Question

 

A sample of an unkown metal is reacted with hydrochloric acid and collected over water in a 50.00mL buret. Given the balanced chemical equation, determine the empirical molar mass and identify the metal: 2X(s)+2HCL(aq)->2XCL(aq)+H2(g)

Mass of X	0.0636g
Volume of unmarked region of buret	5.2mL
Volume of meniscus (final)	19.77mL
Volume of difference of heights of water	13.00cm
Temperature	24.5°C
Corrected Barometric pressure	757.2 torr

Answer 1

To calculate the molar mass of the unknown metal, we need to know the amount of H₂ collected in the buret and apply a stoichiometric factor between X and H₂, with the reaction given.

H₂ is a gas. Then, we can apply the ideal gas equation:

To solve it for n (H₂):

(1)

The total pressure in the sistem is given by:

Where P_T is the barometric pressure, and P_H2O is the water vapor pressure at given temperature.

For a temperature of T = 24,5ºC, the water vapor pressure is P_H2O = 23.076 torr

Then, the pressure of H₂ collected is:

Converting pressure units:

The volume of difference of heights of water must be sustracted in terms of pressure, because this is the reference level for hydrostatic pressure:

Finally:

The volume occupied by the collected H₂ is given by the volume difference in the buret, it is to say:

Converting volume units:

The temperature in Kelvin is:

And the gas constant is:

The number of moles of H₂ is:

The number of moles of X metal:

The empirical molar mass of X is given by:

According to the periodic table, and the formula of product given in the reaction, the unknown metal is sodium (Na) with an atomic weight of 22.99 g/mol