Another student was given a pale violet solid. He was told that it contained two cations (positiveions) from this listLi+ Ca2+ Fe2+ NH+4 Fe3+He performed a flame test on the solid.He then dissolved a small sample of the solid in water, a yellow solution was formed.He added sodium hydroxide solution and then warmed the mixture.The table shows his observations.Test Observationflame test no positive resultadd sodium hydroxide solution and warm brown precipitatea pungent - smelling gas was evolvedthe gas turned damp red litmus paper blue(i) The flame test gave no positive result.State the two cations from the list that are not present in the solidand(ii) Identify the pungent - smelling gas given off and explain why the red litmus paper must bedamp before it is used.(iii) Identify the two cations present in the pale violet solidand5. Some iron (II) sulfate (FeSO4) is dissolved in water to make a solution.(a) A reaction takes place when sodium hydroxide solution is added to a solution of iron (ⅠⅠ) sulfate.(i) Complete the word equation to show this reaction(ii) State what you would observe in this reaction._______________________________________________________________________________________________________________(b) Barium chloride is used to test for sulfate ions.(i) Barium chloride solution is added to another solution of iron (ⅠⅠ) sulfate. A whiteprecipitate forms. Identify the white precipitate.________________________________________________________________________________________________(ii) In this test, another substance should be added to react with any carbonate ions thatmight be present. Identify this other substance and state one observation that would be madeif carbonate ions were present.Other substance ___________________________________Observation __________________________________________________________________________________(C) A compound with the formula (NH4 )2Fe(SO4)2 gives the same results in the tests in parts (a)and (b) as iron (ⅠⅠ) sulfate (FeSO4). Describe how you could show that a solution of (NH4)2Fe(SO4)2contains ammonium ions.____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
Question
Another student was given a pale violet solid. He was told that it contained two cations (positiveions) from this listLi+ Ca2+ Fe2+ NH+4 Fe3+He performed a flame test on the solid.He then dissolved a small sample of the solid in water, a yellow solution was formed.He added sodium hydroxide solution and then warmed the mixture.The table shows his observations.Test Observationflame test no positive resultadd sodium hydroxide solution and warm brown precipitatea pungent - smelling gas was evolvedthe gas turned damp red litmus paper blue(i) The flame test gave no positive result.State the two cations from the list that are not present in the solidand(ii) Identify the pungent - smelling gas given off and explain why the red litmus paper must bedamp before it is used.(iii) Identify the two cations present in the pale violet solidand5. Some iron (II) sulfate (FeSO4) is dissolved in water to make a solution.(a) A reaction takes place when sodium hydroxide solution is added to a solution of iron (ⅠⅠ) sulfate.(i) Complete the word equation to show this reaction(ii) State what you would observe in this reaction.(b) Barium chloride is used to test for sulfate ions.(i) Barium chloride solution is added to another solution of iron (ⅠⅠ) sulfate. A whiteprecipitate forms. Identify the white precipitate.(ii) In this test, another substance should be added to react with any carbonate ions thatmight be present. Identify this other substance and state one observation that would be madeif carbonate ions were present.Other substance Observation (C) A compound with the formula (NH4 )2Fe(SO4)2 gives the same results in the tests in parts (a)and (b) as iron (ⅠⅠ) sulfate (FeSO4). Describe how you could show that a solution of (NH4)2Fe(SO4)2contains ammonium ions.________________________________________________________________________________________________________________________________________________________________________________________________
Solution
(i) The flame test gave no positive result. This means that the cations Li+ and Ca2+ are not present in the solid. These two ions are known to give distinctive colors in a flame test (Li+ gives a crimson color and Ca2+ gives a brick red color).
(ii) The pungent-smelling gas given off is ammonia (NH3). The red litmus paper must be damp before it is used because ammonia is a base and bases turn red litmus paper blue. However, ammonia is a weak base and is in gaseous form, so it needs the water in the damp litmus paper to dissolve in so it can react with the litmus dye.
(iii) The two cations present in the pale violet solid are Fe2+ and Fe3+. The yellow solution formed when the solid was dissolved in water indicates the presence of Fe3+ ions. The brown precipitate formed when sodium hydroxide solution was added and the mixture was warmed indicates the presence of Fe2+ ions.
- (a) (i) The word equation for the reaction when sodium hydroxide solution is added to a solution of iron (II) sulfate is: Iron (II) sulfate + Sodium hydroxide -> Iron (II) hydroxide + Sodium sulfate (ii) You would observe a green precipitate forming in this reaction.
(b) (i) The white precipitate formed when barium chloride solution is added to a solution of iron (II) sulfate is barium sulfate. (ii) The other substance that should be added to react with any carbonate ions that might be present is hydrochloric acid. If carbonate ions were present, you would observe effervescence (bubbling) due to the production of carbon dioxide gas.
(c) To show that a solution of (NH4)2Fe(SO4)2 contains ammonium ions, you could add sodium hydroxide to the solution and heat it. If ammonium ions are present, they will react with the sodium hydroxide to produce ammonia gas, which can be detected by its pungent smell and its ability to turn damp red litmus paper blue.
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