Chemistry Saturday Study Session 1, Class 1--Stoichiometry. Page 1 of 6

Transcription

1 Page 1 of 6

2 Page 2 of 6 1. A 27.0g sample of an unknown hydrocarbon was burned in excess oxygen to form 88.0g of carbon dioxide and 27.0g of water. What is a possible molecular formula for the hydrocarbon? A. CH 4 B. C 2 H 2 C. C 4 H 3 D. C 4 H 6 2. When a hydrate of Na 2 CO 3 (106g/mol) is heated until all the water is removed, it loses 54.3% of its mass. The formula of the hydrate is A. Na 2 CO 3 7 H 2 O B. Na 2 CO 3 5 H 2 O C. Na 2 CO 3 3 H 2 O D. Na 2 CO 3 H 2 O BrO Br - + 6H + 3Br 2 + 3H 2 O 3. If 25.0mL 0.200M BrO 3 - is mixed with 30.0mL of 0.500M Br - solution that contains a large excess of H +, the amount of Br 2 formed, according to the equation above, is A x 10-3 mol B x 10-3 mol C x 10-2 mol D x 10-2 mol CS 2 (l) + 3O 2 (g) CO 2 (g) + 2SO 2 (g) 4. What volume of O 2 (g) is required to react with excess CS 2 (s) to produce 4.0L of CO 2 (g) at 0 C and 1atm? A. 1/3 x 22.4L B. 12L C. 22.4L D. 3 x 22.4L 5. A compound contains 1.10mol of K, 0.55mol of Te, and 1.65mol of O. What is the empirical formula of this compound? A. KTeO B. KTe 2 O C. K 2 TeO 6 D. K 2 TeO 3

3 Page 3 of 6 4NH 3 + 5O 2 4NO + 6H 2 O 6. The balanced chemical equation for the reaction of ammonia and oxygen gas is given above. Given the initial condition shown below which of these answer choices best depicts the same container after the reaction goes to completion? A B C D

4 Page 4 of 6 NaOH(aq) + MgCl 2 (s) 2NaCl(aq) + Mg(OH) 2 (s) 7. MgCl 2 and NaOH react according to the equation shown above. A 0.050mol sample of solid MgCl 2 is added to 150.mL of 0.200M NaOH solution. Which of the diagrams below best depicts the results after the mixture reacts as completely as possible? OH - OH - A B No precipitate Solid Mg(OH) 2 C D Solid Mg(OH) 2 Solid Mg(OH) 2

5 Page 5 of 6 8. A dilute aqueous solution contains 0.25mol NaBr and 0.25mol CaBr 2. What is the minimum number of moles of AgNO 3 that must be added in order to precipitate all the Br - as AgBr(s)? A. 1.0mol B. 0.75mol C. 0.50mol D. 0.25mol 3Ag(s) + 4HNO 3 3AgNO 3 + NO(g) + 2H 2 O 9. The reaction of silver metal and dilute nitric acid proceeds according to the equation above. If 10.0mol of powdered silver is added to 10.0mL of 6.0M nitric acid, the number of moles of NO gas that can be formed is A mol B mol C mol D mol 10. The weight of H 2 SO 4 (98.1g/mol) in 50.0mL of 6.00 molar solution is A. 3.10g B. 12.0g C. 29.4g D. 294g

6 Page 6 of 6 1. Answer the following questions that relate to chemical reactions. a) Iron(III) oxide can be reduced with carbon monoxide according to the following equation. Fe2O3(s) + 3 CO(g) 2 Fe(s) + 3 CO2(g) A 16.2 L sample of CO(g) at 1.50 atm and 200. C is combined with g of Fe2O3(s). i) How many moles of CO(g) are available for the reaction? ii) What is the limiting reactant for the reaction? Justify your answer with calculations. iii) How many moles of Fe(s) are formed in the reaction? b) In a reaction vessel, mol of Ba(NO3)2(s) and mol of H3PO4(aq) are combined with deionized water to a final volume of 2.00 L. The reaction represented below occurs. 3 Ba(NO3)2(aq) + 2 H3PO4(aq) Ba3(PO4)2(s) + 6 HNO3(aq) i) Calculate the mass of Ba3(PO4)2(s) formed. ii) Calculate the ph of the resulting solution. iii) What is the concentration, in mol L 1, of the nitrate ion, NO3 (aq), after the reaction reaches completion? 2. A student placed a sample of an unknown hydrate of copper(ii) sulfate into a clean, dry crucible and heated it three times, with the results shown below mass of clean, dry crucible 15.96g mass of hydrated compound and crucible 20.03g mass of crucible and contents after 1 st heating 19.01g mass of crucible and contents after 2 nd heating 18.56g mass of crucible and contents after 3 rd heating 18.55g a) Justify the student s conclusion that the compound was dry after the third heating. b) If the student failed to cover the crucible and some solid CuSO 4 spattered out during the heating process, would you expect the student s calculated mass of water in the hydrate to be too high, too low, or correct? Explain. c) Explain how you would use the data collected by the student to determine the formula of the unknown hydrate (CuSO 4 H 2 O). Calculations are not required.