Chapter 7: Problem 49
Write the electron configuration for (a) the \(\mathrm{Ni}^{2+}\) ion and (b) the \(\mathrm{Sn}^{2+}\) ion. How many unpaired electrons does each contain?
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Chapter 7: Problem 49
Write the electron configuration for (a) the \(\mathrm{Ni}^{2+}\) ion and (b) the \(\mathrm{Sn}^{2+}\) ion. How many unpaired electrons does each contain?
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(a) Which will have the lower energy, a 4 s or a \(4 p\) electron in an As atom? (b) How can we use the concept of effective nuclear charge to explain your answer to part (a)?
A historian discovers a nineteenth-century notebook in which some observations, dated 1822 , on a substance thought to be a new element, were recorded. Here are some of the data recorded in the notebook: Ductile, silverwhite, metallic looking. Softer than lead Unaffected by water. Stable in air. Melting point: \(153^{\circ} \mathrm{C}\) Density: \(7.3 \mathrm{~g} / \mathrm{cm}^{3} .\) Electrical conductivity: \(20 \%\) that of copper. Hardness. About \(1 \%\) as hard as iron. When \(4.20 \mathrm{~g}\) of the unknown is heated in an excess of oxygen, \(5.08 \mathrm{~g}\) of a white solid is formed. The solid could be sublimed by heating to over \(800^{\circ} \mathrm{C}\). (a) Using information in the text and a handbook of chemistry, and making allowances for possible variations in numbers from current values, identify the element reported. (b) Write a balanced chemical equation for the reaction with oxygen. (c) Judging from Figure 7.2, might this nineteenth- century investigator have been the first to discover a new element?
Potassium superoxide, \(\mathrm{KO}_{2}\), is often used in oxygen masks (such as those used by firefighters) because \(\mathrm{KO}_{2}\) reacts with \(\mathrm{CO}_{2}\) to release molecular oxygen. Experiments indicate that \(2 \mathrm{~mol}\) of \(\mathrm{KO}_{2}(\mathrm{~s})\) react with each mole of \(\mathrm{CO}_{2}(g) .\) (a) The products of the reaction are \(\mathrm{K}_{2} \mathrm{CO}_{3}(s)\) and \(\mathrm{O}_{2}(g) .\) Write a balanced equation for the reaction between \(\mathrm{KO}_{2}(\mathrm{~s})\) and \(\mathrm{CO}_{2}(\mathrm{~g}) .\) (b) Indicate the oxidation number for each atom involved in the reaction in part (a). What elements are being oxidized and reduced? (c) What mass of \(\mathrm{KO}_{2}(s)\) is needed to consume \(18.0 \mathrm{~g}\) \(\mathrm{CO}_{2}(g) ?\) What mass of \(\mathrm{O}_{2}(g)\) is produced during this reaction?
When magnesium metal is burned in air (Figure 3.5), two products are produced. One is magnesium oxide, \(\mathrm{MgO}\). The other is the product of the reaction of \(\mathrm{Mg}\) with molecular nitrogen, magnesium nitride. When water is added to magnesium nitride, it reacts to form magnesium oxide and ammonia gas. (a) Based on the charge of the nitride ion (Table 2.5), predict the formula of magnesium nitride. (b) Write a balanced equation for the reaction of magnesium nitride with water. What is the driving force for this reaction? (c) In an experiment a piece of magnesium ribbon is burned in air in a crucible. The mass of the mixture of \(\mathrm{MgO}\) and magnesium nitride after burning is \(0.470 \mathrm{~g}\). Water is added to the crucible, further reaction occurs, and the crucible is heated to dryness until the final product is \(0.486 \mathrm{~g}\) of \(\mathrm{MgO}\). What was the mass percentage of magnesium nitride in the mixture obtained after the initial burning? (d) Magnesium nitride can also be formed by reaction of the metal with ammonia at high temperature. Write a balanced equation for this reaction. If a \(6.3-\mathrm{g} \mathrm{Mg}\) ribbon reacts with \(2.57 \mathrm{~g} \mathrm{NH}_{3}(\mathrm{~g})\) and the reaction goes to \(\mathrm{com}\) pletion, which component is the limiting reactant? What mass of \(\mathrm{H}_{2}(\mathrm{~g})\) is formed in the reaction? (e) The standard enthalpy of formation of solid magnesium nitride is \(-461.08 \mathrm{~kJ} / \mathrm{mol}\). Calculate the standard enthalpy change for the reaction between magnesium metal and ammonia gas.
Write a balanced equation for the reaction that occurs in each of the following cases: (a) Potassium metal burns in an atmosphere of chlorine gas, (b) Strontium oxide is added to water. (c) A fresh surface of lithium metal is exposed to oxygen gas. (d) Sodium metal is reacted with molten sulfur.
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