IX Practical Chemistry KBSE Experiment No. 12

To Identify Cl, Br and I Ions in Sodium Chloride, Sodium Bromide and Sodium Iodide.


Q.1. What is an Ion?

Ans. When an electrolyte dissolves in water then it breaks into positive and negative parts known as Ion.


Q.2. What is Cation?

Ans. The positive Ion is called as Cation.


Q.3. What is Anion?

Ans. The negative ion is called Anion.


Q.4. Explain clearly what do you understand by Ion?

Ans. Ion is an atom or a collection of atoms which are positively or negatively charged.


Q.5. What happens when a salt is dissolved in water?

Ans. A salt when dissolved in water breaks into ions.


Q.6. What is the colour of Chlorine Vapours?

Ans. Greenish Yellow.


Q.7. What is the colour of Bromine Vapours?

Ans. Brown.


Q.8. What is the colour of Iodine Vapours?

Ans. Violet.


Q.9. On addition of Manganese Dioxide and conc H2SO4 to the salt, if greenish yellow gas is given out then what do you suspect?

Ans. Chlorine Gas.


Q.10. Give an equation to explain the reaction of MnO2, H2SO4(conc) and the salt?

Ans. 2NaCl + MnO2 + 2H2SO4 ------> MnSO4 + Na2SO4 + 2H2O + Cl2


Q.11. What happens when Silver Nitrate (AgNO3) solution is added to the solution of Chlorine Salt.


Ans. It gives white precipitate of Silver Chloride.

AgNO3 + NaCl ------> AgCl + NaNO3


Q.12. What happen if we added Ammonium Hydroxide (NH4OH) to the test tube containing Silver Chloride precipitate?

Ans. Precipitate disappears.

AgCl + 2NH4OH -------> [Ag(NH3)2] Cl + H2O (Complex Diamine Chloride)


Q.13. Why do you use concentrated H2SO4?

Ans. Concentrated Sulphuric Acid helps us in displacing these ions in the form of Vapours.


Q.14. What happen if we add cold H2SO4 and salt to it?

Ans. At low temperature HCl is evolved and so we get colourless vapours of HCl, HBr and Hl, Hence these ions cannot be separated.


Q.15. Why is heating necassary after adding cone H2SO4?

Ans. On heating HCl, HBr and Hl are oxided by concentrated H2SO4 to brown vapours of Bromine and violet vapours of Iodine.


Q.16. Why do we get white fumes in the test of Cl ions with Ammonium Hydroxide?

Ans. It is due to formation of Ammonium Chloride.


Cl + NH4OH -------> NH4Cl + OH.


Q.17. Why do we add Chlorine in confirmatory test for Bromine and Iodine?

Ans. Chlorine water is used for displacing Bromine (Br) and Iondine (I) ions to Br2 and I2 respectively.


Q.18. What is the function of Chloroform or Carbon Tetrachloric in the confirmatory test for Br- and I-?

Ans. The function of Chloroform or Carbon Tetrachloride is to dissolve Br2 and I2 which are displaced by Chlorine water. The reddish brown and violet colours of the layers are because of dissolved Br2 and I2 in Carbon Tetrachloride.


Q.19. Why does Br ion give brown vapours when heated with concentrated H2SO4?

Ans. It first forms HBr which upon heating is oxidised to form brown vapours of Br2.


Q.20. Why does I ions give violet vapours when heated with Concentrated H2SO4?

Ans. It first form Hl, which upon heating is oxidised to form violet vapours of I2.


Q.21. What are the sources of errors and precautions in this experiment?

Ans.

1. Do not throw acid directly into sink. To destroy it pour it first into water in a breaker and then throw it into the sink.

2. The solution should be prepared in distilled water.

3. Tests tube should be thoroughly washed.

4. Small quantity of Chemicals should be taken in test tube while carrying out tests.

5. Add small quantity of Sulphuric Acid each time.

6. Heating of test containing acid should be done carefully.


Q.22. What is the reaction of Concentrated H2SO4 on Na Br at low temperature?

Ans. When Bromide is treated with Concentrated H2SO4 gives H Br and NaHSO4

Na Br + H2SO4 -------> NaHSO4 + H Br


Q.23. What happen when a Bromide and Concentrated H2SO4 are heated?

Ans. First of all sodium Bi Sulphate is formed which on heating gives Bromine Water and Sulphur Dioxide.


Q.24. What is the reaction of Conc. H2SO4 on NaCl at low temperature?

Ans. Sodium Hydroxide Sulphate and Hydrochloric Acid are formed.


Q.25. What happen when Potassium Iodide is treated with Conc. H2SO4?

Ans. Potassium Hydrogen Sulphate and Hydrogen Iodide are formed.


Q.26. What happen when Potassium Iodide is heated with Conc. H2SO4?

Ans. When Potassium Iodide is heated with Conc. H2SO4 then Iodine water and Sulphur Dioxide are produced:

Kl + H2SO4 -------> K HSO4 + Hl

2Hl + H2SO4 ------> I2 + 2H2O + SO2


Q.27. What happens when a salt is dissolved in water?

