[tou]

Hi

The question is already solved, its from a book. I don't get the bold step or rather why it is 1000?

Calculate the volume of hydrogen gas evolved at 273K and 1atm pressure when 0.623g of Mg reacts with 27.3 cm³ of 1.25mol dm^-3 HCl.

Mg(s) + 2HCl(aq) -> H₂(g) + MgCl₂(aq)

Mg: 0.623/24.31 = 2.56 x 10^-2 mol
HCl: 1.25 x (27.3/1000) = 3.41 x 10^-2 mol

Thanks!

[Guitarmaniac86]

Its a thousand because you need to keep it in decimeters cube to keep both sides of the equation equal with respect to units.

There are 1000 cm3 in 1 decimeter.

Hope that helps.

[tou]

Aha, I thought the difference is 10, I guess I was mistaken. 

Thank you!

[boesmanprinses]

Hey Tou, hope this can Help you a bit

1Km--->1000 000mm
1Hm--->100 000mm
1Dm--->10 000mm
1m---->1000mm
1dm--->100mm
1cm--->10mm
1mm--->1mm

          but..

1 square mm =1mm X 1mm               ---->AREA(2)
         and
1cubic mm   = 1mm  x   1mm X 1mm  ---->VOLUME(3)

         thus..
10cm  X  10cm  X   10cm = 1000cm(3)
         and
1dm   X   1dm   X    1dm =  1dm(3)

         and therefor

1dm(3) = 1000cm(3)