Answer:
The periodic table
Step-by-step explanation:
As you can see in the screenshot. Each element on the periodic table has an atomic number and a mass number. The atomic numbers are arranged in numerical order from right to left in the periodic table. The second number there is the atomic mass.
When doing stoichiometric ratios, you need to use the atomic mass of each element to determine the molecular/molar mass.
example. Find the molar mass of
H₂SO₄
Hydrogen (2) + sulphur (1) +oxygen (4)
= atomic mass of H(2)+ atomic mass S(1)+ atomic mass oxygen(4)
=1(2) + 32(1)+16(4)
=2+32+64
=98
N.B We do not use the co-efficient when looking for molar mass, we only use the atom and subscript