Unit 2) 2) Brønsted Lowry definitions of acids+bases And Ionic Product Of Water + pH Scale Flashcards
What are acids
What are bases/ alkali
Acids have pH below 7 and have a higher concentration of hydrogen (H+) ions than pure water
Alkalis have pH above 7and have a higher concentration of hydroxide (OH-) ions than pure water
- What is the hydrogen ion considered as for AH chem
- when does a hydrogen ion exist in aqueous solutions
- a hydrogen ion is basically a proton ( a hydrogen atom that has lost an electron)
- in an aqueous solution, a hydrogen ion only exists when surrounded by water molecules. These are known as hydronium ions (written as H3O+ (aq) ) when the hydrogen ion concentration is discussed , what is being referred to is the hydronium ion but for simplification is shortened to H+.
theory put forward Brønsted and Lowry 1932, acids and bases are considered as…
- an acid can be considered as a proton donor
- a base can be considered as a proton acceptor
What happens when
- an acid donates a proton
- a base accepts a proton
- when an acid donates a proton, the species left is called a conjugate base
- when a base accepts a proton , the species formed is a conjugate acid
Look at notes for examples
In water and all aqueous solutions some water molecules _________ or ________ into hydrogen and hydroxide ions. An equilibrium is established between the ________ molecules and the hydrogen and hydroxide ions
In water and all aqueous solutions some water molecules disassociate or ionise into hydrogen and hydroxide ions. An equilibrium is established between the water molecules and the hydrogen and hydroxide ions
How can the ionisation of water be represented (equation )/ how does water dissociate slightly a
H20(l) + H20(l) —> H3O+(aq) + OH-
(This is an equilibrium the arrow should actually go both ways
What does it mean if a substance is amphoteric
Substances that act as both an acid and a base are called amphoteric
How is water amphoteric
- if we look at the equation for the ionisation of water , we see that water molecules produce both hydronium (hydrogen) ions H30+ , and hydroxide ions OH-, in other words acting as both an acid and a base
How is the ionisation of energy shown in a more simple way
H20(L) —-> H+(aq) + OH- (aq) +ve
What is ionic product of water
The dissociation constant for the ionisation of water is known as the ionic product
How is the ionic product (dissociation constant for the ionisation of water) written and represented as
Represented by Kw
Kw = [H3O+(aq)] [OH-(aq)]
Or simply
Kw = [H+][OH-]
Recap - why are the reactants (the liquid water) not included in the dissociation constant for the ionisation of water
The reactants are not included in the equilibrium expression due to water being a pure liquid and having a value of 1
- What is the value of the ionic product / equilibrium constant Kw at 25 degrees
- what does and increase / decrees in temperature do to its equilibrium
- the equilibrium constant Kw is temperature dependent and the value is approximately 1x10^-14 at 25 degrees
- since it is an endothermic reaction , an increase in temperature moves the equilibrium to the right (endothermic way) (products side) and a decrease moves it to the left (reactants side )
pH and distribution of ions in
- acidic solutions
- neutral solutions
- alkali solutions
- acidic solutions have pH below 7 and H+ > OH-
- neutral solutions have pH of 7 and H+ = OH-
- alkali solutions have pH above 7 and H+ < OH-
The greater the concentration of hydronium (hydrogen) ions the ________the pH and vice versa
The greater the concentration of hydronium (hydrogen) ions the lower the pH and vice versa
