1.7 Flashcards
What is dynamic equilibrium
Forward and reverse reaction occur at the same rate
What is position of equilibrium
Proportion of products of reactants in an equilibrium mixture
What affects the position of equilibrium?
Concentration, pressure, temperature
What doesn’t affect the position of equilibrium but helps reach equilibrium faster
Catalyst
State Le Chatelier’s principle
If a system at equilibrium is subjected to a change, the equilibrium tends to shift so as to minimise the effect of the change
If the concentration of a reactant is increased the position of equilibrium moves to the
Right
Increasing the pressure moves the position of equilibrium to
Whichever side has fewer gas molecules
An increase in temperature moves the position of equilibrium
In the endothermic direction
What is an acid
Proton donor
What is a base
Proton acceptor
What is a strong acid
Fully dissociates in aqueous solution
What is a weak acid
Partially dissociates in aqueous solution
What is a concentrated acid
Consists of a large quantity of acid and a small quantity of water
What is a dilute acid
Contains a large quantity of water
Equation for pH
-log10[H+]
What is a standard solution
One whose concentration is accurately known
How is the point of neutralisation measured in an acid-base titration
Indicator
What must a standard solution have
High purity
Stability
Low hygroscopicity
High molar mass
How to prepare a standard solution
- calculate the mass of solid required and accurately weigh this amount into a weighing bottle
- transfer all of the solid into a beaker. Wash out the weighing bottle so that any residue runs into the beaker. Add water and stir until all the solid dissolves
- pour all the solution carefully through a funnel into a volumetric flask, washing all the solution out of the beaker and the glass rod. Add water until just below the graduation mark
- Add water drop by drop until the graduation mark is reached and mix the solution thoroughly
How to perform a titration
- pour one solution into a burette, using a funnel, making sure that the jet is filled. Remove the funnel and read the burette
- use a pipette to add a measured volume of the other solution into a conical flask
- add a few drops of indicator to the solution in the flask
- run the acid from the burette to the solution in the conical flask, swirling the flask
- stop when the indicator just changes colour (end-point)
- read the burette again and subtract to find the volume of acid used (titre)
- repeat the titration, making sure that the acid is added drop by drop near the end-point, until you have at least 2 readings that are within 0.20cm3 of each other and calculate a mean titre
Why would a back titration need to be used
Reaction between determined substance and titrant can be too slow, there can be a problem with end-point determination or the base is an insoluble salt
What to do in back titration calculations
A= the known excess
B= unknown amount
- amount of A that has been used (starting amount-titre)
* amount of reagent B thats reacted
When to do a double titration
If a solution contains a mixture of two bases which are of different strengths
What is done differently in a double titration
Use of 2 different indicators at different stages to calculate the concentrations of both bases
