Electrolytes are compounds that ionize in water to produce aqueous solutions that conduct an electric current. Nonelectrolytes are substances that do not ionize, remain as molecules, and do not conduct an electric current.

Strength: Strong electrolytes are molecules that ionize 100% (or nearly so) and conduct an electric current well. Weak electrolytes barely or partially ionize; most molecules remaining un-ionized, and conduct an electric current poorly.

Examples: Nitric acid (HNO₃) is a strong electrolyte. HNO₃ => H⁺¹ + NO₃^-1

If 1.00 mole of HNO₃ is dissolved in water, it will ionize to produce 1.00 mole of H⁺¹ and 1.00 mole of NO₃^-1 . There will not be any HNO₃left, unionized. By contrast, one mole of a weak electrolyte will produce much less than 1.00 mole of its constituent ions. One mole of acetic acid

HC₂H₃O₂ <=> H⁺¹ + C₂H₃O₂^-1

might produce .05 moles of H⁺¹ and .05 moles of C₂H₃O₂^-1 and still contain .95 moles of the original acetic acid.

Some problems with detailed solutions:

1. Calculate the concentrations of ions in .020 M HCl solution. HCl is a strong electrolyte.

	HCl =>	H+1	+ Cl-1
moles/liter before ionization	.020
moles/liter after ionization	none	.020	.020

2. Calculate the concentrations of ions in .015 M Ba(OH)₂ solution. Ba(OH)₂ is a strong electrolyte.

First, how will Ba(OH)₂ ionize? Ba, in group 2A, should ionize by losing 2 electrons to form a +2 ion. [Recall that during the mass spectrometry/combining capacity unit you discovered that Ba would have a combining capacity of 2; and during the ionization potential unit, you discovered that this was because Ba had two outer electrons with very low ionization potentials.] Barium’s electronegativity is 1.0 indicating a very weak hold on electrons. Oxygen’s electronegativity is 3.5, meaning an electronegativity difference of 2.5, a condition for ionic bonding. What about the two OH groups? H’s electronegativity is 2.1, so there is an electronegativity difference with oxygen of 1.4, suggesting a polar but NOT an ionic bond between O and H. Where will barium’s two lost electrons go? One will go to each OH group.

	Ba(OH)2 =>	Ba+2	+ 2OH-1
moles/liter before ionization	.015
moles/liter after ionization	none	.015	.030

3. Calculate the concentrations of ions in a solution that contains .92 g of magnesium bromide in 500 mL of solution.
Magnesium bromide, with its big electronegativity difference, is a strong electrolyte. The formula, molecular weight and ionic charges are easily obtained from the periodic table.

formula: MgBr2	molecular weight: 24.3 + 80.0 + 80.0 = 184.3
ionic charges: Mg+2 +2Br -1	Molarity = (.92/184.3) moles /.500 liter = .010 moles/liter

	MgBr2 =>	Mg+2	+ 2Br -1
moles/liter before ionization	.010
moles/liter after ionization	none	.010	.020

More problems:

Problem	Solution
What are the concentrations of the ions in .010 M NaCl?	[Na+1] = [Cl -1] = .010 M
What are the concentrations of the ions in .015 M K2SO4	[K+1] = .030M, [SO4 -2] = .015M
3.63 g of KAl(SO4)2 are dissolved in .250 L of solution. What are the ionic concentrations?	[K+1] = [Al+3] = .0562 M, [SO4 -2] = .112 M
.269 g HNO3 are added to 36.3 mL of 1.18 M HNO3 solution. Assume no change in solution volume. What are the final concentrations of the ions?	[H+1] = [NO3-1] = 1.30 M

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