Question

A 0.105-g sample of X2 contains 8.92x1020 molecules. The compound MX3 consists of 54.47% X by mass. What are the identities of M and X, and what is the correct name for MX3?

Answer 1

Answer:

The element X is chlorine.

The element M is Ytterium.

Ytterium (III) chloride is the correct name for $YCl_3$

Explanation:

Molecules of $X_2, N = 8.92\times 10^{20}$

Moles of $X_2, n= ?$

$N=n\times N_A$

$n=\frac{N}{N_A}=\frac{8.92\times 10^{20}}{6.022\times 10^{23} mol^{-1}}$

n = 0.001481 mol

Mass of $X_2, m=0.105 g$

Molar mass of $X_2=M$

$m=M\times n$

$M=\frac{m}{n}=\frac{0.105 g}{0.001481 mol}$

M = 70.87 g/mol

Atomic mass of X = $\frac{70.87 g/mol}{2}=35.435 g/mol$

X is a chlorine atom.

The compound $MX_3$ consists of 54.47% X by mass.

M' = Molar mass of compound $MX_3$

Percentage of X in compound = 54.47%

$54.47\%=\frac{3\times 35.435 g/mol}{M'}\times 100$

M' = 195.16 g/mol

Atomic mass of M = a

$195.16 g/mol=a+3\times 35.435 g/mol$

$a = 195.16 g/mol-3\times 35.435 g/mol$

a = 88.86 g./mol

The element M is Ytterium.

Ytterium (III) chloride is the correct name for $YCl_3$