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CHEM 120 EXAM 3 QUIZ STUDY CORRECTLY ANSWERED AND RATED A
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CHEM 120 EXAM 3 QUIZ STUDY CORRECTLY ANSWERED AND RATED A
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CHEM 120 EXAM 3 QUIZ STUDY CORRECTLYANSWERED AND RATED A
1.
Question: Magnesium reacts with oxygen to form magnesium oxide, and the
following balanced chemical equation is given: 2 Mg + O₂ → 2 MgO. How many
moles of MgO are produced when 4 moles of O₂ react completely?
Correct Answer: 8 moles
Explanation: According to the balanced equation, 1 mole of O₂ reacts with 2
moles of Mg to form 2 moles of MgO. Therefore, 4 moles of O₂ would produce 8
moles of MgO.
2.
Question: (a) Determine the number of atoms for each element present in the
following molecule: Cu(CN)₂.
(b) Using the periodic table of elements, determine the molar mass for this
molecule. Show your work.
Correct Answer:
(a) Number of atoms:
• Cu = 1
• N=2
• C=2
(b) Atomic Mass:
• Cu = 63.546
• N = 14.007 (2)
• C = 12.01 (2)
Molar Mass: 115.6 g per mole
Explanation: To calculate the molar mass, sum the atomic masses of
each element in the molecule based on their quantities in the formula.
, 3.
Question: (a) Determine the number of atoms for each element present in the
following molecule: Mg(NO₃)₂.
(b) Using the periodic table of elements, determine the molar mass for this
molecule. Show your work.
Correct Answer:
(a) Number of atoms:
• Mg = 1
• N=2
• O=6
(b) Atomic Mass:
• Mg = 24.305
• O = 15.999
• N = 14.007
Molar Mass = 148.31 g per mole
Explanation: This involves counting the atoms in the formula and using
the atomic masses to calculate the molar mass.
4.
Question: You were asked to calculate the concentration of a NaCl (in water)
solution in several ways and are given the following information:
• 30 g NaCl
• 300 mL solution
• Molecular weight of NaCl = 58.44 g/mol
(a) Calculate the mass/volume percent concentration.
(b) Calculate the molarity of the solution.
Correct Answer:
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