1) Prepare a lesson carnestly before the experiment. Clarify the related basic principle, sequence of the operation, and safety measures in the experiment. 2) Put on the working clothes before entering the laboratory. Record the experimental phenomena and data. 3) Keep the floor neat. Don’t throw anything into the water trough so as to avoid stops up. 4) After every experiment, the students being on duty shall take responsibility for cleaning up the laboratory, inspecing the switch of water and electricity, and closing the window. 5) write the experiment report according to the primary record and turn in. Laboratory safety regulations
1) Corrosive acids and alkali must be treated carefully, and be sure not to splash on clothes, skin and eyes. While diluting strong sulfuric acid, the acid should be poured slowly into the water with stirring, but not water into the acid. 2）It’s not allowed to handle solid drugs with the hand directly. Don’t mix different kinds of chemicals arbitrarily. Basic operations in chemical experiment
1. Get knowledge of all kinds of common glassware, grasp the names and uses of them such as 1) Beaker. prepare solution, when heated, it must be puted on the asbestos gauze. 2) Erlenmeyer flask. heat samples or titration. when heated, must open the stopper. puted on the asbestos gauze. 3) Rounded(flat)-Bottom flask. heat liquid or for distillation. It can be heated in the heating jacket. 4) Washing bottle. filled with distilled water or washing liquid. 5) Measuring cylinder. It is mainly used to measure liquid roughly. 6) Volumetric flask. prepare accurate volume standard solution or unknown concentration to be determined. It can not be heated directly, it must be heated by hot water bath 7) Weighing bottle. determine water content of sample or oven dry, weigh primary standard substance. 8) Reagent bottle. narrow- necked bottle store liquid. wide-mouthed bottle store solid reagents. Brown bottle easy to decompose when seeing light. can not be heated. Don’t store basic solution for long time. 9) Dropping bottle. The solution need to dropwise.
10) Separating funnel. separate two mutual non-homogenous liquids. check leak . 11) Condenser. distillation. Coiled shape condensing low boiling point liquid. from the bottom up. 12) Filter flask. receive filtrate when suction filtration.
13) Watching glass. cover beaker or other containers.
14) Desiccator. dry small amount of samples. bottom placed by silicone. blue turn to red when absorb water. 15) measuring pipet. transfer accurately a certain quantity of liquid. It has scale. 16) transfer pipette. transfer accurately a certain quantity of liquid , no scale. 17) Burette. titration. check leak. Acid solution with stopcock, basic solution with rubber pipe. 2. Practice the use of the glassware provided in the plastic box, with a focus on Practicing operation of measuring pipet, transfer pipette, Volumetric flask and Burette. 1) Use of measuring pipette and transfer pipette. Transfer pipette has no scale, there is a bulb in the middle of it. measuring pipet has scale division. Firstly, wash. washed by tap water and then by distilled water. Keep it level, Rotate. hold the pipette by right hand and suction ball by left hand. Secondly, rinse. Pour some solution into a beaker, draw the solution and rinsed three times. draw the solution to the level beyond the scale and press the mouth of the pipette with first finger of right hand immediately. wipe dry.
Thirdly, adjust the solution level. Hold a beaker with left hand and lean the beaker against the pipette. beaker 45º , pipette vertical. Loosen finger slowly, rotate the pipette untill the lowest surface of solution drop to the same level as the scale. 2) Use of volumetric flask. We can dilute the concentrated solution to a certain volume or prepare a certain volume solution of some solids. Leakage check: fill in tap water, stopper and press the stopper with first finger of the left hand; right hand hold the bottom; turn it up-side-down. turn the stopper 180º, repeat. Washing. washed by tap water and distilled water. Transfer. Precisely weigh the solid, dissolve it in beaker and transfer the solution to the volumetric flask. Insert a glass rod into the flask and pour the solution into flask along the rod. Rinse the beaker with distilled water 3-5 times, transfer the rinsing solution to the flask. Dilution. Add distilled water till 3/4 volume, shake. Continue adding distille water near the scale; use a dropper to drip till the lowest point of the solution rises to the scale. Cover it tightly. Shaking. Press the stopper with right hand and hold the flask with fingers of left hand. Turn around the flask Up side down. 3) Use of burette(see also experiment two)
Experiment Two Acid-base titration
Objectives 1. Prepare the solution with certain concentration. 2. Practice the operation of titration. 3. Grasp the choice of indicator and judge the equivalence point. Principle With the volume of the base added Vb and the original volume of the acid Va and the concentration of acid Ca already known, we can calculate the concentration of base Cb. Ca Va = Cb Vb. We can titrate the HCl of coarsely known concentration with NaOH solution, then CNaOH can be obtained, phenolphthalein as indicator. Equivalence point: colorless to pink. We can also titrate the NaOH of coarsely known concentration with HCl solution, so CHCl can be obtained, methyl orange as indicator. Equivalence point: yellow to orange. Equipment Burette, pipette…….and so on
Chemicals NaOH(solid) , HCl(37%, 1.19g/cm3) , phenolphthaleins and so on Procedures
