# Chemistry the Central Science

## Educators

### Problem 1

The reaction between reactant A (blue spheres) and reactant $\mathrm{B}($ red spheres) is shown in the following diagram:
Based on this diagram, which equation best describes the reaction? [ Section 3.1$]$
$$\begin{array}{l}{\text { (a) } \mathrm{A}_{2}+\mathrm{B} \longrightarrow \mathrm{A}_{2} \mathrm{B}} \\ {\text { (b) } \mathrm{A}_{2}+4 \mathrm{B} \longrightarrow 2 \mathrm{AB}_{2}} \\ {\text { (c) } 2 \mathrm{A}+\mathrm{B}_{4} \longrightarrow 2 \mathrm{AB}_{2}} \\ {\text { (d) } \mathrm{A}+\mathrm{B}_{2} \longrightarrow \mathrm{AB}_{2}}\end{array}$$

### Problem 2

The following diagram shows the combination reaction between hydrogen, $\mathrm{H}_{2},$ and carbon monoxide, $\mathrm{CO},$ to produce methanol, $\mathrm{CH}_{3} \mathrm{OH}$ (white spheres are $\mathrm{H},$ black spheres are $\mathrm{C},$ red spheres are O). The correct number of CO molecules involved in this reaction is not shown. [ Section 3.1$]$
(a) Determine the number of CO molecules that should be shown in the left (reactants) box.
(b) Write a balanced chemical equation for the reaction.

Md M.
Auburn University Main Campus

### Problem 3

The following diagram represents the collection of elements formed by a decomposition reaction. (a) If the blue spheres represent $N$ atoms and the red ones represent $\mathrm{O}$ atoms, what was the empirical formula of the original compound? (b) Could you draw a diagram representing the molecules of the compound that had been decomposed? Why or why not? [Section 3.2$]$

### Problem 4

The following diagram represents the collection of $\mathrm{CO}_{2}$ and $\mathrm{H}_{2} \mathrm{O}$ molecules formed by complete combustion of a hydrocarbon. What is the empirical formula of the hydrocarbon? [Section 3.2$]$

Md M.
Auburn University Main Campus

### Problem 5

Glycine, an amino acid used by organisms to make proteins, is represented by the following molecular model.
(a) Write its molecular formula.
(b) Determine its molar mass.
(c) Calculate how many moles of glycine are in a $100.0-g$ sample of glycine.
(d) Calculate the percent nitrogen by mass in glycine. [Sections 3.3 and 3.5$]$

### Problem 6

The following diagram represents a high-temperature reaction between $\mathrm{CH}_{4}$ and $\mathrm{H}_{2} \mathrm{O}$ . Based on this reaction, find how many moles of each product can be obtained starting with 4.0 $\mathrm{mol} \mathrm{CH}_{4} .[$ Section 3.6$]$

Md M.
Auburn University Main Campus

### Problem 7

Nitrogen $\left(\mathrm{N}_{2}\right)$ and hydrogen $\left(\mathrm{H}_{2}\right)$ react to form ammonia $\left(\mathrm{NH}_{3}\right) .$ Consider the mixture of $\mathrm{N}_{2}$ and $\mathrm{H}_{2}$ shown in the accompanying diagram. The blue spheres represent $\mathrm{N},$ and the white ones represent H. (a) Write the balanced chemical equation for the reaction. (b) What is the limiting reactant? (c) How many molecules of ammonia can be made, assuming the reaction goes to completion, based on the diagram? (d) Are any reactant molecules left over, based on the diagram? If so, how many of which type are left over? [ Section 3.7]

### Problem 8

Nitrogen monoxide and oxygen react to form nitrogen dioxide. Consider the mixture of NO and O $_{2}$ shown in the accompanying diagram. The blue spheres represent $\mathrm{N},$ and the red ones represent $\mathrm{O}$ . (a) How many molecules of $\mathrm{NO}_{2}$ can be formed, assuming the reaction goes to completion? (b) What is the limiting reactant? (c) If the actual yield of the reaction was 75$\%$ instead of 100$\%$ , how many molecules of each kind would be present after the reaction was over?

