The Mole For he shall be great before the Lord.And he shall convert many of the children of Israel to the Lord their God.. Luke 1:15-16 Introduction In the lab Counting by Measuring Mass, we explored the usefulness of having a unit for counting or measuring small substances such as atoms or molecules. This counting unit for atoms is called the mole. In this lab we will work with the mole concept to convert between grams and molecules of a substance. Review (Figure 1 below and your text) that the mole links grams of a substance to the number of molecules of a substance, since there can be no direct conversion between the two. FIGURE 1: INTERCONVERSION MAP Learning Objectives: Compare the number of moles and molecules in given amounts of substances Determine the number of moles and molecules in a cup and in a mouthful of water Interconvert between moles, grams, and molecules of different substances Materials Required: From Chemistry Kit Student Supplied Scale Distilled water Weigh paper Hydrogen peroxide (H 2O 2) Graduated Cylinders Table salt (NaCl) Pipettes 3 small plastic cups Measuring cup, ½ cup Safety Do not spill the hydrogen peroxide on clothing Do not drink the hydrogen peroxide or leave near children 2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 1
PART 1: MOLE CONCEPT COMPARISONS In last week s lab, we saw that a mole of paperclips would weigh 1.75 x 10 17 tons (over a million billion tons!). Now, we will explore the mole concept as it applies to atoms and compounds. Experiment 1. Obtain 3 clear, small, identical plastic cups or glasses 2. Locate the scale from your kit Tare (zero) the scale SALT (NaCl) 3. Place one of the cups on the scale Tare (zero) the scale 4. Measure out exactly 58.4 grams of table salt (NaCl) into the cup 5. Measure Volume: Pour the 58.4 g NaCl into the 100 ml graduated cylinder Use a kitchen funnel to prevent loss of material Measure the volume to the appropriate number of significant figures Record the volume in Table 1 6. Return the NaCl to the plastic cup 7. Set aside for the moment HYDROGEN PEROXIDE (H2O2) 8. Zero the mass of a second cup on the scale 9. Measure out exactly 34.0 grams of hydrogen peroxide (H2O2) into the cup Use a pipette to remove or add H2O2 to the exact amount 10. Measure Volume: Pour the 34.0 g H2O2 into the graduated cylinder Use a kitchen funnel to prevent loss of material Measure the volume to the appropriate number of significant figures Record the volume in Table 1 11. Return the H2O2 to the plastic cup 12. Set aside for the moment WATER (H2O) 13. Zero the mass of the third cup on the scale 14. Measure out exactly 18.0 grams of water (H2O) into the cup Use a pipette to remove or add H2O to the exact amount 15. Measure Volume: Pour the 18.0 g H2O into the graduated cylinder Use a kitchen funnel to prevent loss of material Measure the volume to the appropriate number of significant figures Record the volume in Table 1 16. Return the H2O to the plastic cup 2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 2
17. Compare: Set the three cups side by side Compare the amount of material in the three identical cups What does 1 mole of table salt (NaCl) look like? How does it compare to 1 mole of hydrogen peroxide (H2O2,) and 1 mole of water (H2O)? Is this amount surprising to you? Place your observations in the last row of Table 1 18. Calculate the amount of material in the three cups: SHOW WORK IN QUESTION 1 Calculate molar masses for salt, hydrogen peroxide and water Using a periodic table, calculate the molar mass (in g/mol) of each substance Place results in Table 1 Calculate the moles of substance Use the molar mass of table salt and the 58.4 grams measured in order to calculate moles of NaCl Use the molar mass of hydrogen peroxide and the 34.0 grams measured in order to calculate moles of H2O2 Use the molar mass of water and the 18.0 grams measured in order to calculate moles of water Place results in Table 1 Calculate the number of molecules of each substance Use Avogadro s number and the moles of each substance found in the step above in order to find the number of molecules of table salt, hydrogen peroxide and of water Place results in Table 1 19. Continue on to Part 2 PART 2: INTERCONVERSIONS MOUTHFUL WATER (H2O) 20. Prepare a cup for the water Locate small, clean, clear cup Tare (zero) the scale from the kit Place the cup on the scale and tare (zero) the scale again 21. Carefully measure water Using the 100 ml graduated cylinder, measure out 200 ml of water in two aliquots Be exact! Use the cup pipette to remove or add water Ensure the bottom of the meniscus is exactly on the 100 ml line Make sure you are viewing the meniscus at eye level Pour 200 ml of water into the cup on the scale Record the mass of the water and record in Table 2 2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 3
22. Measure a mouthful of water Take a drink from the cup containing 200 ml of water Reweigh the cup of water and make a note of the new mass Calculate the mass of a mouthful of water Subtract the new from the mass of 200 ml of water Record the mass of a mouthful of water in Table 2 Half-Cup of Salt (NaCl)g 23. Measure and weigh salt: Obtain the one-half-cup measuring cup from the kit Fill the half-cup with table salt Use the flat edge of a knife to ensure the level is even with rim of the measuring cup Tare the scale and weigh the salt Record the mass in Table 2 24. Interconvert amounts: SHOW WORK IN QUESTION 6 Note: Molar mass for water and salt have been previously calculated and placed in Table 1 Calculate the moles of each substance Use the molar mass and the grams of substance weighed Place results in Table 2 Calculate the number of molecules of each substance Use Avogadro s number and the number of moles Place results in Table 2 25. Perform Data Analyses and Conclusions 2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 4
Lab Report for: Substance NaCl (58.4 grams) H2O2 (34.0 grams) H2O (18.0 grams) 18 TABLE 1 Mole Concept Comparisons Volume Molar Mass Moles (ml) (g/mol) Molecules Give a Visual Comparison of 1 Mole Amounts of Each Material Below: NaCl H2O2 H2O TABLE 2 Interconversions Substance Molecules Moles Grams H2O (200 ml) H2O (a mouthful) NaCl ( ½ cup ) PART 1: MOLE CONCEPT COMPARISONS 1. TABLE 1 CONVERSIONS Show the molar mass, mole and molecule calculations for: NaCl Show the molar mass, mole and molecule calculations for: H2O2 Show the molar mass, mole and molecule calculations for: H2O 2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 5
2. Comparisons Compare the moles of salt, hydrogen peroxide and water in the cups Compare the number of molecules salt, hydrogen peroxide and water in the cups How did the amounts in the cups compare visually with the number of molecules present? Explain any visual differences. 3. In last week s lab, we saw that 1 mole of paperclips would weigh about 1.75 x 10 17 tons - over a million-billion tons. How many paperclips are in 1 mole of paperclips? How many water molecules are in 1 mole of water? Compare the mass of 1 mole of paperclips with 1 mole of water Why do we use the mole concept with atoms and compounds? 4. Using the data collected in Table 1, calculate the density (g/ml) of: SHOW WORK NaCl H2O2 H2O 5. The density of water at 20 o C is 1.008 g/ml. The density of hydrogen peroxide is 1.11 g/ml. How did the densities you calculated compare to the reported values? Experimental Reported %Error = x 100% Experimental PART 2: INTERCONVERSIONS 6. TABLE 2 Calculations Show the mole and molecule calculations for: 200 ml of water Show the molar mass, mole and molecule calculations for: A mouthful of water Show the molar mass, mole and molecule calculations for: ½ cup of salt 7. In a beaker you are given 3.28 x 10 18 molecules of water. What is the mass of the water? Show your calculations. 8. How many molecules of water are in 34.0 grams of water? Show your calculations. 9. Were you able to interconvert between grams and molecules directly? Explain your answer. 2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 6