Seneca C4 Flashcards
Acids
Acids are substances that form hydrogen (H+) ions when they dissolve in water (aqueous solutions).
The pH scale
The pH scale is used to measure how acidic or alkaline a substance is.
Alkalis
Alkalis are substances that form hydroxide (OH-) ions when they dissolve in water (aqueous solutions).
An alkali is a type of base.
Oxidation
An oxidation reaction involves gaining oxygen.
Oxidation reactions can also involve losing electrons.
Reduction
A reduction reaction involves losing oxygen.
Reduction reactions can also involve gaining electrons.
Oxidation in terms of electrons
When a substance is oxidised (gains oxygen), it always loses electrons.
Reduction in terms of electrons
When a substance is reduced (loses oxygen), it always gains electrons.
OIL RIG
Which non-metals are often included in the reactivity series of metals for reference?
Carbon, Hydrogen
Displacement order
A metal can only displace another metal from a compound if it is located above it in the reactivity series.
Potassium and water
Potassium is the most reactive so reacts very quickly.
The hydrogen produced ignites instantly and the metal also sets alight, sparking and burning with a lilac flame.
Sodium
Sodium fizzes rapidly and melts to form a ball that moves around on the water surface.
Lithium
Lithium fizzes steadily and floats, becoming smaller until it eventually disappears.
Metals that dont react with dilute acids
Copper, silver, gold and platinum.
Why is carbon used to extract metals?
Reducing a metal with carbon will result in the extraction of the metal if the metal is lower in the reactivity series than carbon.
Carbon is used because it is cheap and abundant
How is carbon used to extract metals
In the reduction, the metal oxide loses oxygen to form a pure metal.
Reduction with carbon normally involves heating the metal oxide in the presence of the carbon, which is often used in the form of coal.
When acids react with metals what is formed?
When acids react with metals, hydrogen and a salt are always formed
What are redox reactions
Redox reactions involve a reduction reaction (one reactant gains electrons) and an oxidation reaction (one reactant loses electrons)
What is a base
an alkali is a base that dissolves in water
How can acids be neutralised
Acids can be neutralised by reacting with bases
What are examples of bases
Metal carbonates, metal oxides and metal hydroxides
What forms when acids react with hydroxides and oxides
Salt + water
What forms when acids react with carbonates
salt + water + carbon dioxide
OILRIG
Oxidation
Is
Loss (of electrons)
Reduction
Is
Gain (of electrons)
What must be reacted together to produce a soluble salt?
Solid, insoluble substance
Acid
Required Practical - Separating Mixtures
Preparation
Use a Bunsen burner to gently warm the acid.
Add the insoluble solid (with stirring) until the reaction no longer happens.
Required Practical - Separating Mixtures
Filtration
Filter the solution to remove the excess insoluble solid.
This will leave a solution of the salt dissolved in water.
Required Practical - Separating Mixtures
Crystallisation
Heat the solution in an evaporating basin above a beaker of water.
The ‘water bath’ ensures gentle heating.
Let the solution cool and allow more water to evaporate.
As water evaporates, the solution will become more concentrated and the salt will begin to crystallise.
What are the main ways of measuring pH
pH probe
Universal indicator
pH probe
The probe returns a number that represents the pH of a solution.
Universal indicator
The indicator changes to a particular colour depending on the pH of a solution.
What ions react together in neutralization reactions
Hydrogen ions
Hydroxide ions
Titration
Titration is a technique that measures the volumes of acid and alkali solutions that are needed in a neutralisation reaction.
What are the key variables for titrations
The concentration of the acid to be added.
The volume of the alkali.
Weak acids
Only partially ionise in water, meaning that not all of the acid molecules break up to form H+ ions.
Strong acids
Fully ionise in water, meaning that all of the acid molecules break up to form H+ ions.
What is electrolysis
Electrolysis is the process that splits ionic compounds into the different elements that they are made of
Electrolyte
When ionic compounds are melted or dissolved in water, the ions (charged particles that have gained/lost electrons) are free to move around, and the liquid/solution will conduct electricity.
Ionic compounds that dissolve in water to make a solution that conducts electricity are called electrolytes.
Electrodes
When a voltage (direct current) is applied across an electrolyte, the charged ions are attracted to the electrode with the opposite charge to the ion.
Positively charged ions are attracted to the negative electrode (cathode).
Negatively charged ions are attracted to the positive electrode (anode).
Elements
When an ion touches an electrode, electrons can be transferred, producing elements.
What happens at the anode
Oxygen forms at the carbon anode. The carbon and oxygen react to give carbon dioxide.
What happens at the cathode
The aluminium is formed at the cathode.
Disadvantages of electrolysis
Lots of energy is needed to:
Melt the solid ionic compound to allow the ions to flow.
Produce the electrical current.
All this energy costs money, and a lot of it!
Electrolysis of aqueous solutions at the cathode
What is formed at the cathode depends on the reactivity of the metal
Hydrogen is produced if the metal is higher than hydrogen in the reactivity series.
The metal is produced if the metal is lower than hydrogen in the reactivity series.
Electrolysis of aqueous solutions of at the anode
What is formed at the anode depends on if there are halide ions present:
If there are halide ions present, the respective halogen forms.
If there are no halide ions, oxygen forms.
Half equations at the cathode
Reduction reactions happen i.e. positively charged ions gain electrons
Half equations at the anode
Oxidation reactions happen i.e. negatively charged ions lose electrons
