Chapter Questions
How many atoms of each element are in a formula unit of aluminum nitrate?
How many atoms of each element are in a formula unit of ammonium phosphate?
Why is it proper to speak of the molecular mass of water but not of the molecular mass of sodium nitrate?
It may be said that because atomic, molecular, and formula masses are all based on carbon- $12,$ they are conceptually alike. What then are their differences?
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?
In what units are atomic, molecular, and formula mass expressed? Define those units.
Find the formula mass of each of the following substances:a) Lithium chlorideb) Aluminum carbonatec) Ammonium sulfated) Butane, $C_{4} H_{10}$ (molecular mass)e) Silver nitratef) Manganese(IV) oxideg) Zinc phosphate
Determine the formula or molecular mass of each substance in the following list:a) Nitrogen trifluorideb) Barium chloridec) Lead(II) phosphate
What do quantities representing one mole of iron atoms and one mole of ammonia molecules have in common?
Explain what the term mole means. Why is it used in chemistry?
Is the mole a number? Explain.
Give the name and value of the number associated with the mole.
Determine how many atoms or molecules are in each of the following:a) 7.75 moles of methane, $\mathrm{CH}_{4}$b) 0.0888 mole of carbon monoxidec) 57.8 moles of iron
a) How many molecules of boron trifluoride are present in 1.25 moles of this compound?b) How many moles of boron trifluoride are present in $7.04 \times 10^{22}$ molecules of this compound?c) How many moles of nitrogen dioxide are present in $7.89 \times 10^{22}$ molecules of this compound?d) How many molecules of nitrogen dioxide are present in 1.60 moles of this compound?
Calculate the number of moles in each of the following:a) $2.45 \times 10^{23}$ acetylene molecules, $\mathrm{C}_{2} \mathrm{H}_{2}$b) $6.96 \times 10^{24}$ sodium atoms
a) How many atoms of hydrogen are present in 2.69 moles of water?b) How many moles of oxygen are present in $1.39 \times 10^{22}$ molecules of water?
In what way are the molar mass of atoms and atomic mass the same?
How does molar mass differ from molecular mass?
Find the molar mass of all the following substances.a) $C_{3} H_{8}$b) $C_{6} C l_{5} O H$c) Nickel phosphated) Zinc nitrate
Calculate the molar mass of each of the following: a) Chromium(II) iodideb) Silicon dioxidec) Carbon tetrafluoride
Find the number of moles for each mass of substance given.a) 6.79 g oxygenb) $9.05 \mathrm{g}$ magnesium nitratec) $0.770 \mathrm{g}$ aluminum oxided) $659 \mathrm{g} \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}$e) $0.394 \mathrm{g}$ ammonium carbonatef) $34.0 \mathrm{g}$ lithium sulfide
Find the number of moles for each mass of substance given.a) $53.8 \mathrm{g}$ berylliumb) $781 \mathrm{g} \mathrm{C}_{3} \mathrm{H}_{4} \mathrm{Cl}_{4}$c) 0.756 g calcium hydroxided) 9.94 g cobalt(III) bromidee) $8.80 \mathrm{g}$ ammonium dichromate (dichromate ion, $\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}$ )f) $28.3 \mathrm{g}$ magnesium perchlorate
Find the number of moles for each mass of substance given.a) 0.797 g potassium iodateb) $68.6 \mathrm{g}$ beryllium chloridec) 302 g nickel nitrate
Find the number of moles for each mass of substance given.a) 91.9 g sodium hypochloriteb) $\left.881 \mathrm{g} \text { aluminum acetate (acetate ion, } \mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}^{-}\right)$c) $0.586 \mathrm{g}$ mercury(I) chloride
Calculate the mass of each substance from the number of moles given.a) 0.769 mol lithium chlorideb) 57.1 mol acetic acid, $\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}$c) 0.68 mol lithiumd) 0.532 mol iron(III) sulfatee) 8.26 mol sodium acetate (acetate ion, $\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}^{-}$ )
