Question

The edge length of the unit cell of tungsten is 316 pm; The unit cell is intrinsic cubic. Tungsten has a density of 19,26g/cm (a) Calculate the mass of actes tungsten atom. (b) Calculate the atomic weight of the tungsten ing Imol.

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Answer 1

Tongsten is a body centered cubic(intrisic cubic)

Given edge length , a =316pm = 316 × 10-¹⁰cm

Density = 19.26g/ cm³

Number of unit cell in BCC = 2

To determine mass of a tongsten atom first we have to calculate atomic weight

Hence the answer of part b is given first and

b) atomic weight of tongsten

From the equation

Density = atomic mass × 2/unit cell volume × NAa

Atomic mass = density × NA × unit cell volume /2

Where NA = 6.023×10²³

Unit cell volume = a³ =( 316×10-¹⁰)³ = 31554496 × 10-³⁰

= 3.2×10-²³cm³/unit cell

Then atomic mass =( 3.2×10-²³ × 19.26 × 6.023× 10²³)/2

= 185.60g/mol

a) 185.60g/ mol contain 6.023×10²³ atoms then mass of one atom tongsten is given by

Mass of a tongsten atom = 185.60/ 6.023×10²³

=3.1×10-²²g / atom

Ans:

a) mass of a tongsten atom = 3.1 ×10-²²g / atom

b) atomic weight of tongsten = 185.60g/mol