Name_____________________________________________ Date___________________ Block ______ The Measure of Success Overview: Measurement is as old as humanity itself. Even primitive cultures needed measurements to build homes, fashion clothes, and barter with each other. But if everyone measures things differently, how will you know if you’re getting a good deal, buying the right amount of lumber, or being shortchanged at the grocery store? In this lab, you’ll learn and carry out the established practice for reading the instruments that help us make measurements. Focus: Measurement Place Value Units The Metric System Challenge: Complete nine (9) different measurements of mass, volume, distance, and temperature by reading instruments appropriately and reporting out the correct information. Time Limit: You will have half of a block (45 minutes) to complete your measurements. Background: Many instruments (rulers, graduated cylinders, etc.) have small lines on them that help us measure distances, volume, and masses. These are called lines of graduation (or simply graduations). To read these instruments properly, we must estimate how far the object goes beyond a line on the instrument. We are, effectively, reading between the lines of the instrument. All reported measurements should include whatever digits are marked on the instrument itself plus one extra estimated digit. For example, see the ruler below: centimeters The ruler is marked (graduated) to the tenths of an centimeter (i.e. each mark represents 1/10th of a centimeter: 7.0, 7.1, 7.2, etc.) . A reasonable eye would see the pencil point as falling between the “7” and the next mark to the right – or between 7.0 and 7.1 centimeters. As such, we must report an estimate in our measurement that goes beyond the marked place value. Since the ruler is graduated to the tenths place, a proper measurement would go to the next place value, which is the hundredths place. Appropriate measurements would be numbers like 7.02 cm or 7.06 cm. If you think the pencil falls exactly on the “7”, then the way to express that would be 7.00 cm. We may only estimate one place value; therefore “7.003 cm” would be an improper measurement because that would reflect too Name_____________________________________________ Date___________________ Block ______ much guessing (we would be estimating both the hundredths and thousandths place values). Measurements like “7 cm” or “7.0 cm” are improper because they aren’t specific enough. Procedures: Measuring Mass You will measure the mass of an object using three different instruments: a triple-beam balance, an electronic balance, and an analytical balance (also electronic). Triple Beam Balance: You should be familiar with one of these from previous science classes. Triple beam balances have a pan on one side and a series of sliding weights that move away from that pan. The weights come in three different sizes – one for each place value of a weight measurement (100s, 10s and 1s). This is similar to a scale in a doctor’s office or a weight room. Procedure: Move the weights all the way to the pan, place the object on the pan, and then begin to slide the weights away from the pan, starting with the largest weight. The goal is to get the lever to match up with the fixed marked line. The 100s and 10s measurements come in discrete (fixed) amounts, but the 1s slider can move between measurements. Make sure you make your estimate in your measurement! Record the weight of the object in the data table. Electronic Balance: This is the most common mass-measuring tool of our chemistry lab. An electronic balance has a digital readout. There is no way for you to read “beyond” the given place value on the digital display as you would with a graduated (lined) instrument. What you will notice when you measure an object is that the last digit on the readout may fluctuate between two numbers or may “drift” in one direction (i.e. the number keeps getting higher or lower). It will be up to you to decide where the measurement lies. Choose the number that the balance stays on most often. Procedure: To use the balance, make sure the beginning number reads 0.00 g. If it doesn’t, press the button that says ZERO or TARE or 0/T. This will set the balance back to 0.00 g. Place the object on the balance and record its mass. The standard report of uncertainty is ±0.01 g; that is, the last digit may be off by 0.01 grams in one direction or the other. Put that report of uncertainty in the data table with your measurement. Analytical Balance: This is also an electronic balance, but you will notice that is has a much higher degree of precision – that is, it measures to more decimal places than the electronic balance. You’ll also notice doors on each side of the balance pan. These doors are designed to reduce air movement in the balance pan chamber. Make sure they stay closed when you read your measurement. Also, do not touch the table, as small vibrations on the surface of the table can affect the analytical balance’s reading. Name_____________________________________________ Date___________________ Block ______ Procedure: Follow the same procedure for using this balance that you would for the electronic balance. The standard report of uncertainty is ±0.0001 g. Put that report of uncertainty in the data table with your measurement. Measuring Volume You will measure the volume two different liquids using two different instruments: a graduated cylinder and a buret. In addition, you will be using the electronic balance to make mass readings. Graduated Cylinder: This tool is the workhorse of the chemistry lab when measuring volume; it is our standard instrument of use. When reading the graduated cylinder, make sure to get eye level with the instrument and read the measurement straight-on instead of at an angle (this does not mean to pick up the cylinder and put it at your head height. Move your head down to where the cylinder is resting on the table). When measuring liquids, each liquid will have some kind of curvature because of adherence to the walls of the glass. The curvature of the liquid is called the meniscus. Read the liquid level to the bottom of the meniscus. Procedure: Place the graduated cylinder on the balance. Press the ZERO, TARE, or 0/T button to get the balance to read 0.00 g. Use the wash bottle containing water to fill the graduated cylinder until the balance reads near 10 g (it does not have to read 10.00 exactly). Record the mass of the liquid you measured out from the balance onto the data table. Next, read the level of the liquid on the graduated cylinder. Remember to follow the rules of reading between the lines! Record the volume measurement appropriately in the data table. Buret: A buret is like an upside-down graduated cylinder. You will notice that “0” is at the top. Rather than pouring a liquid into the buret and reading how high the liquid goes, like we do with a graduated cylinder, you will fill the buret, let some of the liquid out of the bottom, then read how far down the liquid dropped. The advantage of the buret over a graduated cylinder is that you don’t have to worry about losing some of the liquid in transfer. A buret has a small stopper at the end that can be turned to allow the liquid to flow out the bottom. When the stopper is turned horizontally, the flow is off. When the stopper is vertical, the flow is on. Procedure: Place a small beaker on the electronic balance. Press the ZERO, TARE, or 0/T button to get the balance to read 0.00 g. Use the wash bottle containing water to fill the buret to some number above 25mL – make sure the stopper is closed (horizontal) before you put liquid in the buret! DO NOT try to get the water level exactly to 0 mL. Just fill it somewhere above the 25mL mark. For faster filling, you may unscrew the wash bottle lid and fill the buret just by pouring the water as opposed to using the squeeze bottle feature. Record the starting liquid level of the buret on the data table (remember to read between the lines!). Move the balance with the beaker underneath the buret (re-tare the balance if the reading isn’t at 0.00 g anymore). Open the stopper (turn it vertical) and let the water flow out until the balance reads about 10 g (it does not have to read 10.00 exactly). Record the mass of the liquid you measured out from the balance onto the data table. Next, read the new level of the liquid on the buret (read between the lines!), and record this number on Name_____________________________________________ Date___________________ Block ______ the data table. The volume of liquid you delivered from the buret to the beaker is the difference between the two numbers you recorded. Calculate the difference between the starting and ending values and record this number in your data table. Measuring Distance You will measure the length, width, and height of a block of wood using three different types of rulers. Rulers: You are, no doubt, familiar with rulers by this point in your life. You will be using three rulers of differing precision. Each ruler’s major graduations are in centimeters. We will not be using inches because of the frustration of measuring between the 16ths-inch mark; measuring to the tenths place value and expressing uncertainty in place value is much easier, so the metric system is much more convenient for these measurements.