Chemistry- Acids, Bases and Alkalis Flashcards by Joe Rowlands

Define an Acid

A molecule or other species which can donate a proton or accept and electron pair in a reaction.

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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.

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What is an Arrhenius acid?

A substance that produces hydrogen ions (H+) in solution.

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What is a Bronsted-lowry acid?

A substance that is a proton donor

A base is a proton acceptor.

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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.

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What is produced when an acid and alkali react together?

Salt + water

Acid + Alkali —-> Salt + Water

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What happens when an acid and base react together?

Salt + Water

Acid + Base —-> Salt + Water

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What is formed when an acid and metal carbonate react together?

Salt + Water + Carbon dioxide
Acid + Metal carbonate —-> Salt + Water + Carbon
Dioxide

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What happens when a metal and acid react together?

Salt + Hydrogen

Metal + Acid —-> Salt + Hydrogen

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Write the dissociation equation for Nitric Acid (HNO3)

HNO3 —-> H+ + NO3-

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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

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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-

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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

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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

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What does pH measure?

Measures the amount of H+ present

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What are the equations linking concentration of H+ ions and pH?

pH = -log([H+])
[H+] = 10^-pH

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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.