46. Which of the following solids dissolves in water to form a colorless solution? (A) CrCl 2 (B) FeCl 2 (C) CoCl 2 (D) CuCl 2 (E) ZnCl 2

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1 Qualitative Analysis AP Review A solution is known to contain an inorganic salt of one of the following elements. The solution is colorless. The solution contains a salt of (A) Cu (B) Mn (C) Fe (D) Ni (E) Zn 69. A white solid is observed to be insoluble in water, insoluble in excess ammonia solution, and soluble in dilute HCl. Which of the following compounds could the solid be? (A) CaCO 3 (B) BaSO 4 (C) Pb(NO 3 ) 2 (D)AgCl (E) Zn(OH) Adding water to some chemicals can be dangerous because large amounts of heat are liberated. Which of the following does NOT liberate heat when water is added to it? (A) KNO 3 (B) NaOH (C) CaO (D) H 2 SO 4 (E) Na A strip of metallic scandium, Sc, is placed in a beaker containing concentrated nitric acid. A brown gas rapidly forms, the scandium disappears, and the resulting liquid is brown-yellow but becomes colorless when warmed. These observations best support which of the following statements? (A) Nitric acid is a strong acid. (B) In solution scandium nitrate is yellow and scandium chloride is color less. (C) Nitric acid reacts with metals to form hydrogen. (D) Scandium reacts with nitric acid to form a brown gas. (E) Scandium and nitric acid react in mole proportions of 1 to Which of the following solids dissolves in water to form a colorless solution? (A) CrCl 2 (B) FeCl 2 (C) CoCl 2 (D) CuCl 2 (E) ZnCl When dilute nitric acid was added to a solution of one of the following chemicals, a gas was evolved. This gas turned a drop of limewater, Ca(OH) 2, cloudy, due to the formation of a white precipitate. The chemical was (A) household ammonia, NH 3 (B) baking soda, NaHCO 3 (C) table salt, NaCl (D) epsom salts, MgSO 4 7H 2 O (E) bleach, 5% NaOCl When a solution of sodium chloride is vaporized in a flame, the color of the flame is (A) blue (B) yellow (C) green (D) violet (E) white 27. Appropriate uses of a visible-light spectrophotometer include which of the following? I. Determining the concentration of a solution of Cu(NO 3 ) 2 II. Measuring the conductivity of a solution of KMnO 4 III. Determining which ions are present in a solution that may contain Na +, Mg 2+, Al 3+ (A) I only (B) II only (C) III only (D) I and II only (E) I and III only 46. Which of the following occurs when excess concentrated NH 3 (aq) is mixed thoroughly with 0.1 M Cu(NO 3 ) 2 (aq)? (A) A dark red precipitate forms and settles out. (B) Separate layers of immiscible liquids form with a blue layer on top. (C) The color of the solution turns from light blue to dark blue. (D) Bubbles of ammonia gas form. (E) The ph of the solution decreases. APReviewQualAnalysis.docx 1

2 56. A yellow precipitate forms when 0.5 M NaI(aq) is added to a 0.5 M solution of which of the following ions? (A) Pb 2+ (aq) (D) SO 2-4 (aq) (B) Zn 2+ (aq) (E) OH - (aq) (C) CrO 2-4 (aq) 70. When 100 ml of 1.0 M Na 3 PO 4 is mixed with 100 ml of 1.0 M AgNO 3, a yellow precipitate forms and [Ag+] becomes negligibly small. Which of the following is a correct listing of the ions remaining in solution in order of increasing concentration? (A) [PO 4 3 ] < [NO 3 ] < [Na + ] (B) [PO 4 3 ] < [Na + ] < [NO 3 ] (C) [NO 3 ] < [PO 4 3 ] < [Na + ] (D) [Na + ] < [NO 3 ] < [PO 4 3- ] (E) [Na + ] < [PO 4 3- ] < [NO 3 ] 71. In a qualitative analysis for the presence of Pb 2+, Fe 2+, and Cu 2+ ions in aqueous solution, which of the following will allow the separation of Pb 2+ from the other ions at room temperature? (A) Adding dilute Na 2 S(aq) solution (B) Adding dilute HCl(aq) solution (C) Adding dilute NaOH(aq) solution (D) Adding dilute NH 3 (aq) solution (E) Adding dilute HNO 3 (aq) solution 2002 Questions 6-7 refer to the following solid compounds. (A) PbSO 4 (B) CuO (C) KMnO 4 (D) KCl (E) FeCl 3 6. Is purple in aqueous solution. 7. Is white and very soluble in water 36. A sample of a solution of an unknown was treated with dilute hydrochloric acid. The white precipitate formed was filtered and washed with hot water. A few drops of potassium iodide solution were added to the hot water filtrate and a bright yellow precipitate was produced. The white precipitate remaining on the filter paper was readily soluble in ammonia solution. What two ions could have been present in the unknown? (A) Ag + (aq) and Hg 2 2+ (aq) (B) Ag + (aq) and Pb 2+ (aq) (C) Ba 2+ (aq) and Ag + (aq) 65. Which of the following substances is LEAST soluble in water? (D) Ba 2+ (aq) and Hg 2 2+ (aq) (E) Ba 2+ (aq) and Pb 2+ (aq) (A) (NH 4 ) 2 SO 4 (B) KMnO 4 (C) BaCO 3 (D) Zn(NO 3 ) 2 (E) Na 3 PO A colorless solution is divided into three samples. The following tests were performed on samples of the solution. Sample Test Observation 1 Add H + (aq) No change 2 Add NH 3 (aq) No change 3 Add SO 2-4 (aq) No change Which of the following ions could be present in the solution at a concentration of 0.10 M? (A) Ni 2+ (aq) (B) Al 3+ (aq) (C) Ba 2+ (aq) (D) Na + (aq) (E) CO 3 2- (aq) APReviewQualAnalysis.docx 2

