Relative molecular mass using unified mass unit

[jadoreux]

The problem
A bubble of kryptopn (Kr) gas is formed underwater. The bubble has a volume of 2.14x10^-6m³ and contains 1.70x10²⁰ krypton molecules each of mass 1.39x10^-25kg. The pressure of the gas inside the bubble is 300kPa.

Calculate the relative molecular mass.The attempt at a solution

When i looked in the markscheme of this paper, the answer was M_r=1.39x10^-25/1.66x10^-27 as the answer. so does this mean to find the relative molecular mass i divide the mass by the unified mass unit?

 

[technician]

What you have calculated is the mass of a Krypton atom in amu (Atomic Mass Units)
= 83

 

[jadoreux]

is that the same as the relative molecular mass? what i worked out is what the markscheme had written as the result.

 

[technician]

I have asked a chemistry teacher friend and he said relative molecular mass is given in grams per mole4

 

[asteriatic]

Yes, to find the relative molecular mass using unified mass units, you would divide the given mass (in kilograms) by the unified mass unit (1.66x10^-27 kg). This will give you the value for the relative molecular mass in unified mass units. In this case, the answer is 1.39x10^-25 kg / 1.66x10^-27 kg = 83.7 unified mass units.