Chapter 22

Without referring to Figure \(22.1,\) state whether each of the following elements are metals, metalloids, or nonmetals: (a) \(\mathrm{Cs},(\mathrm{b}) \mathrm{Ge},(\mathrm{c}) \mathrm{I},\) (d) \(\mathrm{Kr},\) (e) \(\mathrm{W}\), (f) \(\mathrm{Ga},(\mathrm{g}) \mathrm{Te},(\mathrm{h}) \mathrm{Bi}\)

List two chemical and two physical properties that distinguish a metal from a nonmetal.

Make a list of physical and chemical properties of chlorine \(\left(\mathrm{Cl}_{2}\right)\) and magnesium. Comment on their differences with reference to the fact that one is a metal and the other is a nonmetal.

Explain why hydrogen has a unique position in the periodic table.

Describe two laboratory and two industrial preparations for hydrogen.

Hydrogen exhibits three types of bonding in its compounds. Describe each type of bonding with an example.

What are interstitial hydrides?

Give the name of (a) an ionic hydride and (b) a covalent hydride. In each case describe the preparation and give the structure of the compound.

Describe what is meant by the "hydrogen economy."

Elements number 17 and 20 form compounds with hydrogen. Write the formulas for these two compounds and compare their chemical behavior in water.

Give an example of hydrogen as (a) an oxidizing agent and (b) a reducing agent.

Compare the physical and chemical properties of the hydrides of each of the following elements: \(\mathrm{Na}\), \(\mathrm{Ca}, \mathrm{C}, \mathrm{N}, \mathrm{O}, \mathrm{Cl}\).

Suggest a physical method that would enable you to separate hydrogen gas from neon gas.

Write a balanced equation to show the reaction between \(\mathrm{CaH}_{2}\) and \(\mathrm{H}_{2} \mathrm{O}\). How many grams of \(\mathrm{CaH}_{2}\) are needed to produce \(26.4 \mathrm{~L}\) of \(\mathrm{H}_{2}\) gas at \(20^{\circ} \mathrm{C}\) and \(746 \mathrm{mmHg} ?\)

How many kilograms of water must be processed to obtain \(2.0 \mathrm{~L}\) of \(\mathrm{D}_{2}\) at \(25^{\circ} \mathrm{C}\) and 0.90 atm pressure? Assume that deuterium abundance is 0.015 percent and that recovery is 80 percent.

Predict the outcome of the following reactions: (a) \(\mathrm{CuO}(s)+\mathrm{H}_{2}(g) \longrightarrow\) (b) \(\mathrm{Na}_{2} \mathrm{O}(s)+\mathrm{H}_{2}(g) \longrightarrow\)

Give an example of a carbide and a cyanide.

How are cyanide ions used in metallurgy?

Briefly discuss the preparation and properties of carbon monoxide and carbon dioxide.

What is coal?

Explain what is meant by coal gasification.

Describe two chemical differences between CO and \(\mathrm{CO}_{2}\).

Draw a Lewis structure for the \(\mathrm{C}_{2}^{2-}\) ion.

Unlike \(\mathrm{CaCO}_{3}, \mathrm{Na}_{2} \mathrm{CO}_{3}\) does not readily yield \(\mathrm{CO}_{2}\) when heated. On the other hand, \(\mathrm{NaHCO}_{3}\) undergoes thermal decomposition to produce \(\mathrm{CO}_{2}\) and \(\mathrm{Na}_{2} \mathrm{CO}_{3}\). (a) Write a balanced equation for the reaction. (b) How would you test for the \(\mathrm{CO}_{2}\) evolved? [Hint: Treat the gas with limewater, an aqueous solution of \(\left.\mathrm{Ca}(\mathrm{OH})_{2} .\right]\)

Two solutions are labeled A and B. Solution A contains \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) and solution \(\mathrm{B}\) contains \(\mathrm{NaHCO}_{3}\). Describe how you would distinguish between the two solutions if you were provided with a \(\mathrm{MgCl}_{2}\) solution. (Hint: You need to know the solubilities of \(\mathrm{MgCO}_{3}\) and \(\mathrm{MgHCO}_{3}\).)

Magnesium chloride is dissolved in a solution containing sodium bicarbonate. On heating, a white precipitate is formed. Explain what causes the precipitation.

A few drops of concentrated ammonia solution added to a calcium bicarbonate solution cause a white precipitate to form. Write a balanced equation for the reaction.

