- Acids are the substances which have a sour taste. Example, lemon juice, vinegar, tomatoes etc.
- Bases are the substance which has bitter taste. Example washing soda, baking soda etc.
- Salts are the compounds formed from acid and bases. Example sodium chloride, silver nitrate etc.
- 1 Acids and bases in laboratory
- 2 How do acids react with metals?
- 3 How do bases react with metals?
- 4 How do metals carbonates and hydro carbonates react with acid?
- 5 How acid and bases react with each other?
- 6 Reaction of metallic oxide with acids
- 7 Reaction of a non-metallic oxide with bases
- 8 What do all acids and bases have in common?
- 9 Acids and bases in water solution
- 10 How strong are acids and bases?
- 11 Importance of pH in everyday life
- 12 Salts
- 13 Chemistry of crystals
- 14 See Also
- 15 Exam preparation
- 16 References
Acids and bases in laboratory
Acid-base indicators are the substances which help us identify whether a substance is acidic or basic. These show one color in acidic medium and different color in basic medium. Indicators can either be natural or synthetic. Litmus and turmeric (video) are natural indicators. Litmus paper turns red when dipped in an acidic solution and turn blue when dipped in a basic solution. Similarly, turmeric becomes reddish-brown in basic solution. This is the reason why clothes stained by curries (containing turmeric) turn reddish-brown on washing with soap.
The indicator which gives different odor in an acidic and basic medium are called olfactory indicators. Example onion, clove, and vanilla can be used as olfactory indicators.
Know More: Acid-Base Indicators
How do acids react with metals?
Acids react with active metals like Zinc, magnesium etc. to form salts with the evolution of hydrogen gas.For example: Reaction of zinc with dilute sulfuric acidIn this reaction zinc replaces hydrogen from the acid and combines with SO4– and forms a compound called salt.
How do bases react with metals?
Some bases like sodium hydroxide and potassium hydroxide react with active metals like Zinc and aluminum to liberate hydrogen gas along with the formation of salts.For example: reaction of sodium hydroxide with zincSodium zincate is the salt formed in this reaction. But such reaction is not possible with all the metals. Only very reactive metals show such type of reactions with bases.
How do metals carbonates and hydro carbonates react with acid?
On passing carbon dioxide through lime water, white precipitate of calcium carbonates are formedLimestone, chalks and marbles are different forms of calcium carbonates. On passing excess of carbon dioxide following reaction takes place:All metal carbonates and hydrogen carbonates react with acids to give corresponding salts.
Know More: The Lime Cycle
How acid and bases react with each other?
Neutralization is defined as a process in which an acid reacts with a base to form salt and water i.e.For example: Neutralization reaction between sodium hydroxide and hydrochloric acid.Know More: Neutralization Reaction and Net Ionic Equations for Neutralization Reactions
Reaction of metallic oxide with acids
Metal oxides react with acid to give salt and water.For example, the reaction of copper oxide and HCl:Just like acids react with base, metallic oxide reacts with acids to gives salt and water. Hence, metallic oxides are also knows as basic oxides.
Reaction of a non-metallic oxide with bases
Reaction between carbon dioxide and calcium hydroxide is the best example to understand the reactions of non-metallic oxide with bases.Calcium hydroxide which is base reacts with carbon dioxide to give salt and water. This is similar to the reaction between acid and base thus we can conclude that non-metallic oxide are acidic in nature.
What do all acids and bases have in common?
All the acids generate H2 gas on reaction with metals. However, all compounds containing hydrogen are not acidic. Acids contain ions, a cation and an anion. It is seen that acids are able to conduct electricity. However, hydrogen containing compounds such as glucose and alcohol do not conduct electricity. This shows that glucose and alcohol do not contain ions.
Since the acid contains H+ cations, this suggests that acid produce H+ ions which are responsible for their acidic properties. Similarly, alkalis such as sodium hydroxide, calcium hydroxide etc. will be able to conduct electricity because of presence of ions (Na+, Ca2+, etc.). Hence, acids and bases have ions in common and hence, they can conduct electricity.
Acids and bases in water solution
Acids acts as acids, i.e. they release their H+ ions only in the presence of water. HCl without water will not release H+ ions. This is because H+ ions can not exist alone. In presence of water, HCl dissociates into H+ and Cl–.After dissociation of dry HCl in water, a number of water molecules remains attached to H+ and Cl-. Hence H+ ion combines with water molecules to form ion, called hydronium ion (H3O+).Similarly, bases generate OH– ions in the presence of water. The bases that are soluble in water are called alkalis.Hence, the neutralization reaction can be written as:In these reaction H+ ions from acid combines with the OH– ions given by the base. Hence the effect of acid is nullified by base and vice-versa.
Special care must be taken while dissolving acids and bases with water. The process of dissolving acids and bases with water is a highly exothermic reaction. Strong acids such as sulphuric acid, nitric acid must be added slowly to water while constant stirring. Never add water to concentrated acid as the heat generated may cause the mixture to splash out and cause burns. The glass container may also break due to excessive heating.
