Chapter 2

Calculate the amount (moles) represented by each of the following: (a) \(127.08 \mathrm{g}\) of \(\mathrm{Cu}\) (b) 0.012 g of lithium (c) 5.0 mg of americium (d) 6.75 g of Al

You are given 1.0 -g samples of He, Fe, Li, Si, and C. Which sample contains the largest number of atoms? Which contains the smallest?

You are given 0.10 -g samples of \(\mathrm{K},\) Mo, \(\mathrm{Cr}\), and \(\mathrm{Al}\). List the samples in order of the amount (moles), from smallest to largest.

Analysis of a 10.0 -g sample of apatite (a major component of tooth enamel) showed that it was made up of \(3.99 \mathrm{g} \mathrm{Ca}, 1.85 \mathrm{g} \mathrm{P}, 4.14 \mathrm{g} \mathrm{O},\) and \(0.020 \mathrm{g} \mathrm{H} .\) I ist these elements based on relative amounts (moles), from smallest to largest.

A semiconducting material is composed of 52 g of Ga, \(9.5 \mathrm{g}\) of \(\mathrm{Al},\) and \(112 \mathrm{g}\) of As. Which element has the largest number of atoms in this material?

Calculate the molar mass of each of the following compounds: (a) \(\mathrm{Fe}_{2} \mathrm{O}_{3},\) iron (III) oxide (b) \(\mathrm{BCl}_{3},\) boron trichloride (c) \(\left.\mathrm{C}_{6} \mathrm{H}_{8} \mathrm{O}_{6}, \text { ascorbic acid (vitamin } \mathrm{C}\right)\)

Calculate the molar mass of each of the following compounds: (a) \(\mathrm{Fe}\left(\mathrm{C}_{6} \mathrm{H}_{11} \mathrm{O}_{7}\right)_{2},\) iron (II) gluconate, a dietary supplement (b) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{SH},\) butanethiol, has a skunk-like odor (c) \(\mathrm{C}_{20} \mathrm{H}_{24} \mathrm{N}_{2} \mathrm{O}_{2},\) quinine, used as an antimalarial drug

Calculate the molar mass of each hydrated compound. Note that the water of hydration is included in the molar mass. (See Section 2.11.) (a) \(\mathrm{Ni}\left(\mathrm{NO}_{3}\right)_{2} \cdot 6 \mathrm{H}_{2} \mathrm{O}\) (b) \(\mathrm{CuSO}_{4} \cdot 5 \mathrm{H}_{2} \mathrm{O}\)

Calculate the molar mass of each hydrated compound. Note that the water of hydration is included in the molar mass. (See Section \(2.11 .)\) (a) \(\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4} \cdot 2 \mathrm{H}_{2} \mathrm{O}\) (b) \(\mathrm{MgSO}_{4} \cdot 7 \mathrm{H}_{2} \mathrm{O},\) Epsom salt

What mass is represented by 0.0255 mol of each of the following compounds? (a) \(\mathrm{C}_{3} \mathrm{H}_{7} \mathrm{OH},\) 2-propanol, rubbing alcohol (b) \(\mathrm{C}_{11} \mathrm{H}_{16} \mathrm{O}_{2},\) an antioxidant in foods, also known as BHA (butylated hydroxyanisole) (c) \(\mathrm{C}_{9} \mathrm{H}_{8} \mathrm{O}_{4},\) aspirin (d) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CO},\) acetone, an important industrial solvent

Sulfur trioxide, \(\mathrm{SO}_{3},\) is made industrially in enormous quantities by combining oxygen and sulfur dioxide, SO \(_{2} .\) What amount (moles) of \(\mathrm{SO}_{3}\) is represented by \(1.00 \mathrm{kg}\) of sulfur trioxide? How many molecules? How many sulfur atoms? How many oxygen atoms?

How many ammonium ions and how many sulfate ions are present in an 0.20 mol sample of \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4} ?\) How many atoms of \(\mathrm{N}, \mathrm{H}, \mathrm{S}\) and \(\mathrm{O}\) are contained in this sample?

An Alka-Seltzer tablet contains 324 mg of aspirin \(\left(\mathrm{C}_{9} \mathrm{H}_{8} \mathrm{O}_{4}\right), 1904 \mathrm{mg}\) of \(\mathrm{NaHCO}_{3},\) and \(1000 .\) mg of citric \(\operatorname{acid}\left(\mathrm{H}_{3} \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{O}_{7}\right) .\) (The last two compounds react with each other to provide the "fizz," bubbles of \(\mathrm{CO}_{2},\) when the tablet is put into water.) (a) Calculate the amount (moles) of each substance in the tablet. (b) If you take one tablet, how many molecules of aspirin are you consuming?

