NAME: Exam 2 Introduction to General Chemistry Chem23/25 Spring 2011 Please write your name on every page. This exam is a closed-book, closed-notes exam. No outside material may be used and you may not discuss the exam with anyone else. The exam has 13 questions for a total of 94 points. The exam duration is 21/2 hours. Good luck! For grading purposes only: Pages Problems Points Grader 1 1 - 4 ____ ____ 2 5 - 7 ____ ____ 3 8 - 9 ____ ____ 4 10 – 12 ____ ____ 5 13 ____ ____ TOTAL ____ points _____ %NAME: 1 1. (a) Sketch a p-orbital. (2 points) (b) What is the maximum number of electrons the three 2p orbitals can hold? (2 points) 6 2. Write the electron configuration for the Zn2+ ion. (3 points) [Ar] 3d10 3. Based on their names, suggest molecular formulae for the following compounds. (2 point each, 10 points) (a) diphosphorus tetrabromide P2Br4 (b) dinitrogen trioxide N2O3 (c) carbon monoxide CO (d) carbon disulfide CS2 (e) nitrogen trifluoride NF3 4. Identify which of the following are covalent, and which are ionic compounds. (2 points each, 8 points) (a) magnesium phosphate ionic (b) nitric oxide (NO) covalent (c) beryllium oxide ionic (d) phosporus pentoxide covalentNAME: 2 5. Draw Lewis structures of ANY TWO of the covalent compounds in Questions 3 and 4. Include lone pairs of electrons where appropriate. It is not necessary to show the molecular geometry. (4 points each, 8 points) CO and CS2 are probably the easiest 6. Suggest the most likely ion for the following elements. The first is done for you. (2 points each, 8 points) (a) Mg Mg2+ (b) S S2- (c) Br Br- (d) Al Al3+ (e) Zn Zn2+ 7. Carbonate ion has the formula CO32-. Write molecular formulae for the following compounds. (2 points each, 8 points) (a) aluminum carbonate Al2(CO3)3 (b) silver(I) carbonate Ag2CO3 (c) lithium carbonate Li2CO3 (d) ammonium carbonate (NH4)2CO3 C OS C SNAME: 3 8. What is the percentage by weight of: (4 points each, 8 points) (a) calcium in calcium chloride calcium chloride is CaCl2 % weight = 40/111 x 100 = 36.0% (b) oxygen in copper(II) sulfate copper(II) sulfate is CuSO4 % weight = (4 x 16)/160 x 100 = 40.0% 9. Galactose is a sugar containing 40 % C, 7 % H and 53 % O by weight. (a) What is the empirical formula of galactose ? (5 points) ratio of elements is 40/12 : 7/1 : 53/16 which is 3.3 : 7.0 : 3.3 which simplifies to 1:2:1 So the empirical formula is CH2O (b) The molecular weight of galactose is 180 g/mol. What is the molecular formula of galactose ? (3 points) the empirical formula weight is 30 g/mol there are 6 empirical formula weights in the molecular weight so galactose is C6H12O6NAME: 4 10. “Laughing gas”, or nitrous oxide, has the molecular formula N2O. The central atom in the molecule is N. (a) Draw a Lewis structure for nitrous oxide including lone pairs of electrons where appropriate. (6 points) (b) What is the molecular geometry of nitrous oxide? (2 points) linear 11. Acetylene (HCCH) and hydrogen cyanide (HCN) both contain triple bonds. Which do you predict to have the higher boiling point, and why? (4 points) acetylene is a symmetrical linear molecule with no permanent dipole moment hydrogen cyanide is a linear molecule with a permanent dipole moment dipole-dipole intermolecular forces are stronger than London forces, stronger intermolecular forces require more energy to move a molecule from the liquid to the vapor phase, so HCN will have the higher boiling point 12. Classify the following reactions as single replacement, double replacement, decomposition or combination. (2 points each, 8 points) (a) Cu(s) + 2 AgNO3(aq) → Cu(NO3)2 + 2 Ag(s) single displacement (b) MgCO3(s) → MgO(s) + CO2(g) decompopsition (c) Fe2O3(s) + Al(s) → Fe(l) + Al2O3(s) single displacement (d) P2O5(s) + 3 H2O(l) → 2 H3PO4(aq) combination N N ONAME: 5 13. Write a balanced equation for the double replacement reaction between iron(III) carbonate and nitric acid (HNO3). See Question 7 for the formula of the carbonate ion. (5 points) Fe2(CO3)3 + 6 HNO3  2 Fe(NO3)3 + 3 H2CO3 (b) If 2.92 g of iron(III) carbonate are reacted with nitric acid, how many grams of iron(III) nitrate will be formed? (4 points) 2.92 g Fe2(CO3)3 = 0.01 mol 0.01 mol Fe2(CO3)3 gives 0.02 mol Fe(NO3)3 0.02 mol Fe(NO3)3 weighs 4.84