3 In a laboratory class, a student is given three flasks that are labeled Q, R, and S. Each flask contains one of the following solutions: 1.0 M Pb(NO 3 ) 2, 1.0 M NaCl, or 1.0 M K 2 CO 3. The student is also given two flasks that are labeled X and Y. One of these flasks contains 1.0 M AgNO3, and the other contains 1.0 M BaCl2. This information is summarized in the diagram below. (a) When the student combined a sample of the solution Q with a sample of X, a precipitate formed. A precipitate also formed when samples of solutions Q and Y are combined. (i) Identify solution Q. (ii) Write the chemical formulas for each of the two precipitates. (b) When solution Q is mixed with solution R, a precipitate forms. However, no precipitate forms when solution Q is mixed with solution S. (i) Identify solution R and solution S. (ii) Write the chemical formula of the precipitate that forms when solution Q is mixed with solution R. (c) The identity of solution X and solution Y are to be determined using the following solutions: 1.0 M Pb(NO 3 ) 2, 1.0 M NaCl, and 1.0 M K 2 CO 3. (i) Describe a procedure to identify solution X and solution Y. (ii) Describe the observations that would allow you to distinguish between solution X and solution Y. (iii) Explain how the observations would enable you to distinguish between solution X and solution Y. APReviewQualAnalysis.docx 3

4 Answer the following questions that relate to laboratory observations and procedures. (a) An unknown gas is one of three possible gases: nitrogen, hydrogen, or oxygen. For each of the three possibilities, describe the result when the gas is tested using a glowing splint (a wooden stick with one end that has been ignited and extinguished, but still contains hot, glowing, partially burned wood). (b) The following three mixtures have been prepared: CaO plus water, SiO 2 plus water, and CO 2 plus water. For each mixture, predict whether the ph is less than 7, equal to 7, or greater than 7. Justify your answers. (c) Each of three beakers contains a 0.1 M solution of one of the following solutes: potassium chloride, silver nitrate, or sodium sulfide. Three beakers are labeled randomly as solution 1, solution 2, and solution 3. Shown below is a partially completed table of observations made of the results of combining small amounts of different pairs of the solutions. Solution 1 Solution 2 Solution 3 Solution 1 Solution 2 Solution 3 black precipitate no reaction (i) Write the chemical formula of the black precipitate. (ii) Describe the expected results of mixing solution 1 with solution 3. (iii) Identify each of the solutions 1, 2 and 3. APReviewQualAnalysis.docx 4

5 2006 Question 5 5. Three pure, solid compounds labeled X, Y, and Z are placed on a lab bench with the objective of identifying each one. It is known that the compounds (listed in random order) are KCl, Na 2 CO 3, and MgSO 4. A student performs several tests on the compounds; the results are summarized in the table below. Compound ph of an Aqueous Solution of the Compound Result of Adding 1.0 M NaOH to a Solution of the Compound Result of Adding 1.0 M HCl Dropwise to the Solid Compound X >7 No observed reaction Evolution of a gas Y 7 No observed reaction No observed reaction Z 7 Formation of a white precipitate No observed reaction (a) Identify each compound (X, Y, Z) based on the observations recorded in the table. (b) Write the chemical formula for the precipitate produced when 1.0 M NaOH is added to a solution of compound Z. (c) Explain why an aqueous solution of compound X has a ph value greater than 7. Write an equation as part of your explanation. (d) One of the testing solutions used was 1.0 M NaOH. Describe the steps for preparing 100. ml of 1.0 M NaOH from a stock solution of 3.0 M NaOH using a 50 ml buret, a 100 ml volumetric flask, distilled water, and a small dropper. (e) Describe a simple laboratory test that you could use to distinguish between Na 2 CO 3 (s) and CaCO 3 (s). In your description, specify how the results of the test would enable you to determine which compound was Na 2 CO 3 (s) and which compound was CaCO 3 (s). APReviewQualAnalysis.docx 5

