Post-lab 4 Qualitative Analysis-solutions

Post-lab 4 Qualitative Analysis-solutions -...

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Unformatted text preview: choudhury (fac489) – Post-lab 4 Qualitative Analysis – lyon – (51155) 1 This print-out should have 21 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points Identify the spectator ion(s) in the equation CaCl 2 (aq) + Na 2 CO 3 (aq) → CaCO 3 (s) + NaCl(aq). 1. Na + , Cl- correct 2. Na + , CO 2- 3 3. Ca 2+ , Cl- 4. Ca 2+ , CO 2- 3 Explanation: Spectator ions are those that do not par- ticipate in the reaction nor appear in the net ionic equation. Sodium ions (Na + ), potas- sium ions (K + ), nitrate (NO- 3 ) and chloride (Cl- ) are common spectator ions. 002 10.0 points In a precipitation reaction, the precipitate should be shown as 1. the complete formula. correct 2. the separated ions. 3. either the complete formula or the sepa- rated ions. Explanation: Since the precipitate actually exists as a solid compound and not as separated ions it is shown as the complete formula. 003 10.0 points Identify the solid product or products that form when the following aqueous solutions are mixed: (NH 4 ) 2 CO 3 (aq) + AgNO 3 (aq) → 1. Ag 2 CO 3 and NH 4 NO 3 2. NH 4 NO 3 3. Ag 2 CO 3 correct 4. No solid products are formed. Explanation: Ag 2 CO 3 and NH 4 NO 3 are the possible products. Using the solubility rules it can be determined that Ag 2 CO 3 is insoluble and will form a solid product; NH 4 NO 3 is soluble and will remain aqueous. 004 10.0 points Which ions are almost completely precipi- tated from solution when aqueous solutions of HI and Pb(NO 3 ) 2 are mixed? Choose the response that includes all the ions that are precipitated. I . H + II . I- III . Pb 2+ IV . NO- 3 1. II and III correct 2. I, II, III, and IV 3. I and IV 4. II, III, and IV 5. III and IV Explanation: Salts that contain group I A metals, Li, Na, K, Rb and Cs are always soluble in di- lute solutions. Salts that contain nitrate ions or ammonium ions are also soluble in dilute solutions. Most sulfate salts are soluble, but exceptions include BaSO 4 , PbSO 4 , Ag 2 SO 4 and SrSO 4 . 005 (part 1 of 2) 10.0 points Calculate the answer for part 2 of the follow- ing question to six significant figures. choudhury (fac489) – Post-lab 4 Qualitative Analysis – lyon – (51155) 2 An excess of aqueous AgNO 3 reacts with 33 . 5 mL of 5 M K 2 CrO 4 (aq) to form a precip- itate. What is the precipitate? 1. AgNO 3 2. Ag 2 CrO 4 correct 3. K 2 CrO 4 4. KNO 3 Explanation: 2 AgNO 3 (aq) + K 2 CrO 4 (aq) → Ag 2 CrO 4 (s) + 2 KNO 3 (aq) 006 (part 2 of 2) 10.0 points What mass of precipitate is formed? Correct answer: 55 . 5654 g. Explanation: V K 2 CrO 4 = 33 . 5 mL M K 2 CrO 4 = 5 M MW Ag 2 CrO 4 = 2 (107 . 87 g / mol) + 51 . 9961 g / mol +4 (15 . 9994 g / mol) = 331 . 734 g / mol m Ag 2 CrO 4 = 33 . 5 mL K 2 CrO 4 (aq) × parenleftbigg 5 mol K 2 CrO 4 1000 mL K 2 CrO 4 parenrightbigg × parenleftbigg 1 mol Ag 2 CrO 4 1 mol K 2 CrO 4 parenrightbigg × parenleftbigg 331 . 734 g Ag 2 CrO 4 1 mol Ag 2 CrO 4 parenrightbigg...
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Post-lab 4 Qualitative Analysis-solutions -...

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