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Fall 2015 Chem 1A, Test Review #1 1. Perform the following conversions: (a) 1.60 yard to centimeters (cm); (1 yard = 36 inches (exactly); 1 inch = 2.54 cm (exactly)) (b) 25 miles per gallon (mpg) to km per liter (kmpL); (1 mile = 1.609 km; 1 gallon = 3.7854 L) (c) 145 lb to kilograms. (1 lb = 453.6 g) (d) 115oF to degrees Celsius (oC) and to Kelvin, respectively. (e) The masses of four different samples of sodium chloride were measures as follows: 22.5 g, 5.238 g, 5,182 mg, and 723.5 mg. What is the total mass of salt with correct significant figures? 2. Indicate whether each of the following is a physical or chemical process: (a) Silver tarnishes; (b) Butter turns rancid; (c) Salt dissolves in water; (d) The toast is burnt; 3. (e) alcohol vaporizes; (f) the lake is frozen; (g) the wood is rotting; (h) The sugar has re-crystallized. Classify each of the following as an element, a compound, a homogeneous or heterogeneous mixture: (a) A bag of jelly beans; (b) A cup of pure cane sugar; (c) A bucket of muddy river water; (d) A glass of white wine; (e) A gallon of methanol; (f) A tank of gasoline; (g) A block of pure graphite. (h) A sac of saw dust. 4. A cylindrical metal bar that is 5.50 cm long weighs 19.70 g. The bar displaces 7.3 mL of water when completely submerged. Calculate the density the metal and the diameter of the bar? 5. Complete the following table for isotopes of elements. Name of Element Magnesium Atomic Number Mass Number Number of Protons 15 Number of Neutrons 13 16 Number of Electrons 10 Isotope Symbol 15 63 29 Cu 108 47 46 207 82 Pb2+ 1 Fall 2015 Chem 1A, Test Review #1 6. Tungsten exists in two naturally occurring isotopes with the following atomic masses and natural abundance: 185W (184.953 u; 37.07%) and 187W (186.956 u; 62.93%). Calculate the weighted average atomic mass of tungsten. 7. An element E reacts with oxygen gas to form an oxide with the formula E2O3. If the mass percent of oxygen in the oxide is 17.29%, calculate the atomic mass of E and identify the element. 8. Name each of the following compounds: 9. 10. (a) NH4NO3 : ________________________; (g) PCl5:____________________________ (b) Na2CO3: _______________________; (h) HBrO2:__________________________ (c) SiF4 :____________________________; (i) Fe(OH)3:_________________________; (d) K2HPO4:_________________________; (j) K2Cr2O7 :_________________________ (e) NiSO4:___________________________; (k) SF6 :______________________________ (f) CrCl36H2O: ______________________; (l) HIO4 :_____________________________ Write the correct formula of each of the following compounds: (a) Calcium hypochlorite: _____________; (g) Ammonium sulfate:____________ (b) Sodium phosphate: ___________; (h) Hydrosulfuric acid:______________ (c) Phosphoric acid: ____________; (i) Copper(II) sulfate pentahydrate: __________ (d) Lead(II) acetate:_______________; (j) Diboron trioxide:____________ (e) Carbon tetrachloride: __________; (k) Potassium permanganate: __________ (f) Lithium carbonate: _____________; (l) Barium hydroxide: __________ (a) A compound composed of 68.85% carbon, 4.95% hydrogen, and 26.20% oxygen, by mass, has a molecular mass of 122 amu. determine the empirical formula and the molecular formula of the compound. (b) When a 2.451-g sample of a compound that is composed of carbon, hydrogen and oxygen, is completely combusted, it produces 5.821 g of CO2 and 2.979 g of H2O. Determine the mass percent composition of the compound. Calculate the empirical formula of the compound. 