Chapter 3

The "alum" used in cooking is potassium aluminum sulfate hydrate, \(\mathrm{KAl}\left(\mathrm{SO}_{4}\right)_{2} \cdot x \mathrm{H}_{2} \mathrm{O} .\) To find the value of \(x,\) you can heat a sample of the compound to drive off all of the water and leave only \(\mathrm{KAl}\left(\mathrm{SO}_{4}\right)_{2}\). Assume you heat \(4.74 \mathrm{g}\) of the hydrated compound and that the sample loses \(2.16 \mathrm{g}\) of water. What is the value of \(x ?\)

A new compound containing xenon and fluorine was isolated by shining sunlight on a mixture of \(\mathrm{Xe}(0.526 \mathrm{g})\) and \(\mathrm{F}_{2}\) 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, \(\mathbf{F}_{2}\) 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, \(\mathrm{Ge}_{x} \mathrm{Cl}, ?^{2}\)

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 \(\mathrm{SO}_{4}^{2-}\).

How many electrons are in a strontium atom (Sr)? Does an atom of Sr gain or lose electrons when forming an ion? How many electrons are gained or lost by the atom? When Sr forms an ion, the ion has the same number of electrons as which one of the noble gases?

The compound (NH_) \(_{2} \mathrm{SO}_{4}\) consists of two polyatomic ions. What are the names and electric charges of these ions? What is the molar mass of this compound?

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

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

Which of the following compounds (NO, CO, MgO, or CaO) has the highest weight percent of oxygen?

The chemical compound alum has the formula \(\mathrm{KAl}\left(\mathrm{SO}_{4}\right)_{2} \cdot 12 \mathrm{H}_{2} \mathrm{O} .\) Give formulas for the ions that make up this ionic compound.

Knowing that the formula of sodium borate is \(\mathrm{Na}_{3} \mathrm{BO}_{3}\) give the formula and charge of the borate ion. Is the borate ion a cation or an anion?

What is the difference between an empirical formula and a molecular formula? Use the compound ethane, \(\mathrm{C}_{2} \mathrm{H}_{6},\) to illustrate your answer.

Which has the larger mass, 0.5 mol of \(\mathrm{BaCl}_{2}\) or 0.5 mol of \(\mathrm{SiCl}_{4} ?\)

A drop of water has a volume of about \(0.05 \mathrm{mL}\). 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 \(\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{SO}_{4} \cdot \mathrm{H}_{2} \mathrm{O} .\) What are the mass (in grams) of copper and the mass of water in \(10.5 \mathrm{g}\) of the compound?

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

Spinach is high in iron ( 2 mg per 90 -g serving). It is also a source of the oxalate ion, \(\mathrm{C}_{2} \mathrm{O}_{4}^{2-} ;\) however, oxalate ion combines with iron ions to form iron oxalate, \(\mathrm{Fe}_{x}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right),\) a substance that prevents your body from absorbing the iron. Analysis of a \(0.109-\mathrm{g}\) sample of iron oxalate shows that it contains \(38.82 \%\) iron. What is the empirical formula of the compound?

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?

Which of the following pairs of elements are likely to form ionic compounds when allowed to react with each other? Write appropriate formulas for the ionic compounds you expect to form, and give the name of each. (a) chlorine and bromine (b) phosphorus and bromine (c) lithium and sulfur (d) indium and oxygen (e) sodium and argon (f) sulfur and bromine (g) calcium and fluorine

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

Write the formula for each of the following compounds, and tell 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

Fluorocarbonyl hypofluorite is composed of \(14.6 \% \mathrm{C}\) \(39.0 \%\) O, and \(46.3 \%\) F. If the molar mass of the compound is \(82 \mathrm{g} / \mathrm{mol}\), determine the empirical and molecular formulas of the compound.

Azulene, a beautiful blue hydrocarbon, is \(93.71 \%\) C and has a molar mass of \(128.16 \mathrm{g} / \mathrm{mol} .\) What are the empirical and molecular formulas of azulene?

Cacodyl, a compound containing arsenic, was reported in 1842 by the German chemist Robert Wilhelm Bunsen. It has an almost intolerable garlic-like odor. Its molar mass is \(210 \mathrm{g} / \mathrm{mol},\) and it is \(22.88 \% \mathrm{C}, 5.76 \% \mathrm{H},\) and \(71.36 \%\) As. Determine its empirical and molecular formulas.

