PRACTICE CHEMISTRY PLACEMENT EXAM
with Weblinks for SelfGuided Tutorial
 An atom with an electron configuration of 1s^{2} 2s^{2} 2p^{3} has how many valence electrons?
Khan Academy: Electron Configurations ; Wyzant: Atomic Structure 2
 3
 4
 5 (must use highest shell electrons only—2+3)
 7
 The ___ sublevel of an atom has a total of five orbitals.
Khan Academy: Quantum Numbers and Orbitals ; Wyzant: Atomic Structure
 s (all ssublevels have just one orbital)
 p (all psublevels have three orbitals)
 d
 f (all fsublevels have seven orbitals)
 g (all gsublevels have nine orbitals)
 You give a child a balloon, and he goes outside with it to play in the snow. Soon, he returns crying. What happened?
Khan Academy: Ideal Gas Equation ; Wyzant: Gases The balloon expanded and burst.
 The balloon froze solid.
 The balloon shrank. (pressure and temperature directly proportional)
 The balloon dissolved.
 The child forgot Charles’ Law.
 What kind of bonding occurs in the compound potassium oxide?
Khan Academy: Types of Chemical Bonds
 ionic (strongly metallic elements, K, and electronegative nonmetals, O, form ionic bonds)
 nonpolar covalent
 polar covalent (double bond)
 polar covalent (single bond)
 None of the above
 A gas with a temperature of 21.0^{o}C and a volume of 10.0 L is compressed to 5.00 L. What will be the new temperature?
Khan Academy: Ideal Gas Equation ; Wyzant: Gases
 10.5 ^{o}C (don’t forget to change temperatures to Kelvin)
 420. ^{o}C (don’t forget how to change to Kelvin back to Celsius)
 42.0 ^{o}C (several of the above went wrong!)
 –126 ^{o}C
 315 ^{o}C (mixed up initial and final conditions)
 Which of the following sublevels does not exist as written?
Khan Academy: Quantum Numbers and Orbitals
 3f (the fourth fsublevel appears for the first time in the fourth shell)
 6f
 2s
 5d
 8s (the number of sublevels—s, p, d, f, etc.—increase by one as the main energy level increases by one)
 What is the molecular shape of PH_{3}?
Khan Academy: Hybridization and Hybrid Orbitals
 tetrahedral (the lone electron pair isn’t counted in the shape)
 trigonal planar (don’t forget to include the lone electron pair)
 bent
 linear
 trigonal pyramidal
 What is the percent by mass concentration of sodium bromide in a solution which contains 50.0 g of sodium bromide in 200.0 g of water?
Wyzant: Solutions
 40.0 %
 20.0 %
 25.0 % (forgot to add 50+250 for the total solution mass)
 33.3 %
 50.0 %
 How many milliliters of 6.00 M HCl solution would be required to prepare 2.00 L of 0.140 M HCl by dilution?
Wyzant: Solutions
 420 mL (mixed up which volume needed to calculate total moles HCl)
 168 mL
 85.6 mL (moles x volume gives moles)
 46.7 mL (2.00 x 0.140 gives total moles HCl; dividing that by 6.00 gives volume needed)
 30.0 mL
 What is the molar concentration of 2000. mL of aqueous solution containing 135 g of glucose, C6H12O6?
Wyzant: Solutions ; Khan Academy: Introduction to the Atom 12.15 M (don’t forget how to correctly convert grams to moles)
 0.750 M
 67.5 M (don’t forget to change grams to moles)
 0.667 M
 0.375 M
 What is the formula of copper (II) sulfate pentahydrate?
Wyzant: Compounds Cu_{2}(SO_{4})_{2} . 5 H_{2}O (ionic compounds written with simplest subscripts)
 Cu_{2}(SO_{4}) . 5 H_{2}O (wrong charges on your ions)
 CuSO_{4} . 6 H_{2}O (hexahydrate would be the correct name here)
 CuSO_{4} . 5 H_{2}O
 None of the above
 What is the electron configuration for the nitride ion?
Khan Academy: Electron Configurations ; Wyzant: Compounds 1s^{2} 2s^{2} 2p^{1}
 1s^{2} 2s^{2} 2p^{3} (this is just a nitrogen atom by itself)
 1s^{2} 2s^{2} 2p^{5} (nitrogen needs to add three electrons to achieve the noble gas configuration)
 1s^{2} 2s^{2} 2p^{6} (nitride has a negative three charge—adding three electrons to the Natom)
 None of the above
 A tank has a pressure of 30.0 atm at a temperature of 22.0oC. After heating, the temperature rises to
35.0^{o}C. What is the new pressure?
Khan Academy: Ideal Gas Equation ; Wyzant: Gases 54.3 atm
 31.3 atm
 28.7 atm (mixed up initial and final conditions—pressure should go up!)
 47.7 atm (don’t forget to change temperature to Kelvin)
 30.6 atm
 Which pair is immiscible?
Wyzant: Solutions ; Khan Academy: Solubility ethanol and water (both are polar)
 water and octane, C_{8}H_{18} (like dissolves like—water is polar, while octane is nonpolar)
 isopropyl alcohol and water
 acetic acid and water (both are polar)
 octane and oil (both are nonpolar)
 How many grams of sodium hydroxide are required to prepare 250.0 mL of a 6.00 M solution?
