Ch 4 Chemistry The Central Science

Front 1

What is a solution

Back 1

A solution is a homogeneous mixture of two or more substances

Front 2

How is a solution made

Back 2

A solution is made when one substance (the solute) is dissolved in another (the solvent).

Front 3

What is a solute

Back 3

The solute is the substance that is present in the smallest amount.

Front 4

What are aqueous solutions

Back 4

Solutions in which water is the solvent are called aqueous solutions .

Front 5

What is an electrolyte solution?

Back 5

If a substance forms ions in solution, then the substance is an electrolyte and the solution conducts
electricity. An example is NaCl.

Front 6

What is a nonelectrolyte?

Back 6

If a substance does not form ions in solution, then the substance is a nonelectrolyte and the solution
does not conduct electricity. An example is sucrose.

Front 7

What happens when an ionic compound dissolves in water?

Back 7

When an ionic compound dissolves in water, the ions are said to dissociate

• This means that in solution, the solid no longer exists as a well-ordered arrangement of ions in
contact with one another.
• Instead, each ion is surrounded by a shell of water molecules.
• This tends to stabilize the ions in solution and prevent cations and anions from recombining.
• The positive ions have the oxygen atoms of water pointing towards the ion; negative ions have
the hydrogen atoms of water pointing towards the ion.
• The transport of ions through the solution causes electric current to flow through the solution.

Front 8

What happens when a molecular compund dissolves in water?

Back 8

When a molecular compound (e.g. CH3OH ) dissolves in water, there are no ions formed.
• Therefore, there is nothing in the solution to transport electric charge and the solution does not
conduct electricity.

Front 9

What are the molecular compound exceptions that dissolve in water?

Back 9

There are some important exceptions.
• For example, NH3(g) reacts with water to form NH4
+(aq) and OH– (aq).
• For example, HCl(g) in water ionizes to form H+(aq) and Cl– (aq).

Front 10

What are strong electrolytes?

Back 10

Compounds whose aqueous solutions conduct electricity well are called strong electrolytes.
• These substances exist only as ions in solution.
• Example: NaCl
NaCl(aq) -> Na+(aq) + Cl–(aq)
• The single arrow indicates that the Na+ and Cl– ions have no tendency to recombine to form NaCl
molecules.
• In general, soluble ionic compounds are strong electrolytes.

Front 11

What are weak electrolytes?

Back 11

Compounds whose aqueous solutions conduct electricity poorly are called weak electrolytes
• These substances exist as a mixture of ions and un-ionized molecules in solution.
• The predominant form of the solute is the un-ionized molecule.
• Example: acetic acid, HC2H3O2
HC2H3O2(aq) <-> ¾ H+(aq) + C2H3O2–(aq)
• The double arrow means that the reaction is significant in both directions.
• It indicates that there is a balance between the forward and reverse reactions.
• This balance produces a state of chemical equilibrium.

Front 12

What are precipitation reactions

Back 12

Reactions that result in the formation of an insoluble product are known as precipitation reactions.

Front 13

What is a precipitate

Back 13

A precipitate is an insoluble solid formed by a reaction in solution.
• Example: Pb(NO3)2(aq) + 2KI(aq) ->PbI2(s) + 2KNO3(aq)

Front 14

What is solubility?

Back 14

The solubility of a substance at a particular temperature is the amount of that substance that can be dissolved in a given quantity of solvent at that temperature.

Front 15

When is a substance regarded insolouble?

Back 15

A substance with a solubility of less than 0.01 mol/L is regarded as being insoluble.