Lab 8, MOLE RATIOS IN A CHEMICAL REACTION

1
Lab 8, MOLE RATIOS IN A CHEMICAL REACTION
NaHCO3(S) HCl(aq) ? CO2 (aq) H2O(g)
NaCl(S)

• OVERVIEW
• TO COMPARE TWO DIFFERENT COMPOUNDS YOU MUST
• IDENTIFY THE KNOWN COMPOUND, THEN CONVERT THE
  KNOWN TO MOLES.
• RATIO MOLES OF THE KNOWN TO MOLES OF THE
  OBJECTIVE USING THE COEFFICIENTS OF THE BALANCED
  REACTION.
• CONVERT THE MOLES OF THE OBJECTIVE TO THE UNITS
  REQUIRED.

2

• RULES TO KNOW
• DISREGARD SUBSCRIPTS WHEN ASSESSING REACTION
  RATIOS, USE THE COEFFICIENTS.
• DISCREGRD REACTION COEFFICIENTS WHEN CALCULATING
  MOLAR MASS.
• GAS VOLUMES CAN BE USED IN RATIOS WITH REACTION
  COEFFICIENTS AT STP.

THE PROCESS STRUCTURE OR SUFFER!
STEP 3 CONVERT OBJECTIVE TO UNITS REQUIRED
MOLES OF OBJECTIVE
STEP ONE CONVERT KNOWN TO MOLES
STEP TWO-MOLE RATIO MOL KNOWN COEF KNOWN MOL
OBJ COEF OBJ
MOLES OF KNOWN
3

• THE PROCESS STEP ONE ?
• IDENTIFY THE KNOWN YOU MASSED 2.0 g
• OF NaHCO3 IN THE LAB, THAT IS YOUR KNOWN,
• 2) CONVERT THE 2.0 g. OF NaHCO3 TO MOLES.
• 3) THE EQUATION
  WHICH RELATES MOLE TO GRAMS.

STEP ONE CONVERT KNOWN TO MOLES
MOL MASS G.F.M.
MOL 2.00 g 0.02380 MOL
84.0g/mol
NaHCO3,
The moles you will use in step two.
THE PROCESS STEP TWO ??? ? NaHCO3(S) HCl(aq)
? CO2(aq) H2O(g) NaCl(S) NaHCO3 1
0.02380 mol X 0.02380 mol NaCl(s) NaCl
1 X

STEP TWO-MOLE RATIO MOL KNOWN COEF KNOWN MOL
OBJ COEF OBJ
4

• THE PROCESS STEP THREE ??
• IN THIS LAB, YOU MASS YOUR PRODUCT IN
• GRAMS ON THE ELECTRONIC BALANCE. THEREFORE
• WE CALCULATE THE THEORETICAL YEILD IN GRAMS,
• THE REQUIRED UNIT FOR OUR OBJECTIVE NaCl.

STEP 3 CONVERT OBJECTIVE TO UNITS REQUIRED
MOL MASS G.F.M.
0.02380 Mol X g 1.3804 g NaCl
(accepted yield) 58.0
g/Mol
THIS IS THE MASS OF SALT (NaCl) YOU SHOULD HAVE
COLLECTED IN THE LAB, ASSUMMING YOU STARTED WITH
2.0 GRAMS OF NaHCO3. IF YOU USED ANNOTHER MASS OF
THE NaHCO3 TO START WITH, THIS PROCESS WOULD GIVE
A DIFFERENT ACCEPTED VALUE. THE MASS YOU
CALCULATE IS ALSO CALLED THEORETICAL YEILD. WE
WILL ROUND THIS TO 1.38 g (3 SIG FIG) AS THE MASS
IS 3 SIG. FIG.
5

• THE LAB WRITEUP
• THE ABSTRACT SHOULD BE A SUMMARY OF ALL THE LAB
  AND ITS RESULTS.
• LIST ALL OF YOUR DATA THE MASS OF THE EMPTY DISH.
• THE MASS OF THE CLEAN WATCHGLASS.
• THE MASS OF THE NaHCO3 YOU MASSED. SHOW THE MASS
  OF WIEGHTING PAPER IF YOU DID NOT TARE THE
  ELECTRONIC BALANCE.
• SHOW THE MASS OF THE DISH AND WATCHGLASS AFTER
  YOU HAVE HEATED TO CONSTANT MASS, SHOW ALL MASSES
  DURING THE HEATING CYCLE.
• THE FINAL MASS OF THE DISH WITH THE WATCHGLASS
  AND DRY SALT SHOULD BE SUBTRACTED FROM THE EMPTY
  DISH WITH THE WATCHGLASS ON IT. THIS MASS IS YOUR
  EXPERIMENTAL MASS (YIELD) OF THE OBJECTIVE NaCl.
• DO THE 3 STEP CALCULATION WITH THE MASS OF NaHCO3
  YOU ACUALLY USED IN LAB, EVEN IF IT IS 2.00G, DO
  THE CALCULATION IN YOUR OWN HANDWRITTING WITH
  EXTENSIVE EXPLINATIONS FOR EACH STEP. SHOW MOLAR
  MASS CALCULATION.
• USE THE FOLLOWING EQUATION TO CALCULATE YOUR
  ERROR.
• WRITE A CONLUSION BASED ON THE ACCEPTED(CALCULATED
  ) SALT MASS (YEILD) COMPARED TO THE SALT MASS
  (YEILD) YOU ACTUALLY HAD IN THE LAB THAT DAY IN
  REALLITY. DO THE QUESTIONS ON NEXT SLIDE?

ERROR ACCEPTED EXPERIMENTAL X 100
ACCEPTED
EXAMPLE IF YOU COLLECTED 1.20 g OF SALT IN THE
LAB (EXPERIMENTAL). WE CALCULATED THE ACCEPTED
VALUE AS 1.38 g.
ERROR ACCEPTED EXPERIMENTAL X 100
ACCEPTED
ERROR 1.38 1.20 X 100 13.0
1.38
6

• PLACE THESE QUESTIONS AT THE END OF YOUR LAB
  REPORT, be neat and show all structured work.
• 1) BASE YOUR ANSWERS FOR QUESTION ONE ON THE
  FOLLOWING REACTION
• NaHCO3(S) HCl(aq) ? CO2 (aq) H2O(g) NaCl(S)
  
• Calculate the moles of NaHCO3 in 8 grams of this
  compound?
• Can you ratio grams with coefficients?
• If the 8 grams of NaHCO3 reacts in the above
  reaction, how many moles of salt (NaCl) should be
  produced?
• If only 6.0 grams of NaCl is collected, what is
  error.
• How many grams would the NaCl produced (in part
  b) ) weigh in grams?
• How many moles of H2O would result from the
  reaction of the 8.0 grams of NaHCO3?
• 2) FOR THE REACTION 3H2 N2 ? 2NH 3, CALCULATE
  THE FOLLOWING
• a) If 56.0 grams of N2 react, how many moles is
  that?
• b) If all of the N2 from part a) reacts, how
  many moles of NH3 should be produced.
• c) What would the NH3 produced in part b) weigh
  in grams.