get smaller so weaker van der waal forces
write the equation and observation of Mg with water
Mg + 2H2O -> H2 + Mg(OH)2 reacts very slowly
write the equation and observation of Ca with water
Ca (s) + 2H2O (l) -> Ca (OH)2 (aq) +H2 (g) Observations - effervesence, moves along the surface, white precipitate, Universal indicator turns blue.
write the equation and observation of Sr with water
Sr (s) + 2H2O (l) -> Sr (OH)2 (aq) +H2 (g) Observations - fairly vigorous effervesence, Universal Indicator turns blue, moves along the surface, no precipitate.
write the equation and observation of Ba with water
Ba (s) + 2H2O (l) -> Ba (OH)2 (aq) +H2 (g) Observations - Very vigorous effervesence, moves quickly on the surface, no precipitate, Universal Indicator turns purple
Explain the trend of reactivity down group 2.
Increase in reactivity down the group. There is a greater nuclear charge, ofset by more shielding. However there is also a greater atomic radius, so a weaker electrostatic attraction to the outer electron making it more reactive.
What is the trend of solubility with X(OH)2
increases in solubility going down the group (Mg insoluble, Ba and Sr soluble and Ca inbetween)
What is the trend in solubility with XSO4
Solubility decreases going down group 2 (Mg & Ca soluble, Ba insoluble and Sr inbetween)
Uses of Mg(OH)2
Getting rid of indigestion
Use of Ca(OH)2
Used in farmer fields to reduce acidity of soil
Use of BaSO4
Used in medical investigation on the digestive tract using X-Ray machines.
Describe: The test for sulfate ions
Add HCl (aq) to the solution to remove any impurities (e.g. CO3 2- ) Add Barium Chloride (Aq) If SO4 2- ions are present a white precipitate forms with Barium.