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10.2 Laboratory acids and alkalis

Learn about the importance of safety precautions while handling acids and alkalis in the laboratory. Understand how to distinguish between acids and alkalis using indicators like litmus. Explore the pH scale and the usage of universal indicator for simpler testing methods.

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10.2 Laboratory acids and alkalis

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  1. 10.2 Laboratory acids and alkalis

  2. -In the laboratory, the commonly used acids are p.9 nitric acid sulphuric acid hydrochloric acid They are all colourless liquids.

  3. -In the laboratory, the commonly usedalkalis are sodium hydroxide calcium hydroxide ammonium hydroxide They are all colourless liquids.

  4. -Many acids and alkalis are corrosive, especially concentrated acids and alkalis. We must follow necessary safety precautionswhen handlingthe laboratory acids and alkalis.

  5. Can you explain the importance of following the safety precautions below? > Note the hazard warning labelson thebottles of chemicals. > Always wearsafety goggles. > Wear gloves and/or protective coats when necessary. p.9

  6. > After the experiment, pour the wastes into suitable waste bottles. Can you explain the importance of following the safety precautions below? > Do not use too much acids or alkalis. Fill no more than 1/3 of thecontainer with the acids or alkalis.

  7. If accidents happen, e.g.some chemicals are splashed on your arm -report to your teacher immediately, -keep calm, -follow the following emergency treatment: p.10

  8. Emergency treatment involving acids and alkalis > Wash the affected area under slow running water for at least 10 minutes. > If the eye is hurt, wash it with the eye-wash bottle.

  9. Emergency treatment involving acids and alkalis > Gently remove any contaminated clothing while washing the affected area. Avoid further contact with the acids or alkalis. > If the accident is serious, -call for medical aid without delay, - bringthe sample of acids or alkalisto hospitalfor reference.

  10. Distinguishing between acids and alkalis in the laboratory p.10 - Use indicators, e.g. >litmus(石蕊) > universal indicator(通用指示劑) > pH meter(pH 計)

  11. lichen => Obtained from the lichengrown on the surface of rocks and tree trunks. It contains a pigment that changes colour both in acids and in alkalis. Litmus - Litmus shows different coloursin acidic and alkaline environments.

  12. blue litmus => The solution made from it is called litmus solution (石蕊溶液). Litmus - Litmus paper(石蕊試紙)is a strip of filter paper which has been soaked in litmus solution.

  13. red litmussolution blue litmussolution inalkalis inacids turns blue turns red Litmus solution there are

  14. blue litmus paper red litmus paper inalkalis inacids turns blue turns red Litmus paper

  15. p.12 Theoretically, distilled water is neutral(中性的).

  16. Do you know ? If one drop of distilled water is added onto a piece of red litmus paper, what will be the colour changeof the paper? If one drop of distilled water is added onto a piece of blue litmus paper, what will be the colour changeof the paper? distilled water

  17. Universal indicator p.12 - This is quite troublesome to use litmus > have to guess if the red one or the blue one should be used before the test. > have to use both red and blue litmus to confirmwhether the sample is neutral or not. - Using universal indicator can make the testing simpler.

  18. Universal indicator - Shows a wide range of colours depending on the degree of acidity and alkalinity of substances. - Available in solution form or in paper form.

  19. neutral more acidic more alkaline pH scale(pH標度) p.12 - Scientists use this scale to tell the degree of acidity and alkalinity ofsubstances. - Consists of pH values (pH 值) ranging between 0 and 14: 01 2 3 4 5 678 910111213 14

  20. sample or sample pH paper pH colour chart - When a few drops of universal indicator solution is added to the sample or a drop of sample is added onto a piece of pH paper, we can tell the pH value of the substance by matching the colour shown with the pH colour chart. Universal indicator solution

  21. - To indicate the pH valuesof substances, different brands of pH paper and universal indicator solution may show different ranges of colours.

  22. Do you know ? p.16 - The pH value can be of any number from 0 to 14, including decimals. The pH value of the acid inside a car battery is 0. e.g. The pH value of our blood is 7.4.

  23. A car battery containssulphuric acid.

  24. pH meter p.16 - Can measure the pH value of a substance accurately. - The pH value of a substance can be obtained easily by putting the probe into the sample solution. The pH value of this glass of orange juice is3.56.

  25. Do you know ? If some distilled water is added to the glass of orange juice, what will be thepH value of theorange juice?

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