Title: Solution - Construction of Solubility Curve for Potassium Chlorate Objectives: a) To construct the solubility curve for potassium chlorate. b) To determine the solubility of potassium chlorate at different temperature. temperature. Introduction: Potassium chlorate is a white crystalline solid. It forms a very flammable mixture with combustible materials. The mixture may be explosive ex plosive if combustible material is very finely divided. The mixture may be ignited by friction. When it contacts with strong sulfuric acid may cause fires or explosions. It may spontaneously decompose and ignite when mixed with ammonium salts. It may explode under prolonged exposure to heat or fire. It can be used to make matches, paper, explosives, and many other uses. (PubChem, 2016). Molecular weight of potassium chlorate is 122.5495 g/mol. Potassium chlorate is also a useful oxidizer and small amounts can be easily made using household chemicals . Start by boiling a large quantity of household laundry bleach, at least half a liter, until crystals crystals start to precipitate. Immediately take it off heating and let it cool. As it cools make a saturated solution of potassium chloride. Potassium chloride is sold as a "sodium-free" salt. When potassium chlorate was dissolved in water, the solution becomes a homogeneous mixture. On the industrial scale, potassium chlorate is produced by the Liebig process: passing chlorine into hot calcium hydroxide, subsequently adding potassium chloride. 6 Ca(OH)2 + 6CL2 → Ca(CLO Ca(CLO3)2 + 5CaCL2 Ca(CLO3)2 + 2KCL → 2KCLO3 + CaCL2 A solution is homogenous mixture of two or more substances where the proportions of which may vary between certain limits. The types of mixture that can form are gas in gas, gas in liquid, liquid in liquid, and solid in liquid. The experiment is performed to obtain a solubility curve for solid potassium chlorate in water at different temperature.
Procedures: 3.00g of potassium chlorate was weighed accurately into a boiling tube. 10.0cm3 of water was added in from a burette and a thermometer was put into a boiling tube. The boiling tube was put into a beaker of water. The water was heated and the content was stirred in the boiling tube gently with a glass rod until the solid has just dissolved completely. The boiling tube was removed from the hot water, and it was allowed to cool in air with constant stirring. The temperature at which crystals started to form was noted. The experiment was repeated and the temperature was determined again. The average temperature can be taken as the temperature at which the solution was just saturated. Now 5.0cm3 more of water was added from the burette, and the temperature was determined as described above. The procedure was repeated until about 40.0cm3 of water has been added. Results: Volume of water (mL)
Temperature (o C)
Average temperature (o C)
10.00 15.00 20.00 25.00 30.00 35.00 40.00
Set 1 65.0 48.0 36.0 29.0 24.0 20.5 16.0
Volume of water (mL)
Temperature (o C)
3.0069g/15mL x100 = 20.05
3.0069g/20mL x100 = 15.03
3.0069g/25 x100 = 12.03
64.0 46.0 39.0 30.0 25.0 21.5 19.0
64.5 47.0 37.5 29.5 24.5 21.0 17.5 Concentration of potassium chlorate (g/100g water ) 3.0069g/10mL x100 = 30.07
3.0069/30x100 = 10.02
3.0069/35 x100 = 8.59
3.0069/40 x100 = 7.52
Set 1 3.0069
Set 2 3.0069
Mass of potassium chlorate (g) Average mass of potassium chlorate=3.0069 g
Discussion: Solubility is a chemical property referring to the ability for a given substance, the solute, to dissolve in a solvent. It is measured in terms of the maximum amount of solute dissolved in a solvent at equilibrium. The resulting solution is called a saturated solution. Solubility of potassium chlorate in water is an endothermic reaction. This is because the size of the lattice enthalpy (endothermic) is greater than the sum of the enthalpies of hydration of the ions (exothermic). It is the large increase in entropy as the solution forms that makes this a thermodynamically favourable process. A solubility curve relates the concentration of a saturated solution to temperature. Generally, we measure the solubility of a solute in an aqueous solution in grams of solute per 100 grams of water. Solutions are also a mixture of solvents and solutes. For example, a coffee is a solution, which the solute is the coffee powder and is dissolved in the solvent which is water. The solute and solvent can be either a solid, liquid or a gas. A solution forms when the attractive forces between the solute and the solvent are similar. For example, sodium chloride, NaCl, dissolves in water, and forms a polar solvent. When the water molecules collide with the ionic compound which is NaCl, the charged of the water molecule become attracted to the positive Na+ ions and Cl- ions. The water molecules surround the ions and the ions move into solution. The attraction between the water molecules and the ionic compound, NaCl, is called solvation. It will occur until all the crystal has dissolved and all the ions are distributed throughout the solvent.
When determining the solution of a substance, we must know the heat of solution (Hsol), lattice energy and the heat of hydration (ΔHhydr ). Heat of solution is one of the two factors that determine the solubility of a solute. Heat of hydration is the enthalpy change for the hydration of one mole of separated(gaseous) ions while lattice energy is the enthalpy change that occurs when one mole of ionic solid separates into gaseous ions which indicates the strength of ionic interaction in the solid. Heat of solution is the total enthalpy change that occurs when a solution is formed from solute and solvent. Negative value of heat of solution indicates that the process is exothermic (releases heat) while positive value of heat of solution indicates that the process of dissolving of a substance is endothermic (absorbs heat). Most ionic solids have positive heat of solution because their lattice energy is greater than the heats of hydration. Thus, heat is absorbed to form a solution. This indicates that solids are more soluble at higher temperature. Rise in temperature causes the increase of solubility. In this experiment, the graph of the relation between concentration of potassium chlorate (g/100g water) and temperature of KClO3 shows concentration increases when temperature rises. There are some precautions in the experiment. Firstly, the reading of temperature must be taken as soon as the salt crystals start to form. The cr ystallization of salt must be observed carefully. Next, make sure eye level is parallel to the level of water. Make sure that the burette is rinsed with water before carrying out the experiment. Wear goggles and gloves when carrying out the experiment. Conclusion: For many solids dissolved in liquid water, the solubility increases with temperature. The increase in kinetic energy that comes with higher temperatures allows the solvent molecules to more effectively break apart the solute molecules that are held together by intermolecular attractions. In this experiment, the graph of the relation between concentration of potassium chlorate (g/100g water) and temperature of KClO3 shows concentration increases when temperature rises.
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