10.210.2

Laboratory acids anLaboratory acids an

d alkalisd alkalis

- In the laboratory, the commonly used acids are

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nitric nitric acidacidnitric nitric acidacid

sulphuric sulphuric acidacid

sulphuric sulphuric acidacid

hydrochloric hydrochloric acidacid

hydrochloric hydrochloric acidacid

They are all colourless liquids.

- In the laboratory, the commonly used alkalis are

sodium sodium hydroxidehydroxide

sodium sodium hydroxidehydroxide

calcium calcium hydroxidehydroxide

calcium calcium hydroxidehydroxide

ammonium ammonium hydroxidehydroxideammonium ammonium hydroxidehydroxide

They are all colourless liquids.

- Many acidsacids and alkalis alkalis are corrosive, especially concentrated acids and alkalis.

We must follow necessary safety precautions when handling the laboratory acids acids and alkalisalkalis.

Can you Can you explain explain the the importanceimportance of of following thefollowing the safety precautions safety precautions belowbelow? ?

Can you Can you explain explain the the importanceimportance of of following thefollowing the safety precautions safety precautions belowbelow? ?

> > Note the hazard warning labels on the bottles of chemicals.

> > Always wear safety goggles.

> > Wear gloves and/or protective coats when necessary.

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> > Do not use too much acids or alkalis. Fill no more than 1/3 of the container with the acids or alkalis.

Can you Can you explain explain the the importanceimportance of of following thefollowing the safety precautions safety precautions belowbelow??

Can you Can you explain explain the the importanceimportance of of following thefollowing the safety precautions safety precautions belowbelow??

> > After the experiment, pour the wastes into suitable waste bottles.

If accidents happen happen,

- follow the following emergency treatment:

- report to your teacher immediately,

- keep calm,

e.g. some chemicals are splashed on your arm

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Emergency treatment Emergency treatment involving involving acids acids and and alkalisalkalis

Emergency treatment Emergency treatment involving involving acids acids and and alkalisalkalis

> > 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 Emergency treatment involving involving acids acids and and alkalisalkalis

Emergency treatment Emergency treatment involving involving acids acids and and alkalisalkalis

- bring the sample of acids acids or alkalisalkalis to hospital for reference.

- call for medical aid without delay,

Distinguishing between acids and alkalis in the laboratoryDistinguishing between acids and alkalis in the laboratory

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- Use indicators, e.g.

>> litmus (石蕊 )

> > universal indicator (通用指示劑 )

> > pH meter (pH 計 )

LitmusLitmus LitmusLitmus => => Obtained from the lichen grown on the surface of rocks rocks and trtree trunksee trunks. It contains a pigment that changes colour both in acids and in alkalis.

lichen

- Litmus shows different colours in acidicacidic and alkaline alkaline environments.

=> => The solution made from it is called litmus solution (石蕊溶液 ).

LitmusLitmus LitmusLitmus

- Litmus paper (石蕊試紙 ) is a strip of filter paper which has been soaked in litmus solutionlitmus solution.

blue litmus

redlitmus

solution

bluelitmus

solution

turns blue

inalkalis

turns red

inacids

there are

Litmus Litmus solutionsolutionLitmus Litmus

solutionsolution

turns blue

inalkalis

turns red

inacids

LitmusLitmus paper paperLitmusLitmus paper paper

litmus paper red litmus paperblue

Theoretically, distilled water is neutral (中性的 ).

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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 indicatorUniversal indicatorUniversal indicatorUniversal indicator

- This is quite troublesome to use litmus

- Using universal indicatoruniversal indicator can make the testing simpler.

> > have to guess if the red one or the blue one should be used before before the test the test.

> > have to use both red and blue litmus to confirmconfirm whether the sample is neutralneutral or not.

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- Shows a wide range of colours depending on the degree of acidity and alkalinity of substances.

Universal indicatorUniversal indicatorUniversal indicatorUniversal 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 )pH scale (pH 標度 )

0 1 2 3 4 5 6 77 8 9 10 11 12 13 14

more more acidicacidic more more alkalinealkaline

neutral

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- When a few drops of universal indicator solution is added to the samplesample or a drop of samplesample 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 chartthe pH colour chart.

samplesample

orororor

pH paperpH paper

samplesample

pH colour chartpH colour chart

Universal

indicator

solution

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

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- 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 the acid inside a car battery is 0 .

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

e.g.

A car batterycontains

sulphuric acid.

A car batterycontains

sulphuric acid.

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- Can measure the pH value of a substance accurately.

pH meterpH meter

- 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 orange juice is 3.56.

The pH value of this glass

of orange juice orange juice is 3.56.

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