Chemistry - Acid base reactions

Acid

a substance that donates a H+ proton

Base

a substance that accepts a H+ proton

Acidic proton

a hydrogen atom within a molecule that is readily released as a positively charged hydrogen ion (H+)

Monoprotic acid

acids that donate one proton eg. HSO4

Diprotic acid

acids that can donate 2 protons eg. H2SO4

Triprotic

H3PO4 - acids that can donate 3 protons

Amphiprotic

can act as an acid or base eg. HSO4 (-) can become SO4 (2-) or H2SO4

Conjugate acid-base pair

acid → conjugate base ( donates a proton )

base → conjugate acid ( accepts a proton )

acid-base reaction involves an exchange of protons from an acid to a base

Brønsted-Lowry theory

The describes acid-base properties in terms of proton (H+) transfer.

A Brønsted-Lowry acid is a proton donor, and a base is a proton acceptor.

Molecular dipole

the separation of electrical charge within a molecule, creating a partially positive end and a partially negative end

hydronium ion

H3O+ (when H2O gains a proton)

Neutralisation reaction

a chemical reaction in which an acid and a base react quantitatively to produce a salt and water

pH scale

a measure of how acidic or basic (alkaline) a substance is

strong acid

readily donates H+, meaning there is a high percentage ionisation, 99% of the acid molecules break apart into ions

weak acid

only 1% of the molecule ionises, do not readily donate H+, low percentage ionisation

properties of acids

h+ donor

pH < 7

sour taste

turn litmus red

corrosive (destroys living tissue and metal)

neutralised by bases

properties of bases

H+ acceptor

pH > 7

turns litmus blue

bitter taste, feels slippery

caustic (destroys living tissue)

alkali = soluble in water

ETHANOIC ACID!!!!!

CH3COOH CAN ONLY LOOSE ONE PROTON/HYDROGEN

the other 3 are covalently bonded to the carbon so they can’t readily be lost

• the proton is acidic because the oxygen is highly electronegative and attracts

• the bonding electrons therefore weakening the bong to the proton allowing it to be donated

double arrow example

HSO4- is described as a weak acid because its only partially ionised as its able to loose one more to become SO4 to become fully ionised or H2SO4 where its fully ionised

therefore a double (reversible) arrow is used to indicate an incomplete reaction

calculating concentration

solute amount/solvent amount

strength vs concentration

strength - ability to ionise

concentration - how much of a substance is present within a solution.

dilute

not many particles

It means there's a large amount of solvent (like water) compared to the amount of solute (like salt or sugar) dissolved in it

concentrated

a lot of particles

A concentrated solution is one where a large amount of solute is dissolved in a relatively small amount of solvent,

solute

the substance being dissolved

solvent

the substance the solute is dissolved in

chemicals equation for strong acid/base dissociating in water example

HClO4 (aq) + H2O (l) — 99% ionisation → H3O+(aq) + ClO4 (aq)

write on top of the arrow 99% ionisation

chemicals equation for weak acid/base dissociating in water example

NH3 (aq) + H2O (l) — 1% ionisation → NH4+(aq) + OH- (aq)

write on top of the arrow 1% ionisation or use double arrow ( ⇌ )

Reactions of acids

Acid + Metal → Salt + H2 (g)

Acid + Oxide → Salt + H2O (l)

Acid + Carbonate → Salt + H2O (l) + CO2 (g)

Use solubility table when looking for the reactants states to know if its (aq) or (s) example

Ca (s) + HCl (aq) → CaCl2 (aq) + H2 (g)

• aqueous because on the solubility table chloride is soluble with everything except some exceptions, however calcium is not an exception

Ag2O(aq) +HCl (aq) → AgCl (s) +H2O (g)

• solid because on the solubility table chloride is insoluble with silver

Why does ca not have a charge in this equation?

Ca (s) + HCl (aq)→ CaCl2 (aq) + H2 (g)

because it is solid meaning there is no ions present

self ionisation of water

H2O + H2O → H3O+ + OH -

forms a hydronium ion (H3O) and hydroxide (OH-)

Ionisation constant for water

At 25°C: Kw=[H3O+] x [OH-] = 10^-14 M²

Neutral solution the concentration of the hydronium ion and hydroxide ions are equal

acid added to water

when an acid is added the concentration of hydronium increases, whereas the concentration of hydroxide decreases

when a base is added to water

hydroxide increases and hydronium decrease

calculate concentration of acid

H3O+ (or H+) = 10^-14/OH-

calculate concentration of base

OH- = 10^-14/H3O+

changing calc from decimal to 1.69×10^-6 M

ENG button

Spector ions

ions that don’t participate in the acid-base reaction

spectator ions

are ALWAYS AQUEOUS

aqueous to begin with and aqueous on the reactant side

eg. Mg (s) + H2SO4 (aq) → MgSO4 (aq) + H2 (g)