The process of mixing acids with water is called dilution and the solution is said to be diluted. Adding water decreases the concentration of ions (H3O+ / O–) per unit volume.
How strong are acids and bases?
The process of mixing acids with water is called dilution and the solution is said to be diluted. Adding water decreases the concentration of ions (H3O+ / O–) per unit volume. We also know that the concentration of H+ is higher in an acidic solution as compared to a basic solution. Bases have lower concentration of H+. Also, different acids have different concentration of H+ depending on which we call it a strong acid or weak acid. Hence, if we create a universal indicator that can check the concentration of H+ in the solution, we will be able to identify, strong acids, weak acids, strong bases and weak bases. A scale was developed which measures the hydrogen ion concentration in a solution and was named as pH scale. The pH scale consist of universal indicators (mixture of number of indicators) and shows different color at different pH values.
- The pH value of a neutral solution is 7
- If the pH value is less than 7 then the solution is acidic
- If the pH value is more than 7 then the solution is basic
The concentration of H+ is highest at pH 1 and decreases as we go to a higher pH. Also, the concentration of OH– is the least at pH 1 and is the highest at pH 14. At pH 7, the concentrate of H+ and OH– is equal and the solution is said to be neutral.
The strength of acidic or basic solution depends upon the number of H+ and OH– ions produced. Higher the hydronium ion concentration, lower is the pH value. Acids that give more H+ ions are considered as strong acids and vice-versa and hence acids have lower pH values.
For example, when the pH values of HCl and acetic acid are measured, we will find out that pH value of acetic acid is more than HCl because HCl releases more H+ as compared to acetic acid and hence, HCl is a strong acid.
Know More: Check pH of various solutions
Importance of pH in everyday life
Are plants and animal pH sensitive?
Most of the reaction taking place in our body is in the narrow pH range of 7.0 to 7.8. If the pH falls below 7.0 or rises above 7.8, the survival of living organism becomes difficult.
For example the pH of rain water is less than 7.0 (as it is acidic due to dissolution of CO, SO etc of the air). When the pH of rain water falls below 5.6, it becomes more acidic, it is called acid rain. Acid rain reduces the pH of water bodies which makes it difficult for the survival of aquatic animals.
Like animals, plants also require an optimal range of pH for their survival. Soil pH is a very important factor in plant health – if the soil is too acidic or too alkaline, plants will be unable to absorb nutrients properly, and your garden won’t grow. Different types of plants have a different pH requirement. However, it is ideal to maintain a soil pH of 5-6.5.
pH in our digestive system
Our stomach produces hydrochloric acid which is helpful in digestion of food. This HCl does not harm the stomach as it has a special lining of protective material. The acid kills the harmful bacteria that may enter in stomach along with that we eat. However, at times the amount of HCl produced inside the stomach increases which causes pain and irritation in stomach. It can be cured by taking medicines called ‘antacids’. The most commonly used antacid contains magnesium hydroxide (milk of magnesia) which is a weak base and neutralizes the excess acid.
pH change as the cause of tooth decay
The enamel of our teeth is the hardest substance in our body. Chemically it contains calcium phosphate which is insoluble in water. But if the pH of the mouth falls below 5.5, i.e. our mouth is moderately acidic; the dissolution of calcium phosphate starts, i.e. tooth decay begins. Bacteria in the mouth produce acids by degradation of sugar and food particle remaining in the mouth after eating. The best way of preventing tooth decay is to clean your teeth every day.
Self-defense of animals and plants through chemical warfare
Insects such as honey bee or yellow ant use acids for their self-defense. They inject acids into the skin of the enemy which causes pain and irritation. To get relief, we apply the solution of a mild base like baking soda. Similarly, neetle plants have leaves with stinging hairs.
Salts are the ionic compounds consisting of two parts, one part carrying a positive charge (cation) and other part consisting of negative charge (anion). The positive and negative ions are present in such a manner that total positive charge is equal to total the negative charge.
Salts have been categorized into different families. Salts having the same positive or negative radicals are said to belong to the same family.
Chloride family: Sodium chloride and potassium chloride,
Sulphate family: Sodium Sulphate, Calcium Sulphate, Potassium Sulphate, etc.
Know More: Salts
pH of salts
Neutralization reaction is the reaction between acid and bases to form salt and water. Salts of strong acid and strong bases are neutral with pH value of 7. On the other hand, salts of strong acid weak base are acidic with pH value less than 7. Salts of strong base and weak acid are basic in nature, with pH value of more than 7.
Chemicals from common salts
Common salt is sodium chloride with the formula, NaCl. This is the salt that is used in food. Seawater contains many salts dissolved in it including sodium chloride. Seawater is one of the main source of common salt. Solid salt deposits are also found in several parts of the world. These large crystal, also called rock salt are often brown because of impurities. Rock salt is mined like coal.
Common salt is used as a raw material for the manufacturing of many chemicals that we use in our day to day life such as sodium hydroxide, baking soda, washing soda, bleaching powder, etc.
