CHM 132 Lab Manual.pdf

# One end of a spring hangs from this eyelet and so its

• Lab Report
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the laboratory bench by a utility clamp and ring stand. One end of a spring hangs from this eyelet and so its height above the bench is constant. The other end of the spring attaches to a plastic hanger that can hold brass weights of differing thickness and mass. The lower end of the plastic hanger should be about 40 cm above the laboratory bench. To determine the extent of stretching of the spring, a meter stick stands vertically next to the utility clamp. Its perpendicularity to the bench must be visually checked in two directions and fixed by taping the meter stick to the ring stand and to the utility clamp. You will use three springs, each of which has a different stiffness. Attach the first spring to the eyelet. With only the hanger attached to the first spring, measure to the nearest 0.1 cm the height of the lower edge of the mass hanger above the ring stand. A small ruler held horizontally may assist you in making an accurate measurement. Next add a small weight to the hanger. Allow the apparatus to vibrate up and down. When the elevation of the hanger is constant, carefully estimate its height to the nearest 0.1 cm. Continue in the same manner by adding incrementally heavier masses to the hanger. Repeat the process for the second and third springs.

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Chemistry 132 Lab Manual Page 67 For the stiffest spring, begin with a mass of 100 g; otherwise, start with 20 g. The final masses added to the hanger should range from about 200 g for the loosest spring to 300 g for the stiffest spring. Excluding the data points for the mass of 0 g, you should obtain at least 11 and 9 data points for the two loosest springs and the tightest spring, respectively. Part B. Period of Oscillation as a Model of the Chemical Bond? We next investigate whether Hooke’s Law describes the vibrational motion of two bonded atoms. Because photon energies in the infrared region of the spectrum equal energy differences between the vibrational levels of molecules, we will consider the infrared absorption spectra of two compounds, chloroform, CHCl 3 and deuterated chloroform, CDCl 3 . D represents the 2 H isotope of hydrogen, commonly called deuterium, and thus CDCl 3 is often called deuterochlorform. If we have a mass suspended from a spring, then the vibrational motion will be harmonic in nature. According to Galileo’s observations, the period of vibration, T, relates to the suspended mass, m, and force constant, k. as follows: T = 2 p m k (6.2) Because the frequency of vibration, n , varies inversely with the period of vibration, n = 1 T = 1 2 p k m (6.3) Measure the period of oscillation of a spring with both X(+5) grams and with 2X(+5) grams of weight attached. We use the notation X(+5) to remind you that the gray weight holder has a mass of 5 gm which must be added to the mass, X, placed on the holder. A timer is available at each station. On the timers, use the Stop/Start button in the center, and the Clear button. Count either 10 or 20 periods, dividing the total time by the number of periods measured to obtain the time for each period (which should give more precision than measuring only one period). Record all data in your lab notebook and use Eqn. 6.2 to determine if the results obtained agree with the form of
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