Calculate the mass percent of each element in the following compounds: (a) PbS, lead(II) sulfide, galena (b) \(\mathrm{C}_{3} \mathrm{H}_{8},\) propane (c) \(\mathrm{C}_{10} \mathrm{H}_{14} \mathrm{O},\) carvone, found in caraway seed oil

Calculate the mass percent of each element in the following compounds: (a) \(\mathrm{C}_{8} \mathrm{H}_{10} \mathrm{N}_{2} \mathrm{O}_{2},\) caffeine (b) \(\mathrm{C}_{10} \mathrm{H}_{20} \mathrm{O},\) menthol (c) \(\mathrm{CoCl}_{2} \cdot 6 \mathrm{H}_{2} \mathrm{O}\)

Calculate the mass percent of copper in CuS, copper(II) sulfide. If you wish to obtain \(10.0 \mathrm{g}\) of copper metal from copper(II) sulfide, what mass of CuS (in grams) must you use?

Succinic acid occurs in fungi and lichens. Its empirical formula is \(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2},\) and its molar mass is \(118.1 \mathrm{g} / \mathrm{mol}\) What is its molecular formula?

An organic compound has the empirical formula \(\mathrm{C}_{2} \mathrm{H}_{4} \mathrm{NO} .\) If its molar mass is \(116.1 \mathrm{g} / \mathrm{mol},\) what is the molecular formula of the compound?

Acetylene is a colorless gas used as a fuel in welding torches, among other things. It is \(92.26 \%\) C and \(7.74 \%\) H. Its molar mass is \(26.02 \mathrm{g} / \mathrm{mol} .\) What are the empirical and molecular formulas of acetylene?

A large family of boron-hydrogen compounds has the general formula \(\mathrm{B}_{x} \mathrm{H}_{y}\). One member of this family contains \(88.5 \%\) B; the remainder is hydrogen. What is its empirical formula?

Cumene, a hydrocarbon, is a compound composed only of \(\mathrm{C}\) and \(\mathrm{H}\). It is \(89.94 \%\) carbon, and its molar mass is \(120.2 \mathrm{g} / \mathrm{mol} .\) What are the empirical and molecular formulas of cumene?

In \(2006,\) a Russian team discovered an interesting molecule they called "sulflower" because of its shape and because it was based on sulfur. It is composed of \(57.17 \%\) S and \(42.83 \%\) C and has a molar mass of \(448.70 \mathrm{g} / \mathrm{mol} .\) Determine the empirical and molecular formulas of "sulflower."

Mandelic acid is an organic acid composed of carbon \((63.15 \%),\) hydrogen \((5.30 \%),\) and oxygen \((31.55 \%) .\) Its molar mass is \(152.14 \mathrm{g} / \mathrm{mol} .\) Determine the empirical and molecular formulas of the acid.

Nicotine, a poisonous compound found in tobacco leaves, is \(74.0 \% \mathrm{C}, 8.65 \% \mathrm{H},\) and \(17.35 \% \mathrm{N} .\) Its molar mass is \(162 \mathrm{g} / \mathrm{mol} .\) What are the empirical and molecular formulas of nicotine?

A compound containing xenon and fluorine was prepared by shining sunlight on a mixture of \(\mathrm{Xe}(0.526 \mathrm{g})\) and excess \(\mathrm{F}_{2}\) gas. If you isolate \(0.678 \mathrm{g}\) of the new compound, what is its empirical formula?

Elemental sulfur \((1.256 \mathrm{g})\) is combined with fluorine, \(\mathrm{F}_{2},\) to give a compound with the formula \(\mathrm{SF}_{x},\) a very stable, colorless gas. If you have isolated \(5.722 \mathrm{g}\) of \(\mathrm{SF}_{x}\) what is the value of \(x ?\)

Zinc metal ( \(2.50 \mathrm{g}\) ) combines with \(9.70 \mathrm{g}\) of iodine to produce zinc iodide, \(\mathrm{Zn}_{x} \mathrm{I}_{y}\). What is the formula of this ionic compound?

You combine 1.25 g of germanium, Ge, with excess chlorine, \(\mathrm{Cl}_{2} .\) The mass of product, \(\mathrm{Ge}_{x} \mathrm{Cl}_{y},\) is \(3.69 \mathrm{g}\) What is the formula of the product, Ge, \(\mathrm{Cl}_{y}\) ?

