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Let us first look at the overview of this chapter. Let us look at the topics that we are going to study in this Class 7 Acids Bases and Salts chapter.
Class 7 Acids Bases and Salts Notes
- Acids and types of Acids
- Properties of Acids and their uses
- Bases and types of Bases
- Properties of Bases and their uses
- Indicators to identify Acid and Bases
- Types of Indicators
- What are salts
- Type of Salts
What are Acids?
The substances that are sour in taste are called acids. The acid word comes from the Latin word ‘acere’ which means sour.
- The substances that contain acids in them are called acidic substances.
Types of Acids
- Organic and Mineral Acids
- Strong and Weak Acids
- Concentrated and Dilute Acids
Properties of Acids
Lets us talk about some of the important properties of acids. Here is a list of a few properties of Acids-
- Acids are sour in taste
- Acids are corrosive in nature
- Acids turn blue litmus red
- Acids on reaction with based forms salt and water
- Acids on reacting with carbonates produce CO2 gas
Uses of Acids
- Carbonic acids are used in aerated drinks
- Acetic acid is used as vinegar
- Sulphuric acids used in fertilizers
- acids are used in batteries
- used in household cleaning
- Acids such as HCl are used in steel manufacturing
What are bases?
The bases are substances that are bitter in taste and are soapy to touch. Bases give off hydroxide ions (OH–) when dissolved in water.
- The nature of bases is basic
- Soaps, shampoos, toothpaste, and Baking Soda (NaHCO3) are some examples of basic substances.
Types of Bases
- Organic Base and Mineral Base
- Strong and Weak Base
- Concentrated and Dilute Base
Properties of Bases
Let us talk about some of the important properties of bases-
- bases are basic in nature
- bases are corrosive in nature
- bases give off OH- ion in water
- bases turn red litmus blue
- bases are bitter in taste
- Some bases can dissolve in water
- bases react with acids to form salts and water
- bases react with certain metals like Zn, Al, etc to form salt and hydrogen gas
What are alkalis?
The bases that dissolve in water are called alkalis. Ex- NaOH, KOH
Uses of Bases
- Used as an antacid (Milk of Magnesia)
- used in making cement, bleaching powder
- Potash (KOH) is used in alkaline batteries
- used in making soaps, detergents
- used in manufacturing fertilizers
What are Indicators?
Indicators are substances that help us to check whether a given substance or solution is acidic, basic, or neutral in nature by changing its color.
Types of Indicators
The indicators can be divided into two categories, namely natural indicators and synthetic indicators.
These indicators are obtained from natural sources. Example litmus, China rose, red, cabbage, turmeric, etc.
Litmus is obtained from Lichens which are purple in color. When a basic solution is added, it turns blue and when an acidic solution is added it turns red.
- Litmus is available in two strips of paper- Blue and Red.
- If a blue litmus turns red then the solution is acidic in nature
- If a red litmus turns blue then the solution is basic in nature.
- It is purple in color.
- It turns red in acid and green in the base solution.
Turmeric is also used as an indicator which is easily found in our kitchens.
- The yellow color turns brick red in a basic solution and remains yellow in an acidic or neutral solution.
The petals of the china rose are used as an indicator.
- The pink solution of the china rose turns dark pink (magenta) in acids whereas it turns green in the base.
These are the indicators that are prepared by human beings in laboratories using chemicals. Examples- Phenolphthalein, Methyl Orange
Phenolphthalein is a colorless solution that turns pink when a basic solution is added to it and remains colorless if an acidic or neutral solution is added to it.
Methyl Orange- It is an orange color solution that turns yellow in the basic solution and red in the acidic solution.
It is a universal indicator. It is a mixture of different indicators. This indicator is available in a strip of paper called pH paper.
When different nature of substances is added to it, It gives different colors for different pH values.
When an acid reacts with a base salt and water is formed.
The process by which this salt and water are formed is called the Neutralisation Reaction because it neutralizes the properties of each other that is base and acid.
Acid + Base → Salt + Water + Heat
NaOH + HCl → NaCl + H2O + Heat
Types of Salts
The source can be divided into three types acidic salt, basic salt, and neutral salt.
If a strong acid is added to a weak base, the salt obtained is an acidic salt.
Example- NH4Cl is an acidic salt
HCl + NH4OH → NH4Cl + H2O
If a strong base is added to a weak acid, the salt obtained is a basic salt.
CH3COOH + NaOH → CH3COONa + Water
When a strong acid reacts with a strong base, it forms neutral salts.
Example- Sodium Chloride (NaCl)
NaOH + HCl → NaCl + H2O
Uses of Salts
Here are some of the uses of salts.
- Used as a preservative (NaCl)
- Used to add taste to food (NaCl)
- Used as a fungicide (CuSO4)
- Potassium Nitrate is used in making fertilizers (KNO3)
- Sodium bicarbonate used in fire extinguishers (NaHCO3)
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