Calculate the mass of each substance from the number of moles given.a) 0.542 mol sodium hydrogen carbonateb) 0.0789 mol silver nitratec) 9.61 mol sodium hydrogen phosphated) 0.903 mol calcium bromatee) 1.14 mol ammonium sulfite
Calculate the mass of each substance from the number of moles given.a) 0.379 mol lithium sulfateb) 4.82 mol potassium oxalate (oxalate ion, $\mathrm{C}_{2} \mathrm{O}_{4}^{2-}$ )c) 0.132 mol lead(II) nitrate
Calculate the mass of each substance from the number of moles given.a) 0.819 mol manganese(IV) oxideb) 8.48 mol aluminum chloratec) 0.926 mol chromium(II) chloride
Calculate the number of atoms, molecules, or formula units that are in each given mass.a) 29.6 g lithium nitrateb) $0.151 \mathrm{g}$ lithium sulfidec) 457 g iron(III) sulfate
Calculate the number of atoms, molecules, or formula units that are in each given mass.a) 85.5 g beryllium nitrateb) 9.42 g manganesec) $0.0948 \mathrm{g} \mathrm{C}_{3} \mathrm{H}_{7} \mathrm{OH}$
Calculate the number of atoms, molecules, or formula units that are in each given mass.a) $0.0023 \mathrm{g}$ iodine moleculesb) $114 \mathrm{g} \mathrm{C}_{2} \mathrm{H}_{4}(\mathrm{OH})_{2}$c) $9.81 \mathrm{g}$ chromium(III) sulfate
Calculate the number of atoms, molecules, or formula units that are in each given mass.a) 7.70 g iodine atomsb) $0.447 \mathrm{g} \mathrm{C}_{9} \mathrm{H}_{20}$c) 72.6 g manganese(II) carbonate
Calculate the mass of each of the following.a) $4.30 \times 10^{21}$ molecules of $\mathrm{C}_{19} \mathrm{H}_{37} \mathrm{COOH}$b) $8.67 \times 10^{24}$ atoms of fluorinec) $7.23 \times 10^{23}$ formula units of nickel chloride
Calculate the mass of each of the following.a) $2.58 \times 10^{23}$ formula units of iron(II) oxideb) $8.67 \times 10^{24}$ molecules of fluorinec) $7.36 \times 10^{23}$ atoms of gold $(Z=79)$
On a certain day the financial pages quoted the price of gold at $\$ 478$ per troy ounce (1 troy ounce $=31.1 \mathrm{g}$ ). What is the price of a single atom of gold $(Z=79) ?$
How many carbon atoms has a gentleman given his bride-to- be if the engagement ring has a 0.500 -carat diamond? There are$200 \mathrm{mg}$ in a carat. (The price of diamonds doesn't seem so high when figured at dollars per atom.)
A person who sweetens coffee with two teaspoons of sugar, $\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11},$ uses about $0.65 \mathrm{g} .$ How many sugar molecules is this?
The mass of one gallon of gasoline is about 2.7 kg. Assuming the gasoline is entirely octane, $C_{8} H_{18},$ calculate the number of molecules in the gallon.
The stable form of certain elements is a two-atom molecule. Fluorine and nitrogen are two of those elements. Keep in mind that the chemical formula of a molecule identifies precisely what is in the individual molecule.a) What is the mass of $4.12 \times 10^{24} \mathrm{N}$ atoms?b) What is the mass of $4.12 \times 10^{24} \mathrm{N}_{2}$ molecules?c) How many atoms are in $4.12 \mathrm{g} \mathrm{N} ?$d) How many molecules are in $4.12 \mathrm{g} \mathrm{N}_{2} ?$e) How many atoms are in $4.12 \mathrm{g} \mathrm{N}_{2} ?$
The stable form of certain elements is a two-atom molecule. Fluorine and nitrogen are two of those elements. Keep in mind that the chemical formula of a molecule identifies precisely what is in the individual molecule.a) How many molecules are in $3.61 \mathrm{g} \mathrm{F}_{2} ?$b) How many atoms are in $3.61 \mathrm{g} \mathrm{F}_{2} ?$c) How many atoms are in $3.61 \mathrm{g}$ F?d) What is the mass of $3.61 \times 10^{23} \mathrm{F}$ atoms?e) What is the mass of $3.61 \times 10^{23} \mathrm{F}_{2}$ molecules?
