Acids, Bases and Salts

• Acids are sour in taste
• The chemical nature of such substances is acidic
• Acid turns blue litmus red
• It gives hydrogen ion when dissolves in water
• Do not give any colour with phenolphthalein indicator
• Do not absorb carbon dioxide gas
• Acids do not react with ammonium salt
• Acids are generally found in Vinegar, Curd, Spinach, lemons, Citrus fruits, Amla, Tamarind, grapes, unripe mangoes, Citrus fruits such as oranges, etc.

• Bases are bitter in taste and soapy to touch
• Base turns red litmus blue
• The nature of such substances is said to be basic
• It gives hydroxide ions when dissolves in water
• It give pink colour with phenolphthalein indicator
• Some bases like NaOH absorbs carbon dioxide gas
• Bases are generally found in lime water, soap, window cleaner, Milk of Magnesia
• Reacts with ammonium salt to give ammonia gas

Curd, lemon juice, vinegar, orange juice etc. are acids and baking soda, lime water etc. are bases.

Indicators are special type of substance that are used to taste whether a substance is acidic or basic in nature. It change the colour of acidic or basis substances when added into it. Turmeric, litmus, etc. are some natural indicators.

Litmus is extracted from lichens. It is most commonly used as an indicator to determine the chemical nature of substance. It has mauve or purple colour in distilled water. When it is 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.

To test the nature of a substance for an Acid or a base or a neutral, litmus test is performed in which the Acid turns blue litmus red, Bases turn red litmus blue and has no effect on neutral substance.

The Distilled water is neutral. It is neither sour (Acidic) nor bitter (Basic), to very its chemical nature, we can perform litmus test. It neither turns blue litmus red nor red litmus blue hence we can say, distilled water is a neutral substance.

The substances which are neither acidic, nor basic are called neutral substance. These substances neither turn blue litmus red nor red litmus blue, for example distilled water, sugar solution etc.

Turmeric is a natural indicator which when reacts with bases turns it into red colour; here soap solution is basic so it turns red.

On the basis of the property of acids and bases he can differentiate all the drinks. Like an Acidic drink will have a sour taste and will turn blue litmus red. A basic drink will turn red litmus red. A neutral drink will not change the colour of red or blue litmus. A part from this he can also use turmeric solution for checking the drinks.

Turmeric is yellow in colour, when it is exposed to neutral (Sugar Solution) or acidic substances (Hydrochloric Acid) it will retain its yellow colouration. However, if turmeric is exposed to more alkaline substances (sodium hydroxide) it becomes a dark pink/red. So first we detect sodium hydroxide -a basic substance by a colour change from yellow to dark or red. Then will test for an acid or neutral substance with indication of no colour change. Now out of these two, we will mix one with already tested solution for basic substance -sodium hydroxide with dark or red colour, if on mixing the colour reverses back to yellow, the liquid is an acid and the remaining third liquid is neutral.

Red litmus paper when dipped in a solution, if it remains red then the nature of the solution is neutral.

Universal indicator gives a range of colour that can be used to determine the level of acidity or basic of a solution, this level is called the pH value.

Neutralisation is a process in which an acid solution when mixed with base solution, react with each other to produce a salt and water along with generation of heat. Salt so produced, may be acidic, basic or neutral in nature. In this process the acidic nature of the acid and the basic nature of the base are destroyed.
Acid + base salt + water. (heat is evolved)
For example: H C l + N a O H NaCl + H2O.

Acids do not show acidic behaviour in absence of water because hydrogen ions dissociates from an acid only in the presence of water.

Sometimes when we consume spicy food, our stomach releases excess of hydrochloric acid which causes indigestion or acidity. An antacid tablets contains base like milk of magnesia (magnesium hydroxide), it neutralises the effect of excessive acid and bring reliefs.

The sting of an ant contains formic acid. When an ant bites, it injects the acidic liquid into the skin. The effect of the sting can be neutralised by rubbing some moist solution of a basic substance such as baking soda (sodium hydrogen carbonate) or calamine solution, which contains zinc carbonate.

The wastes of many factories contain acids. If they are allowed to flow into the water bodies, the acids will kill fish and other organisms. The factory wastes are, therefore, neutralised by adding basic substances into it.

The acids which are found in plants and animals are called organic acids, for example vinegar contains acetic acid, lemon juice contains citric acid etc.

a. Cholic acid,b. uric acid,c. nucleic acid,d. Tartaric acid e. oxalic acid

Salts are the ionic compounds generally formed by neutralisation of an acid with base. They can be acidic, basic as well as neutral. Example acidic salts: sodium bicarbonate, basic salts: magnesium chloride, neutral salt: sodium chloride.

Salts are the ionic compounds generally formed by neutralisation of an acid with base. They can be acidic, basic as well as neutral. Example acidic salts: sodium bicarbonate, basic salts: magnesium chloride, neutral salt: sodium chloride.

A salt derived from more than one acid or more than one base is called mixed salt. Example: bleaching powder, potash alum etc.