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- 1. Common ion effect and their industrial applications Submitted to; Mam Hajra Zafar Submitted by; Group 3 Aleena Akram 22011514-056 Malaika Amin 22011514-112 Hamial Imtiaz 22011514-090 Sehrish Naz 22011514-092 Sidra Nazir 22011514-064 Muhammad Anas 22011514-128 Rehan Asghar 22011514-114
- 2. Common Ion effect Definition: The phenomenon in which the degree of dissociation of any weak electrolyte is suppressed by adding a small amount of strong electrolyte containing a common ion is called a common ion effect.
- 3. Example – 1: (Dissociation of a Weak Acid): Ionization of weak electrolyte acetic acid (CH3COOH) is suppressed by adding strong electrolyte hydrochloric acid (HCl) containing common hydrogen ion (H+ ) Explanation: Suppose, an electrolyte acetic acid (CH3COOH) is treated with water. It dissociates and an equilibrium exists as follows, CH3COOH(aq) CH ⇌ 3COO– (aq) + H+ (aq) By applying the law of mass action;
- 4. Where ‘Ka’ is the dissociation constant of acid. If a small amount of a strong electrolyte like hydrochloric acid (HCl) is added to the aqueous solution of CH3COOH, it gets dissociated and equilibrium exists, as HCl → H+ + Cl– Here H+ ions are common hence their concentration increases. According to Le-Chatelier’s principle, equilibrium shifts towards the left. To keep the value of Ka constant, the concentration of CH3COOH molecules is increased. In this way ionization of CH3COOH is suppressed by adding HCl. Thus the pH of the solution increases.
- 5. Example – 2: (Dissociation of a Weak Base): Ionization of weak electrolyte Ammonium hydroxide (NH4OH) is suppressed by adding strong electrolyte Ammonium chloride (NH4Cl) containing common ammonium ion (NH4 + ). Explanation: Suppose, an electrolyte Ammonium hydroxide (NH4OH) is treated with water. It dissociates and an equilibrium exists as follows, NH4OH(aq) NH ⇌ 4 + (aq) + OH(aq) By applying the law of mass action, Where ‘Kb’ is dissociation constant of the base.
- 6. If a small amount of a strong electrolyte like Ammonium chloride (NH4Cl) is added to the aqueous solution of NH4OH, it gets dissociated and equilibrium exists, as; NH4 + Cl(aq) → NH4 + (aq) + Cl(aq) Here NH4 + ions are common hence their concentration increases. According to Le-Chatelier’s principle, equilibrium shifts towards the left. To keep the value of Kb constant, the concentration of NH4 + OH molecules is increased. In this way ionization of NH4 + OH is suppressed by adding NH4 + Cl. Thus the pH of the solution decreases.
- 8. Le chatelier’s principle: STATEMENT: “When a system in dynamic equilibrium is acted upon by an external stress, it will adjust in such a way to relieve the stress and establish a new equilibrium” Common ion is an application of le -chatelier principle If common ion is added to weak acid or base, the equilibrium will shift towards the reactant(weak acid or weak base),in order to restore balance.
- 9. In SATURATED SOLUTION; If concentration of any of ion is decreased, more salt dissolves, equilibrium shift towards right until the solubility product constant equals to the product constant Ksp =Qsp If concentration of ion is increased by adding to an electrolytes equilibrium shift towards the left according to le-chatelier’s principle until Ksp = Qsp When a system is in equilibrium addition of any additional reactant or reduction is concentration of products shifts the equilibrium to the right towards the product and vice versa.
- 10. Contd… Thus according to le-chatelier’s principle, reversible reactions are self correcting. Whenever these type of reactions are thrown out of balance by change in concentration, temperature or pressure, system will shift in such a way to re-balance itself after change. In practice, the disassociation of weak electrolyte is decreased by adding to the solution, a strong electrolyte or salt, which has an ion in common with the weak electrolyte. The common ion effect is often used to completely precipitate any one of the ion as its sparingly soluble salt with a very low value of Solubility product for gravimetric estimation.
- 11. IMPORTANCE OF COMMON ION EFFECT: Common ion effect plays important role in: controlling the pH of a solution determining solubility of slightly soluble salts in controlling the formation of precipitate Common ion effect controls the formation of precipitate by either reversing the dissociation of acid , if the acid has already dissociated or reducing the dissociation, if salt is added first.
- 12. Contd… Addition of common ion prevents the weak acid or base from ionizing as much as it would. The common ion effect prevents the ionisation of weak acid from occurring by increasing the concentration of an ion that is produced as a result of this equilibrium ionization.
- 13. Industrial applications of common ion effect; Buffer solution Salt analysis Purification of substances Hard water softening Waste water neutralization Purification of NaCl Precipitation of KClO3 Effect on solubility Manufacture of sodium carbonate Salting out of soap
- 14. Buffer solution
- 15. Buffer solution; Buffer solution is the solution whose pH, on addition of a small amount of strong acid or a base, does not change much. Buffer action; The resistance offered by a buffer solution to change in pH on the addition of acid or base is called a buffer action.
