2007_09_01_archive

Lithium

Name:Lithium

Symbol:Li

Atomic Number:3

Atomic Weight:6.941

Density:13.02 g/cm^3^

Group Number:1

Group Name:Alkali Metals

Standard State:Solid at room temperature

Color:Silvery-white / grey

Classification:Metallic

Lithium is a Group 1 element containing just a single valence

electron.Group 1 elements are called "alkali metals". Lithium is a

solid only about half as dense as water. A freshly cut chunk of

lithium is silvery, but tarnishes in a minute or so in air to give a

grey surface. Lithium is mixed (alloyed) with aluminium and magnesium

for light-weight alloys, and is also used in batteries, some greases,

some glasses, and in medicine.

Isolation

Lithium would not normally be made in the laboratory as it is so

readily available commercially. All syntheses require an electrolytic

step as it is so difficult to add an electron to the poorly

electronegative lithium ion Li^+.

The ore spodumene, LiAl(SiO[3])[2], is the most important commercial

ore containing lithium. The a form is first converted into the softer

b form by heating to around 1100�C. This is mixed carefully with hot

sulphuric acid and extracted into water to form lithium sulphate,

Li[2]SO[4], solution. The sulphate is washed with sodium carbonate,

Na[2]CO[3], to form a precipitate of the relatively insoluble lithium

carbonate, Li[2]CO[3].

Li[2]SO[4] + Na[2]CO[3] -> Na[2]SO[4] + Li[2]CO[3] (solid)

Reaction of lithium carbonate with HCl then provides lithium chloride,

LiCl.

Li[2]CO[3] + 2HCl -> 2LiCl + CO[2] +H[2]O

Lithium chloride has a high melting point (> 600�C) meaning that it

should be expensive to melt it in order to carry out the electrolysis.

However a mixture of Lithium Chloride (55%) and Potassium Chloride

(45%) melts at about 430�C and so much less energy and so expense is

required for the electrolysis.

cathode: Li^+(l) + e^- -> Li (l)

anode: Cl^-(l) -> ^1/[2]Cl[2] (g) + e^-

Posted by Planet Of My Numbers at 8:52 PM 0 comments

Hydrogen

Name:Hydrogen

Symbol:H

Atomic Number:1

Atomic Weight:1.00794

Boiling Point:-252.87 �C

Melting Point:-259.14 �C

Density: 11.42 g/cm^3

Electronic Configuration:1

Group Number:1

Group Name:(none). While normally shown at the top of the Group 1

elements in the periodic table, the term "alkaline metal" refers only

to Group 1 elements from lithium onwards.

Description:Gas at room temperature, colorless , non-metallic.

About it:Hydrogen is the lightest element. It is by far the most

abundant element in the universe and makes up about about 90% of the

universe by weight. Hydrogen as water (H[2]O) is absolutely essential

to life and it is present in all organic compounds. Hydrogen gas was

used in lighter-than-air balloons for transport but is far too

dangerous because of the fire risk.The lifting agent for the ill fated

Hindenberg balloon was hydrogen rather than the safer helium.

Isolation

In the laboratory, small amounts of hydrogen gas may be made by the

reaction of calcium hydride with water.

CaH[2] + 2H[2]O -> Ca(OH)[2] + 2H[2]

This is quite efficient in the sense that 50% of the hydrogen produced

comes from water. Another very convenient laboratory scale experiment

follows Boyle's early synthesis, the reaction of iron filings with

dilute sulphuric acid.

Fe + H[2]SO[4] -> FeSO[4] + H[2]

There are many industrial methods for the production of hydrogen and

that used will depend upon local factors such as the quantity required

and the raw materials to hand. Two processes in use involve heating

coke with steam in the water gas shift reaction or hydrocarbons such

as methane with steam.

CH[4] + H[2]O (1100�C) -> CO + 3H[2]

C(coke) + H[2]O (1000�C) -> CO + H[2]