CHEMISTRY 101 Hour Exam II October 29, 2013 Adams/Lindquist Name Signature Section "It s not that I m so smart, it s just that I stay with problems longer." --Albert Einstein-- This exam contains 17 questions on 7 numbered pages. Check now to make sure you have a complete exam. You have one hour and fifteen minutes to complete the exam. Determine the best answer to the first 15 questions and enter these on the special answer sheet. Also, circle your responses in this exam booklet. Show all of your work and provide complete answers to questions 16 and 17. 1-15 (30 pts.) 16 (12 pts.) 17 (18 pts.) Total (60 pts) Useful Information: 1 L = 1000 ml (exactly) Always assume ideal behavior for gases (unless explicitly told otherwise). PV = nrt R = 0.08206 L atm/mol K K = C + 273 N A = 6.022 10 23 Solubility Rules: 1. Most nitrate salts are soluble. 2. Most salts of sodium, potassium, and ammonium cations are soluble. 3. Most chloride salts are soluble. Exceptions: silver(i), lead(ii), and mercury(i) chloride. 4. Most sulfate salts are soluble. Exceptions: calcium, barium, and lead(ii) sulfate. 5. Most hydroxide salts can be considered insoluble. Soluble ones: sodium, potassium, ammonium, and calcium hydroxide. 6. Consider sulfide, carbonate, and phosphate salts to be insoluble. Soluble ones: sodium, potassium, and ammonium.
Hour Exam II Page No. 1 1. In lecture you saw the elephant s toothpaste demonstration in which hydrogen peroxide (H 2 O 2 ) produced water and oxygen gas. Write the equation for this reaction. What is the coefficient in front of water when this equation is properly written and balanced in standard form? a) 1 b) 2 c) 3 d) 4 e) 6 2. How many moles of sodium ions are present in 5.51 L of a 0.103 M sodium phosphate solution? a) 1.70 mol b) 0.568 mol c) 1.14 mol d) 0.0561 mol e) 53.5 mol Consider the following chemical equation to answer questions 3 and 4. CO 2 (g) + 4H 2 (g) CH 4 (g) + 2H 2 O(l) 3. How many moles of H 2 (g) are required to react completely with 0.500 mole of CO 2 (g)? a) 0.125 mol b) 0.500 mol c) 2.00 mol d) 4.00 mol e) 8.00 mol 4. How many grams of H 2 O(l) are produced when 0.500 mole of CO 2 (g) reacts completely? a) 1.00 g b) 4.50 g c) 9.01 g d) 18.0 g e) 72.1 g 5. How many of the following correctly identifies the precipitate formed when aqueous solutions of the following substances are mixed? Mixed Solutions Precipitate Formed I. Na 2 SO 4 (aq) + BaCl 2 (aq) BaSO 4 II. NH 4 Cl(aq) + AgNO 3 (aq) AgCl III. K 3 PO 4 (aq) + Pb(NO 3 ) 2 (aq) Pb 3 (PO 4 ) 2 IV. NaOH(aq) + CaCl 2 (aq) Ca(OH) 2 a) 0 b) 1 c) 2 d) 3 e) 4 6. Consider a sugar solution A with concentration x. You pour one-third of this solution into a beaker, and add enough water to double the volume to make solution B. What is the ratio of moles of sugar in solutions A and B (A:B)? a) 1:1 b) 1:3 c) 2:1 d) 2:3 e) 1:2
Hour Exam II Page No. 2 7. How many of the following statements are true? I. A balanced equation relates the numbers of molecules of reactants and products (or numbers of moles of reactants and products). II. To convert between moles of reactants and moles of products, we use mole ratios derived from the balanced equation. III. Often reactants are not mixed in stoichiometric quantities (they do not run out at the same time). In that case, we must use the limiting reactant to calculate the amounts of products formed. IV. When a chemical reaction occurs, it must follow the law of conservation of mass. a) 0 b) 1 c) 2 d) 3 e) 4 Consider the following unbalanced chemical equation: CuSO 4 (aq) + KI(s) CuI(s) + I 2 (s) + K 2 SO 4 (aq) Balance the equation above in standard form and then answer questions 8 and 9. 8. Which reactant is the limiting reactant? Choose the best answer. a) Both CuSO 4 and KI are equally limiting since they react in a 1:1 mole ratio. b) CuSO 4 is the limiting reactant because only 2 moles are available as compared to 4 moles of KI. c) KI is the limiting reactant because it is present in excess. d) Neither CuSO 4 nor KI are limiting reactants because 6 total moles are present on the reactant side as compared to 5 total moles on the product side. e) The limiting reactant cannot be determined since the starting amounts are not given. 9. If 10.0 g of I 2 (s) is produced in a chemical reaction that follows this equation, how many grams of KI(s) were reacted? a) 1.64 g b) 6.54 g c) 13.1 g d) 26.2 g e) 52.3 g 10. Consider the reaction between 1.0 L of 3.0 M AgNO 3 (aq) and 1.0 L of 1.0 M CuCl 2 (aq), according to the equation: 2AgNO 3 (aq) + CuCl 2 (aq) 2AgCl(s) + Cu(NO 3 ) 2 (aq) Which of the following will increase the amount of AgCl(s) produced? a) Adding another 1.0 L of 3.0 M AgNO 3 (aq). b) Adding another 1.0 L of 1.0 M CuCl 2 (aq). c) Adding 1.0 L of water to the original AgNO 3 (aq) solution. d) Allowing all of the water to evaporate from the resulting solution. e) At least two of the above will increase the amount of AgCl(s) produced.
