Background: Understanding the Mole 1. Why was it important for scientists to know the number of atoms in a sample of matter? 2. What was chosen to use as the standard on which to base the atomic masses of all the elements? 3. How many atoms are in 12 g of the standard? 4. What is the name for this number of atoms? 5. What is the SI unit that scientists created to represent this number of atoms? 6. How many marbles are in one mole of marbles? 7. How many atoms are in one mole of sodium? 8. In the study of chemistry, what connection does the mole unit allow you to do? What types of worlds does this unit connect? Be as specific as you can. 1
Background: Understanding the Mole, continued 9. What does percent composition of a chemical compound mean? 10. A formula unit of sodium chloride contains one sodium atom and one chloride atom. What is the percent composition of NaCl? Step 1: Find the molar mass of each element in the compound: Na = Cl = Step 2: Find the total molar mass of the compound: NaCl = Step 3: Divide each individual element s molar mass by the total molar mass of the compound. Multiply by 100 to make a percent. Molar mass of Na Total molar mass of NaCl Molar mass of Cl Total molar mass of NaCl x 100 = x 100 = 11. If done correctly, what should be the sum of the two percentages? 2
Part I: Plan Your Investigation 1. My Question of Inquiry: 2. The Hypothesis: 3. My Prediction: 4. What is the independent variable (also known as the manipulated variable)? 5. What is the dependent variable (also known as the responding variable)? 6. Is there a control group or control variable for this investigation? Explain. 7. What materials, equipment, and technology will be needed for this investigation? 8. List all safety precautions that must be taken. 9. Follow the procedures listed in the Student Guide to conduct this investigation. 3
Part II: Implement Your Investigation Collect, Record, and Organize Data 1. Data Collected Mass of empty crucible and lid: Total mass before heating: Appearance of sample: Total mass after heating: Appearance of sample after heating: 2. Data Calculations Mass of magnesium sulfate hydrate sample before heating: Mass of anhydrous magnesium sulfate after heating: Mass of water driven from sample: Analyze Data 1. Determine number of water molecules in magnesium sulfate hydrate. Mass of water lost by the compound Molar mass of water Moles of water Mass of anhydrous magnesium sulfate Molar mass of anhydrous magnesium sulfate (MgSO 4 ) Moles of anhydrous magnesium sulfate Make a mole ratio of water to anhydrous magnesium sulfate: Moles of H 2 O = Moles of MgSO 4 Round to the nearest whole number 4
Part II: Implement Your Investigation, continued 2. What is the percent composition of water in the hydrate before heating? Show your work in the space provided below. 3. Write the formula for the magnesium sulfate hydrate found in this investigation. 4. What is the name of the hydrate? 5. Write the chemical equation for the decomposition (dehydration) of the magnesium sulfate hydrate based on your results. 6. What happened to the appearance of the compound before and after it was heated, and why do you think this change occurred? 7. Why did you have to leave the lid on the crucible while you were waiting for it to cool down before you weighed the anhydrous compound? 8. What do you think will happen to the anhydrous magnesium sulfate if you leave it out on the laboratory table and check it the next day? 9. What would happen to the results of your experiment if you did not drive off all of the water before weighing the magnesium sulfate left in the crucible? 5
Reflections and Conclusions 1. Does the data support or refute your hypothesis? Explain. 2. Was your prediction correct or incorrect? Explain. 3. What type of data did you collect qualitative or quantitative? Justify your answer. 4. How did the results reveal a relationship between the independent and dependent variable? 5. Where could errors have been made while collecting or organizing data? 6. What do you conclude about this investigation? 7. What would you do differently if you were to conduct this experiment again? 8. Using all of the following terms, develop a graphic organizer. Use additional paper, if needed. Terms: chemical compound, mole, Avogadro s number, 6.02 x 10 23, atoms, molecules, atomic mass, molar mass, SI unit, amount of a substance, relative mass, percent composition, empirical formula, molecular formula 6
Additional Practice Show all your calculations. Use additional paper if necessary. 1. How many atoms are in 7.2 moles of chlorine (Cl)? 2. How many moles are there in 45.9 g of sulfur (S)? 3. How many moles are in 1.0 x 10 25 atoms? 4. What is the mass of 2.18 moles of copper (Cu) in grams? 5. If I have 25 g of silver (Ag), how many moles do I have? 6. What is the mass of 3.01 x 10 23 atoms of iron (Fe)? 7. How many atoms are there in 15.8 g of neon? 7
Additional Practice, continued 8. If I have 3.01 x 10 24 molecules of water, how many moles of water molecules do I have? 9. Find the percent composition of potassium permanganate, KMnO 4. 10. Which compound contains more silicon by percent mass, H 4 SiO 4 (silicic acid) or HSiCl 3 (trichlorosilane)? Show your work. 8