1. Coarsely prepare solutions of 0.1M HCl and 0.1M NaOH.
NaOH: Weigh an empty beaker, object left, weight right. Adjust balance vernier, pointer, balanced. Put solid NaOH into beaker by spoon, weigh 2g NaOH. dissolve by distilled water, dilute to 500ml in a big beaker. Pour to reagent bottle. Label. HCl: get 5ml concentrated HCl in measuring cylinder, Dilute with distilled water to 500ml. Pour to Reagent bottle. Label. 2. Titrate the 0.1M HCl with NaOH solution, then CNaOH can be obtained, phenolphthalein as an indicator. Equivalence point: colorless to pink. Firstly, wash burettes. Washed by water, keep it level, rotate and release water. rinsed by distilled water several times. For basic burette, with the same operations as acidic. ② Leakage check. Take out the paper in the stopcock, flexible rotation, if it necessary, paint vaseline, cannot block the hole. Bind the stopper with rubber ring. Add distilled water till “0” scale; place the burette vertically for 2 min to observe whether the water face will drop. For base burette, check whether the glass bead and rubber tube can flexibly control the water dropping.
Check rubber aging for basic. ③ Solution filling. Rinse the burette with the solution to be added 3 times and let the solution flow out through the stopcock. for acidic burette, quickly open the stopcock and wash the bubble out. For basic, bend the rubber tube 45º upward with left hand. Press and squeeze the point over glass bead with left hand to expell the bubble out of the tip. After that, fill NaOH solution into it, drive away the air bubble in the rubber tube and its tip, then adjust the place of the liquid level to “0. 00”. Add 0.1M 20. 00mL HCl solution with transfer pipette to erlenmeyer flask, then add 2-3 drops of phenolphthalein indicator, shaking constantly. Extrude the glass ball in rubber tube to make the liquid dropping to erlenmeyer flask. pinch the point over glass bead with thumb and first finger of left hand, and control the glass tip with middle finger and ring finger, so as to let out the solution.
Don’t pinch the glass bead too hard, don’t press the rubber tube below or above glass bead. The dropping velocity can be quick at the beginning, but afterwards the operation should be controlled drop by drop and avoiding a current of liquid. When the base solution drops into the erlenmeyer flask, part of the solution appears pink, but the color will disappear quickly while shaking the erlenmeyer flask. pink color disappears slowly near the end-point. In this period the base solution should be added a drop at a time and allow a half drop of liquid hanging on the tip. It should not fall directly only make it touch the inner wall of the Erlenmeyer flask and then shake. If the pink color doesn’t disappear in about half a minute, it means that the end-point is located. Wait a moment, then record the place of the liquid level left in the burette. 3. Titrate the 0.1M NaOH with HCl solution, then C HCl can be obtained, methyl orange as an indicator. Equivalence point: yellow to orange. fill HCl solution into burette, drive away the air bubble, then adjust the place of the liquid level to “0. 00”.
Add 0.1M 20. 00mL NaOH solution with transfer pipette to erlenmeyer flask, then add 2-3 drops of methyl orange indicator, shaking constantly.Operate the stopcock with three fingers of left hand: thumb ahead, first finger and second finger behind; palm center don’t touch the stopcock. Don’t pull stopcock outside. Keep the tip of the burette 1 cm lower than flask mouth, and hold the flask neck with first three fingers of right hand to shake it clockwisely or anti-clockwisely. Titrition speed is controlled at 3-4 drops per second. While approaching titrition end, the solution will change color at some point and after shaking, the color will dispear. After that, titrite drop by drop, and when the color change occures only after 2-3 shakings, control the stopcock to let out half drop of solution, suspended but not dropped, then wash it into the flask with distilled water; repeat the operation till the color changes and will not disapear. 4. Reading. Bring the burette down from the stand and hold it by two fingers. Keep it vertical, Read and record the figure when view sight is parallel with the the lowest point of the solution surface. 5. If you have enough time, Titrate again, whether titrate acid or base is ok. You must pay attention to the following points:
(1) There should not be some air bubbles left inside the tip when the titration is over. (2) The color of the solution after the location of the end-point will disappear because of the effect of CO2 in the open air. That doesn’t mean the acid-base reaction is not complete. (3) During the titration, the base may splash down the upper part of the wall of the Erlenmeyer flask and the last half drop is touched by the wall, so in the immediate vicinity of the end-point it is appropriate to rinse down before completing the titration.