Question #320fe

1 Answer
Aug 25, 2015

You examine the charges on the ions that make up your compound.


When you're dealing with an ionic compound that are not of interest for acid - base reactions, you determine its equivalent weight by using the valency of its constituent ions.

In this context, an ion's valency is given by the absolute value of its charge. So, for example, if you have an ionic compound like #"XY"_2#, which is made up of two #"X"^(+)# cations and one #"Y"^(2-)# anion, you would calculate its equivalent weight like this

#color(blue)("equiv. weight XY"_2 = "molar weight X"^(+)/|"charge of X"^(+)| + ("molar weight of Y"""^(2-))/|"charge of Y"""^(-)|#

For that example, you would have

#"equiv. weight" = "molar weight X"^(+)/|1| + ("molar weight Y"""^(2-))/|(-2)|#

Notice that it does not matter how many cations or anions you get per formula unit.

For your example, barium chloride, #"BaCl"""_2#, each formula unit is made up of one #"Ba"^(2+)# cation and two #"Cl"^(-)# anions.

This means that the equivalent weight per mole of barium chloride is

#"equiv. weight BaCl"""_2 = "137.33 g"/|2| + "35.45 g"/|(-1)|#

#"equiv. weight BaCl"""_2 = "104.1 g"#

So remember, when you're not dealing with acids/bases, and assuming that you're not dealing with oxidants/reductants either, you can use this method to calculate the equivalent weight of ionic compounds.