Chemistry- Acids, Bases and Alkalis Flashcards
Define an Acid
A molecule or other species which can donate a proton or accept and electron pair in a reaction.
What is a strong and weak Acid?
Strong acid can dissociate protons (h+ ions) more than a weak acid.
Weak acids have more un-dissociated protons.
What is an Arrhenius acid?
A substance that produces hydrogen ions (H+) in solution.
What is a Bronsted-lowry acid?
A substance that is a proton donor
A base is a proton acceptor.
What is the difference between strength and concentration?
Strength is how much an acid dissociates H+ ions in solution.
Concentration is the ratio of how much acid present in the solution both dissociated and associated.
What is produced when an acid and alkali react together?
Salt + water
Acid + Alkali —-> Salt + Water
What happens when an acid and base react together?
Salt + Water
Acid + Base —-> Salt + Water
What is formed when an acid and metal carbonate react together?
Salt + Water + Carbon dioxide
Acid + Metal carbonate —-> Salt + Water + Carbon
Dioxide
What happens when a metal and acid react together?
Salt + Hydrogen
Metal + Acid —-> Salt + Hydrogen
Write the dissociation equation for Nitric Acid (HNO3)
HNO3 —-> H+ + NO3-
Write the full ionic equation for the acid-base reaction between sulphuric acid and solid magnesium carbonate?
Full Equation: H2SO4 + MgCO3 ---> MgSO4 + H2O + CO2 Ions: 2H^+ + SO4^2- + MgCO3 ---> Mg^2+ + SO4^2- + H2O + CO2 Ionic Equation: 2H^+ + MgCO3 ---> Mg^2+ + H2O + CO2
What are Mono, Di and Tri Basic acids?
Monobasic Acid= each molecule can release 1 proton
HCl —> H^+ + Cl^-
Dibasic Acid= Each molecule can release 2 protons
H2SO4 —> H^+ + HSO4^-
HSO4^- —> H^+ + SO4^2-
Tribasic Acid= Each molecule can release 3 protons
H3PO4 —> H^+ + H2PO4^-
H2PO4 —> H^+ + H2PO4^2-
HPO4^2- —> H^+ + PO4^3-
What is a conjugate acid-base pair?
A pair of 2 species that transform into each other by gain or loss of a proton.
e.g. HNO2 H^+ + NO^2-
Acid Base
H^+ links an acid with its conjugate base
Identify the acid, base conjugate acid and conjugate base for the reaction of
HClO4 + H2O H3O^+ + ClO4^-
HClO4 + H2O H30^+ + ClO4^-
Acid 1 base1 acid 2 base 2
Acid & base 2 = conjugate acid and base
What does pH measure?
Measures the amount of H+ present
What are the equations linking concentration of H+ ions and pH?
pH = -log([H+]) [H+] = 10^-pH
Key points on the relationship between pH and [H+]
- Low pH means larger [H+]
- High pH means lower [H+]
- A pH change of 1 changes [H+] by 10x
- An acid with a pH of 2 contains 1000x [H+] of an acid with a pH of 5
What is an amphoteric substance?
A substance that can act as an acid or a base.
e.g Water (H2O)
H2O Donate H+ —-> :OH^-
H2O accepts H+ —-> H3O^+
Define a strong acid
An acid that can dissociate completely in aqueous solutions.
HA H+ + A-
How is dissociation measured?
Extent of dissociation is measured by an equilibrium constant and dissociation constant (Ka)
What does a large and small Ka value mean in terms of acidity?
Large Ka value = Strong Acid
Small Ka value = Weak Acid
Since Ka numbers can be large what is done to make them easier to use in calculations?
Logarithmic Scale —> turned into pKa Values
pKa = -log(Ka)
Ka = 10^-pKa
Large pKa = Weak Acid
Small pKa = Strong Acid
What is the equation when using Ka?
Ka = [H+][A-] / [HA]
larger number on top means a stronger acid
What is the ionic product of water equation?
Kw = [H+][OH-]
Kw = 1.0x10^-14 mol^2dm^-6 @ 298K (always)
What affects Ka Values?
Only Temperature:
As temperature increases more H2O dissociates so both [H+] and [OH-] increase.
Therefore the pH of neutrality decreases.
Define Endpoint
The point at which the indicator changes colour.
Define Equivalence point
The term for the moment when neutralisation occurs.
What is an acid-base indicator?
An Acid-base indicator is a weak acid represented as HIn.
An indicator has one colour in its acid form (HIn) and a different colour in its conjugate base form (In-)
eg. Methyl Orange HIn - Red
In^- - Yellow
What is the Value of Kw at 298K?
1x10^-14
Define a weak acid
An acid that does not fully dissociate (ionise) when dissolved in water.
Where does equilibrium for a weak acid and water tend to lie?
The position of equilibrium between the acid and water varies from one weak acid to the other.
The further left equilibrium lies, the weaker the acid.
What is the acid dissociation constant for a weak acid and its equation?
Ka
Ka = [H+][OH-] / [HA]
Lower the value for the constant the more equilibrium lies to the left
What do larger and smaller Ka Values mean?
Larger Ka = Stronger Acid
Smaller Ka = Weaker Acid
Define pKa and what is its relationship to Ka similar to?
pKa = -log(Ka)
Ka = 10^-pKa
Similar relationship to pH and [H+]
What doe larger and smaller pKa values mean?
Larger pKa = Weaker Acid
Smaller pKa = Stronger Acid
How can we calculate pH of weak acids?
Be given a Ka value and [HA] ka = [H+][OH-] / [HA] Ka = [H+]^2 / [HA] [H+] = Square root ( Ka x [HA]) pH = -log[H+]
What does a buffer do?
A buffer can resist changes to pH.
This is achieved by neutralising the H+ ions or OH- ions.
How is a buffer made?
Made from a weak acid and its salt.
eg. Ethanoic acid and sodium ethanoate.
CH3COOH CH3COO-Na+
What happens when an alkali is added to the buffer?
CH3COOH H+ + CH3COO-
- H+ ions would neutralise OH- ions from the alkali and therefore get used up.
- So equilibrium will shift to the right producing more H+ ions
Which means that the pH remains constant.
What happens when an acid is added to the buffer?
CH3COOH H+ + CH3COO-
- Adding more H+ ions would increase the H+ ion concentration
- So equilibrium would shift to the left reducing the [H+] since a large number of ethanoate ions from reaction are added.
Therefore removing H+ and maintaining a constant pH.
