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Density Determinations.

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12 November 2008 Density Determinations Introduction The purpose of this experiment is to become familiar with density, and the process of determining the measure of density within the field of chemistry. The density of a sample of matter represents the mass contained with a unit volume of space within the unit sample. Density is used to determine the concentration of solutions in certain instance. When working with density, it is important to understand that there are factors that affect the results of a density measurement. Temperature is a key factor that is taken into account when determining the density of a liquid substance. Generally, as the temperature gets higher, the density also becomes higher, although a few substances, such as water, do not follow this standard. Another factor that affects density is volume. As the volume of a substance increased per its set mass, the density will decrease. According the handbook, "densities are usually determined and reported at 20�C, or room temperature, because the volume of the sample, and hence the density, will vary with the temperature. When measuring the density of a liquid, it is commonly said that the density of a substance of a sample represents the mass of the sample divided by its volume. This process changes if the density of a solid is to be determined. The densities of solids of regular shape, such as a cube, rectangle, or cylinder, are determined using the same process -the mass divided by the volume is the density. ...read more.


d = 6.04 g/mm Data Table 3. Density of Pure Liquids - Water Mass of Empty Graduated Cylinder 139.59 g Mass of Cylinder and Water 163.36 g Volume of Water 25 mL Density (d = m/v) 0.95 g/mL Temperature 22�C Handbook Density (According to Wikipedia.Org) 0.9977735 g/mL Data Table 4. Density of Pure Liquids - Unknown Liquid Mass of Liquid 19.15 g Volume of Liquid 24 mL Density (d = m/v) 0.79 g/mL Data Table 5. Density of Solutions - Water and Salt % of NaCl Density Measured 5% 1.02 g/mL 10% 1.06 g/mL 15% 1.03 g/mL 20% 1.20 g/mL 25% 1.09 g/mL Error Analysis When determining the density of a liquid, the measure of both mass and volume need to be very accurate in order to attain a precise measure of density. During the experiment, it is seen that the density of water is slightly miscalculated according to the handbook density. Knowing that as volume rises, density lowers, the mistake probably lies in the measurement of the liquid's volume. If the result of the volume had been slightly lower, then the calculation would have been more accurate compared to the handbook density. When measuring the density of solutions, it is very important to measure carefully and precisely. In theory, the higher the percentage of a sample is in a liquid, the higher its density should be. Though the table's calculations did somewhat follow a general lower-to-higher density measurement as the percentage increased, the measurements had been wrong in some spots. The largest variation occurred in the sample with 20%. ...read more.


If air bubbles had remained on the pellets, the resulting density calculation would have been slightly too high. This is because the air bubbles would have taken up more volume, resulting in a greater change in water level. This greater change in water level results in a density that is too high. Your data for the density of sodium chloride solutions should have produced a straight line when plotted. How could this plot be used to determine the density of any concentration of sodium chloride solution? The plot could be used because if the mass of the sodium chloride is recorded, then this set amount can be used in the formula for any given volume of substance in the solution. As the volume of the water increases, the density decreases. As the mass of salt added increases, then the density increases. In this case, if the same amounts of salt were added to any set of water volumes, the line should still be plotted in the same direction. What is the difference between the density of a solution and its specific gravity? Density is the volume a substance or object has per its mass. However, specific gravity is defined as the density of a substance compared to the density of water. The density is a calculated amount using the fact that density is the mass of an object divided by its volume. Specific gravity is the ratio of density of the substance to the density of water. The resulting density measures are values of dimension defined by units -the measure of specific values do not denote dimension, but rather its relation to water. ...read more.

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