Experiment 1 Density of Urine Density is an import physical property of matter. It is the characteristic that tells how closely packed the units of a substance are. It is measured as the mass of the substance per unit of volume of that substance. D = m/V Note: Sometimes,  the Greek letter rho, is used as the symbol for density. There are several units used for density. The most common is grams per milliliter, or g/mL. It is important to know that a milliliter is an equivalent unit to both a cubic centimeter (cm 3 ) or a cc, which is a common unit in medicine. Another important concept for this lab is concentration, which explains the differing densities of solutions of the same chemicals. The basic equation for concentration is parts of solute per parts of solvent. [C]=(parts solute)/(parts solvent) Note: Both square brackets and the letter C are used to indicate a value as being a concentration. The solute is the substance being dissolved and the solvent is what the solute is being dissolved in. An example is the ocean. There are many different compounds dissolved in the water, including common table salt, sodium chloride, NaCl. Here, NaCl is the solute, and water is the solvent. There are many units for concentration. In chemistry, the most common being molarity. However, we will not discuss what molarity is at this point. For the first experiment, we are dealing solely with percent weight per volume.

This is usually symbolized as % w/v and is given by the equation: % w/v = g of solute/ mL of solution * 100% Note: The equation is measured per mL of the total solution, and not just that of the solvent. The final lesson needed for this experiment is the calculation of percent error. Percent error is a measure of accuracy. The equation is: % error = measured value – actual value * 100% actual value The measured value is taken by the observer, i.e. you, and the actual value is determined either by previous experimental methods, or by calculations used to find an expected value. For this experiment, we are using two different methods to measure the density of urine. The first uses graduated cylinders and balances to gather the components of density, (volume and mass). The other is an instrument called a hydrometer, which measures specific gravity, or the density ratio of a substance to water. The latter method will be taken as the actual value. To measure the density using a graduated cylinder and a balance, an aliquot of liquid will be pipetted into a plastic cylinder. The volume will then be recorded. Place the cylinder on the balance, and record the mass. This will be repeated for five different solutions of urine. To measure the density using a hydrometer, simply look at the line on the bob at the surface of the water, and record this value.

Remembering that this value is a specific gravity, we now need to convert to actual density. Posted in the class room will be a thermometer and a chart listing the density of water at various temperatures. Take the temperature from the thermometer, and find the corresponding density on the chart. The density of the fluid is found by multiplying the hydrometer reading by the density of the water, given by the equation: D of fluid = Hydrometer reading * D of water The final thing to calculate will be the % error. To do this, we will use the value from the hydrometer reading as the true value, and the graduated cylinder as the measured value. To find the concentration of the unknown, we will be plotting our data in Excel. View the Excel tutorial to learn how to do this.