What safety precautions have to be taken when handling alkalis?

Transcription

1 Science - Chemistry - Acids, Bases, Salts - 2 Bases (P ) 2.1 Safety precautions to be taken when handling alkalis Experiment by: Phywe Printed: Oct 15, :44:12 PM intertess (Version B200, Export 2000) Task Task What safety precautions have to be taken when handling alkalis? Study the properties of a drainpipe detergent and of concentrated caustic soda solution. Use the space below for your own notes. Logged in as a teacher you will find a button below for additional information

2 Additional information Learning objectives Concentrated alkalis are highly corrosive and capable of decomposing especially organic material. When handling alkalis safety precautions must be taken which are similar to those to be taken when handling acids. Notes on set-up and procedure Preparations Get coloured strings, hair and pieces of meat ready. The wood used for this experiment should be painted in order to show the effect of alkalis serving as paint strippers. Prepare some concentrated caustic soda solution. Remarks on the students' experiments Make sure that the students handle the concentrated solutions carefully. Keep the eyewash bottle ready to hand! Protect the Petri dishes from unauthorised use. Hazard and Precautionary statements Sodium hydroxide: H314: Causes severe skin burns and eye damage. H290: May be corrosive to metals. P280: Wear protective gloves/protective clothing/eye protection/face protection. P301 + P330 + P331: IF SWALLOWED: rinse mouth. Do NOT induce vomiting. P309 + P310: IF exposed or if you feel unwell: Immediately call a POISON CENTER or doctor/physician. P305 + P351 + P338: IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing. Hazards Drainpipe detergents and concentrated alkalis are highly corrosive. Put on protective glasses and rubber gloves! Splashes on skin or cloths must be washed out immediately with a lot of water! - 2 -

3 Splashed alkalis must be diluted with water immediately and absorbed by means of a humid cloth! Remarks on the method These and other (demonstration) experiments are highly recommended when starting to teach the subject of "alkalis" not only in order to train the necessary accident prevention measures to be taken but also to eliminate diffident feelings with the regard to the use of alkalis (see also the experiment "Safety precautions to be taken when handling acids"). Waste disposal Dilute the alkalis in the Petri dishes with a lot of water and then put them into the collecting tank for acids and alkalis. The substance samples can be treated as normal waste

4 Material Material Material from "TESS Chemistry Set Acids, Bases and Salts" (Order No ) Position No. Material Protective glasses, clear glass Order No Quantity Wash bottle, 250 ml Glass beaker DURAN, short, 250 ml Petri dish, d = 100 mm Dish, plastic, mm Knife, stainless Spatulas, double bladed, l = 150 mm, bent Laboratory pencil, waterproof Scissors, straight/blunt points, 110 mm Glass rod, boro 3.3, l = 200 mm, d = 5 mm Pipette with rubber bulb Rubber gloves, size Chemicals, additional material Position No. Material Concentrated caustic soda solution, prepared from Order No Quantity Water, distilled, 5 l Cloth for cleaning Drainpipe detergent Paper sheet (white) Substance samples (string, meat, hair, painted wood) Material required for the experiment - 4 -

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6 Setup Set-up Hazards Drainpipe detergents and concentrated alkalis are highly corrosive. Put on protective glasses and rubber gloves! Splashes on skin or clothes must be washed out immediately with a lot of water! Splashed alkalis must be diluted immediately with water and absorbed by means of a humid cloth! Set-up Cover the working place completely with white paper sheet. Put the required materials and chemicals onto the paper sheet. Pu the cleaning cloth into the trough filled wih water and keep it ready to hand (Fig. 1). Fig

7 Action Action Procedure Fill the glass beaker one quarter full with distilled water (Fig. 2) and add some drainpipe detergent in several steps (Fig. 3). Stir it by means of the glass rod (Fig. 4). Stop adding when the detergent does no longer dissolve. Fig. 2 Fig. 3 Fig. 4 Put the glass beaker aside in order to let it cool down. Number the covers of the petri dishes from 1 to 2 (Fig. 5). Cut the substance samples into small pieces and put some of them into both Petri dishes (Fig. 6). Fig. 5 Fig

8 Use the pipette to drop some of the concentrated caustic soda solution into the first Petri dish (Fig. 7) until the bottom of the dish is covered completely (Fig. 8). Do the same with the solution of the drainpipe detergent and the second Petri dish. Fig. 7 Fig. 8 Wait for 10 minutes and then examine the samples for changes. Write down the result. Then close the Petri dishes with the numbered covers (observe the correct order!) (Fig. 9) and store them in a safe place for the next lesson. Mark the storage place with the caution label GHS05 for caustic substances. Fig. 9 Waste disposal Dilute the alkalis in the Petri dishes with a lot of water and then put them into the collecting tank for acids and alkalis. The sample residues can be treated as normal waste

9 Evaluation Evaluation Question 1: What observations can be made during the preparation of the solution? Write down the changes of the substances after a short time of exposure. When the drainpipe detergent dissolves, the temperature of the water rises strongly. The substance samples affected by the alkali change their colour and disintegrate slightly. Question 2: Enter the changes to be observed after a longer time of exposure into Table 1. Table 1 substance sample string meat hair (painted) wood affected by caustic soda solution drainpipe detergent nnnnnnnnnnnnnnnnnnnn nnnnnnnnnnnnnnnnnnnn nnnnnnnnnnnnnnnnnnnn nnnnnnnnnnnnnnnnnnnn nnnnnnnnnnnnnnnnnnnn nnnnnnnnnnnnnnnnnnnn nnnnnnnnnnnnnnnnnnnn nnnnnnnnnnnnnnnnnnnn - 9 -

10 Table 1a substance sample string meat hair (painted) wood caustic soda solution changes in colour, disintegrates decomposes decomposes disintegrates, paint is stripped off affected by drainpipe detergent changes in colour, disintegrates decomposes decomposes disintegrates, paint is stripped off

11 Questions and exercises Questions and exercises Question 1: What are the effects of concentrated alkalis and what are the resulting safety precautions to be taken as a consequence? Concentrated alkalis are capable of decomposing many substances or of composing them. Paint is stripped off. Just like in the case of acids, rubber gloves and protective glasses must be put on when handling alkalis. Care must be taken that alkalis do not come in contact with skin or clothes. Water for diluting splashed alkalis must be kept ready to hand. Question 2: State the measures to be taken when alkalis have been splashed or sputtered

12 The alkalis must be diluted with water and absorbed by means of a cleaning cloth. The contact areas must be rinsed with a lot of water. Question 3: Explain the effect of drainpipe detergents on clogged drainpipes. Drainpipe detergents contain strong alkalis which disintegrate the substances clogging the drainpipe. When the drainpipe detergent is added, a large amount of heat is generated which has an accelerating effect on the disintegration