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Chapter 7: Problem 104

(a) One of the alkali metals reacts with oxygen to form a solid white substance. When this substance is dissolved in water, the solution gives a positive test for hydrogen peroxide, \(\mathrm{H}_{2} \mathrm{O}_{2}\). When the solution is tested in a burner flame, a lilac-purple flame is produced. What is the likely identity of the metal? (b) Write a balanced chemical equation for the reaction of the white substance with water.

Short Answer

Expert verified
The likely identity of the metal is potassium (K), as the lilac-purple flame is associated with potassium. The balanced chemical equation for the reaction of the white substance (potassium superoxide) with water is: \[ 2 \mathrm{KO}_{2} (s) + 2 \mathrm{H}_{2}\mathrm{O} (l) \longrightarrow 2 \mathrm{KOH} (aq) + \mathrm{H}_{2}\mathrm{O}_{2} (aq) \]

Step by step solution

01

(a) Identify the alkali metal

We are given that the alkali metal reacts with oxygen to form a solid white substance. The presence of a lilac-purple flame is indicative of the alkali metal being potassium (K). This is because each alkali metal produces a characteristic flame color due to its atomic emission spectrum, and the lilac-purple flame is associated with potassium. Thus, the likely identity of the metal is potassium (K).
02

(b) Write balanced chemical equation for the reaction of the white substance with water

We have established that the metal in question is potassium (K). When potassium reacts with oxygen, it forms potassium superoxide (KO₂), which is a solid white substance. The reaction of potassium superoxide with water produces potassium hydroxide (KOH) and hydrogen peroxide (H₂O₂). The balanced chemical equation for this reaction is: \[ 2 \mathrm{KO}_{2} (s) + 2 \mathrm{H}_{2}\mathrm{O} (l) \longrightarrow 2 \mathrm{KOH} (aq) + \mathrm{H}_{2}\mathrm{O}_{2} (aq) \] This equation represents the reaction between the potassium superoxide and water, resulting in the formation of potassium hydroxide and hydrogen peroxide.

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Most popular questions from this chapter

An element X reacts with oxygen to form \(\mathrm{XO}_{2}\) and with chlorine to form \(\mathrm{XCl}_{4} . \mathrm{XO}_{2}\) is a white solid that melts at high temperatures (above \(1000^{\circ} \mathrm{C}\) ). Under usual conditions, \(\mathrm{XCl}_{4}\) is a colorless liquid with a boiling point of $58^{\circ} \mathrm{C}$. (a) \(\mathrm{XCl}_{4}\) reacts with water to form \(\mathrm{XO}_{2}\) and another product. What is the likely identity of the other product? (b) Do you think that element \(\mathrm{X}\) is a metal, nonmetal, or metalloid? (c) By using a sourcebook such as the CRC Handbook of Chemistry and Physics, try to determine the identity of element X.

Which of the following statements about effective nuclear charge for the outermost valence electron of an atom is incorrect? (i) The effective nuclear charge can be thought of as the true nuclear charge minus a screening constant due to the other electrons in the atom. (ii) Effective nuclear charge increases (iii) Valence going left to right across a row of the periodic table. electrons screen the nuclear charge more effectively than do core electrons. (iv) The effective nuclear charge shows a sudden decrease when we go from the end of one row to the beginning of the next row of the periodic table. (v) The change in effective nuclear charge going down a column of the periodic table is generally less than that going across a row of the periodic table.

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 mol of \(\mathrm{KO}_{2}(s)\) 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 \(\mathrm{KO}_{2}(s)\) and \(\mathrm{CO}_{2}(g) .(\mathbf{b})\) 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?

(a) Why is calcium generally more reactive than beryllium? (b) Why is calcium generally less reactive than rubidium?

The electron affinities, in \(\mathrm{kJ} / \mathrm{mol}\), for the group 11 and group 12 metals are as follows: (a) Why are the electron affinities of the group 12 elements greater than zero? (b) Why do the electron affinities of the group 11 elements become more negative as we move down the group? [Hint: Examine the trends in the electron affinities of other groups as we proceed down the periodic table.]
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