- 16. Properties; It has a definite pH, that is a definite reserve acidity or basicity. Its pH does not change over a long period time. Its pH does not change on dilution.
- 17. Types of buffer solution; 1. Acidic buffer; It is solution of weak acid and its salt with a strong base. For example; CH3COOH+CH3COONa Boric acid + borax H2CO3+NaHCO3 Citric acid + sodium citrate 2. Basic buffer; It is a solution of a weak base and its salt with a strong acid. For example, H2CO3+NaHCO3 Glycine + glycine hydrogen chloride Glycerol + glycerine hydrogen chloride
- 18. 3. Ampholytes; These are compounds that contain both acidic and basic groups and therefore exist as zwitter-ions at a certain pH. Hence, proteins and amino acids also act like a buffer solution.
- 19. Preparation of buffer solutions; Acidic buffer Buffer containing weak acid and its highly ionized salt. pH below 7 e.g, CH3COOH / CH3COONa Basic buffer Buffer containing weak base and its highly ionized salt. pH above 7 e.g, NH4OH / NH4Cl
- 20. Acidic buffer; CH3COOH CH3COO ⇌ - + H+ Weak acid CH3COONa CH3COO ⇌ - + Na+ highly ionized salt CH3COO- + H+ CH ⇌ 3COOH adding acid(H+ ) OH- + H+ H ⇌ 2O adding base (OH- ) CH3COOH CH ⇌ 3COO- + H+ NOTE; By the addition of base, equilibrium of H+ ions disturbed so immediately CH3COOH dissociate into ions to stabilize equilibrium CH3COO- + H+ into ions to stabilize equilibrium
- 21. Application of common ion effect; Application in Salt analysis Group 2 salt analysis Group 3 salt analysis Group 4 salt analysis Group 5 salt analysis
- 22. SALT ANALYSIS Basically, in Salt analysis, we have to analyze a given salt that whether it belongs to group 2,3,4,5. We use radicals or cations of respective group and group reagents to analyze a given salt.
- 23. GROUP 2 SALT ANALYSIS Group 2 salt radicals include Pb²+ , Cd²+ ,Hg²+ , Sn²+ etc. Group reagents include dilute HCl And H2S gas. The function of HCl is to suppress the Ionization of H2S gas. The Ionization of HCl and H2S is as follows : It is obvious that H+ ions are common to H2S and HCl.
- 24. Contd… It is obvious that H+ ions are common to both HCl and H2S. Now ions of strong electrolyte suppress the common ion of weak electrolyte and reaction move backward. Now, whatever the sulphide ions left ionized, these form metallic sulphide with cation of second group. This metallic sulphide give precipitation reaction and confirmed that the given salt belong to group 2 elements. In this way, salt of group 2 is analyzed.
- 25. GROUP 3 SALT ANALYSIS; Group 3 salt radicals or cations include Fe²+ , Fe³+ , Al³+ , Cr³+ , etc. The group reagents include NH4CL and NH4OH NH4OH is a weak base and ionized in aqueous solution in very small extent. In the presence of highly ionized NH4Cl , there is increase in number of NH⁴+ ions in the solution.
- 26. Contd… Due to these NH4 + ions , Ionization of NH4 + is further supressed, so that concentration of OH- ions fall very low. These OH- ions react with group 3 radicals basically cations. They form hydroxides. If the precipitation occur, it confirmed that the given salt belong to group 3. In this way, group 3 salts are analyzed.
- 27. GROUP 4 SALT ANALYSIS; Group 4 salt radicals include Zn²+ , Mn²+ , Ni²+ , Co²+ , etc. The group reagents include NH4Cl, NH4OH, H2S gas. Due to the presence of NH4CL, Ionization of NH4OH is restricted to desired extent in which H2S gas precipitated out radicals of this group. The function of NH4OH is to provide OH- ions which remove H+ ions and thus enhance the Ionization of H2S. Thus more H2S ionized , the greater is the concentration of S² ions and more is the precipitation of sulphides.
- 28. The S²- ions are now in higher concentration. These sulphide ions react with group 4 radicals. The reaction show precipitation. This precipitation confirmed that the given salt belongs to group 4 . In this way, group 4 salt is analyzed.
- 29. GROUP 5 SALT ANALYSIS; Group 5 radicals basically cations include Ca²+ , Sr²+ , Ba²+ etc. The group reagents include NH4CL, NH4OH, (NH4)2CO3. Firstly, ammonium nitrate ionized to form ammonium ion and carbonate ion. Ammonium chloride ionized to form ammonium ion and chloride ion. The common ions show common ion effect.
- 30. Contd… The concentration of carbonate ion lessen. Now, this carbonate ion react with radical of group 5. Due to this reaction different carbonates including calcium carbonate, magnesium carbonate etc are formed. They show precipitation. This precipitation confirmed that given salt belong to group 5. In this way, salt of group 5 is analyzed.
- 31. Purification of substances; The common ion effect can be used to purify substances by decreasing their solubility in a solution. Example; Consider precipitation of silver chloride (AgCl) from a solution of silver nitrate (AgNO3) by adding sodium chloride. The reaction is: AgNO3+NaCl AgCl+NaNO3 The solubility of AgCl in water is very low, and adding NaCl to solution increases the concentration of chloride ions which in turn decreases the solubility of AgCl .