Calculate the percentage composition of each compound.a) Ammonium nitrateb) Aluminum sulfatec) Ammonium carbonated) Calcium oxidee) Manganese(IV) sulfide
Calculate the percentage composition of each compound.a) Magnesium nitrateb) Sodium phosphatec) Copper(II) chlorided) Chromium(III) sulfatee) Silver carbonate
Lithium fluoride is used as a flux when welding or soldering aluminum. How many grams of lithium are in 1.00 lb $(454 \mathrm{g})$ of lithium fluoride?
Ammonium bromide is a raw material in the manufacture of photographic film. What mass of bromine is found in $7.50 \mathrm{g}$ of the compound?
Potassium sulfate is found in some fertilizers as a source of potassium. How many grams of potassium can be obtained from $57.4 \mathrm{g}$ of the compound?
Magnesium oxide is used in making bricks to line very-high- temperature furnaces. If a brick contains $1.82 \mathrm{kg}$ of the oxide, what is the mass of magnesium in the brick?
Zinc cyanide, $\mathrm{Zn}(\mathrm{CN})_{2},$ is a compound used in zinc electro- plating. How many grams of the compound must be dissolved in a test bath in a laboratory to introduce $146 \mathrm{g}$ of zinc into the solution?
An experiment requires that enough $\mathrm{C}_{5} \mathrm{H}_{12} \mathrm{O}$ be used to yield 19.7 g of oxygen. How much $C_{5} \mathrm{H}_{12} \mathrm{O}$ must be weighed out?
Molybdenum $(Z=42)$ is an element used in making steel alloys. It comes from an ore called wulfenite, $\mathrm{PbMoO}_{4}$. What mass of pure wulfenite must be treated to obtain $201 \mathrm{kg}$ Mo?
How many grams of nitrogen monoxide must be weighed out to get a sample of nitrogen monoxide that contains 14.7 g of oxygen?
How many grams of the insecticide calcium chlorate must be measured if a sample is to contain 4.17 g chlorine?
If a sample of carbon dioxide contains $16.4 \mathrm{g}$ of oxygen, how many grams of carbon dioxide does it contain?
Explain why $\mathrm{C}_{6} \mathrm{H}_{10}$ must be a molecular formula, while $\mathrm{C}_{7} \mathrm{H}_{10}$ could be a molecular formula, an empirical formula, or both.
From the following list, identify each formula that could be an empirical formula. Write the empirical formulas of any compounds that are not already empirical formulas. $\mathrm{C}_{2} \mathrm{H}_{6} \mathrm{O} ; \mathrm{Na}_{2} \mathrm{O}_{2}$ $\mathrm{C}_{2} \mathrm{H}_{4} \mathrm{O}_{2} ; \mathrm{N}_{2} \mathrm{O}_{5}$
A certain compound is $52.2 \%$ carbon, $13.0 \%$ hydrogen, and $34.8 \%$ oxygen. Find the empirical formula of the compound.
A compound is found to contain $15.94 \%$ boron and $84.06 \%$ fluorine by mass. What is the empirical formula for this compound?
A researcher exposes $11.89 \mathrm{g}$ of iron to a stream of oxygen until it reacts to produce 16.99 g of a pure oxide of iron. What is the empirical formula of the product?
A compound is found to contain $39.12 \%$ carbon, $8.772 \%$ hydrogen, and $52.11 \%$ oxygen by mass. What is the empirical formula for this compound?
