How calculate equivalent weight?

Answer 1

Equivalent Weight is an archaic name for 'Moles'.

Moles = mass(g) / Mr ( Relative molecular mass). or Ar (Relative Atomic Mass).

If we take the reaction of sulphuric acid and sodium hydroxide.

First write down the BALANCED reaction eq'n.

H2SO4 + 2NaOH = Na2SO4 + 2H2O

Notice the molar ratios are 1:2::1:2

So if we have 49g (H2SO4) , how much , by mass of sodium hydroxide, do we need to neutralise the acid. ? This mass of sodium hydroxide is the Equivalent Weight.

First calculate the Mr(H2SO4) from atomic masses on the Periodic Table.

2 x H = 2 x 1 = 2

1 x S = 1 x 32 = 32

4 x O = 4 x 16 = 64

2 + 32 + 64 = 98

So moles(H2SO4) = 49g / 98 = 0.5 mole.

By molar ratios above

1 mole reacts with 2 moles

Hence

0.5 moles reacts with 1 mole.

So we need 1 mole(NaOH)

Again calculate the Mr(NaOH)

1 x Na = 1 x 23 = 23

1 x O = 1 x 16 = 16

1 x H = 1 x 1 = 1

23 + 16 + 1 = 40

Using the moles equation again

moles = mass( g)/Mr

Algebraically rearranging

mass(g) = moles X Mr

Mass(NaOH) = 1 moles X 40 =

mass(NaOh) = 40 g ( The 'Equivalent Weight). This is the mass required to neutralise 49 g of sulphuric acid.

Answer 2

To calculate the equivalent weight of a compound, simply add up the sum of equivalent weight of the ions. For example, Sodium chloride's equivalent weight can be express as 23/1 +35.5/1=58.5. It's unnecessary to multiple the numbers of ions. For instance, Al2O3 is express as 27/3 +16/2=17. For clusters (multiatom particle), divide the molecular mass by the charge. SO4- is expressed as 96/2.

More example: CaCO3 40/2+60/2=50

MgSO4 24/2+96/2=60

Answer 3

To calculate the equivalent weight of a substance, you need to divide the molar mass of the substance by the change in oxidation number per molecule. For example, for an acid or base, the equivalent weight is determined by the number of acidic or basic hydrogen atoms that can be exchanged in a reaction.

Answer 4

Equivalent weight is the molecular weight/functionality. Sulfuric acid is 98 molecular weight with two protons, so its equivalent weight is 49.

Answer 5

molecular weight divide by valency