4 - Acids and redox Flashcards
What is an acid?
All acids contain hydrogen, when acids are dissolved in water, they releases hydrogen ions.
What is a strong acid? Give an example.
A strong acid (HCL) releases all its hydrogen ions into a solution and completly dissociates in aqueous solution.
What is a weak acid? Give an example.
A weak acid (ethanoic acid CH3COOH) only releases a small proportion of its hydrogen into solution. Partially dissociates.
What is a base?
A base neutralises an acid to form a salt. (Metal hydroxides, Metal carbonates, Metal oxides and ammonia).
What is an alkali?
An alkali is a base that dissolves in water to release OH- ions. (NaOH)
Give the word equation of the nutralisation of an acid with a metal carbonate.
Acid + Metal carbonate –> Salt + water + carbon dioxide.
Is sulfuric acid a strong or weak acid?
Sulfuric acid behaves as a strong acid, but it only dissociates one of its hydrogen ions when mixed with water. The resulting HSO4- ion then only partially dissociates; the ion behaves as a weak acid.
What three things can titrations be used for?
Titrations find the exact volume of one solution that reacts with another solution. It can find:
- Concentration of a substance.
- Unknown chemicals.
- Finding purity of a substance.
Give a method for calculating information of a titrated chemical after the titration.
Work out the amount in mols of the known concentration and volume.
- Use the chemical equation to get the amount in mols of the unknown chemical.
- Use the mols and volume of the unknwown to find missing information.
How would you determine the chemical formula of an unknown carbonate.
- Find mass of unknown carbonate.
- Prepare unknown solution of carbonate in volumetric flask.
- Using a pippet, measure 25cm3 of prepares solution to conical flask.
- Using burette, titrate solution using 0.1M HCL.
What is an oxidation number?
The oxidation number is the number of electrons involved in bonding to a different element. The same as the charge on the ion of an element.
What are the special cases for oxidation numbers?
- H in metals (-1)
- O in peroxides (-1) H2O2
- O bonded to F (+2)
When would you use roman numerals to name an element.
Used in elements that form ions with different charges. The roman numerals show the oxidation state.
What is reduced and what is oxidised in:
2Fe(s) +3Cl2(g) –> 2FeCl3(s)
Fe forms a positive ion so it loses electrons and is oxidised. Chlorine forms a negative ion and is reduced.
How would reduction and oxidation be represented by oxidation number?
Reduction is a decrease in oxidation number.
Oxidation is an increase in oxidation number. Oxidation numbers do not have to balence in an equation, the nnumber of elements make them balence.
