Lab 8, MOLE RATIOS IN A CHEMICAL REACTION

NaHCO3(S) + HCl(aq) CO2 (g) + H2O(g) + NaCl(S)

MATERIALS150 mL beaker, pipet, small beaker, balance, weighing paper, hotplate,

sodiumhydrogencarbonate (s) and HCl (aq) 3.0 M.

SAFETYSTUDENTS MUST WEAR GOGGLES, APRONS AND GLOVES

THROUGHOUT, DON NOT REMOVE UNTILL YOU ARE TOLD TO DO SO.

PROCEDURE1. Mass a 150.0 mL beaker, record the mass in your lab

notebook.2. Mass 2.00 grams of NaHCO3 in the beaker.3. Obtain about 30. mL of 3.0 M HCl in a small beaker. Keep

the beaker in your sink when not in use.4. Obtain a plastic pipet, fill it with HCl solution.

PROCEDURE

6. 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.

7. When all of the solid NaHCO3 has dissolved AND the fizzing has stopped, you are finished adding acid.

8. After the HCl has been added, place the beaker on a hotplate and GENTLY boil off the water.

9. 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.

10.Subtract the mass of the empty beaker from the beaker containing the salt to get the EXPERIMENTAL yield of salt.

Lab 8, MOLE RATIOS IN A CHEMICAL REACTION

NaHCO3(S) + HCl(aq) CO2 (g) + H2O(g) + NaCl(S)

OVERVIEW1) 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 KNOW1) 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 ONECONVERTKNOWN TO

MOLES

STEP TWO-MOLE RATIO

MOL KNOWN = COEF KNOWNMOL OBJ = COEF OBJ

MOLES OFKNOWN

STEP 3CONVERTOBJECTIVE

TO UNITS

REQUIRED

MOLES OFOBJECTIVE

THE PROCESS STEP ONE 1) IDENTIFY THE KNOWN: YOU MASSED 2.0 gOF 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 ONECONVERTKNOWN TO

MOLES

MOL = MASS G.F.M.

MOL = 2.00 g = 0.02380 MOL 84.0g/mol

NaHCO3,

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 KNOWNMOL OBJ = COEF OBJ

The moles you will use in step two.

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 3CONVERTOBJECTIVE

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.

THE LAB WRITEUP1) THE ABSTRACT SHOULD BE A SUMMARY OF ALL THE LAB AND ITS RESULTS.2) LIST ALL OF YOUR DATA THE MASS OF THE EMPTY beaker.3) THE MASS OF THE NaHCO3 YOU MASSED. SHOW THE MASS OF WIEGHTING PAPER IF

YOU DID NOT TARE THE ELECTRONIC BALANCE.4) SHOW THE MASS OF THE beaker AFTER YOU HAVE HEATED TO CONSTANT MASS,

SHOW ALL MASSES DURING THE HEATING CYCLE.5) 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.

6) 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.

7) USE THE FOLLOWING EQUATION TO CALCULATE YOUR % ERROR.

8) 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

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.