Potassium has three naturally occurring isotopes \(\left(^{39} \mathrm{K}\right.\) \(\left.^{40} \mathrm{K}, \text { and }^{41} \mathrm{K}\right),\) but \(^{40} \mathrm{K}\) has a very low natural abundance. Which of the other two isotopes is more abundant? Briefly explain your answer.

Which of the following is impossible? (a) silver foil that is \(1.2 \times 10^{-4} \mathrm{m}\) thick (b) a sample of potassium that contains \(1.784 \times 10^{24}\) atoms (c) a gold coin of mass \(1.23 \times 10^{-3} \mathrm{kg}\) (d) \(3.43 \times 10^{-27}\) mol of \(\mathrm{S}_{8}\) molecules

Reviewing the periodic table. (a) Name the element in Group \(2 \mathrm{A}\) and the fifth period. (b) Name the element in the fifth period and Group \(4 B\). (c) Which element is in the second period in Group \(4 \mathrm{A} ?\) (d) Which element is in the fourth period in Group \(5 \mathrm{A} ?\) (e) Which halogen is in the fifth period? (f) Which alkaline earth element is in the third period? (g) Which noble gas element is in the fourth period? (h) Name the nonmetal in Group \(6 \mathrm{A}\) and the third period. (i) Name a metalloid in the fourth period.

Identify two nonmetallic elements that have allotropes and describe the allotropes of each.

In each case, decide which represents more mass: (a) 0.5 mol of \(\mathrm{Na}, 0.5\) mol of \(\mathrm{Si}\), or 0.25 mol of \(\mathrm{U}\) (b) \(9.0 \mathrm{g}\) of \(\mathrm{Na}, 0.50\) mol of \(\mathrm{Na},\) or \(1.2 \times 10^{22}\) atoms of \(\mathrm{Na}\) (c) 10 atoms of Fe or 10 atoms of \(\mathrm{K}\)

The recommended daily allowance (RDA) of iron in your diet is 15 mg. How many moles is this? How many atoms?

Put the following elements in order from smallest to largest mass: (a) \(3.79 \times 10^{24}\) atoms Fe (b) \(19.921 \mathrm{mol} \mathrm{H}_{2}\) (c) 8.576 mol \(\mathbf{C}\) (d) 7.4 mol \(\mathrm{Si}\) (e) 9.221 mol \(\mathrm{Na}\) (f) \(4.07 \times 10^{24}\) atoms Al (g) 9.2 mol \(\mathrm{Cl}_{2}\)

A When a sample of phosphorus burns in air, the compound \(\mathrm{P}_{4} \mathrm{O}_{10}\) forms. One experiment showed that \(0.744 \mathrm{g}\) of phosphorus formed \(1.704 \mathrm{g}\) of \(\mathrm{P}_{4} \mathrm{O}_{10} .\) Use this information to determine the ratio of the atomic weights of phosphorus and oxygen (mass \(\mathrm{P} / \mathrm{mass}\) O). If the atomic weight of oxygen is assumed to be 16.000 u, calculate the atomic weight of phosphorus.

Although carbon-12 is now used as the standard for atomic weights, this has not always been the case. Early attempts at classification used hydrogen as the standard, with the weight of hydrogen being set equal to 1.0000 u. Later attempts defined atomic weights using oxygen (with a weight of 16.0000 ). In each instance, the atomic weights of the other elements were defined relative to these masses. (To answer this question, you need more precise data on current atomic weights: \(\mathrm{H}\), \(1.00794 \mathrm{u} ; \mathrm{O}, 15.9994 \mathrm{u} .)\) (a) If \(\mathrm{H}=1.0000\) u was used as a standard for atomic weights, what would the atomic weight of oxygen be? What would be the value of Avogadro's number under these circumstances? (b) Assuming the standard is \(\mathrm{O}=16.0000,\) determine the value for the atomic weight of hydrogen and the value of Avogadro's number.

A reagent occasionally used in chemical synthesis is sodium-potassium alloy. (Alloys are mixtures of metals, and Na-K has the interesting property that it is a liquid.) One formulation of the alloy (the one that melts at the lowest temperature) contains 68 atom percent \(K ;\) that is, out of every 100 atoms, 68 are \(\mathrm{K}\) and 32 are \(\mathrm{Na}\). What is the mass percent of potassium in sodium-potassium alloy?

