Module 6 - Acids and Bases - Key INFO DO NOT FORGET!

Question 1

What is Arrhenius’ theory of Acids and Bases?

Answer 1

Acids increase the concentration of H⁺ (or H₃O⁺) ions in aqueous solutions.
Bases increase the concentration of OH⁻ ions in aqueous solutions.

Question 2

What is Bronsted-Lowry’s theory of Acids and Bases?

Answer 2

Defined by a proton transfer: Acids are proton donors (they give away H⁺).
Bases are proton acceptors (they take in H⁺).

Question 3

Give me an exaple of a conjugate acid-base pair - explain how they differ.

Answer 3

Conjudate acid-base pair: 2 species that differ by one proton (H+)

When acid donates proton - forms conjugate base.
When base accepts proton - it forms conjugate acid.

E.g. Hcl (Acid) → cl- (HCl Donates proton leaving cl- behind.

NH₃ (ammonia) → NH₄⁺ (ammonium ion)

HF (hydrofluoric acid) → F⁻ (fluoride ion)

Question 4

Define amphiprotic substance.

Answer 4

Can donate AND accept a H+ ion/proton.

e.g. Water

H₂O → OH⁻ + H⁺ (acting as an acid donating proton)

H₂O + H⁺ → H₃O⁺ (acting as a base accepting proton)

Question 5

What do acids taste like? (properties)

Answer 5

Acidic + corrosive to skill

Used for cleaning, fertilisers, explosives.

Question 6

What do bases taste like?

Answer 6

Bitter + corrosive to skins

Used to make soaps.

Question 7

What is an everyday use of indicators?

Answer 7

Maintaining pool water quality
* Needs to be 7.4 ph

Question 8

acid + metal oxide →
acid + metal hydroxide →

Answer 8

a salt + water

Question 9

acid + ammonia→

Answer 9

an ammonium salt

Ammonia is a weak base (NH3)

Question 10

metal carbonate + acid→

Answer 10

salt + water + carbon dioxide

Question 11

Metal carbonate + acid →

Answer 11

a salt + hydrogen gas

Question 12

Define Caloriemetry

Answer 12

Changes in energy of the system- determine the heat released or absorbed in a chemical reaction, by measuring heat of reaction, physical changes and heat capacity.

Think of styrofoam cup measuring temperature experiment with did.

Question 13

What are the weak acids?

Must memorise all of these!!!

Answer 13

Ethanoic Acid (CH3COOH)

Carbonic acid (H2CO3)

Hydrofluoric acid (HF)

Citric acid (C6H807)

Question 14

What are the weak bases?

Answer 14

Ammonia NH4

Methylamine (CH3NH2)

Question 15

What is the lavOisier (1776) theory

Answer 15

Acids must contain oxygens - later proved wrong.

Question 16

Limitations to Arrhenius theory

Answer 16

not applicable in gaseous and non-aqueous solutions - does not explain this.

the presence of H+ ion and OH– ion is essential in the chemical reaction - doesn’t account for reactions that do not contain these ions.

Question 17

Limitations to Bronsted-Lowry theory.

Answer 17

According to the Brønsted-Lowry theory:
An acid-base or neutralisation reaction is actually a proton transfer reaction.

Does not explain the acidity of acidic oxides such as SO2 and SO3.
Does not explain the basicity of basic oxides such as MgO and CaO
Does not explain reactions between acidic and basic oxides as they do not involve proton transfer.

Question 18

Define Polyprotic acids

Answer 18

An acid that can give away multiple hydrogen atoms.

Monoprotic = 1 hydrogen atom
Diprotic = 2 hydrogen atoms
triprotic = 3 hydrogen atoms.

Sometimes a polyprotic acid
only releases one hydrogen
and keeps its other hydrogen
ion(s) attached.

Polyprotic acids will donate
hydrogen ions to water
molecules when in a solution.

Initially, a polyprotic acid will
only lose one hydrogen ion
and keep the others.

Question 19

Define Hyronium ions

Answer 19

When an acid loses a H+ in and aqueous solution and the extra ion forms a coordinate covalent bond with surrounding water molecules becoming H30+

Question 20

What does a large H+ value mean when calculating pH

Answer 20

Greater [H+] ⇒ greater the acidity of the solution ⇒ lower pH

Question 21

What does a small H+ value mean when calculating pH

Answer 21

Lower [H+] ⇒ greater the basicity of the solution ⇒ higher pH

Question 22

What is the equilibrium expression and value for water at 25*

Answer 22

Kw = [H+]×[OH-] = 1.0 ×10-14

Question 23

what is ‘pH + pOH = 14’ used for/mean

Answer 23

says that concentrations of H+ and OH- equal to the above for any aqueous solution at 25 degrees Celsius.

can re-arrange to find pH.