The action of bacteria on meat and fish produces a compound called cadaverine. As its name and origin imply, it stinks! (It is also present in bad breath and adds to the odor of urine.) It is \(58.77 \%\) C, \(13.81 \%\) H, and \(27.40 \%\) N. Its molar mass is \(102.2 \mathrm{g} / \mathrm{mol}\). Determine the molecular formula of cadaverine.

Transition metals can combine with carbon monoxide (CO) to form compounds such as \(\mathrm{Fe}(\mathrm{CO})_{5}\) (Study Question 3.82 ). Assume that you combine 0.125 g of nickel with CO and isolate \(0.364 \mathrm{g}\) of \(\mathrm{Ni}(\mathrm{CO})_{x} .\) What is the value of \(x ?\)

A major oil company has used a gasoline additive called MMT to boost the octane rating of its gasoline. What is the empirical formula of MMT if it is \(49.5 \% \mathrm{C}\) \(3.2 \% \mathrm{H}, 22.0 \% \mathrm{O},\) and \(25.2 \% \mathrm{Mn} ?\)

Chromium is obtained by heating chromium(III) oxide with carbon. Calculate the weight percent of chromium in the oxide and then use this value to calculate the quantity of \(\mathrm{Cr}_{2} \mathrm{O}_{3}\) required to produce \(850 \mathrm{kg}\) of chromium metal.

Stibnite, \(\mathrm{Sb}_{2} \mathrm{S}_{3},\) is a dark gray mineral from which antimony metal is obtained. What is the weight percent of antimony in the sulfide? If you have \(1.00 \mathrm{kg}\) of an ore that contains \(10.6 \%\) antimony, what mass of \(\mathrm{Sb}_{2} \mathrm{S}_{3}\) (in grams) is in the ore?

Direct reaction of iodine \(\left(I_{2}\right)\) and chlorine \(\left(C l_{2}\right)\) produces an iodine chloride, \(I_{x} C l_{y},\) a bright yellow solid. If you completely used up 0.678 g of iodine and produced \(1.246 \mathrm{g}\) of \(\mathrm{I}_{x} \mathrm{Cl}_{y},\) what is the empirical formula of the compound? A later experiment showed that the molar mass of \(\mathrm{I}_{x} \mathrm{Cl}_{y}\) was \(467 \mathrm{g} / \mathrm{mol} .\) What is the molecular formula of the compound?

In a reaction \(2.04 \mathrm{g}\) of vanadium combined with \(1.93 \mathrm{g}\) of sulfur to give a pure compound. What is the empirical formula of the product?

Iron pyrite, often called "fool's gold," has the formula FeS \(_{2} .\) If you could convert \(15.8 \mathrm{kg}\) of iron pyrite to iron metal, what mass of the metal would you obtain?

Which of the following statements about \(57.1 \mathrm{g}\) of octane, \(\mathrm{C}_{8} \mathrm{H}_{18},\) is (are) not true? (a) \(57.1 \mathrm{g}\) is 0.500 mol of octane. (b) The compound is \(84.1 \%\) C by weight. (c) The empirical formula of the compound is \(\mathrm{C}_{4} \mathrm{H}_{9}\) (d) 57.1 g of octane contains \(28.0 \mathrm{g}\) of hydrogen atoms.

A metal M forms a compound with the formula MCl, If the compound is \(74.75 \%\) chlorine, what is the identity of M?

Pepto-Bismol, which helps provide soothing relief for an upset stomach, contains \(300 .\) mg of bismuth subsalicylate, \(\mathrm{C}_{21} \mathrm{H}_{15} \mathrm{Bi}_{3} \mathrm{O}_{12},\) per tablet. If you take two tablets for your stomach distress, what amount (in moles) of the "active ingredient" are you taking? What mass of Bi are you consuming in two tablets?

The weight percent of oxygen in an oxide that has the formula MO, is \(15.2 \% .\) What is the molar mass of this compound? What element or elements are possible for M?

The mass of 2.50 mol of a compound with the formula \(\mathrm{ECl}_{4},\) in which \(\mathrm{E}\) is a nonmetallic element, is \(385 \mathrm{g} .\) What is the molar mass of ECl \(_{4} ?\) What is the identity of E?

