Chapter 1 -- Introduction to Qualitative Analysis. NAME: Lab Section: Date: Sign-Off:

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1 Chapter 1 -- Introduction to Qualitative Analysis NAME: Lab Section: Date: Sign-Off:

2 Chapter 1 -- Introduction to Qualitative Analysis Introduction Qualitative analysis is a way inorganic chemists have to determine what [ions] is [are] present in a chemical sample. Qualitative analysis tells the chemist only what is present, NOT how much is present (the latter used to be called quantitative analysis and is now called analytical chemistry). For all intents and purposes, "Qual" takes advantage of the various solubility rules by manipulating the solubilities of various ions in different solvents, at different ph's and/or as complex ions. Anions are derived from the nonmetals in the upper right of the periodic table. 1 H 2 He 3 Li 4 Be 5 B 6 C 7 N 8 O 9 F 10 Ne 11 Na 12 Mg 13 Al 14 Si 15 P 16 S 17 Cl 18 Ar 19 K 20 Ca 21 Sc 22 Ti 23 V 24 Cr 25 Mn 26 Fe 27 Co 28 Ni 29 Cu 30 Zn 31 Ga 32 Ge 33 As 34 Se 35 Br 36 Kr 37 Rb 38 Sr 39 Y 40 Zr 41 Nb 42 Mo 43 Tc 44 Ru 45 Rh 46 Pd 47 Ag 48 Cd 49 In 50 Sn 51 Sb 52 Te 53 I 54 Xe 55 Cs 56 Ba 57 La 72 Hf 73 Ta 74 W 75 Re 76 Os 77 Ir 78 Pt 79 Au 80 Hg 81 Tl 82 Pb 83 Bi 84 Po 85 At 86 Rn 87 Fr 88 Ra 89 Ac 104 Rf 105 Db 106 Sg 107 Bh 108 Hs 109 Mt 58 Ce 59 Pr 60 Nd 61 Pm 62 Sm 63 Eu 64 Gd 65 Tb 66 Dy 67 Ho 68 Er 69 Tm 70 Yb 71 Lu 90 Th 91 Pa 92 U 93 Np 94 Pu 95 Am 96 Cm 97 Bk 98 Cf 99 Es 10 0 Fm 101 Md 102 No 103 Lr Cations are from the metals below and to the left of the non-metals in the periodic table. There are five classical groups of cations -- NOT to be confused with the GROUPS on the periodic table. These cation groups are based solely on the manner in which they may be identified, table, below, or removed from a mixture containing all of the cations in the table, below: 10

3 Cation Groups [1] Group 1 Group 2 Group 3 Group 4 Group 5 HCl Group Acidic Hydrogen Sulfide Group Basic Hydrogen Sulfide Group Ammonium Carbonate Group Soluble Group Silver (I)* Mercury (II) Aluminum (III) Calcium (II) Sodium (I) Mercury (I) Lead (II) Lead (II) Bismuth (III) Copper (II) Cadmium (II) Arsenic (III & V) Antimony (III & V) Tin (II & IV) Chromium (III) Iron (II & III) Manganese (II) Cobalt (II) Nickel (II) Zinc (II) Strontium (II) Barium (II) Potassium (I) Magnesium (II) Ammonium ion *Roman Numeral following the name of the metal indicates the positive charge on the ion. The anions are not grouped according to reactivity with different solvents as are the cations. Although this experiment is a descriptive introduction to "Qual", it must, nevertheless, be remembered that "Qual" is based also in ionic equations and numerical calculations. This lab experiment will not attempt to cover these latter two bases. This lab, however, WILL cover some simple techniques in Qual" -- you will be expected to learn what the final reaction products are of each experimental method. 11

4 Experimental Supplies and Chemicals 1-spot plate NaNO 3 KBr AgNO 3 1-spatula Na 2 SO 4 KI Cotton Na 2 S 6, 9 or 10 M H 2 SO 4 6 M HNO 3 Red litmus paper Na 2 CO 3 KCl CCl 4 Devarda's alloy KNO 3 6 M HCl 6 M NaOH FeCl M NH 3 NaHCO 3 solution CuSO 4 Test tube rack Magnesia mixture Disposable pipets KMnO 4 1-glass stirring rod Disposable test tubes Anions: Part 1 [2] Do this part in the hood AFTER you have placed a crystal or two of Na 2 S, Na 2 CO 3, NaNO 2 and Na 2 SO 4 in each of 4 wells in the spot plate so that you have 4 wells with one crystal each. Once you have taken this to the hood, add a drop of the sulfuric acid to each crystal and observe each reaction one well at a time. Describe the odor or appearance of the reaction product of each anion in the table below (NOTE: waft the vapors towards you instead of directly inhaling them over the spot plate): Observations for Anions: Part 1 Substance (Anion) Na 2 S (S 2- ) Na 2 CO 3 (CO 2-3 ) NaNO 2 (NO - 2 ) Na 2 SO 3 (SO 2-3 ) Crystal before reaction with sulfuric acid After reaction with sulfuric acid 12

