Lab 8 MOLE RATIOS IN A CHEMICAL REACTION

Lab 8, MOLE RATIOS IN A CHEMICAL REACTION Na. HCO 3(S) + HCl(aq) CO 2 (g) + H 2 O(g) + Na. Cl(S) MATERIALS 150 m. L 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, DON NOT REMOVE UNTILL YOU ARE TOLD TO DO SO. 1. 2. 3. 4. PROCEDURE Mass a 150. 0 m. L beaker, record the mass in your lab notebook. Mass 2. 00 grams of Na. HCO 3 in the beaker. Obtain about 30. m. L 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.

PROCEDURE 6. SLOWLY add the HCl drop wise to the Na. HCO 3 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 Na. HCO 3 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 Na. HCO 3(S) + HCl(aq) CO 2 (g) + H 2 O(g) + Na. Cl(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 CONVERT KNOWN TO 1) IDENTIFY THE KNOWN: YOU MASSED 2. 0 g OF Na. HCO 3 IN THE LAB, THAT IS YOUR KNOWN, MOLES 2) CONVERT THE 2. 0 g. OF Na. HCO 3 TO MOLES. 3) THE EQUATION WHICH RELATES MOLE TO GRAMS. MOL = MASS G. F. M. MOL = 2. 00 g = 0. 02380 MOLNa. HCO 3, 84. 0 g/mol The moles you will use in step two. THE PROCESS STEP TWO-MOLE RATIO Na. HCO 3(S) + HCl(aq) CO 2(aq) + H 2 O(g) + Na. Cl(S) MOL KNOWN = COEF KNOWN MOL OBJ = COEF OBJ Na. HCO 3 = 1 Na. Cl 1 = 0. 02380 mol X X = 0. 02380 mol Na. Cl(s)

THE PROCESS STEP THREE 1) IN THIS LAB, YOU MASS YOUR PRODUCT IN GRAMS ON THE ELECTRONIC BALANCE. THEREFORE WE CALCULATE THEORETICAL YEILD IN GRAMS, THE REQUIRED UNIT FOR OUR OBJECTIVE Na. Cl. STEP 3 CONVERT OBJECTIVE TO UNITS REQUIRED MOL = MASS G. F. M. 0. 02380 Mol = X g = 58. 0 g/Mol 1. 3804 g Na. Cl (accepted yield) THIS IS THE MASS OF SALT (Na. Cl) YOU SHOULD HAVE COLLECTED IN THE LAB, ASSUMMING YOU STARTED WITH 2. 0 GRAMS OF Na. HCO 3. IF YOU USED ANNOTHER MASS OF THE Na. HCO 3 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) 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 Na. HCO 3 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 Na. Cl. 6) DO THE 3 STEP CALCULATION WITH THE MASS OF Na. HCO 3 YOU ACUALLY USED IN LAB, EVEN IF IT IS 2. 00 G, 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. %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 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

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 Na. HCO 3(S) + HCl(aq) CO 2 (aq) + H 2 O(g) + Na. Cl(S) a) Calculate the moles of Na. HCO 3 in 8 grams of this compound? b) Can you ratio grams with coefficients? c) If the 8 grams of Na. HCO 3 reacts in the above reaction, how many moles of salt (Na. Cl) should be produced? d) If only 6. 0 grams of Na. Cl is collected, what is % error. e) How many grams would the Na. Cl produced (in part b) ) weigh in grams? f) How many moles of H 2 O would result from the reaction of the 8. 0 grams of Na. HCO 3? 2) FOR THE REACTION 3 H 2 + N 2 2 NH 3, CALCULATE THE FOLLOWING: a) If 56. 0 grams of N 2 react, how many moles is that? b) If all of the N 2 from part a) reacts, how many moles of NH 3 should be produced. c) What would the NH 3 produced in part b) weigh in grams.