Write formulas for all of the compounds that can be made by combining the cations \(\mathrm{NH}_{4}^{+}\) and \(\mathrm{Ni}^{2+}\) with the anions \(\mathrm{CO}_{3}^{2-}\) and \(\mathrm{SO}_{4}^{2-}\)

Which of the following compounds has the highest mass percent of chlorine? (a) \(\mathrm{BCl}_{3}\) (b) \(\mathrm{AsCl}_{3}\) (c) \(\mathrm{GaCl}_{3}\) (d) \(\mathrm{AlCl}_{3}\) (e) \(\mathrm{PCl}_{3}\)

Which of the following samples has the largest number of ions? (a) \(1.0 \mathrm{g}\) of \(\mathrm{BeCl}_{2}\) (b) \(1.0 \mathrm{g}\) of \(\mathrm{MgCl}_{2}\) (c) \(1.0 \mathrm{g}\) of \(\mathrm{CaS}\) (d) \(1.0 \mathrm{g}\) of \(\mathrm{SrCO}_{3}\) (e) \(1.0 \mathrm{g}\) of \(\mathrm{BaSO}_{4}\)

Ionic and molecular compounds of the halogens. (a) What are the names of \(\mathrm{BaF}_{2}, \mathrm{SiCl}_{4},\) and \(\mathrm{NiBr}_{2} ?\) (b) Which of the compounds in part (a) are ionic, and which are molecular? (c) Which has the larger mass, 0.50 mol of \(\mathrm{BaF}_{2}\) 0.50 mol of \(\mathrm{SiCl}_{4},\) or 1.0 mol of \(\mathrm{NiBr}_{2} ?\)

A drop of water has a volume of about \(0.050 \mathrm{mL}\). How many molecules of water are in a drop of water? (Assume water has a density of \(1.00 \mathrm{g} / \mathrm{cm}^{3} .\) )

Capsaicin, the compound that gives the hot taste to chili peppers, has the formula \(\mathrm{C}_{18} \mathrm{H}_{27} \mathrm{NO}_{3}\) (a) Calculate its molar mass. (b) If you eat 55 mg of capsaicin, what amount (moles) have you consumed? (c) Calculate the mass percent of each element in the compound. (d) What mass of carbon (in milligrams) is there in \(55 \mathrm{mg}\) of capsaicin?

Calculate the molar mass and the mass percent of each element in the blue solid compound \(\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{SO}_{4} \cdot \mathrm{H}_{2} \mathrm{O} .\) What is the mass of copper and the mass of water in \(10.5 \mathrm{g}\) of the compound?

Malic acid, an organic acid found in apples, contains C, H, and O in the following ratios: \(C_{1} H_{1.50} O_{1.25} .\) What is the empirical formula of malic acid?

Your doctor has diagnosed you as being anemic-that is, as having too little iron in your blood. At the drugstore, you find two iron-containing dietary supplements: one with iron(II) sulfate, \(\mathrm{FeSO}_{4},\) and the other with iron (II) gluconate, \(\mathrm{Fe}\left(\mathrm{C}_{6} \mathrm{H}_{11} \mathrm{O}_{7}\right)_{2} .\) If you take \(100 .\) mg of each compound, which will deliver more atoms of iron?

A compound composed of iron and carbon monoxide, \(\mathrm{Fe}_{x}(\mathrm{CO})_{y},\) is \(30.70 \%\) iron. What is the empirical formula for the compound?

Name each of the following compounds and indicate which ones are best described as ionic: (a) \(\mathrm{ClF}_{3}\) (b) \(\mathrm{NCl}_{3}\) (c) \(\mathrm{SrSO}_{4}\) (d) \(\mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2}\) (e) \(\mathrm{XeF}_{4}\) (f) \(\mathrm{OF}_{2}\) \((\mathrm{g}) \mathrm{KI}\) (h) \(\mathrm{Al}_{2} \mathrm{S}_{3}\) (i) \(\mathrm{PCl}_{3}\) (j) \(\mathrm{K}_{3} \mathrm{PO}_{4}\)

Write the formula for each of the following compounds and indicate which ones are best described as ionic: (a) sodium hypochlorite (b) boron triiodide (c) aluminum perchlorate (d) calcium acetate (e) potassium permanganate (f) ammonium sulfite (g) potassium dihydrogen phosphate (h) disulfur dichloride (i) chlorine trifluoride (j) phosphorus trifluoride