Hour Exam II Page No. 3 11. Consider the following chemical equation: N 2 (g) + 3H 2 (g) 2NH 3 (g) What minimum total volume of reactant gases is needed to produce 4.00 g of ammonia if the volume of each gas is measured at 11 C and 0.998 atm? a) 0.469 L b) 2.74 L c) 5.49 L d) 8.23 L e) 11.0 L Consider the reaction between NO(g) and O 2 (g) represented below to answer questions 12 and 13. 12. What is the balanced equation for this reaction? a) 2NO(g) + O 2 (g) 2NO 2 (g) b) 6NO(g) + 6O 2 (g) 6NO 2 (g) c) 6NO(g) + 9O 2 (g) 6NO 2 (g) d) 4NO 2 (g) + O 2 (g) 4NO(g) e) 6NO(g) + 6O 2 (g) 6NO 2 (g) + 3O 2 (g) 13. What is the limiting reactant? a) NO b) O 2 c) NO 2 d) H 2 O e) There is no limiting reactant present.
Hour Exam II Page No. 4 Consider the following unbalanced chemical equation: Co(s) + F 2 (g) CoF 3 (s) Balance the equation above and then answer questions 14 and 15. 14. If 25.0 g of cobalt is reacted with 3.00 L of fluorine gas at 247 C and 2.50 atm, what mass of cobalt(iii) fluoride is produced? a) 0.117 g b) 13.6 g c) 20.4 g d) 28.6 g e) 49.2 g 15. How many mol of excess reactant is leftover? a) 0.117 mol b) 0.160 mol c) 0.176 mol d) 0.307 mol e) 0.424 mol
Hour Exam II Page No. 5 16. Answer the questions below as thoroughly as you can. Please limit your answers to the space provided. a) What do the subscripts in a chemical formula represent? Can the subscripts in a chemical formula be fractions? Explain and provide an example to support your answer. b) What do the coefficients in a balanced chemical equation represent? Can the coefficients in a balanced chemical equation ever be fractions? Explain and provide an example to support your answer. c) Use molecular-level drawings to show the difference between physical and chemical changes. Make sure you are consistent when drawing an element. First clearly state what you are trying to represent in each molecular-level drawing and then provide your drawing. Only clear drawings will receive full credit. Physical Change: Chemical Change:
Hour Exam II Page No. 6 17. An aqueous solution of ammonium sulfide is mixed with an aqueous solution of iron(iii) chloride. a) Write the balanced molecular equation, complete ionic equation, and net ionic equation for the two solutions mixed above. Include all phases and balance in standard form. Molecular: Complete: Net: b) If 50.0 ml of 0.500 M ammonium sulfide and 100.0 ml of 0.250 M iron(iii) chloride are mixed, how many grams of precipitate will form? (Problem #17 continues on to the next page.)
Hour Exam II Page No. 7 c) What are the concentrations of ammonium ion and iron(iii) ion left in solution after the reaction is complete? d) In part b), you started with 100.0 ml of 0.250 M iron(iii) chloride. How do you prepare such a solution in the lab if you started with solid iron(iii) chloride?