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DensitySpecificGravityExperiment(PartAPages4-9)

DensitySpecificGravityExperiment(PartAPages4-9) - DENSITY...

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DENSITY AND SPECIFIC GRAVITY Objectives: 1. Become familiar with making mass and volume measurements. 2. Become familiar with the concept of precision in volume measurements. 3. Determine the density of solid and liquid samples. 4. Determine the specific gravity of a liquid. 5. Calculate the percent error in measurements. Background: The mass of an object is defined as the measure of the inertia of an object or its inherent resistance to any kind of change in motion. (1) We can determine the mass of an object by weighing the object on a balance. Common units of mass in chemistry are grams (g), milligrams (mg), and kilograms (kg). A top loading balance is one type of balance that is used in many laboratories. When recording data all significant figures should be recorded along with any units. Significant figures in measurements are those numbers that we are certain of plus one number that is estimated. An example of a measurement from a top loading balance might be 15.89 g. In this measurement, the numbers 15.8 are all significant and are certain . However the 9 in the hundredths place in 15.89 is uncertain and is an estimate . There is a very good chance that the balance would actually fluctuate between 15.88 g to 15.90 g. This reflects the uncertainty in the measurement. Thus the number 15.89 g has four significant figures . In determining the mass of a liquid, it is necessary to first weigh an empty container such as a graduated cylinder and then place a liquid in the graduated cylinder and then weigh the graduated cylinder with the liquid. The mass of the liquid is then determined by subtracting the mass of the graduated cylinder from the mass of the graduated cylinder and liquid . The volume of an object of an object is the space that it occupies. (1) Common units of volume in chemistry are milliliters (mL), and cubic centimeters (cm 3 or cc). Various devices such as graduated cylinders, volumetric flasks and syringes are used when accurate measurements of volume are needed. Beakers and Erlenmeyer flasks are used when only approximate volume measurements are needed. The graduated cylinders and syringes are more accurate measuring devices because they have calibrations marks that represent smaller divisions than the calibration marks on beakers and Erlenmeyer flasks. Accuracy is defined as the closeness of a measurement to the true value of a measurement. The volume of an object is temperature dependent . When we use graduated cylinders or syringes to make volume measurements, we have to decide which is the smallest division on the scale lines for the graduated cylinder or syringe. We then have to estimate to 1/10 or (0.1) of the smallest division. The estimate to 1/10 of the smallest division is the estimated or uncertain digit . The question now becomes how do we determine the smallest division ? We have to take two points that have numbered calibration marks and find the difference between these two points. We then have to count the number of unmarked calibration lines between these two numbered marks.
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