A compound is $17.2 \%$ C, $1.44 \%$ H, and $81.4 \%$ F. Find its empirical formula.
A compound is found to contain $21.96 \%$ sulfur and 78.04\% fluorine by mass. What is the empirical formula for this compound?
A 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?
A compound is found to contain $31.42 \%$ sulfur, $31.35 \%$ oxygen, and $37.23 \%$ fluorine by mass. What is the empirical formula for this compound? The molar mass for this compound is $102.1 \mathrm{g} / \mathrm{mol} .$ What is the molecular formula for this compound?
A compound is $73.1 \%$ chlorine, $24.8 \%$ carbon, and the balance is hydrogen. If the molar mass of the compound is $97 \mathrm{g} / \mathrm{mol}$, find the molecular formula.
A compound is found to contain $25.24 \%$ sulfur and $74.76 \%$ fluorine by mass. What is the empirical formula for this compound? The molar mass for this compound is $254.1 \mathrm{g} / \mathrm{mol}$. What is the molecular formula for this compound?
Distinguish precisely and in scientific terms the differences among items in each of the following groups.a) Atomic mass, molecular mass, formula mass, molar massb) Molecular formula, empirical formula
Classify each of the following statements as true or false:a) The term molecular mass applies mostly to ionic compounds.b) Molar mass is measured in atomic mass units.c) Grams are larger than atomic mass units; therefore, molar mass is numerically larger than atomic mass.d) The molar mass of hydrogen is read directly from the periodic table, whether it is monatomic hydrogen, H, or hydrogen gas, $\mathrm{H}_{2}$e) An empirical formula is always a molecular formula, although a molecular formula may or may not be an empirical formula.
Would you need a truck to transport $10^{25}$ atoms of copper? Explain.
The stable form of elemental phosphorus is a tetratomic molecule. Calculate the number of molecules and atoms in $85.0 \mathrm{g} \mathrm{P}_{4}$
Is it reasonable to set a dinner table with one mole of salt, NaCl, in a salt shaker with a capacity of 2 oz? How about one mole of sugar, $\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11},$ in a sugar bowl with a capacity of 10 oz?
The quantitative significance of "take a deep breath" varies, of course, with the individual. When one person did so, he found that he inhaled $2.95 \times 10^{22}$ molecules of the mixture of mostly nitrogen and oxygen we call air. Assuming this mixture has an average molar mass of $29 \mathrm{g} / \mathrm{mol}$, what is his apparent lung capacity in grams of air?
Assuming gasoline to be pure octane, $\mathrm{C}_{8} \mathrm{H}_{18}$ (actually, it is a mixture of many substances), an automobile getting 25.0 miles per gallon would consume $5.62 \times 10^{23}$ molecules per mile. Calculate the mass of this amount of fuel.
A researcher took $27.37 \mathrm{g}$ of a certain compound containing only carbon and hydrogen and burned it completely in pure oxygen. All the carbon was changed to $85.9 \mathrm{g}$ of $\mathrm{CO}_{2}$, and all the hydrogen was changed to $35.5 \mathrm{g}$ of $\mathrm{H}_{2} \mathrm{O}$. What is the empirical formula of the original compound? (Hint: Find the mass in grams of carbon and hydrogen in the original compound.)
$\mathrm{Co}_{a} \mathrm{S}_{b} \mathrm{O}_{c} \cdot X \mathrm{H}_{2} \mathrm{O}$ is the general formula of a certain hydrate. When 43.0 g of the compound is heated to drive off the water, $26.1 \mathrm{g}$ of anhydrous compound is left. Further analysis shows that the percentage composition of the anhydrate is $42.4 \%$ Co, $23.0 \%$ S, and $34.6 \%$ O. Find the empirical formula of (a) the anhydrous compound and (b) the hydrate. (Hint: Treat the anhydrous compound and water just as you have treated elements in calculating $X$ in the formula of the hydrate.)