Question

Before Mendeleev published his periodic table, Döbereiner grouped elements with similar properties into "triads," in which the unknown properties of one member could be predicted by averaging known values of the properties of the others. To test this idea, predict the values of the following quantities:
(a) The atomic mass of K from the atomic masses of Na and Rb
(b) The melting point of Br₂ from the melting points of Cl₂ (-101.0°C) and I₂ (113.6°C) (actual value = - 7.2°C)

Answer 1

Answer:

a) The atomic mass of the potassium is 54.23 amu.

b) The melting point of bromine gas is 6.3°C.

Explanation:

a) Atomic mass of Na =22.99 amu

Atomic mass of Rb = 85.47 amu

Döbereiner triad = Na , K ,Rb

Taking average of  atomic masses of  Na and Rb

Atomic mass of the K = $\frac{22.99 amu+85.47 amu}{2}=54.23 amu$

The atomic mass of the potassium is 54.23 amu.

b) Melting point of chlorine gas =-101.0°C

Melting point of iodine gas =113.6°C

Döbereiner triad = Cl, Br , I

Melting point of bromine gas :

=$\frac{-101.0^oC +113.6^oC}{2}=6.3^oC$

The melting point of chlorine gas is 6.3°C.