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Stoichiometry of Reactions Between Ions in Solutions

Key Questions

  • 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.

  • Answer:

    How? The idea that not only mass is conserved but charge is conserved is a tenet of stoichiometry.

    Explanation:

    At its simplest level, stoichiometry embodies conservation of mass. If there are 10 g of reactant, at most there can be 10 g of product. But while mass is conserved in a chemical reaction; charge is also conserved. When we represent a redox reaction we use the addition/removal of electrons to represent reduction/oxidation respectively. Cross multiplication of the individual redox reactions shows how charge is conserved.

Questions