Want chemistry games, drills, tests and more? Aqueous solution of a salt is indicated by placing the letters aq in round brackets, aqto the right of the formula for the ionic compound. An ionic substance that does not dissolve in water is said to be insoluble.
Although it describes the trends, there isn't any attempt to explain them on this page - for reasons discussed later. You will find that there aren't any figures given for any of the solubilities.
There are also important inconsistencies within the books one set of figures doesn't agree with those which can be calculated from another set. I haven't been able to find data which I Solubility of group 2 cations sure is correct, and therefore prefer not to give any.
The Facts Solubility of the hydroxides The hydroxides become more soluble as you go down the Group. This is a trend which holds for the whole Group, and applies whichever set of data you choose.
Some examples may help you to remember the trend: Magnesium hydroxide appears to be insoluble in water. However, if you shake it with water, filter it and test the pH of the solution, you find that it is slightly alkaline.
This shows that there are more hydroxide ions in the solution than there were in the original water. Some magnesium hydroxide must have dissolved. Calcium hydroxide solution is used as "lime water". Barium hydroxide is soluble enough to be able to produce a solution with a concentration of around 0.
Solubility of the sulphates The sulphates become less soluble as you go down the Group. The simple trend is true provided you include hydrated beryllium sulphate in it, but not if the beryllium sulphate is anhydrous. The Data Books agree on this - giving a figure of about 39 g dissolving in g of water at room temperature.
Figures for magnesium sulphate and calcium sulphate also vary depending on whether the salt is hydrated or not, but nothing like so dramatically.
Two common examples may help you to remember the trend: You are probably familiar with the reaction between magnesium and dilute sulphuric acid to give lots of hydrogen and a colourless solution of magnesium sulphate.
Notice that you get a solution, not a precipitate. The magnesium sulphate is obviously soluble. You may also remember that barium sulphate is formed as a white precipitate during the test for sulphate ions in solution.
The ready formation of a precipitate shows that the barium sulphate must be pretty insoluble. In fact, 1 litre of water will only dissolve about 2 mg of barium sulphate at room temperature.
Solubility of the carbonates The carbonates tend to become less soluble as you go down the Group. None of the carbonates is anything more than very sparingly soluble. Magnesium carbonate the most soluble one I have data for is soluble to the extent of about 0.
I can't find any data for beryllium carbonate, but it tends to react with water and so that might confuse the trend. The trend to lower solubility is, however, broken at the bottom of the Group.
Barium carbonate is slightly more soluble than strontium carbonate. There are no simple examples which might help you to remember the carbonate trend.
What - no explanations? Before I started to write this page, I thought I understood the trends in solubility patterns including the explanations for them.
The more I have dug around to try to find reliable data, and the more time I have spent thinking about it, the less I'm sure that it is possible to come up with any simple explanation of the solubility patterns.
If you are interested in the reasons why I am unwilling to give the usual over-simplified explanations, I have described some of the problems as I see them on a separate page.
That page also includes an attempt at a better explanation. Unless your syllabus specifically asks for explanations of these trends, you would be better off ignoring this follow-up page! Questions to test your understanding I am not setting any questions on this page because it is so trivial.
Do you know the statements in red above?This is “The Alkaline Earth Metals (Group 2)”, section from the book Principles of of the heavier alkaline earth metals are quite insoluble because of the higher lattice energy due to the doubly charged cation and anion.
|Solubility Rules as a List||It goes on to look at my misgivings about these. Don't expect this page to be easy - it is probably best avoided unless your syllabus specifically asks for these explanations!|
The solubility of the carbonates and the sulfates decreases rapidly down the group because hydration energies. Group I Cations – Pb+2, Hg2+2, Ag+1 In this qualitative analysis scheme, lead, mercury(I), and silver ions are separated as a group because of the low solubility of their chlorides: PbCl 2, Hg 2 Cl 2, AgCl.
Remember that the solubility of the carbonates falls as you go down Group 2, apart from an increase as you go from strontium to barium carbonate. The general fall is because hydration enthalpies are falling faster than lattice enthalpies. The solubility product constant Ksp can be used to determine the fraction of cation remaining in a solution after alphabetnyc.comMENT 2 Qualitative analysis of Group II Cations: .
Qualitative Analysis of Group II Cations Collect: 5 centrifuge tubes Labels Evaporating dish Introduction: Qualitative Analysis of Group I~V Cations 3.
4 The sulfides are insoluble in KOH solution, only soluble in nitric acid. Qualitative Analysis of Group II Cations Collect: 5 centrifuge tubes Labels Evaporating dish Qualitative Analysis of Group I~V Cations 3.
4 As3+, Sb3+, Sn4+ The sulfides are thioamphoteric that are soluble in KOH(aq) and nitric acid.