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Molality (m)
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Molality is often used as the concentration unit involved in calculations dealing with colligative properties, such as freezing point depression, boiling point elevation and osmotic pressure.
Molarity is based on the volume of the solution, which may change with temperature. That is, if the solution is heated, its volume increases and its molarity decreases, even if the components of the solution do not change. Because chemists sometimes need to measure concentrations in experiments in which different temperatures must be used, they developed other ways to express concentrations. Molality is the number of moles of solute per kilogram of solvent:
Molality is symbolized m. The unit of molality is molal, and the symbol for molal is m. The great similarities in name and meaning between molarity and molality can be confusing. However, the concepts differ in two ways: For molality, (1) mass is used, not volume; and (2) the solvent is measured, not the solution. Be sure to use M (capital) to represent molar, and m (lowercase) to represent molal.
Molarity (M)
Chemical reactions often take place when two solutions are mixed. To perform stoichiometric calculations in such cases, we must know two things: (1) the nature of the reaction, which depends on the exact forms the chemicals take when dissolved, and (2) the amounts of chemicals present in the solutions, usually expressed as concentrations.
The concentration of a solution can be described in many different ways. At this point we will consider only the most commonly used expression of concentration, molarity (M), which is defi ned as moles of solute per volume of solution in liters:
A solution that is 1.0 molar (written as 1.0 M) contains 1.0 mole of solute per liter of solution.
If the volume of preparated solution is not equal to 1 liter, following formula may be used:
where, m – mass of solute, M – molar mass of solute, V – volume of solution (of volumetric flask).
If you know the amount of solute (in moles, ν) you may use:
because 
Molarity is the most common concentration unit involved in calculations dealing with volumetric stoichiometry.
Mole Fraction (mole persent, X%)
The mole fraction of a component of a solution is simply the number of moles of that component divided by the total number of moles in the solution. The mole fraction of component A is symbolized by A mole fraction is similar to a percentage in that it represents a part of a whole. The sum of the mole fractions of all the components of a solution is equal to 1, just as the sum of the percentages of all components of a whole must be 100%. With mole fraction, solute and solvent are not differentiated; every component is treated the same. A mole fraction has no units because it is obtained by dividing moles by moles.
Solution. The mole fraction is:
Normality (molar concentration of equivalent, N, Ceq) Another concentration measure sometimes encountered is normality (symbolized by N). Normality is defi ned as the number of equivalents per liter of solution, where the defi nition of an equivalent depends on the reaction taking place in the solution.
For an acid–base reaction, the equivalent is the mass of acid or base that can furnish or accept exactly 1 mole of protons (H+ ions). The equivalent mass of sulfuric acid is the molar mass divided by 2, since each mole of H2SO4 can furnish 2 moles of protons. The equivalent mass of calcium hydroxide is also half the molar mass, since each mole of Ca(OH)2 contains 2 moles of OH- ions that can react with 2 moles of protons. The equivalent is defi ned so that 1 equivalent of acid will react with exactly 1 equivalent of base.
The equivalent could be also formally defined through the amount of substance which will either:
1. react with or supply one mole of hydrogen ions (H+) in an acid–base reaction; or
2. react with or supply one mole of electrons in a redox reaction.
The mass of one equivalent of a substance is called its equivalent weight.
Equivalent weight of different types of substances can be calculate using formula:
Мeq = feq · М
where Мeq – equivalent molar mass, feq – equivalence factor, М – molar mass
Equivalence factors: for an acids: 
, for a bases: 
, for a salts: 
where n – number of metal atoms, Z – valency.
Parts per notation
" Parts per" is a convenient notation used for low and very low concentrations. Generally speaking it is very similar to weight by weight percentage - 1% w/w means 1 gram of substance per every 100 g of sample and it is (although very rarely) named pph - parts per hundred. Other abbreviations stand for:
ppm parts per million (106)
ppb parts per billion (109)
ppt parts per trillion (1012)
ppq parts per quadrillion (1015)
ppq is rather a theoretical construct than a useful thing, chances are you will never see it in use.
ppt can be confusing as it is sometimes used for parts per thousand - if you want to use " part per" notation in this case it is safer to use ppth abbreviation or " pro mille" ‰ sign.
Parts per million (ppm): This unit of concentration may be expressed in a number of ways. It is often used to express the concentration of very dilute solutions. The " technical" definition of parts per million is:
24 – сұ рақ.
Organic chemistry is the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms. The ranges of chemicals studied in organic chemistry include hydrocarbons, compounds containing only carbon and hydrogen, as well as compositions based on carbon but containing other elements. Organic chemistry overlaps with many areas including medicinal chemistry, biochemistry, organometallic chemistry, and polymer chemistry, as well as many aspects of materials science. Organic compounds form the basis of all earthly life. They are structurally diverse. The range of application of organic compounds is enormous. They either form the basis of, or are important constituents of, many products including plastics, drugs, petrochemicals, food, explosive material, and paints.
Carbon has the ability to bond with itself to form long chains and ring structures; hence it can form molecules that contain from one to an infinite number of C atoms.
Additionally C atoms may:
- be bonded by multiple bonds (i.e. double and triple) as well as single
- contain branches of other carbon chains
- need additional atoms attached to them to make them stable. The most common of
these is H, but, N, O, X, P and S also commonly occurs attached to C and may even be attached in several different ways.
In chemistry, hybridisation (or hybridization) is the concept of mixing atomic orbital’s into new hybrid orbitals (with different energies, shapes, etc., than the actual orbital’s hybridizing) suitable for the pairing of electrons to form chemical bonds in valence bond theory. Hybrid orbital’s are very useful in the explanation of molecular geometry and atomic bonding properties. Although sometimes taught together with the valence shell electron-pair repulsi