Chapter 4.3 - Acidity of Solutions Flashcards
Water self ionizes according to the equation
H2O (L) + H2O (L) H3O+ (aq) + OH- (aq)
- Water is ionic
Why does water self ionize?
Since acids and bases react with each other, this implies that water can react with itself!
- water molecules exchange protons with one another to a very small extent.
- produces 1 hydronium ion (H3O+) for every one hydroxide ion (OH-)
- showcasing amphiprotic properties
- very low concentrations however in 25 degrees Celcius
- ENDOTHERMIC REACTION
What is water’s ionic product/ionization constant?
Kw = [H3O+]x[OH-] = 1.00 x 10^-14 at 25 degrees celcius
What is the ionic product for ACIDIC SOLUTIONS VS BASIC SOLUTIONS
In acidic substances, H3O+ ions are formed by the reaction of the acid with water, as well as the from self-ionisation from water.
So the concentration of OH- ions will remain greater than 10^-7 mol L-1 at 25 degrees celcius.
Because the product [H3O+] [OH-] remains constant, the concentration of OH- Ions in an Acidic solution at this temperature must be less than 10^-7 moles/L-1
OPPOSITE IS TRUE FOR BASIC SOLUTIONS.
- the concentration of OH- ions in a basic solution is greater than 10^-7 mol/L-1
Basic, neutral, and acidic solutions’ ionic constant explanation
at 25 degrees Celcius
pure water and other neutral solutions
[H3O+] = [OH-] = 10^7mol/L-1
Basic solutions
[H3O+] < 10^-7 mol L-1 and [OH-] > 10^-7 mol/L-1
ACIDIC SOLUTIONS
[H3O+] > 10^-7 mol L-1 and [OH-] < 10^-7 mol/L-1
What is Kw?
An expression used to determine the concentrations of hydronium and hydroxide ions in solution, because we know that the value of Kw, in solutions at 25 degrees Celcius is 1.00 x 10^-14
What is the pH scale?
pH is a scale used to specify the acidity, consequently the basicity of an aqueous solution.
- measure of acidity
- refers to the concentration of H+ ion of a solution
Acidic solutions are measured to have lower pH values than basic or alkaline solutions.
The pH solution can be defined as:
equation.
alternative
pH = -log 10 [H3O+]
ALTERNATIVELY ARRANGED TO
[H3O+] = 10 ^(-pH)
What is the effect of temperature on pH?
If the temperature is not 25 degrees Celcius, then the value of Kw will be different.
- Kw value will increase as the temperature increases
- because the self-ionization of water is an ENDOTHERMIC EQUILIBRIUM REACTION.
The pH of water? and what is it in other temps?
Pure water pH at 25 degrees Celcius is 7.
At other temperatures, even though pH IS not equal to 7, PURE WATER CAN STILL BE DESCRIBED AS NEUTRAL because concentrations of H3O+ AND OH- ions are EQUAL.
