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AQA Chemistry Unit GCSE
This a few revision questions for chemistry in GCSE's
What is an endothermic reaction?
A reaction that takes in energy from the surroundings, usually shown by a fall in temperature
What is an acid?
A substance with a pH less than 7
What is the difference between a base and an alkali?
A base is a substance with a pH higher than 7, and alkali is a base which dissolves in water
What is an exothermic reaction?
A reaction that transfers energy to the surroundings, usually shown by a rise in temperature
What is an indicator?
A dye which changes colour depending on whether it's above or below a certain pH
What does (aq) mean?
Aqueous, a substance dissolved in water
What is a catalyst?
A substance which speeds up a reaction without being changed or used up in the reaction
In terms of particles how does a catalyst speed up a reaction?
Solid catalysts work by giving reacting particles something to stick to which increases the successful number of collisions
Why are catalysts important?
For commercial reasons, they increase the rates of reactions which saves money, as reactions require less energy
What are the disadvantages of catalysts?
They are expesive to buy, and often need to be removed from the product and cleaned, different reactions require different catalysts, they are easily denatured
How does increasing the temperature increase the rate of reactions (in terms of particles)?
Increasing the temperature increases the speed of the particles and so they collide more often
In terms of particles, how does a higher concentration increase the rate of a reaction?
There are more particles of a reactant so there are more frequent collisions between reactant particles
In terms of particles how does a higher pressure speed up a reaction?
The particles are compact closer together so there will be more frequent collisions
How does a larger surface area increase collisions between particles in a reaction?
Particles in the solution will have more area to work on so there will be more frequent collisions
State two ways of calculating the rate of a chemical reaction.
Reactant used/ product formed
What is activation energy?
The minimum amount of energy needed by particles to react
What ion is present in alkaline solutions
What ions are present in acidic solutions?
Hydrochloric acid+ copper oxide
Copper chloride + water
How are ammonia salts made?
Ammonia dissolves in water to make an alkaline solution, which is reacted with nitric acid, to get the salt- ammonium nitrate
What is ammonium nitrate used for?
Fertiliser, it is good as it has nitrogen from two sources, plants need nitrogen to make protiens
True or false, water is produced in the neutralisation of ammonia?
Are most oxides and hydroxides soluble or insoluble in water?
How do you make an insoluble salt?
Precipitation reaction- mix two solutions containing ions and filter the salt from the reacted solution
What is the top number on an atomic symbol?
The mass number
What is the atomic number?
The bottom number on the atomic symbol- the number of protons and electrons in an element
What is an isotope?
Different atomic forms of the same element, with the same number of protons but a different number of neutrons
What is the relative formula mass?
The relative formula mass in grams is known as one mole of that substance
What is the relative atomic mass?
The same as the mass number of an element (top number)
How do you work out the number of moles in a substance?
Mass in g (of element or compound)
Relative formula mass
How many moles are in 42g of carbon?
42/12 =3.5 moles
What is a compound?
Substances in which atoms of two or more elements are chemically bonded together
What does chemical bonding involve?
Transferring or sharing electrons in the highest occupied energy levels (shells) of atoms in order to achieve the structure of a noble gas
How do ionic bonds form?
Atoms lose or gain electrons to form charged particles (ions) which become strongly attracted
How do covalent bonds form?
Atoms share electrons with other atoms from the outer shell to form the state of a noble gas with its outer shells full
How do group 1 elements react?
Alkali metals all react with non metals to form ionic compounds- the metal ion has a single + charge
How do group 7 elements react?
Halogens all react with group 1 alkali metals to form ionic compounds- single - charge
How are ionic compounds held together
By strong electrostatic forces between oppositely charged ions- these forces act in all directions in the lattice
What is the structure that sodium and chlorine ions are held together in?
In a regular cuboid lattice
Name two properties of ionic compounds.
High melting points
High boiling points
Methane has 4 outer electrons, so how many covenant bonds must it make to fill it's outer shell?
Name two properties of covalently bonded molecules
Low melting/ boiling points
Don't conduct electricity
In simple molecular substances the intermolecular forces are ____
What is a giant ionic structure called?
In giant covalent structures all the atoms are bonded to each other by ____ covalent bonds...
Name two examples of giant covalent structures.
What is important about the electrons in metallic bonds?
They are delocalised (free)- these electrons hold the atoms together in a regular structure