5 Anions: Part 2 [2] Place three test tubes in a test tube rack. Label them #1, #2, #3. Place about the size of a third of a small pea of the following crystals into the respective tube: Tube #1 Tube #2 Tube #3 KCl KBr KI To each test tube, above, add about 3 cm of distilled water and mix. Now add, in order, to each tube as follows in the table, below: Tube #1 Tube #2 Tube #3 AgNO 3, drop-by-drop HNO 3 (10 gtts) H 2 SO 4 4 cm CCl crystals of NaNO 2 5 gtts KMnO 4 4 cm CCl 4 Cut a piece of parafilm so you can mix tubes #2 and 3 by inversion. CAUTION: CCl4 is a potential carcinogen. For each tube, record your observations in the table, below: Tube #1 Tube #2 Tube #3 Anions: Part 3 [2] Obtain a DRY test tube and place about a third the size of a small pea of crystals of KNO 3 in the bottom of the tube with 0.5 ml of deionized water containing 0.5 ml 6 M NaOH. Transfer the two liquids (the solution of water and NaOH) with a disposable pipet so that he walls of the test tube do not get wet. Place about a quarter the size of a small pea of crystals of Devarda's alloy in the solution, place a loose cotton plug in the test tube (Figure, below) and then place a moistened 13

6 piece of red litmus paper in the tube in the shape of a "V". This reaction requires patience, as it may begin immediately or it may take minutes to begin. CAUTION: this reaction can get very hot! Do NOT hold this in your hand after the reaction has started. The red litmus ought to turn blue as a gas exits the mixture in the test tube. CAREFULLY waft some of the vapors towards your nose. What is the gas? Sketch of apparatus for nitrate determination from KNO 3. The end products of the anion analysis are as follow in this table: Reaction Products from Anion Analysis Anion Product Observation Anion Product Observation S 2- H 2 S Vile Cl -1 AgCl White ppt CO 3 2- CO 2 Odorless, fizzing Br -1 Br 2 Orange to amber in CCl 4 NO 2-1 NO 2 Brown, sharp I -1 I 2 Violet in CCl 4 SO 3 2- SO 2 Sharp, white NO 3-1 NH 3 Litmus turns blue from red 14

7 Cation Analysis Obtain a test tube rack and 20 disposable test tubes. Set up your test tube rack as in the table below, remembering that rows run left to right and columns run top to bottom (or front to back in the rack), placing the reagents as indicated in the tubes, below: Tube Set-Up for Cation Analysis Column 1 Column 2 Column 3 Column 4 Column 5 Row 1 2% CuSO 4 2% CuSO 4 2% CuSO 4 2% CuSO 4 2% CuSO 4 Row 2 AgNO 3 AgNO 3 AgNO 3 AgNO 3 AgNO 3 Row 3 FeCl 3 FeCl 3 FeCl 3 FeCl 3 FeCl 3 Row 4 Magnesia mixture Magnesia mixture Magnesia mixture Magnesia mixture Magnesia mixture One tube and one column at a time, add 4 drops of the following reagents to each tube in the column as indicated, below: Reagent Dispensation Table Column 1 Column 2 Column 3 Column 4 Column 5 6 M HCl H 2 SO 4 6M NaOH 7.4 M NH 3 NaHCO 3 solution 15

8 And record your observations in the table, below: Row 1 Tube Set-Up for Cation Analysis Observations Column 1 Column 2 Column 3 Column 4 Column 5 Row 2 Row 3 Row 4 The end-products of the cation analysis are shown in the table, below: End-Products of Cation Analysis Cation Product Observation Ag +1 AgCl White ppt Fe 3+ Complex Brown ppt Cu 2+ CuCO 3 Light blue ppt Mg 2+ Mg(OH) 2 White ppt 16

9 Questions Complete the questions on a separate piece of paper and attach to this experiment for turn-in. 1. Based upon your results, design a method in flow chart form from which each ion could be separated from a solution containing all of the cations above. 2. Based on the following data, construct a separation scheme in flow chart form from a mixture of the cations listed, below: Cation Ag +1 Cu 2+ Fe 3+ Sr 2+ Reagent 1 HCl HCl HCl HCl Result White ppt No reaction (NR) Yellow solution NR Reagent 2 NaOH NaOH NaOH NaOH Result Brown ppt Powder blue ppt Red ppt NR Reagent 3 (NH 4 ) 2 CO 3 (NH 4 ) 2 CO 3 (NH 4 ) 2 CO 3 (NH 4 ) 2 CO 3 Result NR NR NR White ppt Reagent 4 H 2 S with acid H 2 S with acid H 2 S with acid H 2 S with acid Result Black ppt Brown ppt NR NR Reagent 5 H 2 SO 4 H 2 SO 4 H 2 SO 4 H 2 SO 4 Result NR White ppt NR White ppt 3. Write, using chemical symbols and notation, the ions described in the first table on the first page of this experiment. 17

10 References [1] King, E.J.: Ionic Reactions and Separations: Experiments in Qualitative Analysis. (Harcourt Brace Jovanovich: Austin) 1973, pp. 129, 143, 163, 183, 198. [2] Ibid. pp. 61, 64,