Acid- Base Reactions Acid- Base Reactions

Chapter 4 part IVChapter 4 part IV

Characteristics of acidsCharacteristics of acids SourSour Red litmus testRed litmus test Low pH <7Low pH <7 Arrhenius: Produce Arrhenius: Produce

H+ in water.H+ in water. Brømsted Lowry: Brømsted Lowry:

produce protons.produce protons. Lewis: Electron Lewis: Electron

acceptor.acceptor.

Characteristics of basesCharacteristics of bases

Slippery & bitterSlippery & bitter Blue litmus testBlue litmus test High pH >7High pH >7 Arrhenius: forms Arrhenius: forms

OH- in water.OH- in water. Brømsted Lowry: Brømsted Lowry:

accept protons.accept protons. Lewis: Electron Lewis: Electron

donor.donor.

Net Ionic EquationNet Ionic Equation

Of all strong acids plus strong bases:Of all strong acids plus strong bases:HH++ + OH + OH-- H H22OOBut what about weak acids and bases?But what about weak acids and bases? In a strong acid or base, it dissociates In a strong acid or base, it dissociates

completely in water (strong completely in water (strong electrolyte)electrolyte)

Weak acids and bases do not Weak acids and bases do not dissociate completely in waterdissociate completely in water

Weak electrolytesWeak electrolytes

In fact about 90% of acetic acid In fact about 90% of acetic acid remains intact in aqueous solution.remains intact in aqueous solution.

Therefore the net ionic equation of a Therefore the net ionic equation of a weak acid or base includes the intact weak acid or base includes the intact weak acid or base.weak acid or base.

Example:Example:

HCHC22HH33OO22 +Na +Na+++ OH+ OH-- H H22O+ CO+ C22HH33OO22--

+Na+Na++

Net Ionic:Net Ionic:

HCHC22HH33OO2 2 + OH+ OH-- H H22O + CO + C22HH33OO22--

Weak electrolytesWeak electrolytes

An example of a weak base is NHAn example of a weak base is NH33..So what is the net ionic equation for So what is the net ionic equation for

hydrochloric acid and ammonia?hydrochloric acid and ammonia?HCl + NHHCl + NH33 NH NH44

++ + Cl + Cl--

HH++ + Cl + Cl-- + NH + NH33 NH NH44++ + Cl + Cl--

HH++ + NH + NH33 NH NH44++

Stoichiometry of an acid/base Stoichiometry of an acid/base reaction: The steps.reaction: The steps.

1.1. List species present in the combined List species present in the combined solution, before any reaction occurs.solution, before any reaction occurs.

2.2. Decide what reaction will occur.Decide what reaction will occur.

3.3. Write out net ionic equation.Write out net ionic equation.

4.4. Calculate moles of reactant in Calculate moles of reactant in solution. Use volume of the original solution. Use volume of the original solution and its molarity.solution and its molarity.

5.5. Determine the Limiting reagent.Determine the Limiting reagent.

Stoichiometry of an acid/base Stoichiometry of an acid/base reaction: The steps.reaction: The steps.

6.6. Calculate the moles of required Calculate the moles of required reactant or product formed.reactant or product formed.

7.7. Convert to grams or volume as Convert to grams or volume as required.required.

8.8. In other words, after you answer the In other words, after you answer the question, reread the question and question, reread the question and make sure.make sure.

Example:Example:

What volume of 0.1 M HCl solution is What volume of 0.1 M HCl solution is needed to neutralize 25.0 mL of needed to neutralize 25.0 mL of 0.350 M NaOH?0.350 M NaOH?

AnswerAnswer

List the species: H+ Cl- Na+ OH-List the species: H+ Cl- Na+ OH-What are the possible products?What are the possible products?NaCl (s) And HNaCl (s) And H22O (l)O (l)NaCl is soluble therefore it is not a NaCl is soluble therefore it is not a

possible product in solution.possible product in solution.Write the balanced equation.Write the balanced equation.H+(aq) + OH-(aq) H+(aq) + OH-(aq) H H22O(l)O(l)

AnswerAnswer

Calculate moles of reactants:Calculate moles of reactants:OH- = 25 mL NaOH x (1L/1000mL)x OH- = 25 mL NaOH x (1L/1000mL)x

(0.350 mol OH-/L NaOH) = (0.350 mol OH-/L NaOH) = 8.75 x108.75 x10-3-3 mol OH- mol OH- No limiting reagent, finding volume of No limiting reagent, finding volume of

HClHClMoles of reactant needed: molar ration is Moles of reactant needed: molar ration is

1:1 therefore need 8.75 x 101:1 therefore need 8.75 x 10-3 -3 mols acid.mols acid.Convert to volume: V x M=molConvert to volume: V x M=mol

ThereforeTherefore

V x 0.100 mol H+ /L = 8.75 x 10V x 0.100 mol H+ /L = 8.75 x 10-3 mol -3 mol

H+H+V= 8.75 X 10V= 8.75 X 10-2 -2 LL