<p> Measurement and Uncertainty</p><p>Introduction Are measurements always exact? An exact measurement is a perfectly correct value containing no error. Right now, before you begin this activity, select the one statement below you think is most correct. A. Measurements are exact if correctly done. B. Measurements may or may not be exact. It depends who did them and how they were done. C. There is some inexactness in every measurement.</p><p>As a reminder for later, state of matter changes are not chemical changes; they are physical changes. Additionally, making a solution (mixing something with water) is also a physical change.</p><p>Objective To study the nature of measurement and gather data which will help determine whether [insert my selection of statement A, B, or C here] is correct, and to determine whether matter is conserved.</p><p>Procedure Prepare a data table to organize and record the 48 data values you will obtain. Read the following steps to decide how to organize and label your data table.</p><p>1. Label a clean, dry 150mL beaker with your name and the letter A.</p><p>2. Your partner should label a similar looking beaker with his/her name and the letter B.</p><p>3. Measure the mass of your beaker on two different balances. Your partner should do the same with the other beaker. Record each mass value and the balance number in your data table.</p><p>4. Exchange beakers with your partner. Repeat Step 3.</p><p>5. Record your partner's data in your data table. You should have eight mass values. </p><p>6. Using a spatula, add two scoops of solid potassium sulfate, K2SO4(s), to Beaker A. </p><p>©Institute for Chemical Education 1 7. One partner should use two different balances to measure the mass of Beaker A and its contents. The other partner should measure the mass of a piece of filter paper on two different balances. Record masses as before.</p><p>8. Exchange Beaker A and filter paper. Repeat. You should now have 16 mass values.</p><p>9. Use a graduated cylinder to add 10 mL (± 1 mL) of distilled water to Beaker A. Swirl gently for approximately three minutes.</p><p>10. Set up a funnel with filter paper above Beaker B as shown in the drawing to the left.</p><p>11. Decant (pour) the liquid from Beaker A into the filter paper, collecting the filtered liquid in Beaker B. Do not be concerned if some undissolved solid collects on the filter paper or is left behind in Beaker A.</p><p>12. After filtering is complete, use forceps to remove the filter paper from the funnel. Place the filter paper in Beaker A. Rinse the empty funnel with 5 mL (± 1 mL) of distilled water.</p><p>13. Place Beakers A and B on a hot plate adjusted to medium heat to evaporate water from both beakers. Keep the heat setting low enough to prevent splashing, crackling, or charring.</p><p>(Caution: Do not handle hot beakers with bare hands.) </p><p>14. When all drops of moisture have evaporated from the sides of the beakers, remove them from the heat with beaker tongs. Allow each beaker to cool.</p><p>15. Measure the mass of each beaker on two different balances. Record data and exchange beakers as before. </p><p>16. Save Beakers A and B until you have completed your data analysis. Then dispose of the contents of the beakers as directed by your teacher.</p><p>©Institute for Chemical Education 2 Background Information:</p><p>Write a paragraph that explains the law of conservation of matter. Also explain how to find an estimated number in a measurement and how to perform calculations with sigfigs when adding and subtracting measurements.</p><p>Calculations: USE SIG FIGS! </p><p>1. Average the masses for each item you massed during lab. Show one sample calculation and put the rest of the values into a calculations table.</p><p>2. Using your values from the calculations table above, calculate the mass of the dry K2SO4 at the start of the experiment.</p><p>3. Using your values from the calculations table above, calculate the mass of the K2SO4 at the end of the experiment.</p><p>Questions </p><p>1. The Law of Conservation of Matter states that matter is neither created nor destroyed during any physical or chemical change. Are experimental results obtained by you and others consistent with this law? Explain.</p><p>2. If the procedure had asked you to measure each mass only once instead of four times, would you know more or less about the accuracy of your data? Explain.</p><p>3. Based on experience and knowledge gained in this activity, would you still select the same statement you chose in the Introduction? Explain.</p><p>4. Based on your experimental data, do all 150 mL beakers have equal mass? Explain.</p><p>©Institute for Chemical Education 3</p>