Md M.
Auburn University Main Campus

### Problem 9

Write "true" or "false" for each statement. (a) We balance chemical equations as we do because energy must be conserved. (b) If the reaction 2 $\mathrm{O}_{3}(g) \rightarrow 3 \mathrm{O}_{2}(g)$ goes to completion and all $\mathrm{O}_{3}$ is converted to $\mathrm{O}_{2},$ then the mass of $\mathrm{O}_{3}$ at the beginning of the reaction must be the same as the mass of $\mathrm{O}_{2}$ at the end of the reaction. (c) You can balance the "water-splitting" reaction $\mathrm{H}_{2} \mathrm{O}(I) \rightarrow \mathrm{H}_{2}(g)+\mathrm{O}_{2}(g)$ by writing it this way: $\mathrm{H}_{2} \mathrm{O}_{2}(l) \rightarrow \mathrm{H}_{2}(g)+\mathrm{O}_{2}(g)$

### Problem 10

A key step in balancing chemical equations is correctly identifying the formulas of the reactants and products. For example, consider the reaction between calcium oxide, CaO(s), and $\mathrm{H}_{2} \mathrm{O}(l)$ to form aqueous calcium hydroxide. (a) Write a balanced chemical equation for this combination reaction, having correctly identified the product as $\mathrm{Ca}(\mathrm{OH})_{2}(a q)$ . (b) Is it possible to balance the equation if you incorrectly identify the product as $\mathrm{CaOH}(a q),$ and if so, what is the equation?

Md M.
Auburn University Main Campus

### Problem 11

Balance the following equations:
$$\begin{array}{l}{\text { (a) } \mathrm{CO}(g)+\mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g)} \\ {\text { (b) } \mathrm{N}_{2} \mathrm{O}_{5}(g)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{HNO}_{3}(a q)} \\ {\text { (c) } \mathrm{CH}_{4}(g)+\mathrm{Cl}_{2}(g) \longrightarrow \mathrm{CCl}_{4}(l)+\mathrm{HCl}(g)} \\ {\text { (d) } \mathrm{Zn}(\mathrm{OH})_{2}(s)+\mathrm{HNO}_{3}(a q) \longrightarrow \mathrm{Zn}\left(\mathrm{NO}_{3}\right)_{2}(a q)+\mathrm{H}_{2} \mathrm{O}(l)}\end{array}$$

### Problem 12

Balance the following equations:
$$\begin{array}{l}{\text { (a) } \mathrm{Li}(s)+\mathrm{N}_{2}(g) \longrightarrow \mathrm{Li}_{3} \mathrm{N}(s)} \\ {\text { (b) } \mathrm{TiCl}_{4}(l)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{TiO}_{2}(s)+\mathrm{HCl}(a q)} \\ {\text { (c) } \mathrm{NH}_{4} \mathrm{NO}_{3}(s) \longrightarrow \mathrm{N}_{2}(g)+\mathrm{O}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(g)} \\ {\text { (d) } \mathrm{AlCl}_{3}(s)+\mathrm{Ca}_{3} \mathrm{N}_{2}(s) \longrightarrow \mathrm{AlN}(s)+\mathrm{CaCl}_{2}(s)}\end{array}$$

Md M.
Auburn University Main Campus

### Problem 13

Balance the following equations:
$$\begin{array}{l}{\text { (a) } \mathrm{Al}_{4} \mathrm{C}_{3}(s)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{Al}(\mathrm{OH})_{3}(s)+\mathrm{CH}_{4}(g)} \\ {\text { (b) } \mathrm{C}_{5} \mathrm{H}_{10} \mathrm{O}_{2}(l)+\mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(g)} \\ {\text { (c) } \mathrm{Fe}(\mathrm{OH})_{3}(s)+\mathrm{H}_{2} \mathrm{SO}_{4}(a q) \longrightarrow \mathrm{Fe}_{2}\left(\mathrm{SO}_{4}\right)_{3}(a q)+\mathrm{H}_{2} \mathrm{O}(l)} \\ {\text { (d) } \mathrm{Mg}_{3} \mathrm{N}_{2}(s)+\mathrm{H}_{2} \mathrm{SO}_{4}(a q) \longrightarrow \mathrm{MgSO}_{4}(a q)+\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}(a q)}\end{array}$$

