Analysis of the Earth and Environment Lecture 11: Acids and Bases Flashcards
Define an Acid
Hydrogen containing solution which releases free hydrogen ions
/
A chemical that gives off hydrogen ions in water and forms salts by combining with certain metals
Define and describe a hydrogen ion
A hydrogen ion is an ion with no electrons orbiting the nucleus and no neutrons.
There is only one proton present in nuclei.
All hydrogen ions are cations as they have no electrons.
Describe how acid molecules and water molecules interact.
Many acids are molecules which dissociate into their ionic components in water and the cation is H+
HA –> H+ + A-(Any anion)
The acid molecule (HA) interacts with the water molecule by the hydrogen ion in the acid molecule transferring to the water molecule creating a hydronium ion.
HA + H2O → H3O+(aq) + A-(aq)
Define a strong acid/ what makes acids stronger
A strong acid is fully ionized in water (ie. fully dissociated)
A strong acid reacts completely with water to produce a high concentration of hydronium ions
What are some strong acids?
(Acid rain)
Nitric Acid HNO3
Sulfuric Acid H2SO4
Hydrochloric acid HCl
Nitric acid composition?
HNO3
Sulfuric acid composition?
H2SO4
Hydrochloric acid composition?
HCl
Define a Weak acid?
A “weak acid” is only partially ionized in water (partially dissociated)
A “weak acid” reacts incompletely with water to produce few hydronium ions
CH3COOH + H2O ----> CH3COO- + H3O+
What is the chemical composition of ethanoic acid
CH3COOH
What is ethanoic acid and how does it respond to water
CH3COOH is an example of an “organic acid”
It contains the carboxylic acid group –COOH
–COOH group gives up its proton H+
to leave the anion –COO-
What are some weak acids?
Carbonic acid HOCOOH
Ethanoic acid CH3COOH (previously known at acetic acid)
Citric acid C5H7O5COOH
Describe the chemical process of carbon dioxide dissolving into water
H2CO3 or HOCOOH
CO2(g) + H2O ⇌ H2CO3 ⇌ HCO3− + H+
⇌
CO32− + H+
What is a base?
“Compound that produces hydroxide ions in water”
“Any substance which acts as a proton acceptor”
A substance which can neutralise an acid
use the words BASE and ALKALI interchangeably. (However technically it is only an alkali if it is a molecule)
eg. NH3(g) + H2O(l) → NH4+(aq) + OH-(aq)
NH3(Ammonia) being the base as it receives a proton becoming NH4
What are some strong bases/ alkalis
Strong bases dissociate 100% into the cation and the hydroxide anion OH-
KOH - potassium hydroxide
NaOH - sodium hydroxide
Ca(OH)2 - calcium hydroxide
How do weak bases behave
Weak bases do not simply dissociate to produce OH- ions. They indirectly generate OH- ions from the water molecules they are dissolved in.
How does ammonia interact with water?
Ammonia NH3 is a gas at room temperature.
It is frequently used a household cleaner dissolved in water.
NH3 accepts a proton H+ from the water to form the ammonium ion NH4+ Leaving a free hydroxide ion OH-
Describe how chlorine reacts with water
Cl2(g) + H2O(l) ⇌ HOCl(aq) + HCl(aq)
When chlorine gas (Cl2 ) is added to water it reacts to form a equilibrium mixture of hypochlorous acid (HOCl) and hydrochloric acid (HCl)
Chlorine gas Cl2 accepts protons so is acting as a WEAK BASE
Describe the erosion of limestone(CaCO3) when in contact with Carbon dioxide and water
CaCO3(s) + H2O(l) + CO2(g) → Ca(HCO3)2 (aq)
The calcium carbonate ACCEPTS hydrogen ions (protons) to make soluble calcium hydrogen carbonate .
Define pH
The pH of a solution is a measure of the concentration of hydronium ions in the solution
What is the calculation for pH
pH = -log [molar concentration of/molarity of susbtance]
e.g. 1.0 x 10-12 moles/dm or 0.3m
Press -, then log
What is an equilibrium reaction
After a time, a steady state is reached where the rates of the forward reaction and the reverse reactions are constant. This state is called equilibrium.
Forward reaction
CH3COOH + H2O → H3O+ + CH3COO-
Reverse reaction
CH3COOH + H2O H3O+ + CH3COO-
Define the equilibrium constant/K
At a given temperature the ratio of the concentration of reactants to the concentration of products is always the same at steady rate.
Concentration of reactants on left
This ratio is the equilibrium constant.
The equilibrium constant is referred to as K.
What does the magnitude of K signify and what are the three categories
Large values (K>1000) = the equilibrium favours the products on the right
Intermediate values (K 0.001 to 1000) =reactants and products in equal amounts
Small values (<0.001) = the equilibrium favours the reactants on the left
What is K referred to as when in an acid
Dissociation constant K
Describe how to calculate the K/Ka (Dissociation constant) of an acid
What is the equation for Ka
x²
Ka = —————————–
Acid amount - x
x = 10⁻ᵖʰ (10 to power of pH (Minus)
Define the pKa
The pKa is simply the -log of Ka constant. What you get when you put Ka into -log.
