C3 QUANTITATIVE CHEMISTRY

Question 1

law of conservation of mass?

Answer 1

no atoms are lost or made during a chemical reaction so the mass of the products equals the mass of the reactants

Question 2

what is the relative formula mass?

CaF2

Answer 2

Ca = 40
F = 19
Ca = 40 + (19 x2)
= 78

Question 3

the following reaction occurs in a test tube under a bunsen burner:
4MgO + CH4 -> 4Mg + 2H20 + CO2

the carbon dioxide and water escapes from the test tube
explain why?

Answer 3

both gases

Question 4

avogrado constant?

Answer 4

number of atoms, molecules , ions in a mole of a given substance. the value of the constant is 6.02 x 10 to the power of 23

Question 5

formula that links mass , molecular mass , and moles together

Answer 5

mass = mr x moles

Question 6

what is the mass of 20 moles of calcium carbonate CaCO3?

Answer 6

Mass = Mr x Moles
Mr = 100
100 X 20 = 2000g

Question 7

calculate the amount of carbon dioxide in moles in 0.32g of carbon dioxide.
relative atomic masses = carbon = 12 , oxygen = 16

Answer 7

Moles = Mass/Mr
0.32/44 = 0.007

Question 8

calculate the mass of nitrogen needed to form 6.8 tonnes of ammonia?

Answer 8

s1. work out the number of moles of ammonia (Mr of ammonia = 17)
s2. 6800000/17 = 400000 moles of ammonia
s3. use the balanced equation and number of moles of ammonia to work out the number of moles of nitrogen.
s4. the ratio of nitrogen to ammonia is 1:2
s5. therefore the number of moles of nitrogen is 400000/2 = 200000
s6. work out the mass of nitrogen (mr of N2 is 28)
s7. 200000 x 28 = 5600000g =5.6tonnes

Question 9

limiting reactant?

Answer 9

the reactant that is all used up

Question 10

how much oxygen will be given off from 40.8 g of hydrogen peroxide?

Answer 10

balanced equation - 2H202 -> 2H20 + O2
number of moles in 40.8g: 40.8/34 = 1.2 moles
ratio in balanced equation of H2O2:O2 = 2:1
therefore the number of moles of o2 = 0.6moles
mass of oxygen = 0.6 x 32 (Mr of o2) = 19.2

Question 11

2 formulas that link concentration , mole/mass and volume together

Answer 11

concentration (g per dm cubed) = mass (g)/volume (dm cubed)

concentration (mole per dm cubed) = nr of moles/volume (dm cubed)