### Problem 14

Balance the following equations:
$$\begin{array}{l}{\text { (a) } \mathrm{Ca}_{3} \mathrm{P}_{2}(s)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{Ca}(\mathrm{OH})_{2}(a q)+\mathrm{PH}_{3}(g)} \\ {\text { (b) } \mathrm{Al}(\mathrm{OH})_{3}(s)+\mathrm{H}_{2} \mathrm{SO}_{4}(a q) \longrightarrow \mathrm{Al}_{2}\left(\mathrm{SO}_{4}\right)_{3}(a q)+\mathrm{H}_{2} \mathrm{O}(l)} \\ {\text { (c) } \mathrm{AgNO}_{3}(a q)+\mathrm{Na}_{2} \mathrm{CO}_{3}(a q) \longrightarrow \mathrm{Ag}_{2} \mathrm{CO}_{3}(s)+\mathrm{NaNO}_{3}(a q)} \\ {\text { (d) } \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{NH}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(g)+\mathrm{N}_{2}(g)}\end{array}$$

Md M.
Auburn University Main Campus

### Problem 15

Write balanced chemical equations corresponding to each of the following descriptions: (a) Solid calcium carbide, $\mathrm{CaC}_{2}$ , reacts with water to form an aqueous solution of calcium hydroxide and acetylene gas, $\mathrm{C}_{2} \mathrm{H}_{2}$ . (b) When solid potassium chlorate is heated, it decomposes to form solid potassium chloride and oxygen gas. (c) Solid zinc metal reacts with sulfuric acid to form hydrogen gas and an aqueous solution of zinc sulfate. (d) When liquid phosphorus trichloride is added to water, it reacts to form aqueous phosphorous acid, $\mathrm{H}_{3} \mathrm{PO}_{3}(a q)$, and aqueous hydrochloric acid. (e) When hydrogen sulfide gas is passed over solid hot iron(III) hydroxide, the resulting reaction produces solid iron(II) sulfide and gaseous water.

### Problem 16

Write balanced chemical equations to correspond to each of the following descriptions: (a) When sulfur trioxide gas reacts with water, a solution of sulfuric acid forms. (b) Boron sulfide, $B_{2} S_{3}(s),$ reacts violently with water to form dissolved boric acid, $H_{3} B O_{3},$ and hydrogen sulfide gas. (c) Phosphine, PH $_{3}(g),$ combusts in oxygen gas to form water vapor and solid tetraphosphorus decaoxide. (d) When solid mercury(II) nitrate is heated, it decomposes to form solid mercury(II) oxide, gaseous nitrogen dioxide, and oxygen.(e) Copper metal reacts with hot concentrated sulfuric acid solution to form aqueous copper(II) sulfate, sulfur dioxide gas, and water.

Md M.
Auburn University Main Campus

### Problem 17

(a) When the metallic element sodium combines with the nonmetallic element bromine, $\mathrm{Br}_{2}(l),$ what is the chemical formula of the product? (b) Is the product a solid, liquid, or gas at room temperature? (c) In the balanced chemical equation for this reaction, what is the coefficient in front of the product if the coefficient in front of $\mathrm{Br}_{2}(l)$ is 1$?$

### Problem 18

(a) When a compound containing $\mathrm{C}, \mathrm{H},$ and $\mathrm{O}$ is completely combusted in air, what reactant besides the hydrocarbon is involved in the reaction? (b) What products form in this reaction? (c) What is the sum of the coefficients in the balanced chemical equation for the combustion of one mole of acetone, $\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}(l),$ in air?

