chemistry viva questions

Chemistry viva questions

For RRB JE, IBPS SSC, BANK PO, Clerk, ASM, CTET, GATE, MAT, CAT, JEE, Exam. Viva-Voce of CHEMISTRY practical for class12th.













Q1. Why is the use of HNO₃ avoided in the preparation of Solution for qualitative analysis?
Ans: Because HNO₃ is an oxidizing agent. It oxidizes H₂S gas into free sulphar when it is used in group analysis.
Q2. What is aqua-regia? What is its importance?
Ans: It is a mixture of conc.HCl and conc.HNO₃ in the ratio 3:1.
It can supply nascent chlorine and forms Soluble Chlorides.
Q3.By what test can chlorine be confirmed? What is the formula of the end product of this test?
Ans: By Chromyl Chloride test and its formula is CrO₂Cl₂.
Q.4 What is fusion mixture? Why it is used? 
Ans: It is a mixture of Na₂CO₃ and K₂CO₃ in equivalent proportion. It is used to convert any salt into Carbonate salt.
Q5. Which substance give reddish brown fumes when heated with conc. H₂SO₄?
Ans: Bromide salt, due to the evolution of Br₂ gas.
Q6.Milkiness of lime water by Carbonate salt is due to the formation of what compound?
Ans: Insoluble Calcium Carbonate.
Q7. Why is Pt. (platinum ) wire is used in a flame test?
Ans: Because it has a high melting point and it imparts no colour to the flame. Moreover, Pt wire does not react with the salt.
Q8. Why is flame test avoided for lead salt?
Ans: Because of it carrots the Pt wire.
Q9. Why is conc. HCl used in the flame test but not conc. HNO₃ and conc. H₂SO₄?
Ans: To convert any salt into most volatile chloride salt. But conc.HNO₃ oxidized the salt and if conc.H₂SO₄ is used then sulphar itself imparts colour to the flame. Due to which conc. HNO₃ and conc. H₂SO₄ are not used in the flame test. 
Q10. At what condition is Cobalt-Nitrate test done?
Ans: If the residue, after Charcoal reduction test remain white infusible.
Q11."Salt is soluble in dilute HCl,"- what is the information of group analysis can be obtained from this?
Ans: Basic radicals of group-I absent.
Q12. If for salt, all groups are absent then what may be the basic radicals of the salt?
Ans: Na⁺ or K⁺ or NH₄⁺ .
Q13.By what test we can confirm Bromide and  Iodide radicals?
Ans: By Carbon tetrachloride test.
Q14.What is the Chemical Combination of the brown ring of the ring test for nitrate radical?
Ans: Nitroso Ferrous Sulphate ( FeSO₄ NO).
Q15. The precipitate (Ppt) of a group -II are of what class of compound?
Ans: Sulphide of Basic radicals.

Q16. The precipitate (Ppt) of a group -IIIA  are of what class of compound?
Ans: Hydroxide of Basic radicals.
Q17. The precipitate (Ppt) of a group -IIIB  are of what class of compound?
Ans: Sulphide of Basic radicals.
Q18.The precipitate (Ppt) of a group -IV  are of what class of compound?
Ans: Carbonate of Basic radicals.
Q19.What is the rule of yellow ammonium Sulphide in the salt analysis?
Ans: It is used to divide group II ppt into two subgroups as Gr-IIA and Gr-IIB.
Q20.What is the formula of the following reagent and compounds?
Potassium Ferrocyanide, Sodium Cobaltinitrite, Ammonium Oxalate, Microcosmic Salt, Prussian Blue.
Ans: Potassium Ferrocyanide-K₄Fe(CN)₆
Sodium Cobaltinitrite-Na₃[CO(NO₂)₆]
Ammonium Oxalate-(NH₄)₂C₂O₄,
Microcosmic Salt-Na(NH₄)HPO₄,
Prussian Blue-Fe₄[Fe(CN)₆]₃
Q21.What is the end product of the test for Fe+++?
Ans: Ferric Ferrocyanide -Fe₄[Fe(CN)₆]₃
Q22.Why Sulphide salts give black ppt with lead acetate solution?
Ans: Due to the formation of black lead Sulphide ppt.
Q23.Why do we get sometimes a white ppt in group-II even when no radical of this group is present?
Ans: Due to precipitation of colloidal Sulphar. 
Q25.Why is it essential to add HCL before passing H₂S in group II?
Ans: HCl suppresses the ionization of H₂S by common ion effect. This low concentration of Sulphide in is sufficient to ppt the group II metal as their Sulphide but not metals of groupIII B.
Q26.Why is it essential to add NH₄Cl and NH₄OH before passing H₂S in group III B?
Ans: Which increase the concentration of Sulphide ion, This higher concentration of Sulphide ion precipitate the metals of groupIII B as their Sulphide.
Q27.White is the composition of ppt of group V?
Ans: MgNHPO₄ (White).
Q28.What is Nessler's reagent?
Ans: Alkaline solution of K₂[HgI₄]with NaOH is called Nessler's reagent.
Q29.White is the composition of ppt of the end product of Zineuranyl test for Na+?
Ans: Sodium-Zinc-uranyl acetate- NaZn(UO₂)₃(CH₃COO)₂.
Q30.What is the composition of a colorless bead of Borax-bead test?
Ans: Boric anhydride B₂O₃ &  Sodium metaborate NaBO₂.
Q31.What is the composition of a coloured bead of Borax-bead test?
Ans: Metaborate of basic radicals.
Q32.White is the composition of Chocolate brown ppt for the test of Cu++?
Ans: Potassium Cupricyanide-K[Cu(CN)].

