Molina, Nathaniel S. BS-ECE1 Th 7:30-10:30AM Experiment No.7 PROPERTIES AND PURIFICATION OF WATER Purpose of the Experiment *Identify and explain some properties of water *Give the function of each part of a simple distillation set up *Trace how water can be purified by distillation and addition of softener *Rationalize the difference in hardness of various kinds of water Chemical formula of the materials and names of the apparatus used 20g rock salt Standard Soap Solution Crushed ice 1% Sodium Chloride soln. Tap water 1% Sodium Sulfate soln. Muddy water 1% Aluminum Sulfate soln. Boiled water detergent solution Distilled water glycerol Impure colored solution Procedure and Observations A. Surface Tension The students have filled the 50 ml beaker with water, and then they’ve put a small needle on top and it floated, afterwards, they’ve pricked the water with a toothpick and the small needle moved. The students then coated the toothpick with standard soap solution and pricked the water again, this time, the needle moved and then it sank. B. Viscosity The students prepared two baths in separate 250 ml beakers, an ice bath containing crushed ice with small amount of water and a boiling water bath. The students prepared four test tubes containing 5 mL of each respective solvents namely IA- 5 mL glycerol, IB-5mL glycerol, IIA- distilled water and IIB-distilled water. The test tube labelled A were putted in the ice bath and the test tube labelled B in the boiling bath. After several minutes, test tubes were pulled out and their viscosity were tested. Glycerol in hot water easily flowed while Glycerol in cold water hardly flowed, it is safe to say that Glycerol in cold water was more viscous than the glycerol in hot water while, Distilled water both in cold and hot water readily flowed therefore, water is non viscous. C. Freezing Point Depression The students filled a 250mL beaker with ¾ crushed ice and 10mL distilled water. The students then measured the temperature of the ice and it is above 0 degrees Celsius, Afterwards, the students added one tablespoon of rock salt and stirred it continuously, after several minutes, the students measured the temperature and saw that the temperature went down dramatically, after adding the salt the temperature was below 0 degree Celsius. D. Distillation After observing the distillation set up, the students identified the different parts of the set up and its uses. The Distilling flask contained the solution to be distilled, it is then moved forward to the delivery tube where the gaseous water passes through towards the test tube and it served as the receiver, the test tube was putted in a beaker with water and it served as a condenser. E. Testing the Hardness of Water the students prepared 3 test tubes and placed 5mL each of the following water: distilled water, boiled water, and tap water.The students then added few drops of standard soap solution in all of those water to test their hardness. In conclusion, Distilled water was the softest water with the least number of standard soap solution to make a lather, there was no more dissolved salts and ions. Due to the dissolved sulfates & chloride salts found in water boiled water remained permanent hardness. Lastly, Tap water is the hard water, it has the most number of drops of standard soap solution to make a lather. This contained the dissolved salts due to temporary and permanent hardness. F. Purification of Water by Flocculation The students set upped four test tubes in the test tube rack and labelled it accordingly, the test tube were added 5mL of muddy water. The students then added 5mL of each of the following onto the test tubes. Test tube 1 5mL of distilled water, Test tube 2 1% of sodium chloride solution, Test tube 3 1% of sodium sulfate solution and Test tube 4 1% of aluminum sulfate solution. Each of the test tubes we’re stirred and for a few minutes and observations were recorded after 5 to 15 mins. In conclusion aluminum sulfate managed to purify the water completely while the other substance didn’t purify it well, some were still muddy and some were still blurry but with aluminum sulfate the water was cleared. Significance of the study At the end of the activity, the students successfully achieved the objectives and they were able to perform and identified the different purposes of the chemicals use in terms of Surface Tension, Viscosity, Freezing Point Depression, Distillation, Testing the Hardness of Water and Purification of Water by flocculation. The students also successfully applied the different concepts of science in determining the reason of the outcome produced. (To be discussed in Theoretical Discussion) Theoretical Discussion A. Surface Tension “Needle floats due the invisible force over the water which is due to the surface tension. Surface tension is due the H-bonding along the surface water molecules Needle sinks because the hydrogen bonding of water was broken by the detergent.” B. Viscosity “Informally, viscosity is the quantity that describes a fluid's resistance to flow. Fluids resist the relative motion of immersed objects through them as well as to the motion of layers with differing velocities within them. Viscosity is first and foremost a function of material. The viscosity of water at 20 ℃ is 1.0020 millipascal seconds (which is conveniently close to one by coincidence alone). Most ordinary liquids have viscosities on the order of 1 to 1,000 mPa s, while gases have viscosities on the order of 1 to 10 μPa s. Pastes, gels, emulsions, and other complex liquids are harder to summarize. Some fats like butter or margarine are so viscous that they seem more like soft solids than like flowing liquids. Molten glass is extremely viscous and approaches infinite viscosity as it solidifies. Since the process is not as well defined as true freezing, some believe (incorrectly) that glass may