Formation of Stalactites and Stalacmites

Stalactites are formed by the deposition of calcium carbonate and other minerals, which is precipitated from mineralized water solutions.

Limestone is calcium carbonate rock which is dissolved by water that contains carbon dioxide, forming a calcium bicarbonate solution.

The chemical formula for this reaction is:

CaCO3(s) + H2O(l) + CO2(aq) → Ca(HCO3)2(aq)

This solution travels through the rock until it reaches an edge and if this is on the roof of a cave it will drip down. When the solution comes into contact with air the chemical reaction that created it is reversed and particles of calcium carbonate are deposited.

The reversed reaction is:

Ca(HCO3)2(aq) → CaCO3(s) + H2O(l) + CO2(aq)

Every stalactite begins with a single mineral-laden drop of water. When the drop falls, it leaves behind the thinnest ring of calcite. Each subsequent drop that forms and falls deposits another calcite ring. Eventually, these rings form a very narrow (0.5 mm), hollow tube commonly known as a "soda straw" stalactite.

Soda straws can grow quite long, but are very fragile. If they become plugged by debris, water begins flowing over the outside, depositing more calcite and creating the more familiar cone-shaped stalactite.

The same water drops that fall from the tip of a stalactite deposit more calcite on the floor below, eventually resulting in a rounded or cone-shaped stalagmite. Unlike stalactites, stalagmites never start out as hollow "soda straws." Given enough time, these formations can meet and fuse to create columns.

Concrete stalactites

Stalactites can also form on concrete, and on plumbing where there is a slow leak and limestone (or other minerals) is in the water supply, although they form much more rapidly there than in the natural cave environment

The way stalactites form on concrete is due to different chemistry than those that form naturally in limestone caves and is the result of the presence of calcium oxide in concrete. This calcium oxide reacts with any rainwater that penetrates the concrete and forms a solution of calcium hydroxide.

The chemical formula for this is:

CaO(s) + H2O(l) → Ca(OH)2(aq)

Over time this calcium hydroxide solution reaches the edge of the concrete and, if the concrete is suspended in the air, for example, in a ceiling or a beam, then this will drip down from the edge.

When this happens the solution comes into contact with air and another chemical reaction takes place. The solution reacts with carbon dioxide in the air and precipitates calcium carbonate.

Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)

When this solution drops down it leaves behind particles of calcium carbonate and over time these form into a stalactite. They are normally a few centimeters long and with a diameter of approximately half a centimeter.

SiO2 and TiO2

How i can selectively dissolve only silica from a mixture of titanium dioxide and silica?

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Silica is SiO2. It is an acidic oxide.

TiO2 is basic oxide.

SiO2 being an acidic oxide will dissolve in conc. sodium hydroxide solution whereas TiO2 will not.

Rate Law

What is the rate law for the uncatalyzed reaction?

2Ce4++(aq) + Tl+ (aq) --->2Ce3+(aq)+Tl3+(aq)?


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You can't simply create a rate law from a chemical equation. The rate law can only be determined by experiments.

There are various ways to determine the rate law by experiment, One way is by altering the concentration of the reactants and determine the effect on the rate of the reaction. By doing so, the order of reaction with respect to the reactant can be asertained.

Repeating the same process with other reactant and finally the overall order of reaction can be determined.

After the overall order of reaction is determined, then only the rate law can be established.

Name of Complex

How to write systematic name of each compound?

eg: k3[Fe(CN)6].?

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You have to know the rules in naming the complex ions.

1) the cation is named first followed by the anion.
2) for identical ligands, use di, tri, tetra ect
3) the names of negative ligands end with 'o'
4) the ligands are named first followed by the metal or metal ion.
5) if the complex is cation, the metal is named as usual name
6) if the complex is anion, the name of metal should end with -ate.
7) the oxidation state of metal in the complex should be stated in roman in a bracket

So, K3 is the cation. Just called it potassium.
No need to mention the number of potassium.

[Fe(CN)6]3- is anion.

Six CN- is called hexacyano

Fe3+ is called ferrate because it forms a negative complex.

So, the name is potassium hexacyanoferrate(III)