Molarity

It is one of the most widely used unit of concentration and is denoted by M. It is defined as no. of moles of solute present in 1 liter of solution. Thus,

Molarity = No. of moles of solute / Volume of solution(in Litres)

Normality in chemistry is one of the expressions used to measure the concentration of a solution. It is abbreviated as ‘N’ and is sometimes referred to as the equivalent concentration of a solution. It is mainly used as a measure of reactive species in a solution and during titration reactions or particularly in situations involving acid-base chemistry.

As per the standard definition, normality is described as the number of gram or mole equivalents of solute present in one litre of a solution. When we say equivalent, it is the number of moles of reactive units in a compound.

• Parts per million can be defined as the ratio of number of parts of the component to the total number of parts of all components of the solution multiplied by 10⁶.
• It is denoted by ppm.

Mass per cent is a way of expressing a concentration or describing the component in a particular mixture. The solution composition can be described in mass percentage which shows the mass of solute present in a given mass of solution. The quantity of solute is expressed in mass or by moles. For a solution, the mass per cent is described as the grams of solute per grams of solution, multiplied by 100 to get the percentage.

Mass per cent Formula

The Mass per cent formula is expressed as solving for the molar mass also for the mass of each element in 1 mole of the compound. You can determine the mass percentage of each element with these masses.

Mass by volume percentage

• Mass by volume percentage can be defined as the mass of solute dissolved in 100 mL of the solution.
• For instance, mass by volume percent of a solution with 1 g of solute dissolved in 100 mL of solution will be 1% or 1% (mass/volume).
• Mathematically, Mass by volume% =

The reactant which reacts completely in the reaction is called limiting reactant or limiting reagent.

The reactant which is not consumed completely in the reaction is called excess reactant .

CH₄ + 2O₂ -> CO₂ + 2H₂O

GRAM MOLECULAR MASS OF CO₂ = 12 +2(16) = 44g

From the reaction it is clear that 1 mole of methane on complete combustion produces 44g (1 mole) of carbon dioxide.

therefore moles of CH₄ required to produce 22g of CO₂ are:

(22) * (1/44) = 1/2 moles

• The word ‘stoichiometry’ is derived from two Greek words - stoicheion (meaning element) and metron (meaning measure).
• Stoichiometry deals with the calculation of masses (sometimes volumes also) of the reactants and the products involved in a chemical reaction.
• This is done using balance chemical equation.

This method is also called trial and error method, or inspection method. In this method, coefficient before the formulae or symbols of the reactants and products are adjusted in such a way that the total number of atoms of each element only both the sides become equal. This is called material balance, or mass balance. In this method first of all, atoms of the element which appears least in the chemical equation should be balanced. Then, the next one, and so only.

A chemical equation has its own limitations. They do not provide information about: 

1. The physical state of reactants and products Hence, the symbols ‘s’ for solid, ‘l’ for liquid, ‘g’ for gas and ‘vap’ for vapour are added. 
2. Conditions such as temperature, pressure and catalyst affecting the reaction 
3. Concentration of reactants and products Hence, in some cases, for dilute ‘dil.’ and for concentrated ‘conc.’ are added. 
4. The nature of the chemical reaction; whether it is reversible or irreversible reaction. 
5. Speed of the reaction 
6. Heat changes accompanying the reaction; whether heat is given out or absorbed 
7. Time taken for completion of the reaction A reaction may or may not be complete, and the equation does not reveal it.

The atomic mass of metal M is 56. Calculate the empirical formula of its oxide containing 70% of M.

(i) To calculate the percentage of oxygen.



(ii) To calculate the empirical formula of oxide:

Molecular mass of {tex}KHSO_(4)=39+1=32+64=136.0u{/tex}

Percentage of potassium =(39u) / (136u)×100 = 28.68%
Percentage of hydrogen =(1u) / (136u)×100 = 0.735%
Percentage of sulphur =(32u) / (136u)×100 = 23.53%

Percentage of oxygen =(64u) / (136u)×100 = 47.06%

S o l u t i o n:
The chemical formula of FeSo4 . 7 H2O
= 55.8 + 32.1 + 16x4 + 7x18
= 277.9

The percentage of water of crystallization=
= (7 x 18) / 277.9 x 100 %
= 45.34 %

Pyrophosphates are phosphorus oxyanions that contain two phosphorus atoms in a P-O-P linkage. A number of pyrophosphate salts exist, such as Na₂H₂P₂O₇. Often pyrophosphates are called diphosphates. The parent pyrophosphates are derived from partial or complete neutralization of pyrophosphoric acid.

All s orbitals are spherical in shape and have a spherical symmetry.This means that the wave function will depend on the distance from the nucleus and not on the direction.In any atom,the size of the s orbital increases as the principal quantum number of the orbital increases but its geometrical shape remains same..

  Electrons within an atom can be assessed according to the shell, subshell, and orbital to which they are assigned. These assessments are based on the quantum mechanical model. Shells are numbered as n=1,2,3,4, etc. and increase in size and energy as they get further away from the nucleus.

      Shells can be subdivided into subshells. The maximum number of subshells is equivalent to the shell number. For example, when n=1 (first shell), only one subshell is possible and when n=2 (second shell), two subshells are possible.

      There are four different types of subshells. These various types of subshells are denoted by the letters s, p, d, and f. Each subshell has a maximum number of electrons which it can hold: s - 2 electrons, p - 6 electrons, d - 10 electrons, and f - 14 electrons. The s subshell is the lowest energy subshell and the f subshell is the highest energy subshell.

     As was mentioned previously, the shell number is equal to the possible number of subshells. Thus, when n=1, the only subshell possible is the 1s subshell. When n=2, two subshells are possible the 2s and 2p. When n=3, three subshells are possible the 3s, 3p, and 3d. This means that in the first shell only two electrons are possible and they would be found in the 1s (2 electrons) subshell. In the second shell, 8 electrons are possible and would be found in the 2s (2 electrons) and the 2p (6 electrons) subshells.

     Each subshell is further divided into orbitals. An orbital is defined as a region of space in which an electron can be found. Only two electrons are possible per orbital. Thus, the s subshell may contain only one orbital and the p subshell may contain three orbitals.

     Each orbital has its own distinct shape. An s orbital found in a s subshell is spherical, p orbitals found in p subshells are two-lobed, and d orbitals found in d subshells are four-lobed. Since d and f orbitals do not play an important role in organic chemistry, they will not be discussed further. 

     Since there are three possible orbitals per p subshell, each orbital adopts its own orientation. The p_x orbital lies along the x axis, the p_y orbital lies along the y axis, and the p_z orbital lies along the z axis.