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Acids Bases and Indicators

FLOWER EXTRACT AS ACID/BASE INDICATOR

One way of classifying substances in Chemistry is by finding out whether they are basic or acidic using flower extract .Acids are found in many naturally occuring materials which are used in everyday life. some occur in the foods we eat such as lemons and other citrus fruits, vinegar and some soft drinks. In the laboratory there are various acids which are used for example Sulphuric and Hydrochloric acid. These are referred to as mineral acids.

Bases are substances that react acids to give a salt and water.

Objectives

By the end of the topic you should be able to:

1. Prepare flower extracts as acid- base indicators

2.Use the flower extract as acid- base indicators

3.Use common commercial acid- base indicators to identify acids and bases

4.State simple properties of acid and bases

5.List uses of acids and bases

PREPARATION OF ACID/BASE INDICATOR FROM FLOWER EXTRACTS

Crush some flower petals in a mortal using a pestle.Add a little of propanone or ethanol.

Grind the petals until enough extract of the flower is collected. Filter into a clean test tube.

The flower extract can be used to test if a substance is basic or acidic by adding the extract to different solutions.

EXERCISE

From your observation certain substances show the same colour. Acidic solutions show red colour, Basic solutions show blue while Neutral solutions show green colour.The flower extract acts as an acid-base indicator.
Therefore an indicator is a substance that shows a definite colour in Acid or Basic solution.

COMMERCIAL INDICATORS

Flower extract can be used as acid / base indicators.

 However they give inconsistent results when used.

Commercial indicators give more consistent results.

This is because their composition does not change.

Example of commercial indicators include,

BLUE AND RED LITMUS PAPER

LITMUS SOLUTIONS


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PHENOLPHTHALEIN


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Commercial indicators can be used to test whether a substance is acidic or basic. The following experiment shows what is observed when commercial indicators are added to different acids and bases. Dilute Hydrochloric acid is placed in test-tube 1, 2 and 3 while ammonia solution is placed in test-tube 4,5 and 6.Two drops of methyl orange is added to test-tube 1 and 4. Two drops of phenolphthalein indicator are added to test-tube 2 and 5. Blue and red litmus papers are placed intotest-tube3 and 6

 

 

 

UNIVERSAL INDICATOR AND pH SCALE

Different indicators form different colours in various solutions. The indicators provide no information about the strength of an acid or base. The universal indicator exhibit a range of colours in acids and bases depending on the acidic and basic strength of the solution. These ranges of colours are compared to a continuous acid/base scale called the pH scale. The pH scale has values ranging from 1 - 14.

Substances with

pH 1-3 are classified as strongly acidic

pH 4-6 are weakly acidic

pH 7 is neutral

pH 8-11 are weakly basic,

pH 12-14 are strongly basic.

 

The colours of a universal indicator correspond to different pH values, ranging from 1-14.

A pH chart can be used to show both the colour and pH of a substance.

 

The pH chart can be used to show the strength of different solutions.

Sulphuric acid turns red hence a strong acid.Ethanoic acid turns yellow indicating that it is a weak acid.Water turns to green showing that it is neutral.Ammonia solution turns to blue showing that it is a weak base while Sodium Hydroxide solution turns to a deep blue solution indicating that it is a strong base.

 

ALKALINITY AND ACIDITY ON THE pH SCALE

PROPERTIES OF ACIDS AND BASES

Acids and bases have different properties.

Acids have a shape taste while bases have a slippery feel between the fingers.

QUIZ

REACTION OF METALS WITH DILUTE ACIDS

Acids react with some metals forming a salt and Hydrogen gas. Zinc, Magnesium, Iron, and Lead metals react with dilute acids forming a salt and hydrogen gas only. Lead reacts for a short while with dilute sulphuric acid and hydrochloric acid and stops because insoluble Lead (II) sulphate and lead (II) Chloride respectively . However Copper does not react with dilute acids.The following equations shows how metals react with Hydrochloric acid.

 

REACTION OF CARBONATES AND HYDROGEN CARBONATES WITH DILUTE ACIDS

Carbonates and Hydrogen Carbonates react with dilute acids. Calcium Carbonate is placed in a test tube and 4cm3 of dilute Nitric acid is added.The test-tube is corked and a delivery tube fitted which is then immersed in another test-tube containing lime water.

Acids react with carbonates and hydrogen carbonates forming corresponding salts, water and carbon (IV) oxide gas.

The Carbon (IV) Oxide gas forms a white precipitate with lime water.

REACTION OF DILUTE ACIDS WITH METAL OXIDES/HYDROXIDES

Metal oxides/ hydroxides react with dilute acids. Acids react with metal oxides and metal Hydroxides forming their corresponding salts and water as the only products. Dilute Sulphuric acid is added to a test tube containing Copper (II) Oxide.

Metal oxides and Hyroxides are bases. They react with acids to form salts and water. This reaction is referred to as neutralization.

 

 

CONCLUSION

Acids have a sour taste, turns blue litmus red; react with metals producing hydrogen gas.

They also react with carbonates and hydrogen carbonates forming a salt, carbon (IV) Oxide and water.

Metal oxides are bases and they react with acids forming a salt and water only

CONCLUSION

Acids have a sour taste, turns blue litmus red; react with metals producing hydrogen gas.

They also react with carbonates and hydrogen carbonates forming a salt, carbon (IV) Oxide and water.

Metal oxides are bases and they react with acids forming a salt and water only

USES OF ACIDS AND BASES

Acids and bases have various uses in daily life. Some of the uses are illustrated in the pictures below.Hydrochloric acid is found in our stomach. It helps in digestion of food. Excess acid in the stomach causes stomach upsets. To remove excess acid antiacid tablets such as Eno, actal or milk of Magnesia (Magnesium Hydroxide solution) are used.

Eno

Baking powder


Used in baking to raise the dough.

Car battery

Car battery contains sulphuric acid

Tooth paste

Tooth paste contains calcium Hydroxide

USES OF ACIDS AND BASES

Acids and bases have various uses in daily life. Some of the uses are illustrated in the pictures below

Eno/Actal

Used to remove excess acid in the stomach.

Baking powder

Used in baking to raise the dough.

Car battery

Tooth paste

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