Stoichiometry Diagnostic – Solution Set
Atom to Mole (using Avogadro’s Number = 1 mol/6.02 x 1023 atoms)
1. a) How many moles are in 1.56 x 1032 boron (B) atoms?
= 2.59 x 108 moles
b) How many moles are in 3.01 x 1020 calcium (Ca) atoms?
= 5.00 x 10-4 moles
Mole to Atom (using Avogadro’s Number = 6.02 x 1023 atoms/1 mol)
2. a) How many atoms are in 3.66 moles of phosphorus (P)?
= 2.20 x 1024 atoms
b) How many atoms are in 15.7 moles of argon (Ar)
= 9.45 x 1024 atoms
A note about molecules/compounds: when finding the total number of atoms for a substance that
is composed of multiple atoms (examples include NaCl or O2), perform the same steps as above,
but multiply your answer by the total number of atoms in the compound.
3. a) How many atoms are in 2.98 moles of NaCl?
= 2.98 moles x (6.02 x 1023 molecules/mol) x (2 atoms/1 molecule) = 3.59 x 1024 atoms
b) How many atoms are in 3.75 moles of C2H5OH?
= 3.75 moles x (6.02 x 1023 molecules/mol) x (9 atoms/1 molecule) = 2.03 x 1025 atoms
c) How many carbon (C) atoms are in 3.75 moles of C2H5OH?
= 3.75 moles x (6.02 x 1023 molecules/mol) x (2 atoms/1 molecule) = 4.52 x 1024 atoms
Mass to Mole (using molecular mass = 1 mol/X grams)
4. a) How many moles are in 120 grams of silicon (Si)? (mm = 28.085 g/mol)
= 4.3 moles
b) How many moles are in 55.8 grams of NaCl?
(mm = 22.99 + 35.45 = 58.44 g/mol)
= 0.955 moles
Mole to Mass (using molecular mass = X grams/1 mol)
5. a) What is the mass of 0.937 moles of sodium (Na)? (mm = 22.99 g/mol)
= 21.5 grams
b) What is the mass of 2.05 moles of dinitrogen tetrahydride (N2H4)?
(mm = (2 x 14.01) + (4 x 1.01) = 32.06 g/mol)
= 45 grams
Atom to Mass (combining two steps from above)
6. a) What is the mass of 4.8x1022 atoms of sulfur (S)? (mm = 32.06 g/1 mol)
= 4.8x1022 atoms x (1 mol/6.02 x 1023 atoms) x (32.06 g/1 mol) = 2.6 grams
b) What is the mass of 6.33x1030 molecules of LiOH? (mm = (6.94 + 16 + 1.01) g/1 mol)
= 6.33x1030 molecules x (1 mol/6.02 x 1023 molecules) x ((6.94 + 16 + 1.01) g/1 mol)
= 2.52 x 108 grams
Mass to Atom (combining two steps from above)
7. a) How many atoms are in 62.6 grams of magnesium (Mg)? (mm = 1 mol/24.31g)
= 62.6 g x (1 mol/24.31 g) x (6.02 x 1023 atoms/1 mol) = 1.55 x 1024 atoms
b) How many molecules are in 22.8 grams of CaCl2? (mm = 1 mol/(40.08 + 2(35.45)) g)
= 22.8 g x (1 mol/110.98 g) x (6.02 x 1023 molecules/1 mol) = 1.24 x 1023 molecules
c) How many atoms are in 22.8 grams of CaCl2?
= 22.8 g x (1 mol/110.98 g) x (6.02 x 1023 molecules/1 mol) x (3 atoms/1 molecule)
= 3.71 x 1023 atoms
Mole to Mole (using a balanced chemical equation)
8. Given 1.50 moles of silver (Ag), find the moles of silver nitride (Ag3N) produced. Also
find the moles of magnesium nitride (Mg3N2) you would need for this reaction to go to
completion.
6 Ag + Mg3N2 -> 2 Ag3N + 3 Mg
= 1.50 mol Ag x (2 mol Ag3N/6 mol Ag) = 0.50 mol Ag3N
= 1.50 mol Ag x (1 mol Mg3N2/6 mol Ag) = 0.25 mol Mg3N2
Mass to Mass (using a balanced chemical equation and molar masses)
9. Say you wanted to make 10.0 grams of sodium sulfide from aluminum sulfide and
sodium chloride.
a) Write the balanced chemical equation modelling this reaction.
Al2S3 + 6 NaCl -> 3 Na2S + 2 AlCl3
b) Find the moles of sodium sulfide in 10.0 grams.
= 10.0 grams Na2S x (1 mol/78.04g) = 0.128139 moles Na2S
c) Find the mass of aluminum sulfide you would need for this reaction.
Step 1: moles Na2S to Al2S3 moles = 0.128139 mol Na2S x (1mol Al2S3/3mol Na2S)
= 0.042713 moles Al2S3
Step 2: moles Al2S3 to mass Al2S3 = 0.042713 moles Al2S3 x (150.14g/mol)
= 6.41 grams of Al2S3
d) Find the mass of sodium chloride you would need for this reaction.
Step 1: moles Na2S to moles NaCl = 0.128139 mol Na2S x (6 mol NaCl/3 mol Na2S)
= 0.256278 moles NaCl
Step 2: moles NaCl to mass NaCl = 0.256278 moles NaCl x (58.44g/mol)
= 14.98 grams of NaCl