[darkazz]

Hello,

2NH3 + H2SO4 => (NH4)2SO4 ... there's 68g of NH3; what is the needed mass for H2SO4?
This was in my exam paper - I answered 392g, but it might have been 196g, I'm unsure, can anybody tell me?

Thank you a lot :-P

[DrCMS]

68g NH₃ is 4 moles (68/17 = 4) so you need 2 moles of H₂S0₄ 2x98 = 196g

[darkazz]

68g NH₃ is 4 moles (68/17 = 4) so you need 2 moles of H₂S0₄ 2x98 = 196g

why two moles though? I still don't get it :\

[DrCMS]

2 ammonia's react with 1 sulphuric acid

2NH₃ + H₂SO₄ => (NH₄)₂SO₄

so 4 ammonia's react with 2 sulphuric acids

4NH₃ + 2H₂SO₄ => 2(NH₄)₂SO₄

68g NH₃ = 4 moles of ammonia so they need 2 moles of sulphuric acid to react fully = 196g

[Borek]

http://www.chembuddy.com/?left=balancing-stoichiometry&right=stoichiometric-calculations

Read how to read reaction equation.

[jonnyset]

mole factor is 1/2 so

(1/2)(4) = 2