still flow even after it has completely cooled, but this is not the case. At ordinary temperatures, glasses are as solid as true solids. From everyday experience, it should be common knowledge that viscosity varies with temperature. Honey and syrups can be made to flow more readily when heated. Engine oil and hydraulic fluids thicken appreciably on cold days and significantly affect the performance of cars and other machinery during the winter months. In general, the viscosity of a simple liquid decreases with increasing temperature. As temperature increases, the average speed of the molecules in a liquid increases and the amount of time they spend "in contact" with their nearest neighbors decreases. Thus, as temperature increases, the average intermolecular forces decrease. The actual manner in which the two quantities vary is nonlinear and changes abruptly when the liquid changes phase. Viscosity is normally independent of pressure, but liquids under extreme pressure often experience an increase in viscosity. Since liquids are normally incompressible, an increase in pressure doesn't really bring the molecules significantly closer together. Simple models of molecular interactions won't work to explain this behavior and, to my knowledge, there is no generally accepted more complex model that does. The liquid phase is probably the least well understood of all the phases of matter. While liquids get runnier as they get hotter, gases get thicker. (If one can imagine a "thick" gas.) The viscosity of gases increases as temperature increases and is approximately proportional to the square root of temperature. This is due to the increase in the frequency of intermolecular collisions at higher temperatures. Since most of the time the molecules in a gas are flying freely through the void, anything that increases the number of times one molecule is in contact with another will decrease the ability of the molecules as a whole to engage in the coordinated movement. The more these molecules collide with one another, the more disorganized their motion becomes. Physical models, advanced beyond the scope of this book, have been around for nearly a century that adequately explain the temperature dependence of viscosity in gases. Newer models do a better job than the older models. They also agree with the observation that the viscosity of gases is roughly independent of pressure and density. The gaseous phase is probably the best understood of all the phases of matter. Since viscosity is so dependent on temperature, it shouldn't never be stated without it.” (Elert, G. (n.d.) C. Freezing Point Depression “Freezing point depression is a colligative property observed in solutions that results from the introduction of solute molecules to a solvent. The freezing points of solutions are all lower than that of the pure solvent and is directly proportional to the molality of the solute. ΔTf=Tf(solvent)−Tf(solution)=Kf×m(1.1) (1.1)ΔTf=Tf(solvent)−Tf(solution)=Kf×m where ΔTfΔTf is the freezing point depression,TfTf (solution) is the freezing point of the solution, TfTf (solvent) is the freezing point of the solvent, KfKf is the freezing point depression constant, and m is the molality.”( Libretexts) “Salt lowers the freezing point of water via freezing point depression. Among other processes, the ions from the salt get in the way of water molecules aligning to crystallize into ice. When salted ice melts, the water can't refreeze as readily because the saline isn't pure water anymore and because the freezing point is colder. As more ice melts, more heat is absorbed, bringing the temperature down even lower.”( Helmenstine) D. Distillation “Distillation - a purification process which involves evaporation and condensation. Parts and function of the distillation set-up: 1. Distilling flask- contains the solution to be distilled. 2. Delivery tube – where the gaseous water passes through towards the test tube. 3. Test tube – serves as a receiver. 4. Beaker with water- serves as a condenser.” E. Testing the Hardness of Water “Hardness of Water –refers to the presence of dissolved salts and ions found in water. Two types of water hardness: 1. Temporary hardness- due to the dissolve carbonate salts and bicarbonate salts found in water. - This can be removed by boiling. 2. Permanent hardness - due to the dissolved sulfates & chloride salts found in water.” F. Purification of Water by Flocculation “Aluminum sulfate is the best effective coagulating agent/flocculating agent since it has higher charges compared to NaCl and Na2SO4. Al2(SO4)3, Na2SO4, NaCl --------------------------------- Increasing flocculating effect” “Flocculation, in physical chemistry, separation of solid particles from a liquid to form loose aggregations or soft flakes. These flocculates are easily disrupted, being held together only by a force analogous to the surface tension of a liquid. In industrial processes, flocculation may be a desired or an undesirable phenomenon, and various methods may be used to cause or eliminate flocculates. Formation of flocculates is important in the operation of water supplies and sewage systems.”(Britannica) Bibliography: Notes of Ms. Ginete in Properties and Purification of Water Britannica, T. E. (2017, June 07). Flocculation. Retrieved from https://www.britannica.com/science/flocculation Helmenstine, A. M., & Helmenstine. (n.d.). Here's How Cold Salt Makes Ice. Retrieved from https://www.thoughtco.com/how-cold-does-ice-get-with-salt-4017627 Elert, G. (n.d.). Viscosity. Retrieved from https://physics.info/viscosity/ Libretexts. (2018, November 26). Freezing Point Depression. Retrieved from https://chem.libretexts.org/Textbook_Maps/Physical_and_Theoretical_Chemistry_Textbook_Ma ps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Physical_Properties_of_Matt er/Solutions_and_Mixtures/Colligative_Properties/Freezing_Point_Depression
