Chapter 4 - Acids and Redox
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What is an acid?
A substance that releases H+ ions (protons) when dissolved in water. A proton donor.
What happens when a strong acid reacts with water?
The strong acid releases all its hydrogen atoms into solution as H+ ions and completely dissociates in aqueous solutions.
What happens when a weak acid reacts with water?
The weak acid only releases a small proportion of its available hydrogen atoms into solution as H+ ions. A weak acid partially dissociates in aqueous solution.
What is a base?
A substance that neutralises an acid to form a salt and water. A proton acceptor.
What is an alkali?
A base that dissolves in water releasing hydroxide ions (OH-) into the solution.
Acid + Metal oxide/hydroxide →
Acid + Metal oxide/hydroxide → Salt + Water
What is neutralisation?
A reaction between an acid and a base to produce a salt.
Acid + Metal carbonate →
Acid + Metal carbonate → Salt + Water + Carbon Dioxide
What are titrations used for?
Finding the concentration of a solution
What is a standard solution?
A solution of known concentration.
What is the oxidation number of calcium in Ca2+
+2 (not 2+ like an ionic charge)
Acid + Metal →
Acid + Metal → Salt + Hydrogen
Redox reactions involve…
…reduction AND oxidation
Reduction is…
…the gain of electrons …a decrease in oxidation number
Oxidation is…
…the loss of electrons …an increase in oxidation number
What should one ensure in a titration to prevent human error?
Ensure the bottom of the meniscus is viewed at eye level.
What are the common exceptions of oxidation numbers?
In a metal hydride (e.g. NaH), hydrogen has an oxidation number of -1 When bonded to fluorine, oxygen has an oxidation number of +2 In a peroxide (e.g. H2O2), oxygen has an oxidation number of -1.
What do roman numerals in names of compounds represent?
The oxidation number of an element.
Acid + Ammonia →
Acid + Ammonia → Ammonium Salt HX + NH3 → NH4X
What is a disproportionation reaction?
A reaction where the same element is both oxidised and reduced.
What is a titration?
A form of volumetric analysis in which a known volume and concentration of a solution is reacted with a measured volume of another solution.
What is neutralisation?
A reaction between an acid and a base to produce a salt.
What is an oxidising agent?
A substance which oxidises other things but are themselves reduced. Vice versa for reducing agents.