When testing the thermal stability of Magnesium Carbonate observation of the Limewater showed that the Limewater formed a heavy precipitate before turning clear, the presence of clear Limewater suggesting that there was no precipitate and therefore no carbon dioxide released. However continued bubbling of Carbon Dioxide through Limewater once all of the Calcium Hydroxide has reacted to form Calcium Carbonate and water causes the Calcium Carbonate to be converted into the more soluble Calcium Hydrogencarbonate (Ca(HCO3)2).
Solubilities of the Hydroxides and Carbonates
To test the solubilities of the Hydroxides and Carbonates, Sodium Hydroxide \ Carbonate solution was added to a metal nitrate of Group 2 to produce a metal Hydroxide \ Carbonate of Group 2, Sodium Nitrate and Water. Since sodium Nitrate is completely soluble in water then any precipitate formed must be an insoluble Metal Hydroxide \ Carbonate from Group 2 e.g.
Method
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Add 4cm3 of Sodium Hydroxide to a test tube using a dropping pippet.
- Using a second clean dropping pippet add drops of Magnesium Nitrate to the Sodium Hydroxide until a precipitate can be seen, observing the "weight" or shade of the precipitate.
- Once a precipitate has formed place a bung in the top of the test tube and shake.
- Repeat the above for all of the other metal nitrates Calcium, Barium and Strontium Nitrate.
- Place all four test tubes in a rack and observe how the precipitates settle out after they have been shaken. This should reinforce the observations made on the "weight" or shade of the precipitates, with the "heaviest" settling out first and the "lightest" settling out last.
Results
Solubility of the Carbonates of Group 2 Metals
Solubility of the Hydroxides of Group 2 Metals
g) From my results it is possible to see that all off the Hydroxides and Carbonates of Group 2 metals are to some degree insoluble, and although my results do not show a perfect pattern a general pattern can also been seen that the solubility of Group 2 Hydroxides and Carbonates decreases as you move down the group. This increase in the insolubility is due to the size of the molecule increasing as you move down the group with Magnesium being the smallest molecule tested and Barium the largest molecule tested.
Part 2: Chemistry of Group 1 elements, Lithium, Sodium, Potassium, Rubidium and Caesium
Reaction of the elements with water
When group 1 elements are placed in water they react very vigorously, and are very strongly effervescent, due to their density they float upon the surface of the water. The strength of the reaction increases down Group 1 with Lithium being the least reactive of the Group 1 metals in water and Francium the most reactive in water. The reactions become so violent that sodium melts in the heat of the reaction, while Potassium becomes hot enough to ignite it with Caesium and Francium exploding on contact with water.
All of the Group 1 elements react with water to produce a hydroxide and hydrogen. The general equation for the reaction of the Group 1 elements with water is
Where M is an element from Group 1
Reaction of Group 1 Oxides and Hydroxides with Water and Acids
Reaction of Group 1 Oxides with Water and Acids
In water the Group 1 Oxides react to form alkaline solutions, the general formula for this reaction is
Where M is an element from Group 1
In acid Group 1 Oxides react to form neutral salts this is because the Metal Oxides are alkaline, the general formula for the reaction of a Metal Oxide from Group 1 with Hydrochloric Acid where M is an element from Group 1 is
Similarly the general formula for the reaction of a Metal Oxide from Group 1 with Sulphuric Acid is
Where M is an element from Group 1
Reaction of Group 1 Hydroxides with Water and Acids
In water the Group 1 Hydroxides react to form alkaline solutions. The general formula for this reaction of Group 1 Hydroxides with water, where M is a Group 1 element is
In acid the Hydroxides react to form neutral salts. The general formula for the reaction of a Group 1 Hydroxide with Hydrochloric Acid where M is an element of Group 1 is
The general formula for the reaction of a Group 1 Hydroxide with Sulphuric Acid is
Where M is an element from Group 1
Part 3: Physical Properties of elements from Groups 1 and 2
Physical Properties of Elements from Group 1
Physical Properties of Elements from Group 2
See Graphs G1 -G6
Analysis of graphs showing the physical properties of the Elements of Group 1
First Ionisation Energies of the Elements in Group 1 and 2
Ionisation occurs when sufficient energy is given to the atom to allow the loss of an electron making the atom a positive ion, therefore the first ionisation energy is when 1 electron is pulled from an atom. The electron removed is usually an electron from the very outer shell since they are furthest from the nucleus and the force of nuclear attraction is less. Graphs G1 and G2 show the first ionisation energies of the elements in Groups 1 and 2. From graph G1 is possible conclude that as you move down group 1 the amount of energy needed for ionisation to occur becomes less. This is because as you move down the Group the size of the atom increases giving the atom an increased ionic radius. This results in a smaller force of attraction between the nucleus and the last electron in the outer shell not only making the element more reactive but also meaning that less energy is needed to remove the electron from the atom during ionisation.
Graph G2 shows a similar result to G1 with the amount of energy required for the first ionisation decreasing as you move down the group. Therefore from the graph it is possible to conclude that the amount of energy required for the first ionisation to take place decreases as you move down the group. This is due to an increase in the size of the atom as you move down the group, which has similar effects as the increase in the size of an atom in Group 1. However it can also be seen that more energy is required for the first ionisation to take place in Group 2 that in Group 1. This is because as you move across the periods an electron is being added to the outer shell but also a proton is being added to the nucleus resulting in the nuclear charge becoming more positive and the electrons being held more tightly and so making it harder for in electron to be removed resulting the need for more energy.
Densities of Elements in Groups 1 and 2
Graphs G3 and G4 both show a general pattern that as you go down both Group 1 and Group 2 the density of the elements increase. This is due to the increasing size and mass of the elements. Density depends on the volume an atom occupies and its mass, elements with large mass and a small volume are very dense whereas elements that have a small mass and large volume are not very dense. In both Groups 1 and 2 the elements increase in size and relative molecular mass however these two factors must not be proportional to one another i.e. the mass of the atom must increase at a faster rate than its size for the density to keep increasing as you move down the group. However for elements such as Potassium and Calcium the above must not be true as they have lower densities than the elements before them as you move down their respective groups.
Melting Points of Elements in Groups 1 and 2
Both Graphs G5 and G6 show a general pattern such that in Groups 1 and 2 as you move down the group the melting point of the elements decreases. This is due to the forces acting between the element's particles. To make a substance melt the forces acting between the particles or atoms within it must be overcome. The strength of the forces influence whether an element has a high or low melting point. Therefor it is possible to say that generally as you move down both Group 1 and Group 2 the forces between the atoms within the element become smaller.