- 32. Contd… As a result AgCl will precipitate out of solution and remaining solution will contain a higher concentrations of NaNO3.
- 33. Hard water softening; Hard water contains high levels of calcium and magnesium ions , which can cause scaling and fouling in pipes and boilers, To soften the water sodium carbonate (Na2CO3) is added to water ,crating a common ion with the calcium and magnesium ions . This shifts the equilibrium towards the solid calcium carbonate (CaCO3)and magnesium carbonate (MgCO3) precipitates ,reducing their concentration in solution .
- 34. Contd… The chemical equation for the reaction between calcium bicarbonate Ca(HCO3)2 and sodium carbonate (Na2CO3) is as follows; Ca(HCO3)2 + Na2CO3 CaCO3 + 2NaHCO3
- 35. Waste water Neutralization; The common ion is used in waste water neutralization process to control the pH of water. Example The addition of sodium hydroxide (NaOH) to acidic waste water can neutralize the acidity , while the addition of hydrochloric acid (HCl) to alkaline waste water can neutralize the basicity. Chemical equation NaOH + H2O Na+ + OH-
- 36. Contd.. The addition of Na+ to the solution increases the concentration of hydroxide ions (OH- ) which cause the pH of the solution. Reaction NaOH + H2O Na+ + OH- The addition of Na+ to the solution increases the concentration of hydroxide ions(OH-) which raises the pH of the solution. HCl H+ + Cl- The addition of H+ to the solution increases the concentration of hydrogen ions which lowers the pH of solution.
- 38. PURIFICATION OF NACL; NaCl ⇌ Na+ + Cl– ( Weak Electrolyte) HCl ⇌ H + + Cl– ( Strong Electrolyte) We can use common ion effect for the purification of NaCl. For this purpose hot saturated solution of NaCl will be prepared, which establish the following equilibrium.
- 39. CONTD.. NaCl ⇌ Na+ + Cl– ( Weak Electrolyte) Now the HCl gas which is more ionizable is passed through this solution.It gives the following equilibrium. HCl ⇌ H + + Cl– ( Strong Electrolyte) The concentration of the chloride ions (Cl– ) will be considerably increased so the first equilibrium will be shift to the left. Solid NaCl will be settle down whereas impurities will be left behind.
- 40. Precipitation of Potassium Perchlorate; Highly soluble KCl is added to the saturated solution of less soluble KCIO in which ionized and un-ionized KCIO4 is at equilibrium. Ionization takes place as given below: KClO4(s) K ⇌ + (aq)+ ClO4 – (aq) KCl (s) K ⇌ + (aq) + CI– (aq)
- 41. CONTD… KCl causes to increase the concentration of K+ ion (common ion). According to Le Chatlier’s principle, K + ions will react with Cl04 – ions to form KCIO4 (ppt) to restore equilibrium. This suppresses the ionization of KCIO4, which causes to decrease the solubility of KCl04. It means the solubility of KClO4 is less in the solution of KCl than in pure water.
- 42. Effect on solubility; Adding a common ion decrease the solubility. Reaction shifts towards the left to relieve the stress of the excess product. Adding common ion cause the dissociation reaction equilibrium to shift left toward reactants cause precipitations.
- 44. Solvey process; Solvey process is industrials preparation of Sodiumcarbonate by the use of brine and ammonia. The common ion effect is used in maintaining the buffer solution of (NH3+NH4Cl) when the brine is precipitated as sodium bicarbonate. The Solvay process results in soda ash Sodium trioxocarbonate IV (Na2CO3) from brine (NaCl) and from limestone (CaCO3) .
- 45. Principle Of solvay process: Solvay process based upon low solubility of Sodiuimbicarbonate ie at 15degree .Whereby It gets precipitated in the reaction of sodium chloride with NH4HCO3. Raw material: NaCl CaCO3 NH3
- 46. Steps of solvey process: Solvey process includes four steps: Purification of brine. Sodium hydrogen carbonate formation. Soduim carbonate formation. Ammonia recovery
- 47. Diagram:
- 48. Uses of solvy process: Petrolium refining. Water softner. Manufacture of soap, glass, ceramics, paper, Sodium carbonate and sodium bicarbonate . Cleaner and degreaser in washing compounds Removing sulfurdioxide from waste gases Power stations.
- 50. What is soap? Soap are sodium or potassium salts of long chain fatty acids. What is salting out of soap? Precipitation of soap from the suspension by the addition of salt is called salting out of soap. High concentration of salt decreases the solubility and protein precipitates.
- 52. Salting out is typically used to precipitate out large biomolecules like proteins or DNA. Because a specific salt concentration can be used to precipitate out a soap. Through common ion effect. HCOONa HCOO + Na
- 53. NaCl Cl + Na In both equations Na is common. Initially Before addition of NaCl ionic product(RCOONa) is equall to solubility. After addition of small amount of NaCl ionic product Becomes>ksp hence soap precipi- -tate out.