Sodium hydroxide is hygroscopic-that is, it absorbs moisture when exposed to the atmosphere. A student placed a pellet of \(\mathrm{NaOH}\) on a watch glass. A few days later, she noticed that the pellet was covered with a white solid. What is the identity of this solid? (Hint: Air contains \(\mathrm{CO}_{2}\).)

A piece of red-hot magnesium ribbon will continue to burn in an atmosphere of \(\mathrm{CO}_{2}\) even though \(\mathrm{CO}_{2}\) does not support combustion. Explain.

Is carbon monoxide isoelectronic with nitrogen \(\left(\mathrm{N}_{2}\right) ?\)

Describe a laboratory and an industrial preparation of nitrogen gas.

What is meant by nitrogen fixation? Describe a process for fixation of nitrogen on an industrial scale.

Describe an industrial preparation of phosphorus.

Why is the \(\mathrm{P}_{4}\) molecule unstable?

Nitrogen can be obtained by (a) passing ammonia over red-hot copper(II) oxide and (b) heating ammonium dichromate [one of the products is \(\mathrm{Cr}(\mathrm{III})\) oxide \(] .\) Write a balanced equation for each preparation.

Write balanced equations for the preparation of sodium nitrite by heating (a) sodium nitrate, (b) sodium nitrate with carbon.

Sodium amide \(\left(\mathrm{NaNH}_{2}\right)\) reacts with water to produce sodium hydroxide and ammonia. Describe this reaction as a Brønsted acid-base reaction.

Write a balanced equation for the formation of urea, \(\left(\mathrm{NH}_{2}\right)_{2} \mathrm{CO},\) from carbon dioxide and ammonia. Should the reaction be run at high or low pressure to maximize the yield?

Some farmers believe that lightning helps produce a better crop. What is the scientific basis for this belief?

At \(620 \mathrm{~K}\) the vapor density of ammonium chloride relative to hydrogen \(\left(\mathrm{H}_{2}\right)\) under the same conditions of temperature and pressure is \(14.5,\) although, according to its formula mass, it should have a vapor density of \(26.8 .\) How would you account for this discrepancy?

Explain, giving one example in each case, why nitrous acid can act as both a reducing agent and an oxidizing agent.

Explain why nitric acid can be reduced but not oxidized.

Write a balanced equation for each of the following processes: (a) On heating, ammonium nitrate produces nitrous oxide. (b) On heating, potassium nitrate produces potassium nitrite and oxygen gas. (c) On heating, lead nitrate produces lead(II) oxide, nitrogen dioxide \(\left(\mathrm{NO}_{2}\right),\) and oxygen gas.

Explain why, under normal conditions, the reaction of zinc with nitric acid does not produce hydrogen.

Potassium nitrite can be produced by heating a mixture of potassium nitrate and carbon. Write a balanced equation for this reaction. Calculate the theoretical yield of \(\mathrm{KNO}_{2}\) produced by heating \(57.0 \mathrm{~g}\) of \(\mathrm{KNO}_{3}\) with an excess of carbon.

Predict the geometry of nitrous oxide, \(\mathrm{N}_{2} \mathrm{O},\) by the VSEPR method and draw resonance structures for the molecule. (Hint: The atoms are arranged as NNO.)

Consider the reaction $$\mathrm{N}_{2}(g)+\mathrm{O}_{2}(g) \rightleftharpoons 2 \mathrm{NO}(g)$$ Given that the \(\Delta G^{\circ}\) for the reaction at \(298 \mathrm{~K}\) is \(173.4 \mathrm{~kJ} / \mathrm{mol},\) calculate (a) the standard free energy of formation of \(\mathrm{NO},\) (b) \(K_{P}\) for the reaction, \((\mathrm{c}) K_{\mathrm{c}}\) for the reaction.

Explain why two \(\mathrm{N}\) atoms can form a double bond or a triple bond, whereas two \(\mathrm{P}\) atoms normally can form only a single bond.

When \(1.645 \mathrm{~g}\) of white phosphorus are dissolved in \(75.5 \mathrm{~g}\) of \(\mathrm{CS}_{2},\) the solution boils at \(46.709^{\circ} \mathrm{C}\) whereas pure \(\mathrm{CS}_{2}\) boils at \(46.300^{\circ} \mathrm{C}\). The molal boiling-point elevation constant for \(\mathrm{CS}_{2}\) is \(2.34^{\circ} \mathrm{C} / \mathrm{m}\). Calculate the molar mass of white phosphorus and give the molecular formula.

Starting with elemental phosphorus, \(\mathrm{P}_{4}\), show how you would prepare phosphoric acid.