C3.3 Flashcards
What are redox reactions in terms of oxygen?
A redox reaction is a reaction in which reduction and oxidation happen at the same time.
What is reduction in terms of oxygen
It is the loss of oxygen from a substance
What is oxidation in terms of oxygen
It is the gain of oxygen from a substance
How are 2 steel railways welded together, ready for trains to run on them less than an hour later
The thermite reaction.
This reaction produces molten iron which runs into a small gap between the rails.
The iron cools and solidifies and is then machined to a smooth finish
What happens in the reaction
Aluminium + iron (III) —> aluminium oxide + iron
2Al+ Fe2O3 —> Al2O3 + 2Fe (I)
Aluminium gains oxygen and is oxidised to aluminium oxide. At the same time iron loses oxygen and is reduced to iron. Overall, oxygen is transferred from iron to aluminium
Aluminium acts as a reducing agent because it reduces iron oxide to iron.
Iron oxide acts as an oxidising agent because it oxidises aluminium to aluminium oxide
A thermite reaction includes…
Aluminium and iron (iii) oxide.
What does a half equation show?
A half equation shows the change that happens to one reactant in a reaction.
What is an acid?
An acid is a substance that releases hydrogen ions, H+, when it dissolves in water to make an aqueous solution.
What is a base
A base is a substance that can neutralise acids.
What are alkalis?
Water soluble bases
An alkali releases hydroxide ions OH- when it dissolves in water.
What is the pH scale?
The pH of a solution describes its relative acidity of alkalinity.
pH of an alkaline = ?
More than 7
>7
pH of an acid
Less than 7
<7
What is universal indicator ?
Universal indicator is a mixed indicator. It contains different indicators that change colour over different pH ranges.
What is neutralisation
Neutralisation is the reaction between an acid and a base to form a salt and water
ACID + BASE —> SALT + WATER
how do you predict the salt made?
The names of salts have 2 parts
- The first part comes from the metal in the base or alkali
- The second part of the name comes from the acid used.
What happens during neutralisation in solution?
Acidic solutions contain hydrogen ions and alkaline solutions contain hydroxide ions. These react together during neutralisation to make water
(H+ + OH- —> H2O)
The salt produced depends on the other ions present
What are carbonates?
Carbonates are ionic compounds that contain the carbonate ion (CO3)2-
What happens when acids react with carbonates
Acid + carbonate —> salt + water + carbon dioxide
What happens during this reaction between calcium carbonate and dilute hydrochloric acid?
CaCO3 + 2HCl —> CaCl2 + H2O + Co2
The carbon dioxide is released as bubbles in the acid during the reaction.
Calcium carbonate is insoluble in water but calcium chloride (the salt formed) is soluble in water.
This is why a lump of calcium carbonate appears to dissolve if you add acid to it.
What happens when acids react with metals
If a metal reacts with a dilute acid the reaction produces a salt and hydrogen
ACID + METAL —> SALT + HYDROGEN
What happens in the reaction between magnesium and dilute hydrochloric acid?
Mg + 2HCl —> MgCl2 + H2
The hydrogen is released as bubbles in the acid. As the reaction goes on, soluble magnesium chloride forms. This is why a piece of magnesium ribbon appears to dissolve if you put it into acid, even through magnesium itself is insoluble
Carbon dioxide is given off from carbonates reacting with acids
!!
Hydrogen is produced by and metal if it reacts with water or with an acid
..
What is a dilute acid
It contains a low ratio of acid to volume of a solution
What is a concentrated acid
It contains a high ratio of acid to volume of solution
What are weak acids
Weak acids Are partially ionised
Only a small amount of their molecules release H+ ions
What are strong acids?
They are fully ionised
All of their molecules release H+ ions
What does —>
The reaction does not go to completion
How is pH linked to hydrogen concentration
In an aqueous solution, as the concentration of H+ ions increases by 10, the pH decreases by 1.
This means…
An acid has a lower pH when it is concentrated than when it is dilute
A strong acid has a lower pH than a weak acid at the same concentration,
What does oxidised mean (electron and oxygen)
It describes a substance that has gained oxygen or lost electrons in a chemical reaction
What is an oxidising agent? (Oxygen and electrons)
A substance that oxidises another substance by donating oxygen or by accepting electrons
- one that is reduced
