Topic 4- Chemical Changes Flashcards
What is oxidation/reduction?
Oxidation is when a substance gains oxygen
Reduction is when a substance loses oxygen
What is the reactivity series
Potassium Sodium Lithium Calcium Magnesium Carbon Zinc Iron Hydrogen Copper
What is a displacement reaction?
A reaction where a more reactive metal displaces a less reactive metal from a compound
Redox reaction
Ion is reduced
Atom is oxidised
How can metals less reactive than carbon be extracted?
Reduction with carbon
Carbon displaces the metal in a metal oxide - gets oxidised to carbon oxides.
Metal from the metal oxide gets reduced to the pure metal
How are oxidation and reduction defined in terms of electron transfer?
Oxidation - loss of electrons
Reduction - gain of electrons
What is the general equation for a reaction between metals and acids? What type of reaction is this?
Metal+ acid –> salt + hydrogen
Redox reaction, also a displacement reaction
What is the general equation for the reaction between metal carbonate and acid?
metal carbonate + acid –> salt+water+carbon dioxide
What is the general equation for the reaction between metal oxides and acids?
Metal oxide + acid –> a salt + water
How is a soluble salt formed?
Add the chosen solid insoluble substance to the acid then the solid will dissolve
You know the acid has been neutralised when excess solid sinks to the bottom, so keep adding until this happens
Filter out excess solid leaving the salt solution, the evaporate some water, then leave the rest to evaporate slowly
What do acids and alkalis produce in aqueous solutions?
Acids produce hydrogen ions (H+), alkalis produce hydroxide ions (OH-)
What are bases, acids and alkalis?
Bases are compounds that neutralise acids
Acids produce hydrogen ions in aqueous solutions, alkalis are soluble bases meaning they produce hydroxide ions in aqueous solutions
What is a strong acid and weak acid?
Strong acid is completely ionised in aqueous solution
Weak acid is only partially ionised in aqueous solution
What happens to the pH as concentration of H+ increases?
The pH decreases
What is a concentrated acid and what is a diluted acid? Is this the same as a strong and weak acid?
Concentrated acid has more moles of acid per unit volume than dilute
It is not the same as concentration is not the same as strength of an acid
Strength referred to whether the acid is completely ionised in water (strong) or only partially (weak)
As the pH is decreased by one unit, what change is seen in the hydrogen ion concentration?
Increases by a factor of 10
What is electrolysis?
The passing of an electric current through ionic substances that are molten or in solution to break them down into elements
Ions are discharged (they lose/gain electrons) at electrodes to produce these
What is an electrolyte?
The liquid/solution which conducts electricity
Describe the process of electrolysis
When an ionic substance is melted or dissolved, the ions are free to move about within the liquid or solution
Passing a current through substances that are molten or solution means that the solution can be broken down into elements.
This is electrolysis and the substance being broken down is the electrolyte
During electrolysis, positively charged ions move to the negative electrode
(cathode)
Negatively charged ions move to the positive electrode (anode)
Ions are discharged at the electrodes, producing elements
What occurs at the cathode and what occurs at the anode during electrolysis?
Reduction occurs at the cathode
Oxidation occurs at the anode
In aqueous electrolysis, which element is discharged at the cathode? Oxygen is produced at the anode unless what?
The less reactive element discharges at the cathode. Hydrogen is produced unless there is a less reactive metal, in which case the said metal is produced
Oxygen is produced at the anode unless the solution contains halide ions, in which case halogen molecules are produced
How is aluminium manufactured and why is it expensive?
Aluminium is made through the electrolysis of aluminium oxide and cryolite
Lots of energy is needed to produce the current in electrolysis which makes this process expensive
Why is cryolite used in manufacturing of aluminium?
It lowers the melting point of aluminium oxide, reducing energy costs
In electrolysis, why does the positive electrode (anode) need to be continually replaced?
Oxygen is formed which reacts with the carbon of the positive electrodes, forming carbon dioxide, and they gradually burn away
Why is oxygen formed at the anode?
It is because in the aqueous solution, water molecules break down, producing H+ ions and OH- ions that are discharged