Wyzant: Solutions ; Khan Academy: Introduction to the Atom 1.50 g (these are the moles of sodium hydroxide needed—be sure to convert to grams)
 0.0375 g (don’t forget how to convert moles to grams)
 0.600 g (incorrect conversion of mL to L)
 3.75 g (combined errors from b and c)
 60.0 g
 5.60 L of a gas at STP has a mass of 13.0 g. What is the molar mass of the gas?
Khan Academy: Ideal Gas Equation ; Wyzant: Gases
 33.2 g/mol (keep in mind that STP = 273 K, 1 atm)
 66.4 g/mol (1 mol of gas at STP = 22.4 L)
 26.0 g/mol
 52.0 g/mol
 none of the above
 What volume of 0.62 M sodium hydroxide is required to neutralize 20.00 mL of 0.391 M nitric acid? Word reaction with reactants only. (Students should predict products): Sodium hydroxide + nitric acid
Khan Academy: Balancing Chemical Equations ; Wyzant: Reactions , Basic Stoichiometry
 23.6 mL
 16.9 mL
 9.03 mL
 11.8 mL
 none of the above (correct amount is 12.6 mL; the two reactants are in a 1:1 mol ratio)
 How many moles are in 20.0 g of sodium carbonate?
Khan Academy: Introduction to the Atom ; Wyzant: Moles and Percentages 1.89 mol (no unit conversions of grams are required)
 212 mol
 2.12 x 10^{3} mol (remember how to correctly convert grams to moles)
 0.189 mol
 18.9 mol (no unit conversions of grams are required)
 The percent of nitrogen in magnesium nitride is
Khan Academy: Molecular Composition ; Wyzant: Moles and Percentages , Compounds 27.8%
 36.6% (write correct formula for compound, remembering monatomic charges)
 16.1%
 72.2% (this is the mass percent of magnesium)
 63.4% (write correct formula for compound, remembering monatomic charges)
 What is the molar concentration of 250. mL of aqueous solution containing 48.8 g of glucose, C6H12O6?
Wyzant: Solutions ; Khan Academy: Introduction to the Atom 5.12 M (combination of errors from b and e)
 0.923 M (inverted the definition of molarity = moles ÷ volume in liters)
 0.271 M
 1.08 M
 0.195 M (must convert grams to moles first)
 How many grams of aluminum metal will react with 0.0500 mole of oxygen gas according to the unbalanced equation given? Aluminum + Oxygen > Aluminum Oxide
Khan Academy: Stoichiometry ; Wyzant: Basic Stoichiometry 1.35 g (first balance equation to convert moles diatomic oxygen to moles aluminum)
 1.01 g
 4.32 g
 2.06 g
 1.80 g
 For the equation given, how many grams of methane will react with 125 g of oxygen? Word reaction with reactants only. (Students should predict products):
Methane (CH_{4}) burns in oxygen
Khan Academy: Stoichiometry ; Wyzant: Basic Stoichiometry 39.1 g
 19.5 g
 15.6 g
 31.3 g
 62.5 g (must use diatomic oxygen and its molar mass in this calculation)

For problems 24  25, Given the word reaction with reactants only (students should predict products):
phosphoric acid reacts with magnesium carbonate  From the balanced chemical equation the simplest whole number coefficient for the product magnesium phosphate is:
Khan Academy: Balancing Chemical Equations ; Wyzant: Reactions 1
 2 (be sure to use correct charges on ions when balancing)
 3
 4
 none of the above
 If 50.0 g of magnesium carbonate reacts completely with phosphoric acid, the grams of gas produced is:
Khan Academy: Balancing Chemical Equations ; Wyzant: Reactions , Basic Stoichiometry
 52.2 g
 26.1 g
 13.1 g
 50.0 g (balance the equation to start, then convert reactant grams to moles)
 55.0 g (the gas produced is carbon dioxide, molar mass = 44.01 g/mol)
 How many molecules are in 5.8 g of acetone, C_{3}H_{6}O?
Khan Academy: Atomic Mass and Moles ; ChemTutor: Moles and Percentages 0.10 molecules (this is the number of moles, not molecules)
 6.0 x 1022 molecules
 3.5 x 1024 molecules
 6.0 x 1023 molecules (this is roughly Avogadro’s number, the number molecules in a mol)
 none of the above
 This reaction is an example of which of the following types? Aluminum reacts with bromine to produce aluminum bromide
Wyzant: Reactions combination (two or more reactants produce a single product)
 single displacement
 decomposition
 gas formation
 precipitation
 What is the simplest whole number coefficient for aluminum bromide in the above reaction (#27)?
Khan Academy: Balancing Chemical Equations ; Wyzant: Reactions
 1 (recall that bromine is diatomic, as well as the correct charges on the monatomic ions)
 2
 3
 4
 none of the above
 How many moles of oxygen are required for the complete reaction of 45 g of C_{2}H_{4} when it is burned?
Khan Academy: Balancing Chemical Equations , Stoichiometry ; Wyzant: Reactions , Basic Stoichiometry 1.3 x 102 mol (balance the equation to start, then convert reactant grams to moles)
 0.64 mol
 112.4 mol
 4.8 mol
 none of the above
 If 14.0 g of C_{2}H_{4} is burned and the actual yield of water is 7.84 g, the percent yield in the reaction is:
Khan Academy: Balancing Chemical Equations, Stoichiometry; Wyzant: Reactions , Stoichiometry 0.56%
 43.6%
 87.1% (be sure to balance the equation and convert moles reactant to moles product)
 56.0%
 82.0%
Answers:
1d 2c 3c 4a 5d 6a 7e 8b 9d 10e 11d 12d 13b 14b 15e 16d 17e 18d 19a 20d 21e 22d 23(NA) 24a 25b 26b 27a 28b 29d 30b