| Ideal solutions | Non-ideal solutions | |||
| Positive deviation from Raoult's law | Negative deviation from Raoult's law | |||
| 1. Obey Raoult's law at every range of concentration. | 1. Do not obey Raoult's law. | 1. Do not obey Raoult's law. | ||
| 2. \[\Delta {{H}_{\text{mix}}}=0;\]neither heat is evolved nor absorbed during dissolution. | 2. \[\Delta {{H}_{\text{mix}}}>0.\]Endothermic dissolution; heat is absorbed. | 2. \[\Delta {{H}_{\text{mix}}}<0.\] Exothermic dissolution; heat is evolved. | ||
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The pressure exerted by the vapours above the liquid surface in equilibrium with the liquid at a given temperature is called vapour pressure of the liquid. The vapour pressure of a liquid depends on,
(1) Nature of liquid : Liquids, which have weak intermolecular forces, are volatile and have greater vapour pressure. For example, dimethyl ether has greater vapour pressure than ethyl alcohol.
(2) Temperature : Vapour pressure increases with increase in temperature. This is due to the reason that with increase in temperature more molecules of the liquid can go into vapour phase.
(3) Purity of liquid : Pure liquid always has a vapour pressure greater than its solution.
Raoult’s law : When a non-volatile substance is dissolved in a liquid, the vapour pressure of the liquid (solvent) is lowered. According to Raoult’s law (1887), at any given temperature the partial vapour pressure (pA) of any component of a more...
Certain properties of dilute solutions containing non-volatile solute do not depend upon the nature of the solute dissolved but depend only upon the concentration i.e., the number of particles of the solute present in the solution. Such properties are called colligative properties. The four well known examples of the colligative properties are,
(1) Lowering of vapour pressure of the solvent.
(2) Osmotic pressure of the solution.
(3) Elevation in boiling point of the solvent.
(4) Depression in freezing point of the solvent.
Since colligative properties depend upon the number of solute particles present in the solution, the simple case will be that when the solute is a non-electrolyte. In case the solute is an electrolyte, it may split to a number of ions each of which acts as a particle and thus will affect the value of the colligative property.
Each colligative property is exactly related to other, Relative lowering more...
Concentration of solution is the amount of solute dissolved in a known amount of the solvent or solution. The concentration of solution can be expressed in various ways as discussed below,
(1) Percentage : It refers to the amount of the solute per 100 parts of the solution. It can also be called as parts per hundred (pph). It can be expressed by any of following four methods,
(i) Weight to weight percent
% w/w \[=\frac{\text{Wt}\text{. of solute}}{\text{Wt}\text{. of solution}}\times 100\]
Example : 10% \[N{{a}_{2}}C{{O}_{3}}\] solution w/w means \[10g\] of \[N{{a}_{2}}C{{O}_{3}}\] is dissolved in \[100g\] of the solution. (It means \[10g\] \[N{{a}_{2}}C{{O}_{3}}\] is dissolved in \[90g\] of \[{{H}_{2}}O\])
(ii) Weight to volume percent
% w/v \[=\frac{\text{Wt}\text{. of solute}}{\text{Volume of solution}}\times 100\]
Example : 10% \[N{{a}_{2}}C{{O}_{3}}\] (w/v) means \[10g\] \[N{{a}_{2}}C{{O}_{3}}\] is dissolved in \[100\,cc\] of solution.
(iii) Volume to volume percent
% v/v \[=\frac{\text{Vol}\text{. of solute}}{\text{Vol}\text{. of solution}}\times 100\]
Example : more...
All the three states of matter (gas, liquid or solid) may behave either as solvent or solute. Depending on the state of solute or solvent, mainly there may be following nine types of binary solutions.
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