Unit 3

Acid/Base Equilibria

Defining what an acis is is difficult, there are 3 working definitons.

Properties of Acids

• Low pH

• Turns blue litmus dye to red

• corrosive

• react withe metal to produce H2

• Reacts withe carbonates to produce CO2

• Reacts with bases to produce ionic salts

• sour tasting

• conduct electric current

Base Properties

• High pH

• Turns red litmus dye to blue

• corussive

• reacts with acids to produce ionic salts

• bitter taste

• soapy feel

• will conduct an electric current in solution

Common Acids

• Hydrocloric Acid - HCL

• Nitric Acid - HNO3

• Sulphuric Acid - H2SO4

• Carbonic Acid - H2CO3

• Phospheric Acid - H3PO4

• Acetic Acid - HCH3OO or CH3C00H

Common Bases

• Sodium Hydroxide

• Magnesium Hydroxide

• Aluminium Hydroxide

• Amommonium Hydroxide

Arrhenius definition of acids + bases

Acids - Compunds that can ionise to produce hydrogen ions

Bases- Compounds that can ionise to produce hydroxide ions

Thre types of Arrhenius Acids

• Monoprotic Acids - Ioise to produce one H+ ions

  • Hcl

  • HNO3

  • CH3COOH

• Diprotic Acids - Ioise to produce two H+ ions

  • H2SO4

  • H2CO3

• Triprotic Acids - Ioise to produce three H+ ions

  • H3PO4

Brønsted–Lowry acid–base theory

• Donate a proton -- acids

• Base - accepts a proton

Conjugate Acids and Bases

Acid/Base reaction in closed systems often reach a state of equilibrium

NH3+H2O→NH4+ +OH-

In the foraward reaction water donates a proton (H+) to NH3 therefore it is acting like an acid

NH3 accepts the proton (H+) from water therefore it is acting like a base

In the reverse rtn NH4+ donates the proton (H+) to OH- therefore it is acting like an acid

The compund is known as conjugate acid

In the reverse rtn OH- accepts a proton (H+) from NH4+ therefore it is acting like a base

This compund is known as the conjugate base

Conjugate Acid = The base that has accepted a proton (H+)

Conjugate Base = Is what is left after on acid has donated its proton (H+)

Conjugate acids and bases always exists in pairs

A conjugate Acid/Base pair are two substances that differ by one one hydrogen

Pure water has the ability to conduct an electric curent

water has positive and negativ ions

H20→H++OH

H20→H30++OH-

Buffers:

Buffers are solutions that resiest changes in ph.

They are comprosed of a mixture of weak acids and its conjugate base.

Buffers act like a chemical sponge and absorb excess h+ ions or oh- ions

Disassociation Constants

More Ka/Kb Clc

If K<1 state that the acid at equlibrium is equal to inital concentration:

M1V1=M2V2

Titration

Titrations are used to accuretly measure the concentration of an unkown solution of an acid or a base.

The procuderes involves adding a known value of the unkown solution to a flask.

A solution of known concentration is the titrated until an equivilance point.

The equvilance point occurs when chemicals have reacted according to their molar ratio and no reactant is in excess.

The equvilance point is determined by a colour change in an indicator.

This colour change is know as the end point.

idealy we want the endpoint to be as close to the equivalnce point as possible

and the concetration of the unkown solution can be calulated using the formula

TTo determine the concentration in vinegar by titration against a standardised solution of NAOH, using send to fettling as an indicator