Q33. What is Borax?
Ans: Na₂B₄O₇ 10H₂O .
Q34. Why is the lime water stored in stoppered bottles?
Ans: Because it becomes milky, due to absorption of CO₂ from the atmosphere.
Q35.Is there any gas other than CO₂ which turns lime water milky?
Ans: Yes, it is SO₂ gas.
Q36.Name a salt which smells on heating?
Ans: Borax.
Q37.Name the cation which can be detected by using Potassium Ferricyanide solution?
Ans: Ferrous ion.
Q38.Name the ions which are confirmed by using Potassium Ferrocyanide solution?
Ans: Cu, Zn, Fe+.
Q39.Why does a lead salt turn black when placed in the Laboratory for a long time?
Ans: Because of its formation of black lead sulphide.
Q40.Why Borax bead test is not performed in case of white salt?
Ans: Because white salt does not form coloured metaborates.
Q41.Why do you use freshly prepared FeSO₄ solution in the ring test of Nitrate?
Ans: Because in the air, FeSO₄ oxidizes into Fe₂(SO₄)₃.
Q42.Can we use ammonium nitrate in place of ammonium chloride for groupIII?
Ans: Yes, because we need NH₄+. ion to suppress the ionization of NH₄OH.
Q43. Why excess NH₄OH is avoided in group-III A ppt?
Ans: Because the ppt of Al(OH)₃ and Cr(OH)₃ are dissolved in NH₄OH.
Q44.Why ammonium Chloride added in group-IV?
Ans: Because it suppresses the ionization the of Ammonium Carbonate and prevents Mg to precipitate in group-IV.
Q45.What type of flame is generally used for heating purposes?
Ans: Non-Luminous Flame. It is obtained when the holes of the burner are opened.
Q46. Why there are holes in bunsen burner?
Ans: To make the flame non- luminous.
Q47.What is the smell of H₂S?
Ans: Rotten Egg.
Q48.Can you use AgNO₃ paper instead of lead acetate paper for testing of Sulphide?
Ans: Yes.  AgNO₃ paper also turned black due to the formation of silver Sulphide.
Q49.What is Eq? mass of an acid?
Ans: Equivalent mass of acid
Q50.What is Eq. mass of a base?
Ans: Equivalent mass of a base=.
Q51What is Eq. mass of a salt?
Ans: Equivalent mass of salt=
Q52. What is the equivalent mass of an oxidizing agent?
Ans: Equivalent mass of an oxidizing agent=
Q53.What is the equivalent mass of a reducing agent?
Ans: Equivalent mass of a reducing agent=
Q54.What is standard Solution?
Ans: A solution of known strength is called a standard solution.
Q55. what is a normal solution?
Ans: One unit of a solution containing 1 gm equivalent of acid or base or salt is called normal solution of that acid or base or salt.
Q56. Why is a normal solution is called standard solution?
Ans; Because the strength of all normal solution is 1(N). which is known to all.
Q57.What is a decinormal solution?
Ans: One little of a solution containing 1/10 th of a gm equivalent of solute is callled decinormal solution of that solute.  
Q58.Why is titration between Na₂CO₃ and H₂SO₄ called Acid-base titration?
Ans: Because when Na₂CO₃ dissolved in water, it acts as a base (ALKALI).
Q59.What is an indicator?
Ans: Indicators are organic compounds give different colours in acid and base medium and is used to detect the endpoint of the titration.
Q60.Why is no any indicator is required in the titration between KMnO₄ and oxalic acid?
Ans: Because KMnO₄ acts as self-indicator.
Q61.What is the principle of the acid-base titration?
Ans: At the neutralization point, number of gm equivalent of acid is equal to the number of gm equivalent of base.
Q62.What is the ionic reaction of the acid-base titration?
Ans: H⁺ + OH⁻ =H₂O.
Q63. What do you mean by primary standard substance?
Ans: Those substances whose standard solution can be prepared by direct weighing. eg-  oxalic acid.
Q64.Why HNO₃  or HCl is not used in KMnO₄ titration?
Ans: Because with HCl, Chlorine gas is evolved and  HNO₃ is reduced into NO₂.
Q65. Sometimes brown turbidity is seen in KMnO₄ titration- why?
Ans: It is due to insufficient H₂SO₄ . Brown ppt of MnO₂, H₂O is formed due to incomplete oxidation of KMnO₄.
Q66. Define the terms acidity and basicity?
Ans: Acidity of a base is the number of replaceable OH groups present in per molecule of the base. Basicity of an acid is the number of replaceable H-atom present in the per molecule of the acid.
Q67.Why equivalent mass of  H₂SO₄ is half of its molecular mass?
Ans: Because the basicity of H₂SO₄ is 2.
Q68.Why equivalent mass of HCl is equal to that of its molecular mass?
Ans: Because of the basicity of HCl is 1.
Q69.Under what condition the molar solution is the same as that of a normal solution?
Ans: If acidity of a base is one or basicity of acid is one.
Q70. How does acid strength change with the change of P?
Ans: For acid strength of  Pᵸ less than 7. But the strength of the acid is increased with the decrease of Pvalue.

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