(1) Relative Atomic Mass (Ar) = Sum of (isotope abundance x mass number)
Sum of abundance of all isotopes
(2) Surface area to volume ratio = Surface area
Volume
(3) Percentage mass of an element in a compound
= Ar x number of atoms of that element x 100
Mr of the compound
(4) Relative formula mass (Mr)
= Sum of the relative atomic masses of all atoms shown in the formula
Example:
Find the Mrof water, H2O
Relative atomic masses: H = 1; O = 16.
Mrof H2O = (2 x 1) + (1 x 16) = 18
(5) Quantitative chemistry
One mole of any substance = 6.02 x 1023atoms (Avogadro’s constant)
(6) Quantitative chemistry
Number of moles (mol) = mass (g)
Mr(g/mol)
(7) Quantitative chemistry
Conservation of mass:
Mass of Reactants = Mass of products
(8) Quantitative chemistry
Mole ratio
Example, from the equation below:
2H2 (g)+ O2 (g) 2H2O(l)
The mole ratio: H : O : H2O
2 : 1 : 2
(9) Quantitative chemistry
Percentage yield (of a chemical reaction) = mass of product actually made
Maximum theoretical mass of product
(10) Quantitative chemistry
Atom economy (Atom utilization)
= Sum of Relative Formula Mass of desired product
Sum of Relative masses of all reactants
(11) Quantitative chemistry
Gas volumes
Number of moles (mol) = Volume (dm3)
24 dm3
(12) Quantitative chemistry
Concentration of solutions in g/dm3 = mass (g)
Volume (dm3)
(13) Quantitative Chemistry
Concentration of solutions in mol/dm3 = moles (mol)
Volume (dm3)
(14) Chemical Changes
Finding pH from concentration of solutions in mol/dm3.
A 1.0 x 10 – 3mol/dm3solution of HCl acid has a pH of 3.0
A 1.0 x 10 – 5mol/dm3solution of HCl acid has a pH of 5.0
(15) Chemical changes
Example: Find the pH of a 0.0025 M HCl solution.
Mark Scheme:
pH = -log [H3O+]
pH = -log (0.0025)
= – (- 2.60) = 2.60
(16) Chemical changes
Relationship between pH and pOH
The pH and pOH of a water solution at 25oC are related by the following equation:
pH + pOH = 14
(16a)
Example: A solution has a pOH of 11.76.
What is the pH of this solution?
M/S:
pH + pOH = 14
pH = 14 – pOH
= 14 – 11.76
= 2.24
(17) Rate and Extent of Chemical Change
Mean Rate of Reaction = Quantity of Reactant Used
time
OR
Mean Rate of Reaction = Quantity of Product formed
time
(18) Finding rate of reaction from gradient / slope of graph
Gradient = Change in y
Change in x
(19) Rate and Extent of chemical Change
(Surface) Area = Length x Length
(Surface) Area = Length x Width
Total Surface Area = Surface area of each side x Total number of sides
(20) Chemical Analysis
Chromatography
Rf= Distance moved by substance
Distance moved by solvent
(21) Using Earth’s Resources
Percentage of a metal / non-metal in an alloy
= Proportion (Amount) of metal / non-metal in the alloy x 100
Total Alloy amount
(22) Using Earth’s Resources
Percentage of pure carat gold in alloy = Number of carats x 100
24
Note: Pure Gold is 24 carat. So 75% gold would be 18 carat.
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