stoichometry
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what is relative atomic mass (Ar)
the average mass of naturally occuring atoms of an element on a scale where the 12C atom has a mass of exactly 12 units
formula for Ar
((% of isotope a x mass of isotope a) + (% of isotope b x mass of isotope b))/100
avogadros constant
6.02 x 10^23
triangle for finding moles of all substances
mass/moles x relative formula mass
triangle for finding moles of gases
volume of gas (dm^3) / number of moles of gas x 24
triangle for finding moles of solutions
amount in moles (mol)/ concentration (mol/dm3) x volume (dm^3)
steps for calculating empirical formula
Step 1 Write the element symbols C H 2 Write the masses 4.8 g 1.0 g 3 Write the Ar values 12 1 4 Divide masses by Ar 4.8 ÷ 12 = 0.4 1.0 ÷ 1 = 1 5 Divide by the smallest number 0.4 ÷ 0.4 = 1 1.0 ÷ 0.4 = 2.5 6 Multiply (if needed) to get whole numbers 1 × 2 = 2 2.5 × 2 = 5 7 Write the formula C2H5 C2H5
formula for percentage yield
(experimental yield/theoretical yield) x 100
formula for percentage purity
(amount of pure substance/amount of impure substance) x 100