Lab 8, MOLE RATIOS IN A CHEMICAL REACTION

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

• MATERIALS
• 150 mL beaker, pipet, small beaker, balance,
  weighing paper, hotplate, sodiumhydrogencarbonate
  (s) and HCl (aq) 3.0 M.
• SAFETY
• STUDENTS MUST WEAR GOGGLES, APRONS AND GLOVES
  THROUGHOUT, DO NOT REMOVE UNTILL YOU ARE TOLD TO
  DO SO.
• PROCEDURE
• Mass a 150.0 mL beaker, record the mass in your
  lab notebook.
• Mass 2.00 grams of NaHCO3 in the beaker.
• Obtain about 30. mL of 3.0 M HCl in a small
  beaker. Keep the beaker in your sink when not in
  use.
• Obtain a plastic pipet, fill it with HCl
  solution.

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• PROCEDURE
• SLOWLY add the HCl drop wise to the NaHCO3 in
  the beaker and agitate the mixture by swirling.
  The effervescence is the carbon dioxide escaping.
  You should count the drops of HCl added and
  record that data.
• When all of the solid NaHCO3 has dissolved AND
  the fizzing has stopped, you are finished adding
  acid.
• After the HCl has been added, place the beaker on
  a hotplate and GENTLY boil off the water.
• When the salt looks dry, mass the beaker
  containing the salt and record the mass. Place
  the beaker back on the hot plate for 2 min and
  mass a second time. Continue to mass and heat
  until the mass is constant.
• Subtract the mass of the empty beaker from the
  beaker containing the salt to get the
  EXPERIMENTAL yield of salt.

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

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• 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
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• 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
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• 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.
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• 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
  beaker.
• 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 beaker AFTER YOU HAVE HEATED
  TO CONSTANT MASS, SHOW ALL MASSES DURING THE
  HEATING CYCLE.
• THE FINAL MASS OF THE beaker AND DRY SALT SHOULD
  BE SUBTRACTED FROM THE EMPTY beaker. 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
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• 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.