Alkalis are contained in what substances and what is their purpose? Logged in as a teacher you will find a button below for additional information.

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1 Science - Chemistry - Acids, Bases, Salts - 2 Bases (P ) 2.2 Alkalis - constituents of household detergents Experiment by: Phywe Printed: Oct 15, :45:25 PM intertess (Version B200, Export 2000) Task Task Alkalis are contained in what substances and what is their purpose? Examine household detergents for their components. 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 Alkalis are contained in many household detergents. They are used there because of their decomposing and thus cleaning effect with regard to organic contaminants. In addition to that they are germicidal. Notes on set-up and procedure Preparations Have some household detergent ready. All commercially available household detergents containing ammonia can be used. Remarks on the students' experiments Make sure that when the household detergent is heated, this process is stopped immediately when the first traces of ammonia can be smelled. The test tube must be shaken slightly during heating since otherwise boiling would be delayed. Add some boiling stones, if necessary. 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

3 Phenolphthalein: H226: P210: P233: Flammable liquid and vapour. Keep away from heat/sparks/open flames/hot surfaces. - No smoking. Keep container tightly closed. Hazards Sodium hydroxide is highly corrosive. Do not touch it with bare fingers! Put on protective glasses! When the household detergent is heated, harmful and evil smelling gases are released. The experiment must thus be carried out under the fume hood! Remarks on the method This experiment goes back to the changes of indicator colours already treated in conjunction with the subjects of "acids". If they haven't been taught yet, the experiments given there on the preparation of indicators and theis reactions can be slightly modified and used in this context here, too. Waste disposal Put all the solutions into the collecting tank for acids and alkalis

4 Material Material Material from "TESS Chemistry Set Acids, Bases and Salts" (Order No ) Position No. Material Protective glasses, clear glass Order No Quantity Beaker, 100 ml, short, plastic, stackable Test tube holder, up to d = 22 mm Test tube, mm, 10 pcs Test tube rack for 12 tubes Spatulas, double bladed, l = 150 mm, bent Pipette with rubber bulb Litmus paper, red, 1 box Wash bottle, 250 ml Chemicals, additional material Position No. Material Bunsen burner, natural gas, DIN Order No Quantity 1 Safety gas tubing, DVGW Sodium hydroxide, flakes, 500 g Water, distilled, 5 l Phenolphthalein solution, 0.5%, 100 ml Household detergent Material required for the experiment - 4 -

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6 Setup Set-up Hazards Sodium hydroxide is highly corrosive. Do not touch it with bare fingers! Put on protective glasses and rubber gloves! When the household detergent is heated, harmful and evil smelling gases are released. The experiment must thus be carried out under the fume hood! Set-up Fill the two test tubes one quarter full with household detergent and put them into the test tube rack (Fig. 1). Fig. 1 Fill the glass beaker with distilled water (filling height approximately 1 cm) and add some drops of phenolphthalein solution (Fig. 2). Fig

7 Action Action Procedure Pour the household detergent from one of the test tubes into the distilled water with the added phenolphthalein solution. Use the spatula to put two sodium hydroxide pellets into the second test tube. Heat the household detergent with the added sodium hydroxide very carefully. Carry out smelling tests as short intervals. Stop heating when the first traces of evil smelling gases can be detected. Hold a piece of humidified red litmus paper over the test tube orifice. Waste disposal Put the content of all vessels into the collecting tank for acids and alkalis

8 Evaluation Evaluation Question 1: Write down your observations. When the household detergent is added to the indicator solution, this turns red. When the household detergent mixed with sodium hydroxide is heated, pungent gases smelling like a horse stable are released which cause the humidified strip of litmus paper to turn blue. Question 2: Enter the changes of the indicator colours into Table 1. Table 1 indicator colour phenolphthalein in distilled water phenolphthalein after the addition of the detergent litmus paper before the heating of the detergent litmus paper after the heating of the detergent - 8 -

9 Table 1 indicator colour phenolphthalein in distilled water phenolphthalein after the addition of the detergent litmus paper before the heating of the detergent litmus paper after the heating of the detergent colourless wine-red red blue - 9 -

10 Questions and exercises Questions and exercises Question 1: Draw the conclusions from your observations. The household detergent used in this experiment must contain alkalis since it causes the phenolphthalein solution to turn red. When sodium hydroxide is added, this alkaline constituent escapes in the form of a gas but forms an alkaline solution with water again which causes the humidified litmus paper to turn blue. Question 2: Explain why household detergents contain the determind components. Alkalis are capable of decomposing organic contaminats and thus have a cleaning effect. In additions to that, they are capable of killing bacteria

11 Question 3: State some other indicators that could be used and the change of colour they would show in this experiment. Table 2 indicator colour before colour after the addition of the household detergent Table 2a indicator methyl orange bromthymol blue red cabbage extract colour before orange red yellow red colour after the addition of the household detergent yellow blue bluish green