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Moles, Molar Mass, Molarity, Empirical Formula, Molecular Formula, and Hydrates:
1. Calculate the molar mass for: CoCl 2 · 6 H 2 O
(Hint: the “dot” means that you have a hydrate)
Answers:
g g g g
mol mol mol mol mol
⎛ ⎞ ⎛ ⎞ ⎡^ ⎛ ⎞ ⎛ ⎞⎤
⎜ ⎟ +^ ⎜ ⎟ +^ ⎢ ⎜ ⎟ +^ ⎜ ⎟⎥ =
g
- Calculate molar mass for iron(III) carbonate.
Answers:
2 (^3 ) 3 : 2 55.85^ 3 12.01^ 9 16.00^ 291.
g g g Fe CO mol mol mol mol
⎜ ⎟ +^ ⎜ ⎟ +^ ⎜ ⎟ =
g
3. Calculate the number of moles for 466 milligrams of LiOH.
Answers:
Recall the steps:
mg ↔ g ↔ moles ↔ molecules ↔ atoms
mg LiOH g mol LiOH mol LiOH mg g
× × =
- Calculate the number of moles for 723 grams of magnesium phosphate.
Answers:
Recall the steps:
kg ↔ g ↔ moles ↔ molecules ↔ atoms
(^3 4 2 3 ) (^3 4 )
g Mg PO mol Mg PO mol Mg PO g
× =
5. Calculate the number of molecules for 1.50 kilograms of C 6 H 12 O 6.
Answers:
Recall the steps:
kg ↔ g ↔ moles ↔ molecules ↔ atoms
23 6 12 6 24 6 12 6 6 12 6
kg g mol C H O molecules
molecules C H O
kg g mol C H O
×
× × × = ×
- Calculate the number of molecules for 3.55 moles of chromium(VI) sulfate.
Answers:
A question like this is perfect for LEARNING HOW to read a question – Notice, you DO NOT need to write the formula for the chromium(VI) sulfate to answer the question since it asked only for MOLECULES and you know the number of MOLES !!!
Recall the steps:
kg ↔ g ↔ moles ↔ molecules ↔ atoms
( )
( )
( )
23 (^4 ) (^4 ) (^4 )
mol Cr SO molecules
molecules Cr SO
mol Cr SO
×
× = ×
7. Calculate the number of atoms for 4.23 x 10
- kilograms of tin(IV) nitrate.
Answers:
This will be the LONGEST problem (the one with the most steps)
( )
( ) ( )
5 23 (^3 )
(^3 4 )
kg g mol Sn NO molecules atoms atoms kg g mol Sn NO molecule Sn NO
− × × × × × × = ×
8. Calculate the number of moles of titanium(III) chlorate that are dissolved in 4.22 L of a 12.5 M solution?
Answers:
If you KNOW both the volume and molarity of a substance, ALWAYS start with the VOLUME !!!
L mol mol L
× =
A question like this is perfect for LEARNING HOW to read a question – Notice, you DO NOT need to write the formula for titanium(III) chlorate to answer the question since it asked only for MOLES !!!
9. Calculate the number of grams of sodium hydroxide are needed to make three liters of a 6.99 M NaOH solution?
Answers:
If you KNOW both the volume and molarity of a substance, ALWAYS start with the VOLUME !!!
L mol NaOH g g L mol NaOH
× × =
- What is the formula for the hydrate that is 89.62% CuWO 4 and 10.38% H 2 O?
Answers:
4 4
g mol CuWO CuWO mol g
× =
mol
mol
2 2
g mol H O H O mol g
× =
mol
mol
CuWO 4 · 2 H 2 O
