Acids + bases Flashcards
What are acids?
*Sour taste
*Colour change
of dyes
What are alkali?
*bitter taste
*Feel soapy
*“to bring low”
What do you use to measure pH?
- pH meter (electrochemistry)
- pH indicators
What is the definition of an acid?
An acid is a substance that, when dissolved in water,
increases the concentration of H+ ions
What is the definition of a base?
A base is a substance that, when dissolved in water,
increases the concentration of OH ions
Brønsted-Lowry definition of acids and bases ?
- Transfer of H+
ions from one substance to another - An acid is a substance (molecule or ion) that donates a
proton to another substance. - A base is a substance that accepts a proton.
What does equilibrium mean?
Equilibrium: the forward and reverse reactions occur
at equal rates, and the concentrations of products and reactants
remain constant.
In an acid-base equilibrium both the forward and the
reverse reaction involve proton transfer.
What is Conjugate acid-base pairs?
- Acid = proton donor
- Base = proton acceptor
Examples of strong and weak acids and bases
- HCl
- HBr
- HI
- HNO3
- HClO3
- HClO4
- H2SO4
Strong bases:
NaOH
* KOH
* RbOH
* CsOH
* Ca(OH)2
* Sr(OH)2
* Ba(OH)2
CHECK THE LECTURE NOTES FOR EXAMPLES ON HOW TO IDENTIFY AND BALANCE EQULIBRIUM AND WORKING OUT
What is the effects of a strong acid
- A strong acid completely transfers its protons to water
- Its conjugate base does not readily accept protons
What is the effects of a weak acid?
- A weak acid only partially ionises in aqueous solution
- Exists as mixture of acid and its conjugate base
- The conjugate base of a weak acid is a weak base
Acid dissociations constant Ka
- Magnitude of Ka
indicates tendency of acid to ionize in
water - The larger the value of Ka
, the stronger the acid
What is Base dissociation constant?
- Kb
: refers to the equilibrium in which a base reacts with
H2O to form the corresponding conjugate acid and OH-
What is a buffer?
- Resists changes in pH because it contains both
- an acid to neutralise added OHions
- a base to neutralise H+
ions - The acid and base MUST NOT consume each other
*Weak acid-base conjugate pair
How to neutralise a reaction?
- Adding a strong acid to a weak or strong base results in
complete conversion to the salt and water - Adding a strong base to a weak or strong acid results in
complete conversion to the salt and water
How to make a buffer
- Mix weak acid or weak base with a salt of that acid or base
- Make the conjugate acid or base from a solution of weak
base or acid by the addition of a strong acid or base
What are acid base titrations and why do we use them?
- To determine the concentration of an acid or base
- To determine the equilibrium constant for the reaction
- Solution containing known concentration of base is slowly
added to an acid (or the acid is added to the base) - Equivalence point: moles of base = moles of acid and the
solution only contains salt and water. - pH titration curve: pH as function of the volume of titrant
added
What happens when a positive amino acid charge equals a negative?
When the positive charge equals the negative charge, the amino acid is a zwitterion
This pH at which the amino acid is a zwitterion, is called the pI
