Question

Each of the observations listed was made on a different solution. Given the observation, state which ion studied in this experiment is present. If the test is not definitive, indicate that with a question mark. a. Addition of 6 M NaOH and Al to the solution produces a vapor that turns red litmus blue. Ion present: b. Addition of 6 M HCI produces a vapor with an acrid odor. Ion present: c. Addition of 6 M HNO_3 produces an effervescence. Ion present: d. Addition of 6 M HNO_3 plus 0.1 M AgNO_3 produces a precipitate. Ion present: e. Addition of 6 M HNO_3 plus 1 M BaCl_2 produces a precipitate. Ion present: f. Addition of 6 M HNO_3 plus 0.5 M (NH_4)_2MoO_4 produces a precipitate. Ion present: An unknown containing one or more of the ions studied in this experiment has the following properties: a. No effect on addition of 6 M HNO_3. b. No effect on addition of 0.1 M AgNO_3 to solution in (a). c. White precipitate on addition of 1 M BaCl_2 to solution in (a). d. Yellow precipitate on addition of (NH_4)_2MoO_4, to solution in (a). On the basis of this information which ions are present, which are absent, and which are in doubt? Present Absent In doubt

Answer 1

Ans 1 a) The aluminium metal will come from aluminium nitrate [Al(NO₃)₃]

Now Al(NO₃)₃ + 3NaOH -> Al(OH)₃+ NaNO₃

Now when we will add NaOH and Al it will form Na₃AlO₃ complex and H₂vapour.This vapour will turn red litmus to blue indicating the presence of nitrate ion.

b) We will take a pinch of salt ad mix it with dilute HCl , a colourless pungent smelling gas indicates the presence of SO₃^2- ion

c) When 6M HNO₃ reacts with a salt and produces brisk effervescence it means that it gives CO₂ which turns lime water milky indicating the presence of carbonate ion CO₃^2- .

d) We will acidify a portion of the extract formed(prepared during confirmatory test i.e.Sodium carbonate extract) with HNO₃ and boil it for some time and cool and add AgNO₃ . A white precipitate is formed indicating the presence of chloride ion.

e) To the solution extract we will add few drops of BaCl₂ in it . We will observe a white precipitate which is insoluble in HNO₃ is formed indicating the presence of SO₄^2- ion

f) To the aqueous solution of the extract formed from the salt used add HNO₃ and boil it for sometime. Then Add ammonium molybdate solution in excess and boil it again. We will observe a yellow precipitate indicating the presence of phosphate ion PO₄^3-

2) a) when there is no effect of HNO₃ it means that carbonate is absent

b) When there is no effect on addition of AgNO₃ , it means chloride ion is absent

c) When it forms white precipitate on addition of BaCl₂ , it means SO₄^2- is present

d) When it forms yellow precipitate on addition of ammonium molybdate it means PO₄^3- is present.