Acids, Bases and Salts Notes for SSC Exams
Rahul Kumar
SSC Exam Expert & Content Editor
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PDF Notes: Acids, Bases and Salts Notes for SSC Exams
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Acids, bases and salts are a basic chapter of Chemistry, and SSC asks direct questions on the natural acids, the pH of common substances, the indicators and the uses of the common salts. These acids, bases and salts notes for SSC give all the facts in simple tables with practice questions.
Acids and Bases
| Property | Acid | Base |
|---|---|---|
| Taste | Sour | Bitter |
| Touch | Not slippery | Soapy |
| Litmus paper | Turns blue litmus red | Turns red litmus blue |
| Ion in water | Gives hydrogen ions (H+) | Gives hydroxide ions (OH−) |
| Examples | HCl, H2SO4, HNO3 | NaOH, KOH, Ca(OH)2 |
- A base that dissolves in water is called an alkali.
- Strong acids are hydrochloric acid, sulphuric acid and nitric acid.
- Sulphuric acid is called the king of chemicals.
Natural Acids
| Acid | Source |
|---|---|
| Citric acid | Lemon, orange |
| Acetic acid | Vinegar |
| Lactic acid | Sour milk, curd |
| Tartaric acid | Tamarind, grapes |
| Oxalic acid | Spinach, tomato |
| Formic acid | Ant sting |
| Malic acid | Apple |
| Ascorbic acid (Vitamin C) | Amla, citrus fruits |
Common Bases and Their Uses
| Base | Common name | Use |
|---|---|---|
| Sodium hydroxide | Caustic soda | Soap making, paper industry |
| Calcium hydroxide | Slaked lime | Whitewash, water treatment |
| Magnesium hydroxide | Milk of magnesia | Antacid to treat acidity |
| Ammonium hydroxide | Ammonia solution | Window cleaner, fertiliser |
The pH Scale
- The pH scale measures how acidic or basic a solution is, on a scale from 0 to 14.
- The pH scale was introduced by S. P. L. Sorensen.
- pH 7 is neutral, below 7 is acidic and above 7 is basic.
- The lower the pH, the stronger the acid.
| Substance | Approximate pH |
|---|---|
| Gastric juice | 1.5 to 2 |
| Lemon juice | 2.2 |
| Vinegar | About 3 |
| Tomato juice | About 4 |
| Pure water | 7 |
| Human blood | 7.4 |
| Baking soda solution | About 8.3 |
| Soap solution | About 9 to 10 |
| Sodium hydroxide solution | About 14 |
- Acid rain has a pH below 5.6.
- Tooth decay starts when the pH of the mouth falls below 5.5.
Indicators
| Indicator | In acid | In base |
|---|---|---|
| Litmus | Blue turns red | Red turns blue |
| Phenolphthalein | Colourless | Pink |
| Methyl orange | Red | Yellow |
| Turmeric | Yellow | Red-brown |
Neutralisation
When an acid reacts with a base, they form a salt and water. This is called a neutralisation reaction. Example: HCl + NaOH gives NaCl + H2O. An antacid (a base) is used to cure acidity in the stomach, and a baking soda paste is applied on an ant sting (formic acid).
Common Salts and Their Uses
| Salt | Chemical name and formula | Use |
|---|---|---|
| Common salt | Sodium chloride, NaCl | Food, preserving, making other chemicals |
| Baking soda | Sodium hydrogen carbonate, NaHCO3 | Cooking, antacid, fire extinguisher |
| Washing soda | Sodium carbonate, Na2CO3.10H2O | Washing clothes, softening hard water |
| Bleaching powder | Calcium oxychloride, CaOCl2 | Disinfecting water, bleaching |
| Plaster of Paris | Calcium sulphate hemihydrate, CaSO4.½H2O | Plastering fractured bones, statues |
| Marble and limestone | Calcium carbonate, CaCO3 | Building, making cement |
Other Facts
- Aqua regia is a mixture of three parts concentrated hydrochloric acid and one part concentrated nitric acid, and it can dissolve gold and platinum.
- Metals react with acids to form a salt and hydrogen gas.
- Carbonates react with acids to give a salt, water and carbon dioxide, which turns lime water milky.
- Gypsum is CaSO4.2H2O, and heating gypsum gives plaster of Paris.
Quick Tips
- Learn the pH of five common items: gastric juice, lemon, pure water, blood and soap.
- Learn the natural acids with their sources in one table.
- Remember the common names of salts, such as baking soda, washing soda and bleaching powder.
- Remember that phenolphthalein turns pink in a base.
Quick Revision Points
- pH 7 is neutral, below 7 is acidic and above 7 is basic.
- The pH scale was introduced by Sorensen.
- Acid plus base gives salt and water.
- Baking soda is NaHCO3.
- Plaster of Paris is CaSO4.½H2O.
Practice Questions With Answers
- What is the pH of a neutral solution?
Answer: 7 - Which acid is present in lemon?
Answer: Citric acid - Which acid is present in vinegar?
Answer: Acetic acid - Which acid is present in curd?
Answer: Lactic acid - What is the chemical name of baking soda?
Answer: Sodium hydrogen carbonate - What is the chemical formula of bleaching powder?
Answer: CaOCl2 - Which indicator turns pink in a base?
Answer: Phenolphthalein - What is the pH of human blood?
Answer: About 7.4 - What is aqua regia?
Answer: A mixture of HCl and HNO3 in the ratio 3 : 1 - What do an acid and a base form when they react?
Answer: Salt and water
How to Practise This Chapter
Make three tables for natural acids, the pH of substances and the common salts, and revise them every week. Solve ten questions daily from our practice papers, the free SSC quizzes and the previous year papers page. Read the previous chapter, Blood and Circulatory System, and see all topics on the General Science notes page. Also read the General Awareness notes.
Frequently Asked Questions
What is an acid?
An acid is a substance that tastes sour, turns blue litmus red and gives hydrogen ions in water.
What is a base?
A base is a substance that tastes bitter, feels soapy, turns red litmus blue and gives hydroxide ions in water.
What is an alkali?
An alkali is a base that dissolves in water, such as sodium hydroxide and potassium hydroxide.
What is the pH scale?
The pH scale from 0 to 14 shows how acidic or basic a solution is. 7 is neutral, below 7 is acidic and above 7 is basic.
What is the pH of blood?
The pH of human blood is about 7.4, which is slightly basic.
What is neutralisation?
Neutralisation is the reaction between an acid and a base that forms a salt and water.
What are the common names of NaHCO3 and Na2CO3?
NaHCO3 is baking soda, and Na2CO3 is washing soda.
What is plaster of Paris?
Plaster of Paris is calcium sulphate hemihydrate, made by heating gypsum. It is used for fractured bones and statues.
What is aqua regia?
Aqua regia is a mixture of concentrated hydrochloric acid and nitric acid in the ratio 3 : 1, and it dissolves gold and platinum.
What is acid rain?
Acid rain is rain with a pH below 5.6, caused by gases like sulphur dioxide and nitrogen oxides.
Which acid is in an ant sting?
An ant sting contains formic acid.
How many questions come from acids and bases in SSC exams?
Usually one or two questions come from this chapter in SSC General Science papers, but the number changes from year to year.
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Rahul Kumar
SSC Exam Expert & Content Editor
Rahul is a senior SSC exam strategist with 8+ years of experience helping aspirants crack CGL, CHSL and MTS exams. He writes in-depth notification breakdowns, exam pattern guides and preparation strategies.