Acid-Base PROTON Transfer reactions

Unit 2

Bronsted-Lowry acid and base theory

Acid - DONATES proton (H+)

Base - ACCEPTS proton

Acid-base reaction - exchange of protons from acid to base.

Conjugate Acid / Conjugate Base Pair

Conj. Acid = formed when Base gains H+

Conjugate Base = formed when Acid loses H+

Conjugate acid-base pair is a pair of species that differ by a proton (H+)

Amphiprotic and features.

Behaves as acid or base, can donate/accept proton depend on what they react with. E.g. H2O, HCO3^-, HSO4^-

-Has a H, and usually a negative charge.

Monoprotic vs Polyprotic (diprotic, triprotic).

Monoprotic - only donate 1 p. E.g. nitric, hydrochloric, ethanotic.

Polyprotic - donate more than one, in steps.

Diprotic - 2 protons donate, in 2 steps. E.g. sulfuric, carbonic.

Triprotic - 3 protons donate, ionise in 3 steps. E.g. Phosphoric, boric.

Concentration definition vs Dilute

concentration = acid/base - refers to no. of solute particles in a given volume.

Concentrated = large no.

Dilute = small no. of particles.

Strength, and ionisation of ACIDS

-how easily acid/base donates/accepts a proton, H+.

-Strong acid readily donates a proton, so they completely ionise.

-Weak acid doesn’t, partial ionisation (small proportion of acid) w/ reversable arrow.

Strength and Bronsted-Lowry theory - the connection between acid and base.

Acid strength - ability to donate hydrogen ions to base. Base strength - ability to accept H ions from acid.

Strength, and ionisation of BASES

Strong base - accepts proton easily. Weak base - doesn’t fully ionise.

Strength and Conjugate pairs

Strong Acid = Weak Conjugate Base

Strong Base = Weak Conjugate Acid

Molarity (M)

• concentration of a solution in moles per litre

• c=n/v

• 1 M, 1 molar, concentration of 1 mol/L, molarity of 1 M

pH formulas, relationship between [h30+] and [OH-]

If [h30+] or [OH-] increases, then the c of the over must decrease in proportion.

[h30+][OH-] expression - ionic product/ionisation constant, and represented by Kw.

Higher [h30+] = more acidic

pH definition and what pH is of neutral, acidic and basic

pH scale - used to measure the acidity of a solution.

at 25C: neutral - pH 7, acidic - pH less than 7, basic - pH greater than 7.

Stronger acid = lower pH.

In the labs, you can prepare solutions of a base of a required concentration by…

-diluting a more concentrated solution

-dissolving a weighed amount of the base in a measured volume of water.

Dilution and pH

Diluting acid - pH increase close to 7

Diluting base - pH decrease close to 7

How is pH measured

• quantitatively: a pH meter with accurate measurement

• qualitatively: pH indicators.

pH meters

instruments to acucrately measure pH, with varying sensitivity and accuracy, can be connection to computers to measure continuous pH changes with accuracy, and aren’t affected by colour/cloudiness of solutions.

Must be calibrated (with solution of accurately known pH), and temp considered, as pH varies w/ temp.

pH indicators, pros and cons

substances that are different colours in acid and base solution. Many from plants. Universal indicator helps estimate pH, and indicators are weak acids/bases.

Conjugate acid form of indicator - 1 colour.

Conjugate base form - another colour.

Pros: inexpensive, available.

Cons: chosen carefully for particular reaction, subjective aspect (naked eye), affected by temp, if solution tested is colour, may interfere with indicator colours.

Accuracy + Precision

Accurate data - close to actual, true value of measurement. Precise - all different data points close together.

Errors: 3 types.

Systematic (equipment, system errors), Random (variations in measurements), Personal (human error, shouldn’t be included in analysis).

metal + water →

metal hydroxide + hydrogen gas

Metal + oxygen →

metal oxide

Acid + metal →

salt + hydrogen gas  HX + M → MX + H2

Acid + metal carbonate →

salt + carbon dioxide + water HX + MCO3 → MX + CO2 + H2O

Acid + metal hydrogen carbonate →

salt + carbon dioxide + water HX + MHCO3 → MX + CO2 + H2O

Acid + metal hydroxide →

salt + water HX + MOH → MX + H2O

Ionic equation -

These reactions can be represented by an ionic and an overall equation:

Salt produced in reactions of ionic compounds - consists of metal cation + nonmetal anion from the acid. Salt will be in solution, so there will be spectator ions.

Neutralisation reaction -

when a solution of metal hydroxide is added to an acid solution, and the hydroxide ions react w/ hydronium ions.

Acid and base are neutralised when all hydroxide ions reacted w/ hydronium ions, forming water.