Chemistry is an important part of SSLC Science, and one of the most scoring chapters is “Acids, Bases and Salts.” This chapter explains the properties of acids and bases, pH values, neutralization reactions, salts, and their daily life applications. The uploaded LBA document contains important MCQs, short answers, and long-answer questions from this chapter.
Learning Points of the Chapter
According to the document, the chapter mainly covers:
- Physical properties of acids and bases
- Chemical properties of acids and bases
- Strength of acids and bases
- Importance of pH in daily life
- Salts and their uses
- Preparation and applications of common salts
What are Acids?
Acids are substances that produce hydrogen ions in aqueous solution.
Examples of Acids
- Hydrochloric acid $\ce{(HCl)}$
- Sulphuric acid $\ce{(H2SO4)}$
- Nitric acid $\ce{(HNO3)}$
- Acetic acid $\ce{(CH3COOH)}$
Properties of Acids
- Sour in taste
- Turn blue litmus paper red
- Conduct electricity in aqueous solution
- React with metals to release hydrogen gas
- pH value is less than 7
Common Natural Acids
- Citric acid → Lemon
- Lactic acid → Curd
- Methanoic acid → Nettle plant
- Hydrochloric acid → Gastric juice
The document also asks questions about natural acids such as methanoic acid present in nettle plant leaves.
What are Bases?
Bases are substances that produce hydroxide ions in water.
Examples of Bases
- Sodium hydroxide $\ce{(NaOH)}$
- Calcium hydroxide $\ce{(Ca(OH)2)}$
- Potassium hydroxide $\ce{KOH}$
Properties of Bases
- Bitter in taste
- Feel soapy
- Turn red litmus paper blue
- pH value is greater than 7
Metal oxides are called basic oxides because they react with acids to form salt and water.
pH Scale
The pH scale is used to measure acidity and basicity.
0 ≤ pH ≤ 14
- pH < 7 → Acidic
- pH = 7 → Neutral
- pH > 7 → Basic
Importance of pH in Daily Life
- Tooth decay starts when mouth pH becomes less than 5.5
- Antacids are used to reduce excess stomach acid
- Soil pH affects plant growth
- Acid rain has pH less than 5.6
Questions related to pH values and acidic/basic nature are repeatedly asked in examinations.
Neutralization Reaction
A neutralization reaction occurs when an acid reacts with a base to produce salt and water.
$\ce{NaOH + HCl -> NaCl + H2O}$
The document highlights this as one of the most important reactions in the chapter.
Reactions of Acids
1. Acid + Metal
Acid reacts with metals to release hydrogen gas.
$\ce{Zn + H2SO4 -> ZnSO4 + H2}$
Hydrogen gas can be tested using the “pop” sound test.
2. Acid + Metal Carbonate
Acids react with metal carbonates to release carbon dioxide gas.
$\ce{Na2CO3 + 2HCl -> 2NaCl + H2O + CO2}$
Carbon dioxide turns lime water milky.
Important Salts and Their Uses
1. Washing Soda
Chemical Name
Sodium Carbonate Decahydrate
$\ce{Na2CO3 . 10H2O}$
Uses
- Removes permanent hardness of water
- Used in glass and soap industries
2. Baking Soda
Chemical Name
Sodium Hydrogen Carbonate
$\ce{NaHCO3}$
Uses
- Used in baking powder
- Used in fire extinguishers
- Used as antacid
3. Bleaching Powder
Chemical Formula
$\ce{CaOCl2}$
Uses
- Disinfecting drinking water
- Bleaching cotton and paper
4. Plaster of Paris
Chemical Formula
$\ce{CaSO4 . \dfrac{1}{2}H2O}$
Uses
- Used for fractured bones
- Making statues and toys
Plaster of Paris should be stored in moisture-proof containers because it absorbs water easily.
Important Exam Questions
One Mark Questions
- What is the neutralization reaction?
- What are amphoteric oxides?
- What are bases?
- Write two uses of washing soda.
- What is baking powder?
Two Mark Questions
- Why should acid be added to water?
- Explain the importance of pH in daily life.
- Why does rainwater conduct electricity?
- Explain curd formation with pH change.
Three and Four Mark Questions
- Explain chlor-alkali process.
- Differentiate acids and bases.
- Explain tooth decay and prevention.
- Write preparation and uses of bleaching powder.
These questions are repeatedly found in the LBA document.
Preparation Tips for Students
- Learn all chemical equations properly.
- Remember formulas of salts and compounds.
- Practice pH-based questions carefully.
- Study litmus paper colour changes.
- Revise reactions involving metals and carbonates.