The elements A and Z combine to produce two different compounds: \(\mathrm{A}_{2} \mathrm{Z}_{3}\) and \(\mathrm{AZ}_{2}\). If 0.15 mol of \(\mathrm{A}_{2} \mathrm{Z}_{3}\) has a mass of \(15.9 \mathrm{g}\) and 0.15 mole of \(\mathrm{AZ}_{2}\) has a mass of \(9.3 \mathrm{g}\) what are the atomic masses of \(\mathrm{A}\) and \(\mathrm{Z} ?\)

Polystyrene can be prepared by heating styrene with tribromobenzoyl peroxide in the absence of air. A sample prepared by this method has the empirical formula \(\mathrm{Br}_{3} \mathrm{C}_{6} \mathrm{H}_{3}\left(\mathrm{C}_{8} \mathrm{H}_{8}\right)_{n},\) where the value of \(n\) can vary from sam- ple to sample. If one sample has \(10.46 \%\) Br, what is the value of \(n ?\)

A sample of hemoglobin is found to be \(0.335 \%\) iron. If hemoglobin contains one iron atom per molecule, what is the molar mass of hemoglobin? What is the molar mass if there are four iron atoms per molecule?

A piece of nickel foil, \(0.550 \mathrm{mm}\) thick and \(1.25 \mathrm{cm}\) square, is allowed to react with fluorine, \(\mathrm{F}_{2},\) to give a nickel fluoride. (a) How many moles of nickel foil were used? (The density of nickel is \(8.902 \mathrm{g} / \mathrm{cm}^{3} .\) ) (b) If you isolate 1.261 g of the nickel fluoride, what is its formula? (c) What is its complete name?

When analyzed, an unknown compound gave these experimental results: \(\mathrm{C}, 54.0 \% ; \mathrm{H}, 6.00 \% ;\) and \(\mathrm{O}, 40.0 \%\) Four different students used these values to calculate the empirical formulas shown here. Which answer is correct? Why did some students not get the correct answer? (a) \(\mathrm{C}_{4} \mathrm{H}_{5} \mathrm{O}_{2}\) (c) \(\mathrm{C}_{7} \mathrm{H}_{10} \mathrm{O}_{4}\) (b) \(\mathrm{C}_{5} \mathrm{H}_{7} \mathrm{O}_{3}\) (d) \(\mathrm{C}_{9} \mathrm{H}_{12} \mathrm{O}_{5}\)

Uranium is used as a fuel, primarily in the form of uranium(IV) oxide, in nuclear power plants. This question considers some uranium chemistry. (a) A small sample of uranium metal \((0.169 \mathrm{g})\) is heated to between 800 and \(900^{\circ} \mathrm{C}\) in air to give \(0.199 \mathrm{g}\) of a dark green oxide, \(\mathrm{U}_{x} \mathrm{O}_{y}\). How many moles of uranium metal were used? What is the empirical formula of the oxide, \(\mathrm{U}_{x} \mathrm{O}_{y} ?\) What is the name of the oxide? How many moles of \(\mathrm{U}_{x} \mathrm{O}_{y}\) must have been obtained? (b) The naturally occurring isotopes of uranium are \(^{234} \mathrm{U}\) " \(^{235} \mathrm{U},\) and \(^{238} \mathrm{U} .\) Knowing that uranium's atomic weight is \(238.02 \mathrm{g} / \mathrm{mol},\) which isotope must be the most abundant? (c) If the hydrated compound \(\mathrm{UO}_{2}\left(\mathrm{NO}_{3}\right)_{2} \cdot z \mathrm{H}_{2} \mathrm{O}\) is heated gently, the water of hydration is lost. If you have \(0.865 \mathrm{g}\) of the hydrated compound and obtain \(0.679 \mathrm{g}\) of \(\mathrm{UO}_{2}\left(\mathrm{NO}_{3}\right)_{2}\) on heating, how many molecules of water of hydration are in each formula unit of the original compound? (The oxide \(\mathrm{U}_{x} \mathrm{O}_{y}\) is obtained if the hydrate is heated to temperatures over \(800^{\circ} \mathrm{C}\) in the air.)

The common chemical compound alum has the formula \(\mathrm{KAl}\left(\mathrm{SO}_{4}\right)_{2} \cdot 12 \mathrm{H}_{2} \mathrm{O} .\) An interesting characteristic of alum is that it is possible to grow very large crystals of this compound. Suppose you have a crystal of alum in the form of a cube that is \(3.00 \mathrm{cm}\) on each side. You want to know how many aluminum atoms are contained in this cube. Outline the steps to determine this value, and indicate the information that you need to carry out each step.