Experiment VI.4 - Complete Analyse The Ions found I the unknown substance were: NH 4 +, K +, Sr 2+, Cu 2+ ;B(OH) 4 -, Br -, Cl -, CrO 4. The testing process is described below. Cation analyse In a first part of the experiment a flame test was made with the unknown substance. The salt mixture was therefore separated into its components specifiable by the naked eye. 6 different components were found. With each component the flame test was done and the results were summarised. The following colours have been observed: Green Cu, Tl, Ba Violet K, Rb Carmine Li, Sr In a second part of the experiment the unknown substance was firstly solved in water (almost completely soluble). Then 2 M HCl was added and all salt was soved. The solution had a very intensive yellow color, characteristic for chromate CrO 4 The solution smelled weakly of ammoniac + NH 4 Ion Group A Then the ph of the solution was raised into basic area by adding Na 2 CO 3 so all polyvalent cations excepting Mg 2+ precipitated. The remaining solution contained now the group A of only singlevalent cations and Mg 2+. The ph of the solution was reduced into acidic area and a solution of BaCl was dropped in to exchange all sulfate and phosphate with chloride. Na 2 SO 4 + BCl 2 BaSO 4 + 2 NaCl No precipitation was observed No SO 4 and PO 4 3- The solution was vaporised and the remaining salt was solved in ethanol. Soluble part: LiCl, MgCl 2 Insoluble part: K + very less of substance could be solved a lot of insoluble substance remained The soluble part was tested for: Li + : - negative flame test - Na 2 HPO 4 was added to a solution of this part in water. A white precipitate which is easily soluble in acids proofs Li+: Date: 29.01.2009 Page 1
3 Li + + Na 2 HPO 4 + NaOH Li 3 PO 4 + 3 Na+ + H 2 O No precipitation was observed No Li + Mg 2+ : Na 2 HPO 4 and NH 3 are added to the solution. A flocky white precipitate proofs Mg 2+ : MgCl 2 + Na 2 HPO 4 + NH 3 MgNH4PO4 + 2 NaCl No precipitation was observed No Mg 2+ The insoluble part was solved in water and tested for K +. Therefore NaOH was added to the solutions to get the ammonia out: NH 4 + + NaOH NH 3 + Na + + H 2 O Then HClO4 is added. After a few minutes the building of octahedral crystals proofs K + : K + + HClO 4 + H 2 O KClO 4 + H 3 O + There were some octahedral crystals and the flame test showed a violet colour K + NH4 + : Some of the unknown substance was solved in water and NaOH was added to the solution: NaOH + NH 4 + NH 3 + Na + + H 2 O Concentrated HCl was added to the slution. A white fog of NH 4 Cl proofs NH 4 + : NH 3 + HCl NH 4 Cl There was such a fog and it smelled of ammoniac NH 4 + Ion Group B The precipitate from the first step (getting solution A) is solved in 2 M HCl and NH 3 is added until ph 9 is reached. All cations not building ammine complexes (Al, Cr, Fe, Mn) will precipitate (Group B). There was no precipitate No Al 3+, Cr 3+, Fe 3+, Mn 2+ The remaining solution was deeply blue (copper-ammine complex) Cu 2+ NaOCl solution is added to the precipitate and the whole thing is boiled: Cr(OH) 3 + NaClO CrO 4 + NaCl + 3 H + 3 Mn(OH) 2 + 2 NaClO 2 NaCl + 3 MnO 2 + 2 H 2 O + 4 H + NH3 is added to reduce the ClO: 2 NH 3 + 2 ClO N 2 +2 Cl - + 2 H 3 O + The solution is neutralised with acetic acid. A possible precipitation is washed in water and taken for the Cr 3+ proof. Date: 29.01.2009 Page 2