Ans. A salt on dissolving into water is dissociated into its ions.


Q.28. What do you understand by confirmatory test?

Ans. Confirmatory test is a test by which an ion can be confirmed.


Q.29. Define a Salt?

Ans. Salt is a product of neutralisation between an acid and a base.


Q.30. Give some names of salt used in our daily life.

Ans.

1. Sodium Chloride (NaCl) It is a common salt that we use in our meals.

2. Calcium Carbonate (CaCO3) It is marble and used in construction of buildings.

3. Magnesium Sulphate (MgSO4) It is used a Laxative.

4. Calcium Phosphate [Ca3(PO4)2] It is moist essential for our bones.


Q.31. What is the name given to the process in which salt after being dissolved in water gets converted into ions?

Ans. This process is called Ionisation.


Q.32. When does an atom become Cation?

Ans. Atom is neutral but when it loses electron the positive charge appears on it and then it becomes Cation.


Q.33. When does an atom become Anion?

Ans. If an atom gains an electron then negative charge appears on it and then it becomes Anion.


Q.34. What is a Precipitate?

Ans. If two solutions are mixed and chemical reaction takes place between then then a result of which an insoluble compound is formed. This insoluble compound is called Precipitate.


Q.35. What are Ionic Compounds?

Ans. Those compounds which are formed by the combinations of ions are called Ionic Compounds. They are formed by ionic bonds.


Q.36. What happens when ionic compounds are dissolved in water?

Ans. When Ionic compounds are dissolved in water they break into positive and negative ions.


Q.37. What is the function of Chlorine Water in layer test for identification of Bromine and Iodine.

Ans. Chlorine is more active Chemically than Bromine and Iodine. It displaces Bromine and Iodine from their salt and liberates them in free state.


Q.38. What is the function of Carbon Tetrachloride in layer test?

Ans. Carbon Tetrachloride is used as SOlvent in this test. Free Bromine and Iodine become soluble in it.


Q.39. What are Halogens and Halides?

Ans. The word Halogen has been derived from the word HALDS meaning sea salt. Chlorine, Bromine and Iodine which form salts like sea salts are called Halogens. Salts of these elements are called Halides.


Q.40. How will you test for Chloride?

Ans.

1. If we heat the mixture with Conc. H2SO4 colourless pungent gas (HCl) is evolved. If a gas rod dipped in NH4OH is brought near the mouth of the test tube white dense fumes are formed.

NaCl + H2SO4 --------> Na HSO4 + HCl

NH4OH + HCl ---------> NH4Cl + H2O (White Fumes)

2. On heating the mixture with Conc. H2SO4 and MnO2 a greenish yellow gas (Chlorine) is evolved.

2NaCl + MnO2 + 2H2SO4 -------> 2NaHSO4 + MnSO4 + H2O + Cl2


Q.41. Can we use HCl in the test of Chloride?

Ans. No, HCl itself contains chloride.


Q.42. How do you test for Bromide?

Ans. When the mixture containing Bromide is heated with Conc. H2SO4 heavy brown vapours of Bromine are evolved.

NaBr + H2SO4 -------> NaHSO4 + HBr

2HBr + H2SO4 -------> 2H2O + SO2 + Br.


Q.43. What is Confirmatory test for Bromide?

Ans. When a Bromide is heated with MnO2 and H2SO4 reddish brown vapours of Br (Bromide) are evolved.


Q.44. How do you test for Iodide?

Ans.

1. Heat the mixture with Conc. H2SO4 when violet vapours are evolved

NaI + H2SO4 --------> NaHSO4 + Hl

2Hl + H2SO4 --------> 2H2O + SO2 + I2

2. On adding a pinch of MnO2 to the above mixture more violet vapours are evolved.

2Nal + MnO2 + 3H2SO4 -------> 2NaHSO4 + MnSO4 + 2H2O + l2


Q.45. Can you see Silver Nitrate for the detection of Halibes?

Ans. Yes we can use Silver Nitrate for the detection of Halides but the following precautions must be observed:

1. Distilled water must be used throughout.

2. Nitric Acid free from Chloride must be used Ordinary Nitric Acid contains Chloride as impurity.

3. Test tube and breakers must be washed with distilled water.


Q.46. Why Ordinary water should not be used for the test of Chloride?

Ans. Ordinary water contains chloride as an impurity. It produces a white precipitate with AgNo3 solution even in the absence of Chloride in the mixture.


Q.47. How many members are there in Halogen group?

Ans. Five members Flourine, Chlorine, Bromine, Iodine and Astatine.


Q.48. To which group of Periodic Table the Halogen elements belong?

Ans. The Halogen elements belong to VII B group.


Q.49. Is Astatine a radio active element?

Ans. Yes.


Q.50. Is Astatine found in Large quantities?

Ans. No, it is found in very small quantity.


Q.51. Whether Halogens are Electropositive or Electronegative?

Ans. They are Electronegative.