Chemistry 20

 A solution consists of a solute or solutes dissolved in a solvent: › The substance that is present in the largest quantity (whether by volume, mass or amount) is usually called the solvent. › The substances that are dissolved in the solvent are called the solutes.

 Solutes and solvents can come in different states of matter.

 Substances that dissolve in water to form solutions that conduct electric current are called electrolytes.  Electrolytes include soluble ionic compounds (including bases) and acids.  Substances that do not conduct electric current when they dissolve in water are called non-electrolytes.  Non-electrolytes include molecular compounds.

 As a soluble ionic compound is dissolved in water, the ionic bonds between the cations (+) and anions (-) are broken and the ions dissociate apart from one another.  Examples of dissociation equations:  NaCl (s) in water Na + (aq) + Cl - (aq)  CaS (s) in water Ca 2+ (aq) + S 2- (aq)  (NH 4 ) 2 CO 3(s) in water 2 NH 4 + (aq) + CO 3 2- (aq)  Al 2 (SO 4 ) 3(s) in water 2 Al 3+ (aq) + 3 SO 4 2- (aq)

 Some ionic compounds do not dissolve to any great extent – they are insoluble (or only slightly soluble ).  When placed in water, very little of the actual compound (if any) will dissociate.  CuCl (s) in water CuCl (s)  Sn 3 (PO 4 ) 3(s) in water Sn 3 (PO 4 ) 3(s)

Chemistry 20

 Most molecular compounds are non- electrolytes.  In pure form, the molecules of these compounds are held together by intermolecular forces such as London (dispersion) forces and dipole-dipole forces.  When these compounds dissolve, the intermolecular bonds break and the solute molecules disperse throughout the solvent.  While this process (known as separation ) happens, the individual molecules remain intact.

Examples of separation equations:  C 12 H 22 O 11(s) in water C 12 H 22 O 11(aq)  C 3 H 7 OH (l) in water C 3 H 7 OH (aq)  CO 2(g) in water CO 2(aq)

 As with ionic compounds, not all molecular compounds are soluble in water.  Paraffin wax, C 25 H 52(s), is used in wax paper and helps to keep the paper from falling apart when it becomes damp because the wax is insoluble in water. C 25 H 52(s) in water C 25 H 52(s)

 Some molecular compounds are found to conduct electricity after they have been dissolved.  For example, hydrogen chloride, HCl (g), is a molecular compound, yet an aqueous solution of hydrogen chloride conducts electric current.  HCl (g) in water H + (aq) + Cl - (aq)  Acids are electrolytes because they ionize (form ions) in water.

 An electric conductivity apparatus can be used to determine whether a solution is an electrolyte or non-electrolyte.  Non-electrolytes can be classified as molecular compounds.

 Ionic compounds and acids are electrolytes. Further testing with litmus paper can help to differentiate between ionic compounds and acids.  Some ionic compounds contain the hydroxide ion. For example, sodium hydroxide, NaOH (s). These compounds are bases.

 You have 4 solutions in unidentified beakers: › hydrochloric acid (HCl (aq) ) › sodium chloride (NaCl (aq) ) › sodium hydroxide(NaOH (aq) ) › sucrose (C 12 H 22 O 11(aq) ).  Test each solution with an electrical conductivity apparatus, red litmus paper and blue litmus paper.  Record your observations and the identification of each solute.