Md M.
Auburn University Main Campus

### Problem 19

Write a balanced chemical equation for the reaction that occurs when (a) $\mathrm{Mg}(s)$ reacts with $\mathrm{Cl}_{2}(g) ;$ (b) barium carbonate decomposes into barium oxide and carbon dioxide gas when heated; (c) the hydrocarbon styrene, $\mathrm{C}_{8} \mathrm{H}_{8}(l),$ is combusted in air; (d) dimethylether, $\mathrm{CH}_{3} \mathrm{OCH}_{3}(g),$ is combusted in air.

### Problem 20

Write a balanced chemical equation for the reaction that occurs when (a) titanium metal reacts with $\mathrm{O}_{2}(g) ;(\mathbf{b})$ silver(I)oxide decomposes into silver metal and oxygen gas when heated; (c) propanol, $\mathrm{C}_{3} \mathrm{H}_{7} \mathrm{OH}(l)$ burns in air; (d) methyl tert-butyl ether, $\mathrm{C}_{5} \mathrm{H}_{12} \mathrm{O}(l),$ burns in air.

Md M.
Auburn University Main Campus

### Problem 21

Balance the following equations and indicate whether they are combination, decomposition, or combustion reactions:
$$\begin{array}{l}{\text { (a) } \mathrm{C}_{3} \mathrm{H}_{6}(g)+\mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(g)} \\ {\text { (b) } \mathrm{NH}_{4} \mathrm{NO}_{3}(s) \longrightarrow \mathrm{N}_{2} \mathrm{O}(g)+\mathrm{H}_{2} \mathrm{O}(g)} \\ {\text { (c) } \mathrm{C}_{5} \mathrm{H}_{6} \mathrm{O}(l)+\mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(g)} \\ {\text { (d) } \mathrm{N}_{2}(g)+\mathrm{H}_{2}(g) \longrightarrow \mathrm{NH}_{3}(g)} \\ {\text { (e) } \mathrm{K}_{2} \mathrm{O}(s)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{KOH}(a q)}\end{array}$$

### Problem 22

Balance the following equations and indicate whether they are combination, decomposition, or combustion reactions:
$$\begin{array}{l}{\text { (a) } \mathrm{PbCO}_{3}(s) \longrightarrow \mathrm{PbO}(s)+\mathrm{CO}_{2}(g)} \\ {\text { (b) } \mathrm{C}_{2} \mathrm{H}_{4}(g)+\mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(g)} \\ {\text { (c) } \mathrm{Mg}(s)+\mathrm{N}_{2}(g) \longrightarrow \mathrm{Mg}_{3} \mathrm{N}_{2}(s)} \\ {\text { (d) } \mathrm{C}_{7} \mathrm{H}_{8} \mathrm{O}_{2}(l)+\mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(g)} \\ \text { (e) } \mathrm{Al}(s)+\mathrm{Cl}_{2}(g) \longrightarrow \mathrm{AlCl}_{3}(s) \end{array}$$

Md M.
Auburn University Main Campus

### Problem 23

Determine the formula weights of each of the following compounds: (a) nitric acid, HNO $_{3} ;$ (b) $\mathrm{KMnO}_{4} ;$ (c) $\mathrm{Ca}_{3}\left(\mathrm{PO}_{4}\right)_{2}$ (d) quartz, SiO $_{2} ;$ (e) gallium sulfide, (f) chromium(III) sulfate, (g) phosphorus trichloride.

### Problem 24

Determine the formula weights of each of the following compounds: (a) nittrous oxide, $\mathrm{N}_{2} \mathrm{O}$ , known as laughing gas and used as an anesthetic in dentistry; (b) benzoic acid; $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH}$ a substance used as a food preservative; $(c) \mathrm{Mg}(\mathrm{OH})_{2},$ the active ingredient in milk of magnesia; (d) urea, $\left(\mathrm{NH}_{2}\right)_{2} \mathrm{CO},$ a compound used as a nitrogen fertilizer; (e) isopentyl acetate, $\mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{C}_{5} \mathrm{H}_{11},$ responsible for the odor of bananas.

