Indicators: Litmus, Turmeric, China Rose, Red Cabbage, Phenolphthalein, Methyl Orange YouTube Lecture Handouts

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Indicators: Litmus, Turmeric, China Rose, Red Cabbage, Phenolphthalein, Methyl Orange| Acid, Base


Latin Word: β€œacere” means sour

Citrus fruits & Vinegar

Acids can be organic or mineral

Strong or weak

Concentrated or diluted

  • Acids that are found occurring naturally in plants and animals are called organic acids
  • Acids that are derived from inorganic (does not come from either) sources are called mineral acids
  • Acids are sour in taste. They are soluble in water.
  • Acids are corrosive in nature. They can cause burns on clothes and skin.
  • Zinc + Hydrochloric acid Zinc chloride + Hydrogen gas (Acids react with metals to form salt and hydrogen gas)
  • Hydrochloric acid + Calcium carbonate Calcium chloride + Water + Carbon dioxide (Acids react with carbonates to form salt, water and carbon dioxide gas.)
  • Sodium hydroxide (base) + Hydrochloric acid (acid) Sodium chloride + Water (Acids react with bases to form salt and water.)
  • Used in fertilizers (nitric acid) , dyes, detergents – HCl in steel manufacturing; acetic acid (vinegar) for preservative
  • Several acids are used in descaling (removing salt deposits formed when water is heated) equipment such as kettles and water heaters.
  • Ascorbic acid occurs naturally as vitamin C in citrus fruits and fresh vegetables
  • Organic or Inorganic
  • Strong or Weak
  • Concentrated or Dilute
  • Organic: Naturally in plants and animals
  • Inorganic or mineral –
  • Strong acid – highly corrosive HCl, – causes burns; stored in glass bottles
  • Weak acid – not that corrosive - citric acid , Acetic acid , oxalic acid
  • Concentrated – small amount of water
  • Dilute – more amount of water - 3 % Hydrochloric acid is an example of dilute acid - Most acids used in the laboratory are diluted with water because their concentrated form can be too dangerous to handle
Most Acids Used in the Laboratory
Lactic acidMilk, Curd
Oxalic acidTomatoes
Tartaric acidTamarind
Citric acidLemons, oranges
Ascorbic acidAmla, guava
Acetic acidVinegar
Maleic acidApple
Formic acidAnt sting, nettle sting


  • Bitter & Soapy Baking Soda, Toothpaste, Shampoo
  • Examples of strong bases are sodium hydroxide and potassium hydroxide . bases are corrosive in nature and should be handled with care
  • Weak bases are not as corrosive as strong bases.
  • Magnesium hydroxide , ammonium hydroxide and copper hydroxide are an example weak basis
  • Some bases, but not all, can dissolve in water. Bases that dissolve in water are called alkalis. Sodium hydroxide and potassium hydroxide , are examples of alkalis.
  • Example – soap, detergent, drain cleaner, antacids, fertilizers like ammonium hydroxide; KOH in batteries and fertilizers

Name of base are found in

  • Calcium hydroxide in Lime water
  • Ammonium hydroxide in Window cleaner
  • Sodium hydroxide/Potassium hydroxide in soap
  • Magnesium hydroxide in Milk of magnesia
  • Zinc + Sodium hydroxide Sodium zincate + hydrogen gas (Bases react with certain metals such as zinc and aluminium to form salt and hydrogen gas.)
  • Ammonium hydroxide + Hydrochloric acid Ammonium chloride + Water (Bases react with acids to form salt and water.)


Test whether acid or base

An indicator is a substance that helps us to identify whether a given solution is acidic or basic or neutral with the help of a change in colour.

Indicator can be natural or synthetic


  • Extracted from lichens it is mauve (purple) colour in distilled water. When added to an acidic solution, it turns red and when added to a basic solution, it turns blue. It is available in the form of a solution, or in the form of strips of paper, known as litmus paper.
  • Generally, it is available as red and blue litmus paper
  • The solutions which do not change the colour of either red or blue litmus are known as neutral solutions. These substances are neither acidic nor basic.

China Rose

  • To make the indicator, fresh petals are left in warm water for some time until the water acquires a pink colour.
  • Petals of the China rose or Hibiscus flower are used to make a juice that is used as a natural indicator.


Turmeric or haldi is a common ingredient used in Indian dishes. It can also be used as a natural indicator. Turmeric solution is yellow in colour.

Turmeric stain on my white shirt is turned to red when it is washed with soap. It is because the soap solution is basic.

Red Cabbage

Juice obtained from red cabbage is also used as an indicator. This indicator is purple in colour.


Methyl Orange

Methyl orange is an orange-coloured solution. It turns red in acidic and yellow in basic solutions

Universal Indicator

Universal Indicator
  • Universal indicators are a mixture of different indicators that gives a different colour for different pH values. These indicators are available in the form of strips of paper called pH paper.
  • The colour obtained when a few drops of a solution are added to the pH paper strip is compared to a standard colour chart to estimate the pH of the solution.
  • Ph of 0 to 6 is acidic; 7 is neutral (water) and 8 to 14 is basic
  • The Universal Indicator Color Guide shows that Universal Indicator turns red when it is added to a strong acid, it turns purple when it is added to a strong base, and it turns a yellowish-green when it is added to a neutral solution. All acids in the range of 1 to 4 turn the indicator red.

PH Scale

PH Scale Acidic


  • When phenolphthalein is added to the acid solution in the flask, it remains colourless. As the base is added to the acid, after a certain point, the solution turns pink.
  • Change in colour of the solution to pink indicates that the entire volume of the acid has undergone neutralization by the base and the salt has been formed.
  • Indigestion: Antacids such as Milk of Magnesia (magnesium hydroxide) and baking soda (sodium hydrogen carbonate) are used to neutralize the excess acid, relieving the symptoms of indigestion.
  • Ant Bite: The acid is neutralized by rubbing moist baking soda (sodium bicarbonate) , calamine solution (containing zinc carbonate) or even toothpaste on the area.
  • Soil: Acidic soil can be neutralized using slaked lime or quicklime, which is a base. If the soil is too basic, organic matter is added to it.
  • Waste Water: Slaked lime or calcium hydroxide is often used to neutralize the acidic substances in the effluent.
  • Neutral Substance: Salts, most cosmetics, lotions, eye drops have pH of 7 - Safe to ingest and leave on skin.


  • In neutralisation reaction a new substance is formed. This is called salt. Salt may be acidic, basic or neutral in nature. Thus, neutralization can be defined as follows: The reaction between an acid and a base is known as neutralisation. Salt and water are produced in this process with the evolution of heat. Acid + Base gives Salt + Water (Heat is evolved)
  • Strong Acid + Weak base Acidic Salts () formed by strong acid hydrochloric acid and the weak base ammonium hydroxide .
  • Weak acid + strong base Basic Salts (sodium acetate formed by weak acid acetic acid and the strong base sodium hydroxide .
  • Strong acid + strong base Neutral Salts formed by and NaOH

Uses of Salts

  • Sodium chloride: Flavoring agent & preservative
  • Sodium carbonate: Detergents
  • Sodium bicarbonate: Baking, antacids and fire extinguishers
  • Potassium nitrate: Gun powder and fertilizers
  • Calcium carbonate : Marble & cement
  • Copper sulphate : Fungicide

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