21.1 Defining an acid Flashcards
What is a bronsted-lowry acid
What is a bronsted-lowry base
An acid is a substance that can donate a proton (H+ ion)
A base is a substance that can accept a proton
What do acids and bases react to produce
Eg in equation
HCl(g) + NH3(g) —> NH4Cl(s)
They make a salt.
Water is only produced when the acid has a H+ and the alkali has an OH-
So HCl is the acid here and donates a proton to the NH3 acting as a base by accepting this proton
Acids and bases react in pairs: One acid and one base
How do acids and bases react in equation
H2SO4 + HNO3 —> H2NO3+ + HSO4-
Sulfuric acid donates a proton to nitric acid so is acting as the acid in this reaction.
Why are OH- ions formed when reacting water with a base
Because the water must act as an acid so releases a H+ ion to give to the base.
So this makes OH- ions
How can water act as a base
What is a H3O+ ion
Explain reaction
HCl + H2O —-> H3O+ + Cl-
Oxonium ion aka Hydronium ion
It is formed when water acts like a base, so accepts a proton.
Here, HCl is donating a proton to water so water is a base
How can water act as an acid
H2O + NH3 —> OH- + NH4+
Here, water is donating a proton to ammonia so acts as an acid
What is a H+ ion
Why does it have unusual properties
It is simply a proton
Because hydrogen consists of one proton and one electron so when an electron is lost it only contains a proton.
It is tiny with an intense electric field so compared to other positive ions it has unusual properties
How do H+ ions act in solutions
They are never found on their own, it is always bonded to at least one water molecule to form ion H3O+ .
Since H+ ions have no electrons, they can only bind with molecules with a lone pair
However for simplicity we represent protons as H+ rather than H3O+
Write equation for ionisation of water
H2O(l) <–> H+(aq) + OH-(aq)
So equilibrium reaction
It also may be written as:
H2O(l) + H2O(l) –> H3O+(aq) + OH-(aq)
What is Kw
It is the ionic product of water, and at 298k it is 1 x 10^-14 mol^2dm^-6
Because you can write Kc expression for ionisation where it is [H+][OH-] divided by [H2O].
But the concentration of water is constant so Kw = Kc x [H2O]
So this makes [H2O] –> [OH-][H+]
What are the values for the ionic products of water
. Ionic product of water is 1 x 10^14
. Each H2O splits to make one H+ ion and one OH- ion.
So in pure water at 298K
[OH-] = [H+]
So (1 x 10^14) = [H+]^2
so [H+] = 1 x 10^7moldm^-3
And this is also the value for [OH-]
