TEST Flashcards
Describe an experiment to determine the empirical formula for a compound
Weigh crucible
Put a sample of magnesium into the crucible and weigh it.
Calculate the mass of magnesium by subtracting the mass of the empty crucible
Heat over Bunsen burner
Carefully lift lid from time to time to allow some oxygen into the crucible for the magnesium to fully oxidise without letting any magnesium oxide escape.
Heat until mass of crucible it at its max
Repeat step 2
To find ep formula you need mass of magnesium and mass of oxygen- to find mass of oxygen atoms subtract the mass of magnesium used from the mass of magnesium oxide.
Divide two masses by relative atomic masses and simplify.
What is a mole of particles
One mole is the Avogadro number of particles (atoms, molecules, ions or electrons) in a substance.
What is the mass of a product formed in a reaction controlled by?
The mass of reactant that is not in excess
State the meaning of the term ‘electrolyte’
An ionic substance/liquid with freely moving ions that electrolysis takes place in
What happens in electrolysis? (SUMMARY!!!!!)
The process of using electricity to break apart the ions in an ionic substance that is either dissolved in water or molten.
Explain the movement of ions during electrolysis
Positively charged ions move to the negative electrode (CATHODE) during electrolysis. They gain electrons and are reduced.
Negatively charged ions move towards the positive electrode (ANODE) during electrolysis. They lose electrons and are oxidised.
What happens to the electrons in oxidation
Electrons are lost (+ charge)
What happens to the electrons in reduction
Electrons are gained (- charge)
Where does oxidation occur
At the anode
Where does reduction occur
At the cathode
Recall the products formed from the electrolysis of a variety of common compounds and solutions
Copper chloride solution Sodium chloride solution Sodium Sulphate solution Acidified water Molten lead Bromide
HOW TO REMEMBER the order of the reactivity series from most reactive downwards
People Say Little Children Make A Zebra Ill Constantly Sniffing Giraffes.
Why are displacement reactions redox reactions
displacement reactions are when more reactive elements replace other elements in a compound, Redox means reduction/oxidation (having to do with reactivity and electron transfer)
what is a cation
a positively charged ion which would be attracted to the cathode
recall meaning of the term ORE
naturally occurring rocks that contain metal or metal compounds in sufficient amounts to extract them.
Recall some metals that are found uncombined in the earths crust
GOLD
SILVER
COPPER
(LESS REACTIVE)
How and why are some metals extracted from their ores by heating carbon
Less reactive metals such as iron are extracted by reduction with carbon. The metal oxide loses oxygen, and therefore is reduced. The carbon gains oxygen and therefore is oxidised
Explain how and why some metals are extracted from their ores by electrolysis
More reactive metals such as aluminium are extracted by electrolysis.
Oxidation in terms of oxygen
The addition of oxygen to a substance in a reaction, or the reaction of a substance with oxygen
How are all metals extracted
by reduction of their ores
Advantages and disadvantages of recycling a metal
Helps limit amount of metals that must be produced
SUSTAINABLE
Process of recycling metals usually creates much less pollutants
and uses less energy therefore less fossil fuels are being burnt
HOWEVER
Can be expensive
Time consuming
Requires energy
How do we recycle plastic
Sorting it into different polymers and then chipping it and melting i- re shaping and molding it
Pros and Cons of recycling
Reduces pollution Reduces global warming Reduce energy usage Be sustainable However High in cost Recycling sites can be unsafe, unsightly and unhygienic
What happens in reversible reactions
The products can react to produce the original reactants again
⇄ (Use of the symbol in chemical equations)
Shows the reaction goes both ways
What is dynamic equilibrium
Both the backwards and forwards reactions occur but the substances are in balance
Describe the formation of Ammonia
Also known as the haber process
Nitrogen from the air reacts with hydrogen derived mainly from natural gas (methane) into ammonia.
This reaction is reversible and exothermic
Recite the equation for Ammonia creation
N2 + 3H2 ⇄ 2NH3 (+heat)
Recite the 3 conditions used in the Haber process
450*
200 atmosphere pressure
Iron catalyst
Uses of Haber processes
Fertilizers
Explosives
Cleaning fluids
Changes in pressure will not affect the position of equilibrium if…
the number of moles of gases on both sides of equation are equal
How does changes temperature effect equilibrium
Increasing the temperature always favours the endothermic reaction.Decreasing the temperature always favours the exothermic reaction.
Describe the difference between endothermic and exothermic
Endothermic- requires energy
Exothermic- gives out/releases energy
What is LCA
A life cycle assessment –is used to work out the environmental impact of a product from the raw materials to dispose of the product
Describe the position of transition metals in the periodic table
In the center of the periodic table between groups 2 and 3
What are the chemical and physical properties of transition metals
Chemical- Acts as a catalyst and forms a colored compound and has variable oxidation states
Physical- High density and high melting points
Why has iron got typical properties of a transition metal
High density - 7.8
High melting point- 1538*
Uses as a catalyst- haber process
What is corrosion of metals a result of
oxidation
How does rusting of iron occur
When iron is exposed to oxygen and moisture for a long period of time
Over time, the oxygen combines with the metal at an atomic level forming a new compound oxide
How does sacrificial protection work
Covering the object with a thin layer of zinc (sacrificial metal), this stops the oxygen and water reaching the metal underneath. The zinc is more reactive than iron, so it oxidises in preference to the iron object
Why do metal objects need to become electroplated
increases life of metal
prevent corrosion
Recall some common examples of electroplating
Copper Nickel Tin Zinc Gold Silver
Recall the name of a common alloy
steel
an alloy of iron and carbon
What is an alloy
A mixture of a metal element with one or more other elements (usually metals)
What happens in alloying
Within the mixture of two or more elements, where at least on element is a metal (the alloy) Alloys contain atoms of different sizes, which distort the regular arrangement of atoms. This makes it more difficult for the layers to slide over each other, so alloys are harder than the pure metal
Why is iron alloyed with other metals
Pure iron is to soft for many uses
Common uses for Aluminium, copper and gold
Aluminum- bodies of planes
Copper- Electrical wires as its a good conductor
Gold- Jewelry (lack of reactivity)
Common alloys that contain aluminum or copper
Duralium (contains both)
Bronze- copper+tin
Brass-copper+zinc
Difference between empirical formula and molecular formula
Empirical formula tells you the simplest or most reduced ratio of elements in a compound. WHEREAS molecular formula tells you how many atoms of each element are in a compound
Describe a closed system
Same mass after as before the reaction