ACID AND REDOX Flashcards
Which element do all acids contain?
Hydrogen
What happens when an acid is dissolved in water?
When an acid is dissolved in water, it releases hydrogen ions as protons, H+, into the solution
What is the equation that shows hydrogen chloride gas dissolving to form an aqueous solution?
HCl (g) + aq ———–> H+ (aq) + Cl- (aq)
+aq shows the excess of water present
What is an example of a strong acid?
Hydrochloric acid
What happens to a strong acid when placed in an aqueous solution?
The strong acid releases all its hydrogen atoms into solution as H+ ions
It completely dissociates in an aqueous solution
What happens to a weak acid when placed in an aqueous solution?
A weak acid only releases a small proportion of its available hydrogen atoms into solution as H+ ions.
It partially dissociates in aqueous solution.
What is an example of a weak acid?
Ethanoic acid - Ch3COOH
Why is ethanoic acid a weak acid?
A molecule of ethanoic acid contains 4 hydrogen atoms.
But only the hydrogen atom on the COOH group is released as H+
What is a base?
A base neutralises an acid to form a salt
What are example of bases?
Metal oxides
Metal hydroxides
Metal carbonates
Ammonia, NH3
What is an Alkali?
An alkali is a base that dissolves in water releasing hydroxide ions (OH-) into the solution.
What is the equation that shows alkali sodium hydroxide dissolving in water?
NaOH releases hydroxide ions as it dissolves in water
NaOH (s) + aq ——–> Na+ (aq) + OH- (aq)
What is the formula of hydrochloric acid?
HCl
What is the formula of sulfuric acid?
H2SO4
What is the formula of nitric acid?
HNO3
What is the formula of Ethanoic acid?
CH3COOH
Name 4 common acids
Hydrochloric acid
Sulfuric acid
Nitric acid
Ethanoic acid
Name 3 common metal oxide bases
MgO - Magnesium oxide
CaO - Calcium oxide
CuO - Copper oxide
Name 3 common metal carbonate bases
Na2CO3 - Sodium carbonate
CaCO3 - Calcium carbonate
CuCO3 - Copper carbonate
Name 3 common Alkali bases
NaOH - Sodium hydroxide
KOH - Potassium hydroxide
NH3 - Ammonia
What are the products of a neutralisation of acid
Acid + metal oxide/hydroxide —-> Salt + water
How do you form a salt from an acid?
The hydrogen in the acid is replaced by a metal or ammonium ion to form the salt
E.g. Hcl —–> NaCl
What do you use to neutralise an acid?
A metal oxide or metal hydroxide
To form a salt and water only
Acid + Alkali —->
Acid + Alkali —–> salt + water
Carbonates neutralise acids to form…
salt + water + carbon dioxide gas
Whats the differenc between a strong and a weak acid?
Strong acid fully dissociates in aqueous solution
Weak acid partially dissociates in aqueous solution
Neutralisation of an acid
The H+ ions react with a base to form a salt + water.
H+ is replaced by metal or ammonium ions from base
With alkalis, all reactants for neutralization are…
Aqueous
What is a titration?
A titration is a technique used to accurately measure the volume of one solution that reacts exactly with another solution
Titrations can be used for:
Finding the concentration of a solution
Identification of unknown chemicals
Finding the purity of a substance
Why is finding the purity of a substance important?
Important for pharmaceuticals
Just a tiny amount of impurity in a drug could cause a great deal of harm to a patient
Volumetric flask typical tolerances
100cm^3 +/- 0.2cm^2
250cm^3 +/- 0.3cm^3
Experimentally preparing standard solutions procedure:
Solid weighed + dissolved in beaker using less distilled water than needed to fill volumetric flask
Transfer to volumetric flask + last traces rinsed into flask with distilled water
Add distilled water dropwise until bottom of meniscus matches up with the mark
Flask inverted slowly several times to mix, if not titration results will be inconsistent
Pipette Typical tolerances
10 cm^3 +/- 0.04cm^3
25cm^3 +/- 0.06 cm^3
Burette: 50cm^3 +/- 0.1
How is a burette measured and recorded?
Burette is recorded to the nearest half division, to 2dp (last 5 or 0)
Acid - base titration procedure
Add measured volume one solution to conical flask with pipette
Add other solutions to burette, recording initial reading
Add few drops of indicator to conical flask
Run solution from burette into conical flask, swirling it, until it reaches the end point
Record first reading
1st titre carried out quickly to get approx, then repeat accurately adding solution dropwise as end point approached. Carry out until two accurate titres are concordant (within 0.1cm^3)
What is the oxidation number of oxygen?
-2
What is the oxidation number of hydrogen?
+1
What is the oxidation state of fluorine?
-1
What is the oxidation state of ions
Charge on the ions
What are the special cases in oxidation numbers
H in metal Hydrides: -1
O in peroxides: -1 (02 ^2-)
O boded to F: +2
Reduction is
Gain of electrons
Decrease in oxidation numbers
Oxidation is
Loss of electrons
Increase in oxidation numbers
