Introduction ! Sodium hydroxide is categorised as metal halide salt, composed of sodium and chlorine.! The ions present in the solid crystals of potassium chloride dissolve and gain mobility in water. When potassium chloride is dissolved in water, the following endothermic reaction occurs:! NaOH(s) + H2O(l) > Na+(aq) + OH–(aq) + H2O(l)! This reaction takes place because water is a polar solvent and display a permanent dipole status. Therefore ionic compounds will break into two or more ions when dissolved in such solvent.
The solubility of the compounds may be affected by different aspects that in? uence the energy of the molecules in the solvent. This experiment is speci? cally designed to measure the solubility of sodium hydroxide in waters of different temperatures.! ! Hypothesis! Higher temperature of water allow the particles of sodium hydroxide(s) more mobility between the solution and their solid state because the particles are absorbing energy from their surrounding. Therefore, higher the temperature of water, higher the solubility of sodium hydroxide.
! ! Table of variables! Variable measured Dependent Variable Method of measuring The solubility of Sodium hydroxide The mass of a 50ml beaker – Final mass of the 50ml beaker Independent Temperature of water Variable The temperature will be manipulated using a heating plate and kept consistent at desired level using a thermometer Variable controlled Method of controlling Controlled variables • The volume of distilled water! • The volume of solution extracted! • The amount of Sodium hydroxide!
• Mass of the 50ml beakers! • Syringe insertion point! • Time dedicated to stirring the solutions! • Use of the same type but separate syringes for each solution! • Room temperature! • Time taken between weighing and the heating procedure! • The volume of distilled water and the amount of Sodium hydroxide are recorded in order to calculate the molar concentration of Sodium hydroxide dissolved in water. The amount of both variables are kept consistent throughout the experiment, less likely being the sources of errors. !
• The initial amount of Sodium hydroxide is 50g and will be measured using a electric scale. Any uncertainty and inaccuracy must be recorded in order to make accurate calculation at the end. ! • All seven solutions will have to be supersaturated in Sodium hydroxide in order to detect the increase in solubility. ! • All of the solutions must be subjected under the same experimental conditions, therefore the amount of time spent to stir the mixture should kept approximately the same. !
• Using same syringes for all of the solutions may cause contamination and alter the ?nal result. Separate syringes must be used for each solutions. ! • When extracting a solution, the syringe should be inserted at the midpoint between the bottom of the beaker and the surface of the mixture. This is to prevent air particles and condensed Sodium hydroxide particles from entering the syringe, which may increase the actual concentration value of the solution that will be tested. ! • All beakers containing solutions will be placed in the same environment in order to avoid any possible errors. !
• After heating the beaker with the extracted solution sample, droplets may form due to re-condensing of the evaporated water, leading to an increase in the calculated weight of Sodium hydroxide. Thus it is important to weigh the beaker immediately while it is still hot after the evaporation process. Apparatus! Electric heating plate! Electric Scale! 100ml Beakers (7)! 50ml Beakers (7)! Stirring rods! Disposable syringes! Thermometer! ! Materials! Distilled water! Sodium hydroxide! ! Method/Procedure! 1. Measure and record the mass of the 50ml beakers. ! 2.
Pour 100ml of distilled water into the 100ml beakers and label them. ! 3. The labelled beakers are held at 10? C, 20? C, 30? C, 40? C, 50? C, 60? C and 70? C respectively using the heating plate. ! 4. Weigh 50g of sodium hydroxide and dissolve the measured amount into each beaker. Stir until completely dissolved using a stirring rod. ! 5. Using syringes, extract approximately 30ml of each solution from the labelled beakers. (The syringe should be inserted at the midpoint between the solution’s surface and the bottom of the beaker)!
6. Introduce the contents of the syringes into the 50ml beakers and label them. ! 7. Heat each of the 50ml beakers until the water becomes completely evaporated and immediately record the mass of each beaker. ! 8. Subtract the mass of the corresponding 50ml beaker from the combined mass of the salt residue. This will give the mass of the salt dissolved in the extracted solution. ! 9. Calculate the number of moles with following formula: n = mass of the salt ? the molar mass of Sodium hydroxide. Then divide the number of moles by the volume of the extracted sample (30ml), this will give the concentration.! ! ! ! !