Chapter 5 Grade VII PPT e content
E N D
Presentation Transcript
Ch-5 Acids,Bases and Salts By-Kirti Nanoti DA,Pune
Learning Objectives • To enable the students to know about acid, base and salts. • To enable the students to differentiate the acids and bases. • To study different indicators and their color changes on different substances • To understand neutralization reaction and formation of salt. • To study neutralization by taking examples from everyday life. • Uses of Acid & Base in day- to-day life.
Acids: • Many food items such as lemons, curd, vinegar and orange taste sour because of the presence of acid in them. • Acidic Substances are the substances that contain acid in them. • Natural Acids are the acids that occur in nature, for example, acids found in fruits are natural acids. • Acids can be classified into mineral acids and organic acids. • Most of the mineral acids are strong and corrosive in nature. They are extremely dangerous to handle. E.g- Hydrochloric acid, nitric acid, sulphuric acid, etc. • Organic acids are naturally occurring weak acids. They are non-corrosive in nature, and are safe to handle even in their concentrated state. • Examples: Acetic acid (present in vinegar), Lactic acid (present in milk), Citric acid (present in citrus fruits), etc.
Base: • A base is a chemical substance that has a bitter taste and a soapy texture. • Bases are found in different substances such as bleach, ammonia, washing powder and soap. Bases are also called Alkali when soluble in waterBases turn the colour of red litmus paper to blue. • Salts are ionic compounds that contain two groups of positively charged ions (H+) and negatively charged ions (OH-). • In chemistry, salt is produced when acids and bases are combined together in equal proportions
Indicators: • We cannot taste every substance and find its nature. Therefore, we use indicators. • An indicator is a substance that can determine if the substance is acidic or basic in nature. • The indicators indicate the presence of an acid or base in a substance by changing their colour. For Example Turmeric, China rose petals and Litmus are some natural indicators. Red cabbage: It turns acidic solutions to red and basic solutions to blue. • Olfactory Indicators Olfactory indicators are substances whose smell changes when they are mixed with an acidic or a basic solution. Onion, clove oil and vanilla extract are examples of such indicators
Indicators and color changes: • Natural indicators:- Litmus ,turmeric , petals of flowers(marigold , china rose) Synthetic indicators:- Phenolphthalein, Methyl Orange . • Turmeric Test:-When turmeric sol. Reacts with base it turns pale yellow to reddish-brown in color . No colour change with acids • China Rose indicator turns acidic solutions to dark pink (magenta)and Basic solutions to green. • When a drop of Phenolphthalein is added to acid, it remains unchanged. When a drop of Phenolphthalein is added to base it turns colorless to pink . When a drop of methyl orange is added to an acid it turns red in colour. When a drop of methyl orange is added to a base it turns yellow in colour
Neutralization reaction • Neutralization reaction is the process in which an acid reacts with a base to produce salt and water while evolving a good amount of heat. In this reaction, both the acid and base loose their properties to produce a new substance which is neutral in nature, i.e., the salt formed will neither be acidic nor basic. Acid + Base → Salt + Water [with evolution of heat] • The preparation of common salt (sodium chloride) involves the neutralization reaction between hydrochloric acid and sodium hydroxide (base). The acid and base reacts to produce sodium chloride (salt), water and heat. • The reaction is represented by the following equation: • HCl + NaOH → NaCl+ H2O
Acid Rain When the rainwater has increased amounts of acids in it, it is called Acid Rain. The acid rain is formed because of the presence of air pollutants such as Nitrogen dioxide, Carbon dioxide and Sulphur dioxide in the air. These pollutants mix with the rainwater and form acids such as Nitric acid, Sulphuric acid and Carbonic acid respectively. The acid rain in severely affect the vegetation, animal life and even buildings of the region where it falls.
Neutralization in Everyday Life Ant Bite • The irritation of the skin due to ant bite is caused because of the presence of formic acid that the ant injects into the skin while biting. Hence we use a basic substance to neutralize the effect. For Example, baking soda or hydrogen carbonate, calamine solution or zinc carbonate are generally used to treat ant bites Soil Treatment • Plants need a soil which is neutral in nature but using chemical fertilizers on soil can turn it into acidic. To treat acidic soil we use quicklime (calcium oxide) or slaked lime (calcium hydroxide). Basic soil can be treated by adding organic substances to it as they release acids while decomposing into the soil. Factory Wastes • The factory waste is acidic in nature and cannot be directly dumped anywhere. Hence bases are added to it before it falls off into a river or stream so that the aquatic life does not get affected.
Indigestion We know that our stomach produces hydrochloric acid which helps in the digestion of food. But sometimes the stomach releases too much of acid which leads to indigestion or sometimes hyperacidity. Hence, we need to neutralize this acid by taking substances that are basic in nature commonly known as antacids. For Example, milk of magnesia is a basic substance that can neutralize the acid of the stomach.
