EXPERIMENT REPORT (PREPARATION OF CdS) Experiment Purposes 1. To master the proper operations as well as the suitable situations of atmospheric pressure filtration, vacuum filtration, centrifugal separation & precipitation washing 2. To understand the relation between precipitation state % precipitating conditions 3. To learn the way to examine whether reactants are fully precipitated 4. To learn the principals of powder material synthesizing through room temperature solid phase method & liquid phase method directional growing rystal form of precipitation Experiment Principals 1. the process of precipitation forming constitutive crystal ion accumulating growing forming nuclei sediment particals amorphous precipitation crystal nuclei 2. the classification of precipitations amorphous precipitation, particle diameter smaller than 0. 02 m, ex. Fe(OH)3. the hydroxide of metals of high oxidation number would grow directionally with low rate, but accumulate very fast, forming amorphous precipitation curd-like precipitation, particle diameter 0. 02~0. 1 m, ex.
AgCl crystal form of precipitation, diameter 0. 1~1 m, ex. BaSO4. Inorganic salts with strong polarizability grow directionally with high rate, forming crystal form of precipitation 3. CdS is a semiconductor material widely use. It can be preparated through room temperature solid phase method & liquid phase method & gas phase method. Use CdSO4 and NaS as reactants, through both room temperature solid phase method & liquid phase method to prepare CdS(s). Compare the two ways of preparation and their influence on product separation. Reactions as ollows, CdSO4+2NaS=CdS+Na2SO4 Chemical reagents: CdSO4(s), Na2S(s), 0. 3M HCL(aq), 0. 5M CdSO4(aq), 1M BaCl2(aq), widely pH tests strips, mortar, centrifugal text tube, bake oven, centrifuge, vacuum filtration apparatus, etc. Experiment Steps And Phenomena Room temperature solid phase method 1. according to the theoretically volume of product should be 1. 44g, weigh certain amount of CdSO4(s) and NaS(s), mix in dried mortal, then grind for 10-20 min. | In the mortal, White particles slowly turned into orange powders, bad egg smell is output. | 2. he product is transferred to a beaker and washed with distilled water for 3 times, until the supernatant is tested pH<6 with pH test strips, and white precipitation is not observed when BaCl2(aq) is added in the supernatant. then the precipitation is separated through vacuum filtration. Then precipitation is washed with ethanol. | In the beaker, yellow solution is obtained and there’s orange precipitations. The pH test strips shows its pH is smaller than 6, and no white precipitation is observed. After filtration, we can get deep orange wet solid on the filter paper| 3.
The product is dried in oven for 0. 5hr under 130 degrees, weigh until the product is cooled down and calculate the product rate. | orange dried powders are obtained, weighed 1. 22g. | Liquid phase method 1, weigh certain amount of hydrated NaS, to prepare 1M of NaS solution| Colorless solution is obtained. | 2. measure 20ml of CdSO4 solution, slowly mix with NaS(aq) while stirring in the beaker. then suck up 1-2 drops of supernatant and place them in a test tube, acidized with 0. 3M HCl, then drop 1M NaS(aq). f yellow precipitation is not observed, it proves Cd2+ is precipitated completely. | The mixed solution turned into yellow and orange precipitation is formed. yellow precipitation is not observed. Also smells like bad egg. | 3. transfer the product into centrifugal test tubes, and separated in centrifuge. after centrifugation, the supernatant in test tubes is drawn with droppers, the precipitation is washed with distilled water, until the supernatant is tested pH;6 with pH test strips, and white precipitation is not observed when BaCl2(aq) is added in the supernatant.
Then the precipitation is separated through vacuum filtration. Then precipitation is washed with ethanol. | After centrifugation, colorless supernatant and orange precipitation in the bottom of the tube is observed. The pH test strips shows its pH is smaller than 6, and no white precipitation is observed. After filtration, we can get deep orange wet solid on the filter paper| 4. The product is dried in oven for 0. 5hr under 130 degrees, weigh until the product is cooled down and calculate the product rate. | orange dried powders are obtained, weighed 2. 2g. | Experiment Result Comparision | Liquid phase method| Solid phase method| Appearance of products| Orange dried powders, with slightly bigger particles| Orange dried powders, particles are small| Theoretically volume of product| 1. 44g| 1. 44g| Volume of product| 2. 62g| 1. 22g| Product rate| 181. 9%| 84. 7%| Reasons that may lead to the difference between theory value and true value| 1. product is not fully dried2. errors while weighing NaS| 1. part of products are lost during experimental process| Discussions 1.
What is the advantage of solid phase method? The experiment steps are simplified, and less step will cause less lost of product during operations, the product is purer. 2. While filtration, does the filter paper expand after wetted by water? If wet filter paper has a diameter bigger than the Buchner funnel’s , how will the filtration be influenced? The filter paper expands a little after wetted. the filter paper cannot be stuck to surface of funnel close together, and lead into lost of precipitation during filtration.