10.2 Laboratory acids and alkalis

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

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

acidsalkalis - Many acids and alkalis are corrosive, especially concentrated acids and alkalis. acids alkalis We must follow necessary safety precautions when handling the laboratory acids and alkalis.

Can you explain the importance of following the safety precautions below? Can you explain the importance of following the safety precautions below? > > Note the hazard warning labels on the bottles of chemicals. > > Always wear safety goggles. > > Wear gloves and/or protective coats when necessary. p.9

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

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

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.

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

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 )

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

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

red litmus solution blue litmus solution turns blue in alkalis turns red in acids there are Litmus solution

turns blue in alkalis turns red in acids Litmus paper litmus paper redlitmus paperblue

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

If one drop of distilled water is added onto a piece of red litmus paper, what will be the colour change of the paper? If one drop of distilled water is added onto a piece of blue litmus paper, what will be the colour change of the paper? distilled water

Universal indicator - This is quite troublesome to use litmus universal indicator - Using universal indicator can make the testing simpler. > have to guess if the red one or the blue one should be used b bb before the test. > have to use both red and blue litmus to c cc confirm whether the sample is n eutral or not. p.12

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

- Consists of pH values (pH 值 ) ranging between 0 and 14: - Scientists use this scale to tell the degree of acidity and alkalinity of substances. pH scale (pH 標度 ) more acidic more alkaline neutralp.12

samplesample the 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.sample oror pH paper sample pH colour chart Universal indicator solution

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

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. The pH value of our blood is 7.4. e.g.

A car battery contains sulphuric acid. A car battery contains sulphuric acid.

p.16 - Can measure the pH value of a substance accurately. pH meter - The pH value of a substance can be obtained easily by putting the probe into the sample solution. orange juice The pH value of this glass of orange juice is 3.56.

orange juice orange juice If some distilled water is added to the glass of orange juice, what will be the pH value of the orange juice?