Worksheet on Concept of Acid and Base
Those substance which produces hydrogen ions [H+] when dissolved in water is known as Acid. Acids are sour in taste. When acid is droped on a litmus paper it changes litmus into red. Acids react with zinc, magnesium, aluminum and form hydrogen. Base are those substance which produces hydroxide ions [OH-] when dissolved in water. Base are soapy and slippery. Base is capable of changing litmus into blue. Bases are bitter in taste. Here you can find some question related to “Acid and Base” and their answers: Questions: 1. Which of the...
read moreIndicators
Indicators It is a substance which is used to indicate the end point or completion of a reaction by it’s colour change. Type of Indicators (A) Redox Indicators: These are used for redox titration. E.g. (Self indicator) (external indicator) (B) Acid base Indicators: Here indicate. gives different colours in acidic and basic medium. E.g. HPH gives pink colour in basic medium but it is colourless in acidic medium. (C) Adsorption Indicators: Here indicator adsorb a particular thing E.g. Starch adsorb iodine in ...
read moreHenderson’s Equation
Henderson derived an equation to calculate the pH value of a buffer solution. Let any weak acid HA have dissociation constant , it strong salt is NaA which ionises completely. The ionisation of HA may be given as: Because is due to concentration of salt as it ionises completely and [HA] is the concentration of acid as it ionises upto small extent. Similarly, we can prove...
read moreImportance of Buffer Solution
Buffer solutions find extensive applications in plant and animal physiology, in laboratory and in industry. (a) In living beings: The chemical changes of the processes in living being can only take place in a medium of definite pH1falue. Some pH values of biological interest are; blood 7.3 — 7.5, saliva 6.5 — 7.5, bile juice 7.1, gastric juice 1-3. If these are not kept constant, disorder takes place in the system. The buffer system present in blood is . (b) In laboratory: They are employed in studying the speed of chemical...
read moreBasic buffer
Let a basic buffer solution be prepared by mixing to ammonium chloride solution. is a weak base and does not produce appreciable ions. Further, in presence of highly ionised , its ionization is largely suppressed. Now, when few drops of decinormal NaOH are added to this mixture, all its ions combine with ions to form feebly ionised and thus are consumed. S0, no appreciable change in ion concentration occurs, hence pH value remains...
read moreAcidic buffer
Let an acidic solution be prepared by acetic acid to sodium acetate solution. Acetic acid is a weak acid and sodium acetate is highly ionised. The ionisamon of acetic acid is further suppressed due to the concentration of ions obtained from . Now, when a few drops of decinormal HCI are added to it, its ions combine with ions present in solution and form feebly ionised , with the result, all the ions are consumed and no appreciable change in ion concentration occurs. Hence pH value remains...
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It is practically observed that when a drop of decinormal HCI or NaOH is added to a litre of pure water, larger increase in the concentration of ions or ions takes place respectively and thus the pH value is changed. But when a drop of decinormal HCI is added to a mixture of weak acid and its strong salt (e. g. , there is a very slight change of ion concentration. Similarly, when a decinormal solution of N aOH is added in a mixture of weak base and its strong salt (e. g., then a slight change in OH ion concentration takes place. It means...
read morepH SCALE: (Puissance of Hydrogen)
Sorenson (1909) introduced a convenient means of expressing the concentration of ions. It is called hydrogen exponent or pH scale value of simply pH. On this scale the ion concentration is written as the power. Thus the pH of a solution is the numerical value of the negative power to which 10 must be raised in order to express the ion concentration, It is –ve logarithm of Or Mathematically, pH is the logarithm of the reciprocal of the hydrogen ion concentration. Since for pure water hence the pure water is neutral. Similarly for...
read moreIonic Product, Kw and lonisation Constant, K of water
Though water is regarded as a non-conductor, yet even the purest water has a small conductivity as it ionises to a very slight extent. Since it is a reversible process, the law of mass action can be applied to the equilibrium, therefore, where K is called the Dissociation constant or ionisation constant of water. Since the degree of ionisation of water is very low (nearly one molecule ionises out of 550 molecules), the concentration of ionised water may be assumed as constant. is a constant at a given temperature and...
read moreSolubility Product
When a sparingly soluble substance, say AB is kept in contact with water for some time at a definite temperature the following equilibrium is established: Applying the law of mass action, But the concentration of the unionised [AB] is constant at a given temperature; if excess of AB is present. Hence Hence in saturated solution, the product of the ionic concentrations of sparingly soluble substance is constant at a given temperature. This constant product is called the solubility products . Relation between solubility ‘s’...
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