SO4^2- is the spectator ion

what does pH stand for?

potential hydrogen

strong acid, neutral, strong base

strong acid, = 1 or 10^-1

neutral, = 7 or 10^-7

strong base, = 14 or 10 ^-14

calculate pH

pH = - log₁₀ [H3O+]

example

pH = - log₁₀ (5×10^-12)

pH = 11.3

or

pH = - log₁₀ (0.0001)

pH = 4

calculate H3O from pH

[H3O+] = 10^-pH

^{calculate the [H3O] of a solution with a pH=5.2}

H+=10^-5.2

H+ = 6.31 × 10^-6 M

REMEMBER TO PUT WHAT AFTER H3O or OH-

M

calculate the pH of a solution of 0.001M magnesium hydroxide

Mg(OH)2 = 0.001M

OH- = 0.002M as in one mole of mg there are 2 OH- so 0.001 × 2

[H3O+]=10^-14/0.002M

H3O+ = 5 × 10^-12 M

pH = - log₁₀(5×10^-12)

pH=11.3

intermolecular forces

between different molecules

dispersion forces, dipole-dipole, hydrogen bonds

weakest to strongest bond ————>

dispersion forces

between all molecules

dipole-dipole

only when a polar bond is present ( BETWEEN 2 POLAR BONDS)

hydrogen bonding

only between H-NOF

nitrogen, oxygen, fluorine

intramolecular bonds

within the molecules

metallic - metal ions, free moving electrons sea of delocalised electrons

covalent - sharing of electrons

ionic - give and take of electrons

polar bonds

• asymmetrical

• difference in electronegativity

lone pairs

electron pairs that don’t partake in the bonding

aqueous

the ability to dissolve in water

potable

drinkable (only 0.3% is drinkable on earth)

waters bonding

water is a polar molecular that can from hydrogen bonds

has 2 lone pairs

bonds between the atoms are covalent bonds which only breaks when. chemical reaction takes place and are strong whereas hydrogen bonds are weak

hydrogen carries a partially positive charge

oxygen carries a partially negative charge

water- boiling point/melting point

high boiling/melting point due to the presence of hydrogen bonds

means it needs more heat energy to break the intermolecular bonds

main force needed to overcome to boil water - hydrogen bonds

max number of hydrogen bonds it can form

4

why does liquid water expand on freezing

it forms a regular pattern as the temp decrease as the kinetic engird decreases

why doesn’t water form 4 hydrogen bonds in a liquid state

due to the high kinetic energy due to movement atoms are moving around to quickly to form any type of regular structures, preventing them from having 4 hydrogen bonds as hydrogen bonds are forming and reforming

gas - water properties

high kinetic energy

no hydrogen bonds between water molecules

can not have a density

liquid - water properties

lower kinetic energy

hydrogen bonds from and reform

higher density

solid - water properties

hexagonal patterns trap more air- more space inside

less density

ice will float as it has less density then water due to the air trapped in the hexagonal patterns

specific heat capacity

amount of energy required to raise the temperature of 1g of the substance by 1 degree celsius

waters specific heat capacity

4.18 Joules per gram per degree celcuis

4.18 J.g^-1.°C^-1

^{4.18 joules is the required mount of energy to raise the temp of 1g of water by 1°C}

properties of waters heat capacity

water absorbs large amounts of heat energy before it gets hots and slowly releases heat energy when it cools

it moderates earths temp and body temp

calculating heat energy

heat energy = specific heat capacity x mass (in grams ) x temperature change (°C)

q=m c △T

KJ → J

J → KJ

KJ → J x1000

J → KJ /1000

Kg → g

g → kg

Kg → g x1000

g → kg /1000

latent heat

energy absorbed by a fixed amount of substance as it changes state

latent heat of fusion

energy needed to convert water from a solid to a liquid ( at 0°C)

6.0095 KJ

latent heat of vaporisation

energy needed to convert water from a liquid to a gas ( at 100°C)

40.657 KJ

why is an ice pack used ons ore muscles

. latent heat of fusion helps to decrease the soreness/inflammation by absorbing the heat energy from the muscle to cool it down.