1.15 Using Solubility Rules to Predict Precipitate Formation

pp. 54 - 60

Chemical Reactions in Solution• A solution is a homogeneous mixture in which

a solute – substance in lesser quantity – is dissolved in a solvent – substance in greater quantity.

• An aqueous solution is a solution in which water is the solvent. – The subscript (aq) denotes an aqueous solution

• A solid that is formed as a result of the chemical reaction of two aqueous solutions is called a precipitate.

Solubililty• Solubility is a measure of the amount of a

substance that dissolves in water at a given temperature and pressure.

• A substance with low solubility will remain solid when mixed with water or precipitate out of the solution.– This is denoted with a subscript (s) for solid.

• Table 1 on p. 54 tells us which ionic compounds are soluble and which has low solubility.

Practice___ AgNO3(aq) + ___ CaCl2(aq)

___ NaOH(aq) + ___ Ca(NO3)2(aq)

• If both products are soluble, there is no reaction – write NR after the arrow

NaNO3(aq) + KCl(aq)

Total & Net Ionic Equations

• A total ionic equation depicts the separation of soluble ionic compounds into their respective ions– Re-write an each aqueous ionic compound as two

ions. If not aqueous just re-write the chemical.– e.g. Na2SO4(aq) = 2Na+

(aq) + SO42-

(aq)

– e.g. CaSO4(s) = CaSO4(s)

• Write the total ionic equation for the following reaction:– Na2SO4(aq) + CaCl2(aq) CaSO4(s) + 2NaCl(aq)

Total & Net Ionic Equations• 2Na+

(aq) + SO42-

(aq) + Ca2+(aq) + 2Cl-

(aq) CaSO4(s) + 2Na+

(aq) + 2Cl-(aq)

• If an ion exists on both sides of an equation it means it does not participate in the reaction and so it is called a spectator ion.

• A net ionic equation depicts only the ions that are involved in a chemical reaction.– Cross out the spectator ions in the total ionic

equation and re-write what’s left.

Net Ionic Equation

• Write the net ionic equation for the above reaction:

• 2Na+(aq) + SO4

2-(aq) + Ca2+

(aq) + 2Cl-(aq) CaSO4(s) + 2Na+

(aq) + 2Cl-(aq)

• After crossing out the spectator ions we are left with:

• SO42-

(aq) + Ca2+(aq) CaSO4(s)