6 2008 Form B 5. The identity of an unknown solid is to be determined. The compound is one of the seven salts in the following table. Use the results of the following observations or laboratory tests to explain how each compound in the table may be eliminated or confirmed. The tests are done in sequence from (a) through (e). (a) The unknown compound is white. In the table below, cross out the two compounds that can be eliminated using this observation. Be sure to cross out these same two compounds in the tables in parts (b), (c), and (d). (b) When the unknown compound is added to water, it dissolves readily. In the table below, cross out the two compounds that can be eliminated using this test. Be sure to cross out these same two compounds in the tables in parts (c) and (d) (c) When AgNO 3 (aq) is added to an aqueous solution of the unknown compound, a white precipitate forms. In the table below, cross out each compound that can be eliminated using this test. Be sure to cross out the same compound(s) in the table in part (d). (d) When the unknown compound is carefully heated, it loses mass. In the table below, cross out each compound that can be eliminated using this test. (e) Describe a test that can be used to confirm the identity of the unknown compound identified in part (d). Limit your confirmation test to a reaction between an aqueous solution of the unknown compound and an aqueous solution of one of the other soluble salts listed in the tables. Describe the expected results of the test; include the formula(s) of any product(s). APReviewQualAnalysis.docx 6

7 Answers E 69. A 73. A D 46. E 52. B B 27. A 46. C 56. A 70. A 71. B C 7. D 36. B 65. C 72. D 2004 Question 5 Answers (a) i. Solution Q is K 2 CO 3 ii. Ag 2 CO 3 and BaCO 3 (b) i. Solution R is Pb(NO 3 ) 2 and solution S is NaCl ii. PbCO 3 (c) i. The identities of solutions X and Y can be determined by adding a sample of NaCl to each solution. OR by adding a sample of Pb(NO 3 ) 2 to each. Other reagents that will differentiate accepted. ii. NaCl will form a white precipitate when added to a solution of AgNO 3, but will not form a precipitate when added to a solution of BaCl 2. OR Pb(NO 3 ) 2 will form a white precipitate when added to a solution of BaCl 2, but will not form a precipitate when added to a solution of AgNO 3. iii. When NaCl is added to solution X, a precipitate of AgCl forms is solution X is AgNO 3. If no precipitate forms, solution X must be BaCl 2. The same logic can be used to identify solution Y. OR When Pb(NO 3 ) 2 is added to solution X, a precipitate of PbCl 2 forms is solution X is BaCl 2. If no precipitate forms, solution X must be AgNO 3. The same logic can be used to identify solution Y Question 5 Answers (a) Nitrogen: When the glowing splint is inserted into the gas sample, it will be extinguished. Hydrogen: When the glowing splint is inserted into the gas sample, a popping sound can be heard. Oxygen: When the glowing splint is inserted into the gas sample, the splint will glow brighter or reignite. (b) CaO plus water: ph > 7; CaO in water forms the base Ca(OH) 2 (or metal oxides are basic anhydrides). SiO 2 plus water: ph = 7; SiO 2 is insoluble in water, so there is no change in ph. CO 2 plus water: ph < 7; CO 2 in water forms the acid H 2 CO 3 (or nonmetal oxides are acidic anhydrides). (c) i. The black precipitate is Ag 2 S. ii. A precipitate will be produced when the two solutions are mixed. iii. Solution 1 is silver nitrate; Solution 2 is sodium sulfide; Solution 3 is potassium chloride. APReviewQualAnalysis.docx 7

8 2006 Question 5 Answers (a) Compound X = Na 2 CO 3 Compound Y = KCl Compound Z = MgSO 4 (b) Mg(OH) 2 (c) CO 3 2- reacts with water to form OH -. CO 3 2- (aq) + H 2 O(l) OH - (aq) + HCO 3 - (aq) (d) 1,000 ml of 1.0 M NaOH contains 1.0 mol NaOH; therefore, 100 ml of 1.0 M NaOH contains 0.10 mol NaOH (i.e, 0.10 mol NaOH is needed for the solution). volume of 3.0 M NaOH needed = 0.10 mol NaOH = 33 ml Step 1: Use the buret to deliver 33 ml of the 3.0 M NaOH stock solution into the clean 100 ml volumetric flask. Step 2: Add distilled water to the flask until the liquid level is just below the calibration line in the neck of the flask; swirl gently to mix. Step 3: Use the small dropper to add the last amount of distilled water, drop by drop, until the bottom of the meniscus in the flask neck is level with the calibration line. Insert the stopper, and invert the flask to mix. (e) A water solubility test would work. Put a small amount of one substance in a beaker of distilled water. If the substance dissolves readily when stirred, then it is Na 2 CO 3 ; if it does not dissolve, it is CaCO 3. OR A flame test would work. Dip a moistened wire into a sample of one of the substances and place the wire in the flame of a Bunsen burner. If a bright orange-yellow color is observed, then the sample is Na 2 CO 3 ; if a brick red color is observed, it is CaCO 3. Note: The student does NOT have to perform a confirmatory test on the other substance if one has already been identified with a test Form B Question 5 Answers (a) (b) (c) (d) (e) Mix an aqueous solution of BaCl 2 2H 2 O with an aqueous solution of CuSO 4 5H 2 O; the BaSO 4 will precipitate. APReviewQualAnalysis.docx 8