Question

1. a student obtains a mixture of the chlorides of two unknown metals, x and z. the percent by mass of x and the percent by mass of z in the mixture is known. which of the following additional information is most helpful in calculating the mole percent of xcl(s) and of zcl(s) in the mixture? a. the number of isotopes of cl b. the molar masses of x and z c. the density of either xcl(s) or zcl(s) d. the percent by mass of cl in the mixture 12. a vessel contains a mixture of gases. the mass of each gas used to make the mixture is known. which of the following information is needed to determine the mole fraction of each gas in the mixture? a. the molar mass of each gas b. the density of the gases in the vessel c. the total pressure of the gases in the vessel d. the number of atoms per molecule for each gas 13. how many unpaired electrons are in the atom represented by the electron - configuration 1s²2s²2p⁶3s²3p⁶ above? a. 0 b. 1 c. 2 d. 3

Explanation:

11.

Step1: Recall mole - percent formula

Mole - percent of a component in a mixture is related to the number of moles of that component and the total number of moles of all components. To find the number of moles of \(XCl\) and \(ZCl\), we need to know the molar masses of \(X\) and \(Z\) since \(n=\frac{m}{M}\) (where \(n\) is the number of moles, \(m\) is the mass and \(M\) is the molar mass). Given the mass - percent of \(X\) and \(Z\), we can calculate the mass of \(X\) and \(Z\) in the mixture. Then, with the molar masses of \(X\) and \(Z\), we can find the number of moles of \(X\) and \(Z\), and subsequently the number of moles of \(XCl\) and \(ZCl\).

Step2: Analyze other options

The number of isotopes of \(Cl\) (A) is not relevant as it does not affect the calculation of the number of moles of \(XCl\) and \(ZCl\). The density of \(XCl\) or \(ZCl\) (C) is related to the physical state and volume - mass relationship, not to the mole - percent calculation. The percent by mass of \(Cl\) in the mixture (D) does not directly help in calculating the mole - percent of \(XCl\) and \(ZCl\) without knowing the molar masses of \(X\) and \(Z\).

Step1: Recall mole - fraction formula

The mole - fraction (\(x_i\)) of a gas \(i\) in a mixture is given by \(x_i=\frac{n_i}{n_{total}}\), where \(n_i\) is the number of moles of gas \(i\) and \(n_{total}\) is the total number of moles of all gases in the mixture. Given the mass of each gas (\(m_i\)), we can find the number of moles of each gas using the formula \(n_i = \frac{m_i}{M_i}\), where \(M_i\) is the molar mass of gas \(i\).

Step2: Analyze other options

The density of the gases in the vessel (B) is related to the mass - volume relationship and is not necessary for calculating mole - fractions. The total pressure of the gases in the vessel (C) is related to the ideal gas law and is not required for calculating mole - fractions from mass data. The number of atoms per molecule for each gas (D) is not relevant for calculating the mole - fraction from the mass of each gas; we need the molar masses to convert mass to moles.

Step1: Write the electron - configuration in orbital notation

The electron - configuration \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}\) corresponds to the element Argon (\(Ar\)). In orbital notation, the \(1s\) orbital has 2 paired electrons, the \(2s\) orbital has 2 paired electrons, the \(2p\) orbitals (\(2p_x\), \(2p_y\), \(2p_z\)) have 6 paired electrons, the \(3s\) orbital has 2 paired electrons and the \(3p\) orbitals (\(3p_x\), \(3p_y\), \(3p_z\)) have 6 paired electrons.

Step2: Determine the number of unpaired electrons

Since all electrons are paired in the orbitals of \(Ar\), the number of unpaired electrons is 0.

Answer:

B. The molar masses of X and Z

12.