Question 24

Define Hydroscopic

Answer 24

the ability of a substance to absorb moisture from the air.

E.G. NaCl.

Question 25

How can you find pH/test pH?

Answer 25

use an indicator or a pH metre

Question 26

T/F - Ammonia is endothermic?

Answer 26

False. Exothermic.

Question 27

What is a strong acid?

Answer 27

A solution that completely de-ionises in water to produce H+ ions.

Question 28

What is a weak acid?

Answer 28

Solution that partially disassociates in water to produce H+ ions. Use reversible arrows when representing this - to show reaction is incomplete. Contain fewer ions and are poorer conductors of electricity.

Question 29

HyrdoLYSIS?

Question 30

Strength of Conjugate acids?

Answer 30

STRONG ACID -> NEUTRAL CONJUGATE BASE (exceedingly weak) MODERATE ACID ->WEAK CONJUGATE BASE WEAK ACID --> MODERATE CONJUGATE BASE VERY WEAK ACID --> MODERATELY STRONG CONJUGATE BASE

Question 31

How can you estimate what the equivalence point for neutralisation reactions are?

Answer 31

Strong acid + Strong base -> neutral salt (pH 7 est) Strong acid + Weak base --> acidic salt (Equivalence point est >7) Weak acid + Strong base --> basic salt (equivalence point pH < 7)

Question 32

Define Equivalence point

Answer 32

Reactants have completely reacted – no excess Reactants combined in the exact mole ratio as the equation for the reaction Reactants are combined in equivalent amounts.

Question 33

Define Endpoint

Answer 33

When indicator changes colour

Question 34

What is the special titration equipment called that you put known concentration and volume of solution in?

Answer 34

Burette.

Question 35

What equation can you use in tritration calcuations

Answer 35

N=CV c(acid) × V(acid)/acid prefix? = cbase × Vbase/base prefix?

Question 36

Draw a titration curve showing SA + SB SA+WB WA +SB

Answer 36

Check answer by self

Question 37

How does the equivalence point change in a Weak Acid Strong Base titration curve

Answer 37

Equivalence point shifts up due to the strong base --> more basic pH.

Question 38

What does a tritration curve showing Ka look like?

Answer 38

Small Ka Value = more basic. e.g. Ka^-10 --> est pH10 - Higher curve.

Question 39

Aboriginal & Torres Strait Islanders Applications

Question 40

Titration Conductivity curves - test self and draw some curves!!!

Answer 40

SA+SB: Mostly look like absolute value graphs - end point is the bottom of the v. WA +SB: __/ shape SA +WB: \__ WA +WB: Goofy looking

Question 41

Define a buffer

Answer 41

A BUFFER is a solution that can minimise (resist) changes in pH when small quantities of acid or base are added. As per LCP - minimises disturbance. buffer system shifts to maintain [H+] concentration at a virtually constant level when samples of strong acid or strong base are added. A buffer solution contains a weak acid mixed with its conjugate base (or a weak base and conjugate acid).

Question 42

Name some buffer solutions

Answer 42

View answers in onenote page

Question 43

Example of Buffer solutions in Nature

Answer 43

Human blood: Since the human body is sensitive to pH levels, high CO2 levels will trigger faster, deeper breathing CO2, favour the forward reaction, decrease [H3O+] and minimise the change in pH

Question 44

Which pieces of glassware should be used when preparing a primary standard solution?

Answer 44

Beaker, filter funnel and volumetric flask

Question 45

Define coordinate covalent bond

Question 46

3 reasons why Back titrations are better than forward/direct titrations

Answer 46

Difficult to determine the endpoint If the unknown sample is unreactive, is in very low concentrations or is a weak acid/base, there won't be a clear endpoint and so a back titration is more suitable. Volatile or gaseous reactants Back titrations ensure that all of the reactant is used up before turning into vapours. This reduces the risk of underestimating the molarity of a substance. Insoluble reactants If the sample is insoluble in water but can react with either an acid or a base, a back titration should be used.