Gcalculate the molecular weights for nh 3 nh3 and sf 6 sf6 . nh 3 = nh3= g / mol g/mol sf 6 = sf6= g / mol g/mol how many grams of nh 3 nh3 are needed to provide the same number of molecules as in 0.45 0.45 g of sf 6 sf6 ?

- the molecular weight of  NH₃ =17 gr/mol

- the molecular weight of  SF₆ = 146 gr/mol

- 0.0524 gr of NH₃ contain the same number of molecules than 0.45 g of SF₆

Explanation:

the molecular weight M of

- M of NH₃ = M of N + 3* M of H = 14 gr/mol + 3 * ( 1gr/mol) = 17 gr/mol

- M of SF₆= M of S + 6* M of F = 32 gr/mol + 6* (19 gr/mol) = 146 gr/mol

since each mole n has the same number of molecules N ( N=6.023*10²³ molecules/mole = constant ) and the number of moles is related to the mass through

n= m/M , where m= mass

then the number of molecules

molecules = n*N =   m/M*N

then

molecules of NH₃ =  m₁/M₁*N

molecules of SF₆ =  m₂/M₂*N

for both to be equal

molecules of NH₃ = molecules of SF₆

m₁/M₁*N = m₂/M₂*N

m₁ = m₂*M₁/M₂

replacing values

m₁ =m₂* (M₁/M₂) = 0.45 g * (17 gr/mol/146 gr/mol) = 0.0524 gr of NH₃

then 0.0524 gr of NH₃ contain the same number of molecules than 0.45 g of SF₆

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