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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 alkali metal is likely potassium (K) due to the lilac-purple flame color. The white substance is potassium oxide (K2O). The balanced chemical equation for the reaction of K2O with water is \(K_{2}O + 2H_{2}O \rightarrow 2KOH + H_{2}O_{2}\).

Step by step solution

01

Identify the alkali metal based on the flame color

The fact that the substance produces a lilac-purple flame when tested in a burner flame points to the alkali metal being potassium (K). This is because the characteristic flame color of potassium is lilac-purple.
02

Determine the formula of the white substance

The white substance is formed when potassium (K) reacts with oxygen (O). Alkali metals typically form compounds with oxygen in the form of M2O, where M is the alkali metal. So, the white substance is likely potassium oxide (K2O).
03

Write the balanced chemical equation for the reaction of K2O with water

When potassium oxide (K2O) reacts with water (H2O), it forms potassium hydroxide (KOH) and hydrogen peroxide (H2O2). To balance the equation, we need to ensure that the number of atoms of each element on the reactant side is equal to the number of atoms of the same element on the product side. The balanced chemical equation for the reaction of K2O with water is: \(K_{2}O + 2H_{2}O \rightarrow 2KOH + H_{2}O_{2}\)

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Most popular questions from this chapter

Moseley established the concept of atomic number by studying X rays emitted by the elements. The \(X\) rays emitted by some of the elements have the following wavelengths: $$ \begin{array}{lc} \hline \text { Element } & \text { Wavelength } \\ \hline \mathrm{Ne} & 14.610 \\ \mathrm{Ca} & 3.358 \\ \mathrm{Zn} & 1.435 \\ \mathrm{Zr} & 0.786 \\ \mathrm{Sn} & 0.491 \\ \hline \end{array} $$ (a) Calculate the frequency, \(\nu\), of the \(\mathrm{X}\) rays emitted by each of the elements, in Hz. (b) Plot the square root of \(\nu\) versus the atomic number of the element. What do you observe about the plot? (c) Explain how the plot in part (b) allowed Moseley to predict the existence of undiscovered elements. (d) Use the result from part (b) to predict the \(\mathrm{X}\)-ray wavelength emitted by iron. (e) A particular element emits X rays with a wavelength of \(0.980 \AA\). What element do you think it is?

Consider the first ionization energy of neon and the electron affinity of fluorine. (a) Write equations, including electron configurations, for each process. (b) These two quantities have opposite signs. Which will be positive, and which will be negative? (c) Would you expect the magnitudes of these two quantities to be equal? If not, which one would you expect to be larger?

Write the electron configurations for the following ions, and determine which have noble-gas configurations: (a) \(\mathrm{Ru}^{3+}\), (b) \(\mathrm{As}^{3-}\), (c) \(\mathrm{Y}^{3+}\), (d) \(\mathrm{Pd}^{2+}\), (e) \(\mathrm{Pb}^{2+}\), (f) \(\mathrm{Au}^{3+}\).

(a) Because an exact outer boundary cannot be measured or even calculated for an atom, how are atomic radii determined? (b) What is the difference between a bonding radius and a nonbonding radius? (c) For a given element, which one is larger? (d) If a free atom reacts to become part of a molecule, would you say that the atom gets smaller or larger?

Detailed calculations show that the value of \(Z_{\text {eff }}\) for the outermost electrons in \(\mathrm{Si}\) and \(\mathrm{Cl}\) atoms is \(4.29+\) and \(6.12+\), respectively. (a) What value do you estimate for \(Z_{\text {eff }}\) experienced by the outermost electron in both \(\mathrm{Si}\) and \(\mathrm{Cl}\) by assuming core electrons contribute \(1.00\) and valence electrons contribute \(0.00\) to the screening constant? (b) What values do you estimate for \(Z_{\text {eff }}\) using Slater's rules? (c) Which approach gives a more accurate estimate of \(Z_{\text {eff? }}\) ? (d) Which method of approximation more accurately accounts for the steady increase in \(Z_{\text {eff }}\) that occurs upon moving left to right across a period? (e) Predict \(Z_{\text {eff }}\) for a valence electron in \(\mathrm{P}\), phosphorus, based on the calculations for \(\mathrm{Si}\) and \(\mathrm{Cl}\).
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