How are stoichiometry and molarity related?

1 Answer
Jul 16, 2018

Answer:

Well, stoichiometry requires EQUIVALENCE with respect to mass and charge....

Explanation:

And for an older treatment of the principles involved, see this old answer. And the fundamental principle of stoichiometry is #"garbage in equals garbage out"#. Every chemical reaction must be balanced with respect to mass and charge. A #10*g# mass of reactants from all sources yields at most a #10*g# mass of products.

#"Molarity"# is a concentration term, i.e. #"molarity"="moles of solute"/"volume of solution"#...and as such it has the units of #mol*L^-1#.. And so if we have TWO of the three quantities, say #"molarity"# and #"volume"#, we can get the third..#"moles of solute"#...

#"molarity"xx"volume"="moles"#....and this is certainly consistent dimensionally. What do I mean by this?

And a practical example? Well suppose I gots a #100*mL# volume of #HCl(aq)#, that is #1*mol*L^-1# with respect to #HCl#. What mass of sodium hydroxide is required for equivalence?

We write out the stoichiometric equation as a preliminary:

#HCl(aq) + NaOH(aq)rarr NaCl(aq) +H_2O(l)#

#n_"HCl"=0.100*Lxx1*mol*L^-1=0.100*mol#

And for equivalence we require equimolar sodium hydroxide...

#0.100*molxxunderbrace(40.0*g*mol^-1)_"molar mass of NaOH"=4.00*g#...i.e. a #4*g# mass of hydroxide is required for equivalence.