Transcript 438LAB_8_WRITEUP-and QUESTIONS_

Lab 8, MOLE RATIOS IN A CHEMICAL REACTION
NaHCO3(S) + HCl(aq)  CO2 (aq) + H2O(g) + NaCl(S)
OVERVIEW
1) TO COMPARE TWO DIFFERENT COMPOUNDS YOU
MUST;
A. IDENTIFY THE KNOWN COMPOUND, THEN
CONVERT THE KNOWN TO MOLES.
B. RATIO MOLES OF THE KNOWN TO MOLES OF
THE OBJECTIVE USING THE COEFFICIENTS OF
THE BALANCED REACTION.
C. CONVERT THE MOLES OF THE OBJECTIVE TO
THE UNITS REQUIRED.
RULES TO KNOW
1) DISREGARD SUBSCRIPTS WHEN ASSESSING
REACTION RATIOS, USE THE COEFFICIENTS.
2) DISCREGRD REACTION COEFFICIENTS WHEN
CALCULATING MOLAR MASS.
3) GAS VOLUMES CAN BE USED IN RATIOS WITH
REACTION COEFFICIENTS AT STP.
THE PROCESS – STRUCTURE OR SUFFER!
STEP ONE
CONVERT
KNOWN TO
MOLES
STEP TWO-MOLE RATIO
MOLES OF
KNOWN
MOL KNOWN = COEF KNOWN
MOL OBJ
= COEF OBJ
MOLES OF
OBJECTIVE
STEP 3
CONVERT
OBJECTIVE
TO
UNITS
REQUIRED
THE PROCESS STEP ONE 
STEP ONE
CONVERT
KNOWN TO
1) IDENTIFY THE KNOWN: YOU MASSED 2.0 g
OF NaHCO3 IN THE LAB, THAT IS YOUR KNOWN,
MOLES
2) CONVERT THE 2.0 g. OF NaHCO3 TO MOLES.
3) THE EQUATION
WHICH RELATES MOLE TO GRAMS.
MOL = MASS
G.F.M.
MOL = 2.00 g
= 0.02380 MOLNaHCO
3,
84.0g/mol
The moles you will use in step two.
THE PROCESS STEP TWO  
STEP TWO-MOLE RATIO
NaHCO3(S) + HCl(aq)  CO2(aq) + H2O(g) + NaCl(S)
MOL KNOWN = COEF KNOWN
MOL OBJ
= COEF OBJ
NaHCO3 = 1
NaCl
1
= 0.02380 mol
X
X = 0.02380 mol NaCl(s)
THE PROCESS STEP THREE 
1) 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
=
58.0 g/Mol
1.3804 g NaCl (accepted yield)
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.
THE LAB WRITEUP
1)
2)
3)
4)
5)
6)
7)
8)
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.
%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
9) 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
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)
a) Calculate the moles of NaHCO3 in 8 grams of this compound?
b) Can you ratio grams with coefficients?
c) If the 8 grams of NaHCO3 reacts in the above reaction, how many moles of salt
(NaCl) should be produced?
d) If only 6.0 grams of NaCl is collected, what is % error.
e) How many grams would the NaCl produced (in part b) ) weigh in grams?
f) 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.