Group 2 metals Flashcards
What happens to atomic radius as you go down group 2?
atomic radius increases due to more filled energy shells, so the outer electrons get further away from the nucleus
What happens to ionisation energy as you go down group 2?
as you go down group 2 ionisation energy decreases, due to greater atomic radius and greater shielding, so electrons are attracted less strongly to the nucleus
What happens to melting point as you go down group 2?
generally decreases down group 2, due to increased atomic radius. increased atomic radius decreases charge/size ratio of the ion which results in weaker metallic bonding, so less energy is required to break the metallic bonds
How does Mg react with cold water?
very very slowly
How does Mg react with steam?
reacts readily with steam
What is the equation for Mg reacting with steam?
Mg(s) + H2O(g) –> MgO(s) + H2(g)
How does Ca, St, Ba react with cold water?
vigorously
What is the general equation for the reaction of Ca/St/Ba with cold water?
Xx(s) + 2H2O(l) –> Xx(OH)2 (aq) + H2(g)
What is a property of Ca(OH)2?
is only sparingly soluble in water so is used as limewater to test for CO2 gas
What happens to the solubility of group 2 hydroxides as you go down the group?
solubility of the hydroxides increases as you go down the group
What does Ba(OH)2 form?
a colourless solution
What is Mg(OH)2 described as in water?
sparingly soluble
Why is it that the more soluble the hydroxide, the stronger the alkali?
higher concentration of OH- ions
What is Mg (OH)2 used for?
as an indigestion medication/antacid as it is a weak alkali so will neutralise excess stomach acid without being corrosive
What is Ca(OH)2 used for?
in farming as a soil as an additive to increase pH
Why can titanium not be extracted by reduction with carbon?
because titanium carbide forms, which makes the metal brittle and useless
What does reduction of titanium with more reactive metals cause?
impurity problems and it is difficult and expensive to eliminate the reducing agent from the titanium
What is step 1 in obtaining Ti?
conversion of titanium(IV) oxide into titanium(IV) choride
-by reaction with chlorine and coke at 900C
-titanium(IV) chloride is a liquid at room temperature so can be purified by fractional distillation
What is step 2 in obtaining Ti?
reduction of titanium(IV) chloride by adding a reactive metal
-usually sodium in the UK
-the temperature of the sodium is initially set at 550C but the exothermic reaction raises it to nearly 1000C during the reaction
Why is step 2 carried out in an inert atmosphere of argon?
to prevent any contamination of the Ti with oxygen or nitrogen
How is the sodium by-product removed?
washing with dilute HCl leaving granules of titanium behind)
What else can be used as the reducing agent for the obtainment of Ti?
magnesium
high temp and inert argon atmosphere
What happens to the solubility of the group 2 sulfates as you go down the group?
solubility of the sulfates decreases as you go down the group
What is special about BaSO4?
it is insoluble in water
How do we test for sulfate ions?
using a solution containing barium ions like BaCl2
-add dilute hydrochloric acid
-add BaCl2
-a white precipitate of BaSO4 is formed if there are sulfate ions present
Why must the BaCl2 solution be acidified first before removing carbonate ions?
carbonate ions interfere with the test as they can also form a white precipitate of barium carbonate
Why can’t you use sulfuric acid?
it contains sulfate ions so would form a white precipitate
What is a medical use of BaSO4?
in a barium meal
-BaSO4 blocks xrays and is not toxic as it is insoluble in water and bodily fluids
-aqueous suspension of it is taken and it coats the digestive tissues so they show up on x-rays
Why can’t other compounds of barium be used in a barium meal?
they’re poisonous
