LAB 5-MASS to MOLE to MASS STOICHIOMETRY

1
LAB 5-MASS to MOLE to MASS STOICHIOMETRY

• OVERVIEW
• At this time, your product is drying and
  therefore you cannot measure the EXPERIMENTAL or
  MEASURED mass in grams. The water would add mass
  and would cause you to overestimate the mass of
  your product, PbCr2O7(s). Please note water is
  not in the reaction, it is the solvent and does
  not interact chemically. You can however
  calculate your THEORETICAL YEILD, the mass of
  product you SHOULD have collected in your filter
  paper cone.

2

• OVERVIEW CONTINUED
• The calculation is performed in three steps
• CONVERT THE GIVEN OR KNOWN TO MOLES.
• RATIO MOLES OF GIVEN TO MOLES OF OBJECTIVE.
• CONVERT MOLES OF OBJECTIVE TO GRAMS, THEN COMPARE
  IT TO WHAT YOU ACTUALLY COLLECTED AND MEASURED IN
  LAB.

3
FLOWCHART OF THE THEORETICAL CALCULATION
Step 1 CONVERT REACTANT(KNOWN) TO MOLES
MOLES KNOWN MASS (GRAMS)
MOLAR MASS
Step 2 MOLE RATIO
(FROM
REACTION) KNOWN . COEFFICIENT KNOWN
MOLES KNOWN OBJECTIVE . COEFFICIENT OBJ.
MOLES OBJ. (X)
Step 3 CONVERT KNOWN REACTANT TO MOLES
MOLES OBJ. MASS (GRAMS) (X)
MOLAR MASS
4
Step 1 CONVERT KNOWN REACTANT Pb(NO3)2 TO MOLES
MOLES KNOWN MASS used 1.13g
0.0034 mol
MOLAR MASS 331.15 g/mol
Pb(NO3)2
Step 2 MOLE RATIO
(COEFFICIENT, from
reaction) KNOWN COEFFICIENT KNOWN
MOLES KNOWN OBJECTIVE COEFFICIENT OBJ.
MOLES OBJ. (X) Pb(NO3)2
1 0.0034 mol
X 0.0034 PbCr2O7(s).
1 X
mol
Step 1 CONVERT OBJECTIVE TO MASS IN GRAMS.
MOLES OBJ. MASS (GRAMS) 0.0034 X
grams 1.438g PbCr2O7 MOLAR
MASS 423.11 g/mol
5
CALCULATION OF MOLAR MASS of K2Cr2O7
LIST SUBSCRIPTS
MULTIPLY By atomic mass
INSERT ATOMIC MASS FROM PERIODIC TABLE
K 2 X 39.09 g/MOL 78.18 g
Cr 2 X 51.99 g/MOL 103.98 g
O 7 X 15.99 g/MOL 111.93 g
LIST ELEMENTS HERE
294.09 g/mol
6
CALCULATION OF MOLAR MASS of Pb(NO3)2
LIST SUBSCRIPTS
MULTIPLY By atomic mass
INSERT ATOMIC MASS FROM PERIODIC TABLE
LIST ELEMENTS HERE
Pb 1 X 207.2 g/MOL 207.2 g
N 2 X 14.00 g/MOL 28.00g
O 6 X 15.99 g/MOL 95.95 g
The number of O atoms is 3 times 2
The number of N atoms is 1 times 2
331.15 g/mol
7



CALCULATION OF MOLAR MASS of PbCr2O7
LIST SUBSCRIPTS
MULTIPLY By atomic mass
INSERT ATOMIC MASS FROM PERIODIC TABLE
LIST ELEMENTS HERE
Pb 1 X 207.2 g/MOL 207.2 g
Cr 2 X 51.99 g/MOL 103.98 g
O 7 X 15.99 g/MOL 111.93 g
The number of O atoms is 7
The number of Cr atoms is 2
423.11 g/mol