Question

Compute the relative molecular masses of the following compound on the ¹²C scale:

(a) P₄O₁₀

(b) BrCl

(c) Ca(NO₃)₂

(d) KMnO₄

(e) (NH₄)₂SO₄

Short answer

(a) 284

(b) 115.357

(c) 164.0854

(d) 158.0323

(e) 132.1016.

Step-by-step solution

Relative molecular mass

The relative molecular mass of a compound is calculated by summing up the molecular mass of each element in that compound. It is symbolized as M_rand has no unit.

Calculating the relative mass of P4O10

The relative mass of P₄O₁₀ is calculated as:

$$\begin{gathered} {\text{P}}_{\text{4}}{\text{O}}_{\text{10}}\text{=(4×MassofP)+(10×MassofO)} \\ =(4\times 31)+(10\times 16) \\ =284 \end{gathered}$$

Thus, the relative mass of P₄O₁₀ is 284.

Calculating the relative mass of P4O10

The relative mass of BrCl is calculated as:

$$\begin{gathered} {\text{BrCl=(1×MassofBr}}^{+}{\text{)+(1×MassofCl}}^{-}\text{)} \\ =\left(1\times 79.904\right)+\left(1\times 35.453\right) \\ =115.357 \end{gathered}$$

Thus, the relative mass BrCl is 115.357.

Calculating the relative mass of Ca(NO3)2

The relative mass of Ca(NO₃)₂is calculated as:

$$\begin{gathered} \text{Ca}{\left({\text{NO}}_{\text{3}}\right)}_{\text{2}}\text{=(1×MassofCa)+}(2\times \mathrm{Mass}\mathrm{of}\mathrm{N})+(6\times \mathrm{Mass}\mathrm{of}\mathrm{O}) \\ =\left(1\times 40.078\right)+\left(2\times 14.0067\right)+\left(6\times 15.99\right) \\ =164.0854 \end{gathered}$$

Thus, the relative massCa(NO₃)₂is 164.0854.

Calculating the relative mass of KMnO4

The relative mass of KMnO₄is calculated as:

$$\begin{gathered} KMn{O}_4=(1\times \mathrm{Mass}\mathrm{of}\mathrm{K})+(1\times \mathrm{Mass}\mathrm{of}\mathrm{Mn})+(4\times \mathrm{Mass}\mathrm{of}\mathrm{O}) \\ =\left(1\times 39.0983\right)+\left(1\times 54.938\right)+\left(4\times 15.99\right) \\ =158.0323 \end{gathered}$$

Thus, the relative massKMnO₄is 158.0323.

Calculating the relative mass of (NH4)2SO4

The relative mass of (NH₄)₂SO₄is calculated as:

$$\begin{gathered} {\left(N{H}_4\right)}_{2}S{O}_4\text{=(2×MassofN)+}(8\times \mathrm{Mass}\mathrm{of}\mathrm{H})+(1\times \mathrm{Mass}\mathrm{of}S)+(4\times \mathrm{Mass}\mathrm{of}\mathrm{O}) \\ =\left(1\times 14.0067\right)+\left(1\times 1.0079\right)+\left(1\times 32.065\right)+\left(4\times 15.99\right) \\ =132.1016 \end{gathered}$$

Thus, the relativemass(NH₄)₂SO₄is 132.1016.