Md M.
Auburn University Main Campus

### Problem 25

Calculate the percentage by mass of oxygen in the following compounds: (a) morphine, $\mathrm{C}_{17} \mathrm{H}_{19} \mathrm{NO}_{3} ;$ (b) codeine, $\mathrm{C}_{18} \mathrm{H}_{21} \mathrm{NO}_{3}$ (c) cocaine, $\mathrm{C}_{17} \mathrm{H}_{21} \mathrm{NO}_{4} ;(\mathbf{d})$ tetracycline, $\mathrm{C}_{22} \mathrm{H}_{24} \mathrm{N}_{2} \mathrm{O}_{8} ;(\mathbf{e})$ digi$\mathrm{toxin}, \mathrm{C}_{41} \mathrm{H}_{64} \mathrm{O}_{13} ;(\mathrm{f})$ vancomycin, $\mathrm{C}_{66} \mathrm{H}_{75} \mathrm{Cl}_{2} \mathrm{N}_{9} \mathrm{O}_{24}$.

### Problem 26

Calculate the percentage by mass of the indicated element in the following compounds: $(\mathbf{a})$ carbon in acetylene, $\mathrm{C}_{2} \mathrm{H}_{2}, \mathrm{a}$ gas used in welding; $(\mathbf{b} )$ hydrogen in ascorbic acid, $\mathrm{HC}_{6} \mathrm{H}_{7} \mathrm{O}_{6}$ also known as vitamin $\mathrm{C} ;(\mathbf{c})$ hydrogen in ammonium sulfate, $\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4},$ a substance used as a nitrogen fertilizer; $(\mathbf{d})$ platinum in $\mathrm{PtCl}_{2}\left(\mathrm{NH}_{3}\right)_{2},$ a chemotherapy agent called cisplatin; $(\mathbf{e})$ oxygen in the female sex hormone estradiol, $\mathrm{C}_{18} \mathrm{H}_{24} \mathrm{O}_{2} ;(\mathbf{f})$ carbon in capsaicin, $\mathrm{C}_{18} \mathrm{H}_{27} \mathrm{NO}_{3},$ the compound that gives the hot taste to chili peppers.

Md M.
Auburn University Main Campus

### Problem 27

Based on the following structural formulas, calculate the percentage of carbon by mass present in each compound:

### Problem 28

Calculate the percentage of carbon by mass in each of the compounds represented by the following models:

Md M.
Auburn University Main Campus

### Problem 29

(a) Write "true" or "false" for each statement. (a) A mole of horses contain a mole of horse legs. (b) A mole of water has a mass of 18.0 $\mathrm{g} .$ (c) The mass of 1 molecule of water is 18.0 $\mathrm{g}$ (d) A mole of NaCl (s) contains 2 moles of ions.

### Problem 30

(a) What is the mass, in grams, of one mole of $^{12} \mathrm{C} ?$ (b) How many carbon atoms are present in one mole of $^{12} \mathrm{C} ?$

Md M.
Auburn University Main Campus

### Problem 31

Without doing any detailed calculations (but using a periodic table to give atomic weights), rank the following samples in order of increasing numbers of atoms: 0.50 mol $\mathrm{H}_{2} \mathrm{O}, 23 \mathrm{g} \mathrm{Na}, 6.0 \times 10^{23} \mathrm{N}_{2}$ molecules.

### Problem 32

Without doing any detailed calculations (but using a periodic table to give atomic weights, rank the following samples in order of increasing numbers of atoms: 42 gof NaHCO $_{3}, 1.5 \mathrm{mol} \mathrm{CO}_{2}, 6.0 \times 10^{24} \mathrm{Ne}$ atoms.

Md M.
Auburn University Main Campus

### Problem 33

What is the mass, in kilograms, of an Avogadro's number of people, if the average mass of a person is 160 $\mathrm{lb}$ ? How does this compare with the mass of Earth, $5.98 \times 10^{24} \mathrm{kg}$ ?