Chapter 7 - Chemical Formula Relationships
37) On a certain day a financial website quoted the price of gold at $1,258 per troy ounce (1 troy ounce = 31.1g). What is the price of a single atom of gold (Z=79)?
$1.32x10^-20
39) A person who sweetens coffee with two teaspoons of sugar, C₁₂H₂₂O₁₁, uses about 0.65 g. How many sugar molecules is this?
1.1x10^21 C₁₂H₂₂O₁₁ molecules
53) How many grams of the insecticide calcium chlorate must be measured if a sample is to contain 4.17 g chlorine?
12.2 g Ca(ClO₃)₂
45) Lithium fluoride is used as a flux when welding or soldering aluminum. How many grams of lithium are in 1.00 lb (454 g) of lithium fluoride?
121 g Li
47) Potassium sulfate is found in some fertilizers as a source of potassium. How many grams of potassium can be obtained from 57.4 g of the compound?
25.8 g K
49) Zinc cyanide (cyanide ion, CN⁻), is a compound used in zinc electroplating. How many grams of the compound must be dissolved in a test bath in a laboratory to introduce 146 g of zinc into the solution?
262 g Zn(CN)₂
51) Molybdenum (Z=42) is an element used in making steel alloys. It primarily comes from an ore called molybdenite, MoS₂. What mass of pure molybdenite must be treated to obtain 201 kg Mo?
335 kg MoS₂
13) Is the mole a number? Explain.
By definition, the mole is the amount of any substance that contains the same number of units as the number of atoms in exactly 12 g of carbon-12. The definition doesn't say what that number is. Through experiment, we have found that, to three significant figures, there are 6.02x10^23 atoms in 12 g of carbon-12.
61) A compound is 17.2% C, 1.44% H, and 81.4% F. Find its empirical formula.
CHF₃
65) A compound is 73.1% chlorine, 24.8% carbon, and the balance is hydrogen. If the molar mass of the compound is 97 g/mol, find the molecular formula.
Cl₂C₂H₂
69) Would you need a truck to transport 10^25 atoms of copper? Explain.
Hardly—the mass of 10^25 atoms of copper is 2 pounds.
1) How many atoms of each element are in a formula unit of aluminum nitrate?
Ag(NO₃)₃ - 1 aluminum atom; 3 nitrogen atoms; 9 oxygen atoms
5) Which of the three terms atomic mass, molecular mass, or formula mass is most appropriate for each of the following: ammonia, calcium oxide, barium, chlorine, sodium carbonate?
Atomic mass, Ba; molecular mass, NH₃ and Cl₂ because these are molecular substances; formula mass, all substances, but particularly CaO and Na₂CO₃ because neither of the other two terms technically fit these ionic compounds.
57) A certain compound is 52.2% carbon, 13.0% hydrogen, and 34.8% oxygen. Find the empirical formula of the compound.
C₂H₆O
63) An antifreeze and coolant widely used in automobile engines is 38.7% carbon, 9.7% hydrogen, and 51.6% oxygen. Its molar mass is 62.0 g/mol. What is the molecular formula of the compound?
C₂H₆O₂
55) Explain why C₆H₁₀ must be a molecular formula, whereas C₇H₁₀ could be a molecular formula, an empirical formula, or both.
C₆H₁₀ must be a molecular formula because both 6 and 10 are divisible by 2. Its empirical formula is C3H5. There is no common divisor for 7 and 10, so C₇H₁₀ can be an empirical formula. An empirical formula can also be a molecular formula.
68a) True or False? The term molecular mass applies mostly to ionic compounds.
False
68b) True or False? Molar mass is measured in atomic mass units.
False
68c) True or False? Grams are larger than atomic mass units; therefore, molar mass is numerically larger than atomic mass.
False
68d) True or False? The molar mass of hydrogen is read directly from the periodic table, whether it is monatomic hydrogen, H, or hydrogen gas, H₂.
False
68e) True or False? An empirical formula is always a molecular formula, although a molecular formula may or may not be an empirical formula.
False
59) A researcher exposes 11.89 g of iron to a stream of oxygen until it reacts to produce 16.99 g of a pure iron (III) oxide. What is the empirical formula of the product?
Fe₂O₃
3) Why is it proper to speak of the molecular mass of water but not of the molecular mass of sodium nitrate?
Molecular mass is a term properly applied only to substances that exist as molecules. Sodium nitrate is an ionic compound.
11) What do quantities representing 1 mole of iron atoms and 1 mole of ammonia molecules have in common?
The quantity of particles of each is the same; that is, the number of iron atoms and ammonia molecules is the same.