Cr 3+ : HNO 3 is added to the testing solution. The solution is covered with a diethyl layer and H 2 O 2 is added. A blue colour of the organic phase proofs Cr 3+. HNO 3 + H 2 O NO 3 - + H 3 O + 2 CrO 4 + 2 H 3 O + Cr 2 O 7 + 3 H 2 O Cr 2 O 7 + 4 H 2 O 2 + 2 H 3 O + 2 [CrO(O 2 ) 2 ] + 7 H 2 O Al 3+ : The precipitate is solved in 2 M HNO 3. Alizarin (az) is added and the solution is neutralized with NH 3. A red precipitation proofs Al 3+ : Al 3+ + 3 NH 3 + H 3 az Alaz + 3 NH 4 + Alizarin S (yellow) Aluminum precipitate (red) Fe 3+ : Concentrated H 2 SO 4 is added to the solution until the red precipitation of Fe(OH) 3 is solved. Then NH 4 SCN is added and the solution is covered with diethyl ether. A red colour of the organic phase after shaking proofs Fe 3+ : 2Fe(OH) 3 + 3H 2 SO 4 2Fe 3+ + 3 SO 4 + 6 H 2 O Fe 3+ + 3SCN Fe(SCN) 3 Mn 2+ : H 2 O 2 is added to the solution containing H 2 SO 4 : Date: 29.01.2009 Page 3
Mn(OH) 2 + H 2 SO 4 Mn2+ + SO 4 +H 2 O Mn2+ + H 2 O 2 MnO 2 + H 2 HNO 3 and PbO 2 are added to the solution. A violet colour of the solution after heating a few minutes proofs Mn 2+ : 2 MnO 2 + 3 PbO 2 + 2 H + 2MnO 4 - + 3 Pb 2+ +H 2 O Ion Group C (NH 4 ) 2 CO 3 is added to the solution from part B. The precipitation is the ion group C (Ba, Sr, Ca). All NH 3 is cooked out of the solution. Ba 2+ : The precipitate is solved in low concentrated acetic acid. Then K 2 CrO 4 is dropped in. The precipitate is solved in 2 M HNO 3. H 2 SO 4 is added to the solution. A white precipitate even not soluble in hot HNO 3 proofs Ba 2+ : Ba 2+ + K 2 CrO 4 2 K + + BaCrO 4 BaCrO 4 + HNO 3 Ba 2+ + NO 3 - + CrO 4 Ba 2+ + H 2 SO 4 BSO 4 + 2 H + There could not be observed any precipitate No Ba 2+ To the remaining solution, where K 2 CrO 4 was dropped in, Na 2 CO 3 is added and the resulting precipitate is washed in water and solved in HNO 3. The solution is vaporised and the remaining salt is solved in ethanol. Ca(NO 3 ) 2 is soluble in ethanol where Sr(NO 3 ) 2 is not. Ca 2+ : The ethanol is vaporised, the salt is solved in water and a drop of acetic acid and K 2 C 2 O 4 is added to the solution. A white precipitate proofs Ca 2+ : K 2 C 2 O 4 + Ca 2+ BaC 2 O 4 + 2 K + There was no such precipitate No Ca 2+ Sr 2+ : The salt not solved in ethanol is solved n water and H 2 SO 4 is added. A white precipitate proofs Sr 2+ : Sr 2+ + H 2 SO 4 SrSO 4 + 2 H + There was a white precipitate Sr 2+ Date: 29.01.2009 Page 4
Ion Group D NaOH is added to the remaining solution from part C. Zn is precipitated as Zn(OH )2, the othe cations are solved as hydroxides or oxides: Zn 2+ + 2 NaOH 2 Na + + Zn(OH) 2 Zn 2+ : HCl is added to the solution. Then K 4 [Fe(CN) 6 ] is dropped in. A clear precipitate proofs Zn 2+. Zn(OH) 2 + K 4 [Fe(CN) 6 ] K 2 Zn[Fe(CN) 6 ] + 2 K + + 2 OH - There was no such precipitate No Zn 2+ The precipitate from the D group solution is solved a 1 M H 2 SO 4 solution. Cu 2+ : KI is added to the solution. A clear precipitate and a brown solution proof Cu 2+ : Cu 2+ + 2KI CuI2 + 2K + CuI 2 is instable; the elementary iodine gives the solution a brown colour: 2 CuI 2 2 CuI + I 2 There was a clear precipitate and a brown solution Cu 2+ Ni 2+ : NH 3 is added until ph 9 is reached. Then a dimethylglyoxime (H 2 dmg) solution is added. The building of a red precipitate proofs N i2+ : Ni 2+ + 2 H 2 dmg Ni(Hdmg) 2 + 2H + There was no red precipitate No Ni 2+ Co 2+ : Acetic acid is added to the testing solution. The solution is covered with diethyl ether after KSCN is added. A deep blue colour of the organic phase proofs Co 2+ : 2 KSCN + Co 2+ Co(SCN) 2 + 2 K + Fe 3+ can disturb the test. To avoid such an error Fe 3+ is masked with F - : F 3+ + 3 NaF FeF 3 + 3 Na + The cations found in the unknown substance were: NH 4 +, K +, Cu 2+, Sr 2+ Date: 29.01.2009 Page 5
