Acids and Bases

The basics… Acids and bases are a group of compounds that share similar chemical properties. There are a few ways that this group can be classified. Lewis Acids and Bases Brønsted-Lowry Acid and Bases Arrhenius Acid and Bases

Arrhenius Acids and Bases Arrhenius’ is the most common definition of acidic and basic compounds. Acid: Releases an H+ (hydronium) ion in solution – HA  H + + A - Base: Releases an OH- (hydroxide) ion in solution – BOH  B + + OH - or H 3 O +

Common Arrhenius Acids and Bases HCl  H + + Cl - Ca(OH) 2  Ca OH -

Regents Question H-H- H+H+ H3O+H3O+ OH - BOH  B + + OH -

An Arrhenius Acid will produce which positively charged ion in solution? 1.Hydronium ion 2.Hydride ion 3.Hydroxide ion 4.Hydrogen

In the following neutralization reaction, which compound is considered an Arrhenius base? HCl + NaOH  H 2 O + NaCl 1.HCl 2.NaOH 3.H 2 O 4.NaCl

Brønsted-Lowry Model While Arrhenius was H + and OH -, Brønsted- Lowry focused exclusively on the H +. Brønsted-Lowry Acid: Donates an H+ ion Brønsted-Lowry Base: Accepts an H+ ion HCl + NH 3  NH Cl - Donates H+ Accepts H+

Who is the Brønsted-Lowry Base? HF + H 2 O  H 3 O + + F - 1.HF 2.H 2 O 3.H 3 O + 4.F -

Who is the Brønsted-Lowry Acid? H 3 O + + Cl -  H 2 O + HCl 1.HCl 2.H 2 O 3.H 3 O + 4.Cl -

Lewis’ Model: Acids and Bases Lewis’ Model further expands the definition of acids and bases Lewis Acid: Electron-Pair Acceptor Lewis Base: Electron-Pair Donor Lewis Acid Lewis Base Accepts Electrons Donates Electrons

Strengths of Acids and Bases Ionize: To break apart into ions in solution A strong acid/base will break apart completely A weak acid/base will produce fewer ions HCl  H + + Cl - HF  HF + H + + F - Completely Ionizes Partially Ionizes

pH Scale We measure the strength of Arrhenius acids using the pH scale. Neutral BaseAcid

pH Scale pH measures the concentration of H+ ions in solution An increase of 1 pH means a 10 times increase in OH - (or a 10 time decrease in H + ) At a pH of 7 (neutral) there are equal amounts of H + and OH - in solution. Acids have more H+ in solution Bases have less H+ in solution

Which of the following compounds is an Arrhenius Acid? 1.NaOH 2.NH 3 3.CaCl 2 4.H 2 SO 4

In the following equation, which compound is the Brønsted-Lowry base? HCl + H 2 O  H 3 O + + Cl - 1.Cl - 2.H 3 O + 3.H 2 O 4.HCl

Measures of Concentration

Concentration The amount of a solute in a solvent is something that we can quantify (assign a number to). We measure this in terms of molarity:

Moles

Calculating Molarity Consider the following statement: In a 500L solution, 50 moles of NaCl are dissolved.

Calculating Molarity Consider the following statement: 30 moles of KCl are disssolved in 60 L solution.

Significant Figures

Not All Numbers Were Created Equal When we are measuring an object, we always guess a little

Guessing Definite Guess

Remember, you can only guess on one number.

Sig Figs Rules When adding or subtracting measurements, your answer can have no more decimal places than the measurement with the fewest decimal places

Sig Figs Rules When multiplying or dividing measurements, your answer can have no more numbers than the fewest number of significant (definite) figures Sig Fig

The Rules of Zero Atlantic Right Pacific Left

The Rules of Zero Atlantic Absent Right Pacific Present Left How many significant figures? Determine if there is a decimal present or absent.

The Rules of Zero Atlantic Right Pacific Left How many significant figures? Start counting with the first non-zero number

The Rules of Zero Atlantic Absent Right Pacific Present Left How many significant figures? 5 Sig Figs

The Rules of Zero Atlantic Absent Right Pacific Present Left How many significant figures? 3 Sig Figs

The Rules of Zero Atlantic Absent Right Pacific Present Left How many significant figures? 4 Sig Figs

Acid-Base Titrations Classic Part II Question

What we know… An Arrhenius acid is one that produces H + or H 3 O + in solution. When an acid reacts with a base, a neutralization reaction occurs. A neutralization reaction produces a salt and water each and every time.

Neutralization Reactions In a neutralization reaction, acid reacts with base to produce salt and water. Neutralization reactions are a type of double replacement reaction HCl + Ca(OH) 2  H 2 O + CaCl 2 AcidBaseWaterSalt

Titration reaction Titration reactions are used to determine the concentration of an unknown acid. M A V A = M B V B Moles H + = Moles OH - We can calculate the amount needed to neutralize any solution.

Titration How many milliliters of 3M NaOH are needed to neutralize 400mL of 2M HCl?

How much 4M NaOH is needed to neutralize 50mL of 2M HCl?

How much 6M HCl are needed to neutralize 100mL of 3M NaOH?

Titrating an Unknown Solution If we combine the information we have about titrations and indicators, we can determine the concentration of an unknown solution. We will need to use an indicator that has a changing point that is close to the neutral point.

Titration Acid of Unknown Concentration Base When the indicator changes color, all of the H+ has been neutralized. If we know the V A, the M B and V B of the system we can back calculate the concentration of the acid. VAVA VBVB MBMB

Titration What is the concentration of 50mL of an acid that is titrated to neutrality with 75mL of 3M NaOH?

Titration What is the concentration of 80mL of a base that is titrated to neutrality with 40mL of 2M HCl?

A student neutralized 16.4 milliliters of HCl by adding 12.7 milliliters of M KOH. What was the molarity of the HCl acid?