Question

Which element has the greatest density at STP?
(1) scandium (3) silicon
(2) selenium (4) sodium

Answer 1

Answer:

            Selenium has the greatest density at STP.

Explanation:

                   According to Ideal gas equation,

                                                P V  =  n R T

where;

             n =  m/M

Therefore,

                                                P V  =  m R T / M

Rearranging,

                                                P M  =  (m/V) R T

Also,

             m/V  =  density  = d

So,

                                                P M  =  d R T

Solving for density,

                                                d  =  P M / R T

According to this equation density is directly proportional to Molar mass of a substance. Hence, the Atomic masses of given compounds are listed below,

                                                Scandium =  44.96 g.mol⁻¹

                                                Selenium  =  78.97 g.mol⁻¹

                                                Silicon  =  28.09 g.mol⁻¹

                                                Sodium  =  22.99 g.mol⁻¹

Therefore, selenium having the greatest Atomic Mass will have the greatest density. The densities of given elements are as follow;

                                                Scandium =  2.98 g.cm⁻³

                                                Selenium  =  4.81 g.cm⁻³

                                                Silicon  =  2.33 g.cm⁻³

                                                Sodium  =  0.96 g.cm⁻³

Answer 2

$\boxed{\left( 2 \right){\text{ Selenium}}}$  has the greatest density at STP.

Further Explanation:

Ideal gas law is the equation of state for any hypothetical gas. The expression for the ideal gas equation is as follows:

${\text{PV}} = {\text{nRT}}$               …… (1)                                                                

Here,

P is the pressure.

V is the volume.

T is the absolute temperature.

n is the number of moles.

R is the universal gas constant.

The formula to calculate the number of moles is as follows:

${\text{n}}=\dfrac{{\text{m}}}{{\text{M}}}$        ...... (2)                                                                              

Here,

n is the number of moles.

m is the mass.

M is the molar mass.

Substitute the value of n from equation (2) in equation (1).

${\text{PV}} = \dfrac{{{\text{mRT}}}}{{\text{M}}}$      …… (3)                                                        

Rearrange equation (3) as follows:

${\text{PM}} = \dfrac{{{\text{mRT}}}}{{\text{V}}}$      …… (4)

                                                       

The formula to calculate density is as follows:

${\rho }} = \dfrac{{\text{m}}}{{\text{V}}}$     ...... (5)                                                                                    

Here,

${\rho }}$ is the density.

m is the mass.

V is the volume.

Substitute equation (5) in equation (4).

${\text{PM}} = \rho{\text{RT}}$      …… (6)                                                                      

Rearrange equation (6) to calculate the density.

${\rho }} = \dfrac{{{\text{PM}}}}{{{\text{RT}}}}$     ...... (7)                                                                      

At STP, T and P remain constant, R is already a constant. So according to equation (7), density of substance is directly proportional to the molar mass of the substance.

The molar mass of scandium is 44.96 g/mol.

The molar mass of selenium is 78.97 g/mol.

The molar mass of silicon is 28.09 g/mol.

The molar mass of sodium is 22.99 g/mol.

The molar mass of selenium is the highest among the given elements so its density will be the greatest.

Learn more:

1. Which statement is true for Boyle’s law: https://brainly.com/question/1158880

2. Calculation of volume of gas: https://brainly.com/question/3636135

Answer details:

Grade: Senior School

Subject: Chemistry

Chapter: Ideal gas equation

Keywords: P, V, n, R, T, ideal gas, pressure, volume, selenium, sodium, scandium, silicon, 22.99 g/mol, 78.97 g/mol, 28.09 g/mol, 44.96 g/mol, density, molar mass.