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Chapter 4 - Acids and redox - Coggle Diagram
Chapter 4 - Acids and redox
Acids
A species that donates a proton, releases H+ ions in solution
When dissolved in water, an acid releases hydrogen ions (protons) into the solution
Strong acids
Completely dissociates in aqueous solution
Releases all of its hydrogen atoms
HCl is an example
Weak acids
Partially dissociates in aqeuous solution
Only releases a small proportion of its available hydrogen atoms into solution
Ethanoic acid is an example
Bases
A base neutralises an acid to form a salt and water
Alkali - base that dissolved in water to release hydroxide ions into the solution
Neutralisation
When an acid is neutralised, Ions react with a base to form a salt and neutral water
H+ ions from acids are replaced by metal/ ammonium ions from the base
Acid is neutralised by a metal oxide/ hydroxide to form salt and water only
With alkalis, the reactant are in solution, overall reaction forms salt and water only
Carbonates neutralise acids to form salt, water and CO2
Redox
Oxidation number
Number of electrons invovled in bonding to a different element
Used when writing formulae and balancing electrons
Oxidation number is always 0 for elements
Redox reactions
Redox involved reduction and oxidation simultaneously
Electrons
Reduction is the gain of electrons
Oxidation is the loss of electrons
Oxidation number
Reduction is the decrease in oxidation number
Oxidation is the increase in oxidation number
Oxidising/ Reducing agents
Oxidising agent accepts electrons from species being oxidised. It gaines electrons and is reduced
Reducing agent donates electrons to the species being reduced, it loses electrons and is oxidised
Disproportion reactions - species is both oxidised and reduced
Acid-base titrations
Technique used to accurately measure the volume of one solution that reacts exactly with another solutions
Uses
Finding the concentration
Identification of unknown chemicals
Finding purity of a substance
Preparing standard solutions
Solution of known concentration
Volumetric flasks are used to makeup a standard solution very accurately
Process
Weigh the solid accurately and dissolve it in a beaker using less distilled water than will be needed to fill the volumetric flask
Transfer the solution to a volumetric flask, the last traces of the solution are rinsed into the flask with distilled water
Carefully fill the flask to the graduation line by adding distilled water a drop at a time until the bottom of the meniscus lines up exactly
If too much water is added, the solution will be too dilute and must be prepared again
Slowly invert the volumetric flask to mix the solution
Common errors
Systematic errors on the balance
Lost substance in tranfer and overfilling of the volumetric flask
Titration procedure
Add measured volume of one solution to a conical flask using a pipette
Add the other solution to a burette, and record the initial burette reading to the nearest 0.05cm3
Add a few drops of an indicator to the solution in the conical flask
Run the burette solution into the conical flask, makes sure to swirl it. Eventually he colour change indicates the end point (used to indicate the volume of one solution that exactly reacts with the volume of the second solution
Record the final burette reading, volume of solutiona added from the burette is called the titre (subtract initial from final volume)
The first titration is the rough and is used to find the approximate titre volume
Repeating the titration, adding the burette solution dropwse until the end point is approached
Furter titrations are carried out until two accurate titres are concordant (within 0.1cm3 of eachother)
Mean titre
By repeating titres until two are within 0.1cm3 of eachother, you can reject inaccurate titres
This keeps accuracy high