2 Fall 2015 Chem 1A, Test Review #1 11. Write a balanced equation for each reaction described below: (a) Solid ammonium dichromate decomposes when heated to produce solid chromium(III) oxide, nitrogen gas, and water vapor. (b) Calcium metal reacts with water to produce aqueous calcium hydroxide and hydrogen gas. 12. Balance the following chemical equations using the smallest integer coefficients. (a) ___C4H10O(l) + ___O2(g) ___CO2(g) + ___H2O(g); (b) ___NH3(g) + ___O2(g) ___NO(g) + ___H2O(g); (c) ___Ca(NO3)2(aq) + ___Na3PO4(aq) ___Ca3(PO4)2(s) + ___NaNO3(aq) 13. The following equation represents the combustion of octane (C8H18): 2C8H18(l) + 25 O2(g) 16CO2(g) + 18H2O(g) (a) How many grams of O2 gas are consumed during the combustion of 345 g of octane? (b) How many grams of CO2 and H2O, respectively, are produced when 345 g of octane is completely combusted? 14. An ammonium phosphate fertilizer is prepared by the following reaction: 3NH3(g) + H3PO4(aq) (NH4)3PO4(s) (a) If a reaction uses 245 g H3PO4 and 115 g NH3, which is the limiting reagent? (b) How many grams of ammonium phosphate, (NH4)3PO4, will be produced when the limiting reactant is completely reacted and the reaction yield is 100%? (c) How many grams of (NH4)3PO4 are produced if the yield is 91.5%? (d) If 318 g of ammonium phosphate were produced, what is the percent yield? (e) How many grams of the excess reactant will remain unreacted at the end of the reaction? 15. Magnesium hydroxide, Mg(OH)2, decomposes when heated to form magnesium oxide and water vapor according the following equation: Mg(OH)2(s) MgO(s) + H2O(g) When a 5.00-g solid mixture that contains Mg(OH)2 and MgO is heated until all of the Mg(OH)2 in the mixture is completely decomposed, the solid residue that remains is found to weigh 3.65 g. (a) Calculate the mass and the number of moles of water vapor given off. (b) How many grams of Mg(OH)2 was present in the original mixture? (c) Calculate the mass percent of Mg(OH)2 in the mixture. 3 Fall 2015 Chem 1A, Test Review #1 Answers: (b) 11 KmpL (c) 65.8 kg (d) 46.1oC; 319.3K 1. (a) 146 cm 2. (a) Chemical change (e) Physical 3. (a) Heterogeneous mixture (d) Homogeneous mixture (g) Element 4. Density = 2.70 g/mL; 5. Element Atomic No. Magnesium 12 Phosphorus 15 Copper 29 Silver 47 Lead 82 6. Weighted average atomic mass of Tungsten = 186.21 amu 7. Atomic mass of element E = 114.8 amu = Sb 8. (a) Ammonium nitrate (d) Potassium hydrogen phosphate (b) Sodium carbonate (e) Nickel(II) sulfate (g) Phosphorus pentachloride (j) Potassium dichromate (h) Bromous acid (k) Sulfur hexafluoride (b) Chemical (f) Physical (c) Physical change (g) Chemical (e) 33.6 g (d) Chemical (h) Physical (b) Compound (c) Heterogeneous mixture (e) Compound (f) Homogeneous mixture (h) Heterogeneous mixture diameter = 1.30 cm (b) Na3PO4 (h) H2S Mass No. 25 31 63 108 207 # Protons 12 15 29 47 82 # Neutrons 13 16 34 61 125 # Electrons 10 15 29 46 80 Isotope 25 Mg2+ 31 P 63 Cu 108 Ag+ 207 Pb2+ (c) Silicon tetrafluoride (f) Chromium(III) chloride Hexahydrate (i) Iron(III) hydroxide (l) Periodic acid 9. (a) Ca(OCl)2 (g) (NH4)2SO4 (c) H3PO4 (d) Pb(C2H3O2)2 (i) CuSO4.5H2O (j) B2O3 10. (a) Empirical formula = C7H6O2 = Molecular formula (b) 64.83% C; 13.60% H and 21.57% O; empirical formula = C4H10O 11. (a) (NH4)2Cr2O7(s) Cr2O3(s) + N2(g) + 4H2O(g) (b) Ca(s) + 2H2O(l) Ca(OH)2(aq) + H2(g) 12. (a) C4H10O(l) + 6 O2(g) 4CO2(g) + 5H2O(g) (b) 4NH3(g) + 5 O2(g) 4NO(g) + 6H2O(g) (c) 3Ca(NO3)2(aq) + 2Na3PO4(aq) Ca3(PO4)2(s) + 6NaNO3(aq) 13. (a) Mass or O2 consumed = 1.21 x 103 g (b) Mass of CO2 produced = 1.06 x 103 g; (e) CCl4 (k) KMnO4 (f) Li2CO3 (l) Ba(OH)2 Mass of H2O produced = 490. G 14. (a) Mole of H3PO4 = 2.50 moles; mole of NH3 = 6.75 moles; NH3 is the limiting reactant; (b) Mass of (NH4)3PO4 = 336 g (at 100% yield); (c) = 307 g (at 91.5% yield; (d) % yield = 94.6%; (e) Mass of H3PO4 unreacted = 24.4 g 15. (a) Mass of H2O = 1.35 g; mole of H2O = 0.0749 mole; (b) Mass of Mg(OH)2 in mixture = 4.37 g; % of Mg(OH)2 in mixture = 87.4% 4