SECTION POSTLABORATORY ASSIGNMENT I. A \"barium/calcium/magnesium\" unknown solu
ID: 555668 • Letter: S
Question
SECTION POSTLABORATORY ASSIGNMENT I. A "barium/calcium/magnesium" unknown solution gave no reaction with aqueous NH4)2SO4. However, the unknown solution produced a white precipitate with aqueous NH)2C204 and a brick-red flame test. After centrifuging and decanting, there was no reaction with aqueous Na2HPO4 and NaOH. State the cation(s) confirmed present and absent in the unknown solution Cation(s) present Cation(s) absent 2. A "barium/calcium/magnesiu" unknown solution produced a white precipitate with aqueous (NH4)2S04 and a green flame test. After centrifuging and decanting, the addition of aqueous (NH4)2C204 gave no reaction, but there was a white precipitate with aqueous Na2HPO4 and NaOH. After dissolving the precipitate in HCI and adding magnesium reagent and aqueous NaOH, the solution gave a blue "lake" gel. State the cation(s) confirmed present and absent in the unknown solution. Cation(s) present Cation(s) absentExplanation / Answer
1. Among the 3 cations Ba, Ca & Mg, only two cations Ca and Mg will not give undergo reaction with aq. (NH4)2SO4. So from this we can say that Ba cation is absent. Then next among the two cations, Ca & Mg, Ca only can give positive test towards Ammonium oxalate by forming white precipitate and also give brick red flame test. Moreover, Ca cation cannot react with aqueous Na2HPO4 and NaOH. Based on these observations, we can confirm that in the unknown solution Ca cation is present and Ba as well as Mg were absent.
2. Among the 3 cations Ba, Ca & Mg, Ba cation will undergo reaction with aq. Ammonium sulfate to give barium sulphate white precipitate and also will give positive green flame test.It cannot react with ammonium oxalate. Moreover it will give white ppt when it reacts with sodium hydrogen phosphate and sodium hydroxide to barium phosphate and barium hydroxide. After dissolving the precipitate in HCl and adding Magnesium reagent and aqueous NaOH, the solution gave a blue lake gel.Based on these observations, Ba cation is present in unknown solution and Ca as well Mg cations are absent.
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