25) Find the number of moles for each mass of substance given. a) 0.797 g potassium iodate b) 68.6 g beryllium chloride c) 302 g nickel (II) nitrate
a) 0.00372 mol KIO₃ b) 0.858 mol BeCl₂ c) 1.65 mol Ni(NO₃)₂
23) Find the number of moles for each mass of substance given. a) 6.79 g oxygen b) 9.05 g magnesium nitrate c) 0.770 g aluminum oxide d) 659 g C₂H₅OH e) 0.394 g ammonium carbonate f) 34.0 g lithium sulfide
a) 0.212 mol O₂ b) 0.0610 mol Mg(NO₃)₂ c) 0.00755 mol Al₂O₃ d) 14.3 mol C₂H₅OH e) 0.00410 mol (NH₄)₂CO₃ f) 0.740 mol Li₂S
17) Calculate the number of moles in each of the following: a) 2.45x10^23 acetylene molecules, C₂H₂ b) 6.96x10^24 sodium atoms
a) 0.407 mol C₂H₂ b) 11.6 mol Na
35) Calculate the mass of each of the following. a) 4.30x10^21 molecules C₁₉H₃₇COOH b) 8.67x10^24 atoms of fluorine c) 7.23x10^23 formula units of nickel (II) chloride
a) 2.22 g C₁₉H₃₇COOH b) 274 g F c) 156 g NiCl₂
31) Calculate the number of atoms, molecules, or formula units that are in each given mass. a) 29.6 g lithium nitrate b) 0.151 g lithium sulfide c) 457 g iron (III) sulfate
a) 2.58x10^23 formula units LiNO₃ b) 1.98x10^21 formula units Li₂S c) 6.88x10^23 formula units Fe₂(SO₄)₃
27) Calculate the mass of each substance from the number of moles given. a) 0.769 mol lithium chloride b) 57.1 mol acetic acid, HC₂H₃O₂ c) 0.68 mol lithium d) 0.532 mol iron (III) sulfate e) 8.26 mol sodium acetate (acetate ion, C₂H₃O₂⁻)
a) 32.6 g LiCl b) 3.43x10^3 g HC₂H₃O₂ c) 4.7 g Li d) 213 g Fe₂(SO₄)₃ e) 678 g NaC₂H₃O₂
43) Calculate the percentage composition by mass of each compound. a) ammonium nitrate b) aluminum sulfate c) ammonium carbonate d) calcium oxide e) manganese (IV) sulfide
a) 35.00% N, 5.037% H, 59.96% O b) 15.77% Al, 28.11% S, 56.12% O c) 29.16% N, 8.392% H, 12.50% C, 49.95% O d) 71.47% Ca, 28.53% O e) 46.14% Mn, 53.86% S
15) Determine how many atoms, molecules, or formula units are in each of the following: a) 7.75 moles of methane, CH₄ b) 0.0888 mole of carbon monoxide c) 57.8 moles of iron d) 0.81 mole of magnesium chloride
a) 4.67x10^24 molecules CH₄ b) 5.35x10^22 molecules CO c) 3.48x10^25 atoms Fe d) 4.88x10^23 formula units MgCl₂
29) Calculate the mass of each substance from the number of moles given. a) 0.379 mol lithium sulfate b) 4.82 mol potassium oxalate (oxalate ion, C₂O₄²⁻) c) 0.132 mol lead (II) nitrate
a) 41.7 g Li₂SO₄ b) 801 g K₂C₂O₄ c) 43.7 g Pb(NO₃)₂
7) Find the formula mass of each of the following substances: a) Lithium chloride b) Aluminum carbonate c) Ammonium sulfate d) Butane, C₄H₁₀ e) Silver nitrate f) Manganese(IV) oxide g) Zinc phosphate
a) 42.39 u LiCl b) 233.99 u Al₂(CO₃)₃ c) 132.14 u (NH₄)₂SO₄ d) 58.12 u C₄H₁₀ e) 169.9 u AgNO₃ f) 86.94 u MnO₂ g) 386.08 u Zn₃(PO₄)₂
21) Find the molar mass of all the following substances: a) C₃H₈ b) C₆Cl₅OH c) nickel (II) phosphate d) zinc nitrate
a) 44.09 g/mol C₃H₈ b) 266.32 g/mol C₆Cl₅OH c) 366.01 g/mol Ni₃(PO₄)₂ d) 189.40 g/mol Zn(NO₃)₂
33) Calculate the number of atoms, molecules, or formula units that are in each given mass. a) 0.0023 g iodine molecules b) 114 g C₂H₄(OH)₂ c) 9.81 g chromium (III) sulfate
a) 5.5x10^18 molecules I₂ b) 1.11x10^24 molecules C₂H₄(OH)₂ c) 1.51x10^22 formula units Cr₂(SO₄)₃
9) What is the molecular mass of each of the following compounds? a) Sulfur trioxide, an atmospheric pollutant that reacts with water to form acid rain. b) Hydrogen fluoride, which will react with SbF₅ to form the strongest known superacid, HSbF₆.
a) 80.06 u SO₃ b) 20.01 HF
41a) What is the mass of 4.12x10^24 N atoms? b) What is the mass of 4.12x10^24 N₂ molecules? c) How many atoms are in 4.12 g N? d) How many molecules are in 4.12 g N₂? e) How many atoms are in 4.12 g N₂?
a) 95.9 g N b) 192 g N₂ c) 1.77x10^23 atoms N d) 8.85x10^22 N₂ molecules e) 1.77x10^23 atoms N
19) In what way are the molar mass of atoms and atomic mass the same?
numerically