Sodium Hydroxide (Caustic soda)
Sodium hydroxide is manufactured by electrolysis of an aqueous solution of sodium chloride called brine. This method is called chloralkali process because the products of electrolysis are chlorine (chlor) and sodium hydroxide (alkali).Chlorine moves towards the anode (positive charge) where they lose an electron to form Cl atoms. These Cl atoms combine to form chlorine gas (Cl2).
Hydrogen moves towards the cathode (negative charge). Here, they gain an electron to form hydrogen atoms which combine to form hydrogen gas (H2). NaOH solution is formed at the cathode.
Bleaching powder is generally represented by the formula CaOCl2, called calcium oxychloride. The chlorine produced during the manufacture of caustic soda is used for the manufacture of bleaching powder. It is produced by the action of chlorine gas on dry slaked lime, Ca(OH)2. The following reaction takes place:Uses of Bleaching powder
- The most important use of bleaching powder is in textile industries for bleaching cotton and linen, in paper industries for bleaching wood pulp and in laundry for bleaching washed clothes.
- Used for disinfecting drinking water by killing germs.
- As an oxidizing agent in chemical industries.
Know More: Bleaching Powder
The soda commonly used in the kitchen for making tasty crispy pakoras is baking soda. Baking soda is sodium hydrogen carbonate with the formula, NaHCO3. It is also called sodium bicarbonate. Baking soda is manufactured from sodium chloride as one of the raw materials. The method is known as Solvay process or ammonia-soda process.NaHCO3 is a mild non-corrosive base. If solid sodium hydrogencarbonate is heated or its aqueous solution is boiled, it gives out carbon dioxide. The carbon dioxide evolved helps in making breads rise up and become fluffy.Uses of baking soda
- The excess acid formed in the stomach due to eating of spicy food is easily neutralized by sodium hydrogen carbonate. Hence, it is used as an ingredient of antacid medicines.
- It is also used in soda-acid fire extinguishers.
Making Baking Powder
Baking powder is a mixture of sodium hydrogen carbonate and a mild edible acid like tartaric acid or citric acid. In making certain food items such as bread, cake etc.
Washing soda is sodium carbonate containing ten molecules of water of crystallization, i.e. it is sodium carbonate decahydrate. Thus, its molecular formula is Na2CO3.10H2O. It is also a basic salt.
- It is used in the laundry for cleaning of clothes.
- It is used for removing permanent hardness of water.
- It is used in the manufacture of a number of useful products like glass, soap, paper, borax etc.
- It is used as a laboratory reagent. For example, its standard solution can be prepared to carry out the acid-base titration.
Know More: The story of washing soda
Chemistry of crystals
The chemical formula of washing soda is Na2CO3.10H2O. Thus, one formula unit contains 10 water molecules. Similarly, there are many other crystalline salts containing water molecules. For example crystalline copper sulfate contain 5 water molecules (CuSO4.5H2O) and gypsum contains 2 water molecules (CaSO4.2H2O). The fixed number of water molecules present in one formula unit of the salt is called water of crystallization. Hence, a crystallized salt may look dry, but it contain water in the form of water of crystallization.
Plaster of Paris
Chemically, plaster of Paris (P.O.P) is calcium sulfate hemihydrates, i.e., it containing half molecule of water crystallization. It is represented by formula CaSO4.1/2H2O. A half molecule of water of crystallization in P.O.P signifies that one water molecule is shared by two formula units of CaSO4.
P.O.P is prepared by heating gypsum. At high temperature, gypsum loses water molecule and becomes calcium sulfate hemihydrates (CaSO4.1/2H2O). This is called Plaster of Paris. On mixing P.O.P with water it changes to gypsum which is a hard solid mass.Uses of Plaster of Paris
- In medical science, it is used for setting fractured bones in the right position and in making casts in dentistry.
- Making toys, casts for statues, decorative material etc
- Making chalks for writing.
- Making fire proof material.
- Harmful effects of acid rain
- Prevention of tooth decay
- What is a Hydronium Ion?
- How to dilute an Acid?
- The strengths and weaknesses of acids and bases
- Video Summary: Acids, Bases, and Salts
- More about gypsum
- MCQs: Acids, Bases, and Salts
- Quiz: Acids, Bases, and Salts
- Extra Questions 1: Acids, Bases, and Salts
- HOTS: Acids, Bases, and Salts
- NCERT Solutions: Acids, Bases, and Salts
- MCQs, Short, and Long Questions: Acids, Bases and Salts
- Extra Questions 2: Acids, Bases, and Salts
- Acid Rains
- Advantages of HCl in our stomach
- How plaster of Paris is formed?
- How to find water of crystallization?
- Electrolysis of Brine
- How Do Acids And Bases React With Metals
- Turmeric as indicator
- Acid-Base Indicators
- The Lime Cycle
- Neutralization Reaction and Net Ionic Equations for Neutralization Reactions
- Check pH of various solutions
- pH level of Human Body
- Bleaching Powder
- The story of washing soda
- Baking Soda, Washing Soda, And Plaster Of Paris