AQA Combined Chemistry 5.3 Flashcards
Revision for Paper 1
Count the number of atoms in the following compounds:
a) CaO
b) Al2O3
c) H2SO4
a) 2 atoms (1 x Ca and 1 x O)
b) 5 atoms (2 x Al and 3 xO)
c) 7 atoms (2 xH, 1 x S and 4 x O)
Count the number of elements in the following compounds:
a) CaO
b) Al2O3
c) H2SO4
a) 2 elements (Ca and O)
b) 2 elements (Al and O)
c) 3 elements (H, S and O)
Calculate the mass of magnesium needed to produce 4.6 tonnes of magnesium oxide
2Mg + O2 - 2MgO
Step 1; make sure the equation is balanced
Step 2; calculate the Mr of 2Mg and the Mr of 2MgO
Mr of 2Mg = 48, Mr of 2MgO = 80
Step 3; you now know 48 tonnes of Mg would produce 80 tonnes of MgO
Step 4; find how much Mg you would need to produce 1 tonne of MgO (48/80) Mg and (80/80) MgO. Therefore 0.6 tonnes of Mg would produce 1 tonne of MgO
Step 5; X both sides by 4.6 to work out how much Mg would be needed to make 4.6 tonnes of MgO - (0.6 x 4.6) = 2.76 tonnes
Calculate the mass of CO2 produced when 50g of CaCO3 is thermally decomposed
CaCO3 - Ca0 + CO2
Step 1; equation needs to be balanced
Step 2; calculate Mr of CaCO3 and CO2 = 100 and 44
Step 3; you now know 100g of CaCO3 would produce 44g of CO2
Step 4; Find what 1g of CaCO3 would produce
(100/100) CaCO3 and (44/100) CO2
1g of CaCO3 would produce 0.44g of CO2
Step 5; X both sides by 50 to work out what 50g of CaCO3 would make
50g CaCO3 would make (o.44 x 50) of CO2 = 22g
Calculate the relative formula mass of eacgh of the compounds below; (Mg = 24; Cl = 35.5; Ca = 40; O = 16; Al = 27)
a) CaO
b) MgCl2
c) Al2O3
a) CaO - 40 + 16 = 56
b) MgCl2 - 24 + (35.5 x 2) = 95
c) Al2O3 - (27 x 2) + (16 x 3) = 102
Write a balanced symbol equation for the following reaction:
48g of Mg reacts with 32g of O2 to produce 80g of MgO
Number of moles = mass in g/Mr
Mg - 48/24 = 2; O2 - 32/32 = 1; MgO - 80/40 = 2
Ratio = 2Mg: 102: 2MgO
Balanced equation = 2Mg + O2 - 2MgO
A piece of magnesium is added to acid. What would happen to the mass reading on the balance and why?
It would decrease because there is no lid on the conical flask so gas can escape and therefore mass is ‘lost’ from the flask
What is a ‘limiting reactant’?
The first reactant that gets used up in a reaction and causes the reaction to stop
Calculate the uncertainty in the following sets of results;
a) 1, 3, 6, 7, 10
b) 22, 25, 26, 25, 24
Uncertainty = range/2
a) 1, 3, 6, 7, 10
Range; 10 - 1 = 9. Uncertainty = (9/2) = +4.5
b) 22, 25, 26, 25, 24
Range; 26 - 22 = 4. Uncertainty = (4/2) = +2
Why is one reactant often added in excess to a reaction?
To ensure that all of the other reactants are used up
Calculate the percenatge mass of hydrogen in:
(N = 14; H = 1; S = 32; O = 16)
a) NH3
b) H2SO4
% mass = Ar x no. of atoms of the element/Mr of compound
a) NH3: (3x1)/17 = 0.176
0. 176 x 100 = 18%
b) H2SO4: (2x1)/98 = 0.02
0. 02 x 100 = 2%
How many molecules, atoms or ions are in one mole of a substance?
6.02 x 10^23^
What does the law of the conservation of mass state?
No atoms are lost or made during a chemical reaction
How many moles are in the following?
a) 46g of CaO?
b) 50g of O2?
Number of moles = mass in g/ Mr a) Mr of CaO = 40 + 16 = 56 Number of moles = 46g / 56 = 0.82 moles b) Mr of O2 = 16 Number of moles = 50g / 32 = 1.6 moles
A piece of magnesium is added to acid. What would happen to the mass reading on the balance and why?
It would stay the same because there is a lid on the conical flask so no gas can escape
