What is the relative mass of a neutron?
What is an atoms mass number?
The number of protons and neutrons in the nucleus.
What is an isotope?
An element with the same number of protons but different number of neutrons
Calculate the relative formula mass for carbon dioxide (CO2)
12+16+16 = 44
What is meant by the term mole?
The relative formula mass of a substance in grams is one mole.
One mole = 6.022 x 10^23 atoms or molecules
Calculate the percentage by mass of carbon in carbon dioxide.
Ar of carbon = 12
Mr of CO2 = 44
(12/44)x100 = 27.3 %
How many atoms of sodium react with 1 molecule of chlorine to make two sodium chlorides? (2Na + Cl2 -> 2NaCl)
What is meant by the term yield?
The amount of useful product obtained from a reaction
Give reasons to explain why the yield of a reaction may be less than expected.
- Reaction may be incomplete
- Some product is lost
- Other unwanted reactions may occur making a different product.
- Reaction may be reversible
What is chromatography used for?
Give an advantage and a disadvantage for using gas chromatography over paper chromatography.
Advantages = rapid, accurate, sensitive. Disadvantages = expensive.
What is a mass spectrometer used for?
Identify substances or measure a compounds relative molecular mass
How do you work out the rate of a reaction?
Rate of reaction = amount of reactant used or product formed / time
What two things needs to happen for particles to react?
Collide with enough energy
State 4 ways to speed up a chemical reaction
Increase concentration, increase temperature, increase surface area and use a catalyst
Why do catalysts not need to be replaced?
They are not used up during a chemical reaction.
What is the difference between exothermic and endothermic reactions?
Exothermic gives out heat (temperature increases) endothermic takes in heat (temperature decreases)
Give a use for exothermic reactions
Self heating cans / hand warmers
In a reversible reaction 500 J of energy is released in the forward reaction. What happens in the reverse reaction?
500 J of energy is absorbed.
What is the pH of an acid?
What is the atomic number of magnesium?
Calculate the relative atomic mass of water (H2O)
1+1+16 = 18
How many atoms of Calcium react with 1 molecule of chlorine to make calcium chloride (Ca + Cl2 -> CaCl2)
Calculate the percentage mass of oxygen in water
Ar of oxygen = 16
Mr of water = (1 + 1 + 16) = 18
(16/18) x 100 = 88.9%