Inorganic chemistry: 9.1 Group 2 - Alkaline Earth Metals

Question 1

Why are group 2 elements called alkaline earth metals?

Answer 1

Group 2 elements are called alkaline earth metals because their oxides and hydroxides are alkaline.

Question 2

What block are group 2 elements in, in the periodic table?

Answer 2

Group 2 elements are s-block elements. This means that they have their outer-shell electron in a s-orbital.

Question 3

How does atomic radii change going down group 2 elements?

Answer 3

The atomic radii increases going down the group. The atomic, metallic radii increases down the group due to the gaining of an extra electron shell.

Question 4

How does the Mp change going down group 2.

Answer 4

The Mp decreases down group 2.
This is because, atomic radii and electron shielding increases down the group.
Hence, the electrons in the ‘sea’ of delocalised electrons are further away from the positive nuclei.
Hence, the strenght of the metallic bonding decreases down group.

Question 5

How does ionisation energy change down group 2?

Answer 5

Note: In all their reactions, atoms of group 2 elements lose 2 electrons. So, an amount of energy equal to the sum of the first and the second ionisation energies is needed for complete ionisation.
Ionisation energy is the minimum amount of energy needed to remove 1 mole of electrons from 1 mole of gaseous atoms.
IE decreases down group 2.
This is because, electron shielding and atomic radii increases. Hence, the electrostatic force of attraction of the valence electrons to the nuclei decreases.

Question 6

What is the oxidation state change in group 2 metals.

Answer 6

As group 2 metals lose 2 electrons, they are oxidised in reactions. Hence, their oxidation state goes from 0 to +2.

Question 7

How does reactivity change going down group 2?

Answer 7

Reactivity increases, as reflected in their decreasing IE. This is because valence electrons more easily lost due to increased atomic radii and electron shielding.

Question 8

What is the reaction of group 2 metal with water.

And what are the changes of oxidation state - you can check ur notes for ans if explanation not clear

Answer 8

M(s) + 2H20(l) > M(OH)2 (aq) + H2 (g)
Where M is a group 2 metal
The oxidation state of :
M is 0 (As single element)
H20 - Hydrogen has an oxidation state of +1. Oxygen has -2.
In M(OH)2 - M has an oxidation state of +2. (you can work it out as O has -2, and Hydrogen is +1.) As oxygen is -2 it is not reduced or oxidised. While M is oxidised. Note: while to work it out you times +1 by 2 and -2 by 2 to get a total of +2 for Hydrogen and -4 for Oxygen. The Oxidation state of Oxygen and Hydrogen is still said to be -2 and +1
In H2 - Hydrogen has an oxidation state of 0. (as it is a single element). Hence as the oxidation number is reduced, Hydrogen has been reduced.

Question 9

What is milk of magnesia composed of and used for?

Answer 9

Milk of magnesia is magnesium hydroxide, and it is used in indigestion remedies to neutralise excess stomach acid which causes heartburn and indigestion. [Mg(OH)2]

Question 10

How does the reaction of group 2 elements with water change going down the group?

Answer 10

Calcium reacts in the same way but more vigorously, even with cold water. Strontium and barium react more vigorously still.

Question 11

Calcium hydroxide is also called …? And, what is it used for?

Answer 11

Slaked lime and is used to treat acidic soil. As we said before, oxides and hydroxides of group 2 metals are alkaline.

Question 12

What is the optimum ph for grass?

Answer 12

6.

Most crops such as wheat,corn, oats and barley have an optimum pH of around 7.

Question 13

What are the useful properties of Ti and hence what is it used for?

Answer 13

Ti is a metal that is strong, low density and high Mp.
Hence, used in aerospace industry and for making replacement hip joints.
It is relatively common to find but hard to extract.

Question 14

How are most metals found in the earth, and how are they extracted?

Answer 14

Most metals are found in earth as oxides, and the metal is extracted by reacting the metal oxide with carbon.
Metal oxide + carbon > metal + carbon dioxide

Question 15

Why cant Ti be extracted from its oxide by adding carbon?

Answer 15

As titanium reacts with carbon to form titanium carbide, TiC - which makes the metal brittle.

Question 16

How is Ti extracted from TiO?

Answer 16

Titanium oxide is first reacted with chlorine and carbon (coke).
To form titanium chloride (TiCl4) and carbon monoxide.
The titanium chloride is then reduced to Ti. (+4 goes to 0)
eq: TiCl4 (l) + 2Mg(s) > 2MgCl2 + Ti(s)
Here Mg is oxidised (0 goes to +2)
Note: TiCl4 is a liquid suggesting it is covalently bonded - simple molecular.

Question 17

Describes the solubilties of group 2 hydroxides and sulfates.

Answer 17

Hydroxides
Are
More (soluble)
Sulphates
Are
Less (soluble)
As (you go)
Down (group 2)

e.g Magnesium Hydroxide (Milk of magnesia) is almost insoluble. It sold as a suspension in water, rather than a solution.
Ca(OH)2 is sparingly soluble. (slaked lime) In solution it is limewater.
Barium Hyrdoxide dissolves almost completely to produce a strongly alkaline solution unlike Ca(OH)2 which in solution is limewater (less alkaline).
Barium sulfate on the other hand is virtually insoluble.

Question 18

What is the use of barium sulfate- and why is it used in this way?

Answer 18

It is taken in as a barium meal to outline the gut in medical X-rays. This test is safe as barium sulfate is insoluble even though the compound is highly toxic.

Question 19

Test for sulfate ion

Answer 19

The solution is first acidified with nitiric or Hydrochloric acid.
Then barium chloride solution is added to the solution under test and if sulfate is present a white percipate of barium sulfate is formed.
Note: This percipate forms due to the fact that barium sulfate is insoluble.
Ba2+ (aq) + SO42- (aq) > BaSO4 (S) NOTE: symbol is solid - as insoluble.

Question 20

For the test for sulfate ion why is either nitric or Hydrochloric acid added?

Answer 20

The addition of acid removes carbaonate ions as carbon dioxide. (Barium carbonate would then otherwise be produced which is also a white insoluble solid, which would be indistinguishable from barium sulfate).

Question 21

Why is extracting Ti expensive?

Answer 21

The expensive cost of Mg.
This is a batch process which makes it expensive because the process is slower, and requires more labour.
As well high temperatures required in both steps (adding carbon and chlorine and then adding mg)