Anion analyse CO 3 : Acetic acid is added to the unknown salt; the arising CO 2 is taken with a pipette and pressed under baryt water. A clouding of the solution proofs CO 3 : CO 3 + 2 H+ CO 2 + H 2 O B(OH) 2 + CO 2 BaCO 3 + H2O There was no clouding No CO 3 CH 3 COO-: The substance is powdered together with four times KHSO 4. An acetic acid smell proofs acetate: CH 3 COO - + HSO4 CH 3 COOH + SO 4 There was no such smell No CH 3 COO- B(OH) 4 - : H 2 SO 4 and Methanol are added to the substance. It is heated and enflamed. A green flame proofs B(OH) 4 - : 2 B(OH) 4 - + H 2 SO 4 2 B(OH) 3 + SO 4 + 2 H 2 O B(OH) 3 + CH 3 OH B(COH 3 ) 3 + 3 H 2 O There was a green flame B(OH) 4 - A soda digestion of a water solution of the unknown substance was made to precipitate all metal ions to avoid them disturbing the following testing reactions. This soda digestion solution was taken for further tests. SO 4 : HCl and BaCl 2 are added to the solution. A white precipitate proofs SO 4 : SO 4 + BCl 2 BSO 4 + 2 Cl - There was no precipitate No SO 4 C 2 O 4 : Acetic acid and CaCl 2 are added to the solution. The resulting precipitate is solved in H 2 SO 4 and KMnO 4 is dropped into the solution. If the solution looses its violet colour under an elusion of CO 2, oxalate is proofed: C 2 O 4 + CaCl 2 CaC 2 O 4 + 2 Cl - 2 MnO 4 - + 5 C 2 O 4 + 16 H + 10 CO 2 + 2 Mn 2+ + 8 H 2 O There was no such reaction observed No C 2 O 4 Sulfite disturbs the test because it also reacts with permanganate: 5 SO 3 + 2 MnO 4 - + 6 H 2 O 5 SO 4 + 2 Mn 2+ + 9 H 2 O Date: 29.01.2009 Page 6
It is therefore oxidised with KI 3 : SO 3 + KI 3 SO 4 + 3 I- + K + NO 3 -: FeSO 4 and H 2 SO 4 are added to the solution. The resulting solution is under covered with H 2 SO 4. A dark ring where the two layers touch proofs NO 3 - : 3 FeSO 4 + 2 H 2 SO 4 + NO 3 - KI 3 NO + 3 Fe 3+ + 5 SO 4 + 2 H 2 O FeSO 4 + 2 H 2 O [Fe(H 2 O) 2 ] 2+ + SO 4 [Fe(H 2 O) 2 ] 2+ + SO 4 + NO [Fe(H 2 O)5NO]SO 4 + H 2 O There was no dark ring observed No NO 3 - Bromide and iodide can disturb the test because they also produce a colour. Therefore they are precipitated with AgNO 3 : X - + AgNO 3 AgX + NO 3 - NO 2 -: To the testing solution, where I- and SO 3 - are removed from as described above, acetic acid, sulfanilic acid and α-naphthalene are added. A red colour proofs NO 2 -: C 6 H 7 NO 3 S + NO 2 - + 2 H + C 6 H 5 N 2 O 3 S + + 2 H 2 O C 6 H 5 N 2 O 3 S+ C 10 H 9 N C 16 H 13 N 3 O 3 S + H + There was no red colour No NO 2 - Halogenides: First of all the halgogenides in the soda digestion are precipitated with AgNO 3 in basic solution (reached by adding NH 3 to the solution). The precipitate is washed and afterwards extracted with concentrated ammoniac where only AgCl and AgBr are solved. AgI remains as a yellow substance. AgI + AgBr + AgCl + 4 NH 3 AgI(s) + 2 [Ag(NH 3 ) 2 ] + Cl - (aq) + Br - (aq) I-: The yellow precipitate is solved in concentrated H 2 SO 4 and zinc powder is added. The resulting solution is under covered with CHCl 3 and a NaOCl solution is added. A violet colour of the organic phase proofs I - : 2 AgI + Zn 2 Ag + Zn 2+ + 2 I - 2 I - + C l2 I 2 + 2 C l- There was no violet colour No I - Cl - : AgBr and AgCl in the solution above are precipitated by making the solution acidic, means adding H 2 SO 4. The resulting precipitate is put into a (NH 4 ) 2 CO 3 solution where only AgCl is solved. To the now clear solution H 2 SO 4 is added. A white precipitate proofs Cl - : AgCl + AgBr + (NH 4 ) 2 CO 3 AgBr(s) + H 2 CO 3 + [Ag(NH 3 ) 2 ] Date: 29.01.2009 Page 7
[Ag(NH 3 ) 2 ] + Cl - + H 2 SO 4 AgCl + SO 4 + 2 NH 4 + There was a white precipitate Cl - Br - : The precipitate from above is solved in H 2 SO 4 and Zn powder is added. The resulting solution is under covered with CHCl 3. A brown organic phase proofs Br - : 2 AgBr + Zn 2 Ag + Zn 2+ + 2 Br - 2 Br - + Cl 2 Br 2 + 2 Cl - There was a brown colour Br - There was also a very typical yellow colour of the unknown substance water solution without any addition of acid or base. CrO 4 The anions found in the unknown substance were: CrO 4, B(OH) 4 -, Cl -, Br - Date: 29.01.2009 Page 8