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Lakhmir Singh Solutions Class 10 Chemistry Chapter 2 Acids, Bases and Salts are provided here. On the basis of the chemical property of compounds, it has been divided into three groups: Acids, bases and salts, where acids and bases combine to form salts. Acid-base Chemistry plays an important role in Chemistry because every chemical reaction can be classified as an acid-base reaction.
In defining acids and bases, so many concepts came forward for the explanation of what acid is and what a base is. Mainly, three concepts are there for acids and bases, and they are the Lewis concept, Arrhenius concept and Bronsted-Lowry concept.
Acid-base Chemistry is applicable both in a laboratory and as well as in biological level, which means acids are present in the human body also. This chapter comprises an introduction to the fundamentals of acid-base Chemistry, and their reaction and uses.
Litmus is used as an indicator to identify whether the solution is acidic or basic by changing its colour from solution to solution. In an acidic solution, the litmus colour changes from blue to red, and in alkali solutions, the colour changes from red to blue.
When hydrochloric acid reacts with active metal hydrogen gas will be evolved at the surface of the metal in the form of bubbles and thus formed gas is passed through soap and bring a candle near the bubble formed. If the gas burns with a pop sound then it can be concluded that it is hydrogen.
Carbon dioxide gas is liberated when hydrochloric acid reacts with sodium hydrogen carbonate. The gas liberated thus will pass through lime water, and lime water turns milky due to the presence of carbon dioxide, further, if we do the same, the solution becomes clear.
(a) An indicator is a dye that shows a distinct change in colour when put in acid or base or as the ion concentration changes. Litmus, Methyl orange and phenolphthalein are the examples for indicators.
Olfactory indicators are those smell or odour changes when it is mixed in an acidic or basic solution. It can be used in laboratory to test whether the solution is base or acid and can perform olfactory titration
(b) Hydrogen gas is liberated when acid reacts with metal. It is observed that a formation of gas bubbles along the surface of the metal. The obtained bubbles is then passed through a soap solution and when a burning candle is brought near to the bubble, the gas present in the soap bubble will burn with a pop sound and hence it can be concluded that it is hydrogen because only hydrogen gas can make a pop sounds when it burns
While diluting an acid, it should always be done in a slow manner with a constant stirring and in small amount. The dilution of an acid is an exothermic reaction. When we add acid to water the heat that evolved gets absorbed by the water but if doing reverse, which is water added to acid a large amount of heat evolved and chances of acid splashing to the person handling will be more.
The gas evolved when the acid reacts with sodium carbonate is passed through lime water, lime water turns milky or white precipitate of calcium carbonate is formed. This confirms the presence of carbon dioxide.
22. What happens when an acid reacts with a base? Explain by taking the example of hydrochloric acid and sodium hydroxide. Give equation of the chemical equation which takes place. What is the chemical name of such a reaction?
When an acid reacts with base, then a salt and water is formed. When hydrochloric acid reacts with sodium hydroxide solution, then a neutralisation reaction takes place to form sodium chloride and water.
An eg: when a small amount of copper oxide is added to sulphuric acid, colour of the solution becomes blue and the copper oxide dissolves. The blue colour of the solution indicates the formation of copper(II) sulphate
Curds and other sour foods stuffs are acidic in nature. Acids react with metal to produce hydrogen gas thus, it spoils the food and also forms some toxic metal compounds which make the foodstuffs to become poisonous
(b) Because dry HCl does not undergo dissociation to form ions because of the absence of aqueous medium. Colour of the litmus paper changes when ions are present. Hence it does not change the colour of litmus paper
(a)Mainly, the acid behaviour of an acid is due to the presence of hydrogen ions when acids are dissolved in water. It does not show acidic character in the absence of water because the dissociation of hydrogen ions from an acid occurs in the presence of water only.
(b) The aqueous solution of an acid conducts electricity due to the presence of charged particles. The charged particles are ions here. Hydrogen and hydronium ions. They carry electric currents thus acids conducts electricity
(c) Distilled water does not conduct electricity because distilled water is the purest water which is free from all the ionic species. But rainwater is not the pure form thus it contains impurities and therefore conducts electricity.
Take about 1g of sodium chloride in a clean dry test tube. Add some concentrated sulphuric acid, a gas will be liberated and comes out through the delivery tube and test the gas evolved with a dry strip of litmus paper.
Take samples of alcohol, glucose and hydrochloric acid. Take 100 mL Beaker and take a fork and fix the nails. Place the cork inside the beaker and connect the nails to two terminals of a 6 volt battery through a bulb and a switch. Add some hydrochloric acid to the beaker and on the current. Repeat the procedure with alcohol and glucose
34. 10 ml of a solution of NaOH is found to be completely neutralised by 8 ml of a given solution of HCl. If we take 20 ml of the same solution of NaOH, the amount of HCl solution (the same solution as before) required to neutralise it will be :
Option (d) is the answer. It is given that 10ml of a solution of NaOH is completely neutralised by 8ml of a solution of HCl. Then 20ml of the solution of NaOH, which is double the amount taken before, will require double the solution of HCl taken earlier. That is 16ml to be completely neutralised.
44. When a piece of limestone reacts with dilute HCl, a gas X is produced. When gas X is passed through water, then a white precipitate Y is formed. On passing excess of gas X, the white precipitate dissolves, forming a soluble compound Z.
(c) Copper oxide is basic in nature. The reaction between a metal oxide and hydrochloric acid is similar to the neutralization where a salt and water is formed thus we can say copper oxide is basic in nature.
47. A white shirt has a yellow stain of curry. When soap is rubbed on this shirt during washing, the yellow stain turns reddish-brown. On rinsing the shirt with plenty of water, the reddish-brown stain turns yellow again.
(b) The yellow stain in the shirt when washed with soap it turns reddish brown because soap is basic and gives a reddish-brown colour when reacts with base and it turns yellow when rinsed with water due to the removal of soap
48. You have been provided with three test tubes. One of these test -tubes contain distilled water and the other two contain an acidic and a basic solution, respectively. If you are given only blue litmus paper, how will you identify the contents of each test tube?
The test tube containing distilled water will not bring any change in the colour of blue litmus paper. It turns blue to red when the same litmus paper is dipped in the solution containing acidic solution and the third test tube will have no change or effect as it is basic solution
49. A substance X which is used as an antacid reacts with dilute hydrochloric acid to produce a gas Y which is used in one type of fire extinguisher. Name the substance X and gas Y. Write a balanced equation for the chemical reaction which takes place.
Tooth decay starts when the pH of the mouth is lower than 5.5 because the mouth turns acidic when pH is below 5.5 the bacteria produces acids by the breaking down of food particles in our mouth. Enamel is made up of calcium phosphate and it is very hardest part in our body. Tooth decay so can be prevented by taking proper treatment by our self.
Universal indicator is used for testing the pH of a solution. It shows different colours at different concentrations of hydrogen ions. Indicator gives us an idea of how strong or weak an acid or base is.
It imparts a red colour when treated with universal indicator. pH is 1 as the pH decreases by 7 the solution become more acid and the hydrogen ion concentration increases. Therefore it will be a strong acid.
15. Two solutions A and B have pH values of 3.0 and 9.5 respectively. Which of these will turn litmus solution from blue to red and which will turn phenolphthalein from colourless to pink?
Solution A is having a pH of 3.0 so it will be acidic as it is lesser than 7. Thus it will change the litmus solution from blue to red and the solution B is basic as it is having a value of pH 9.5 it will turn phenolphthalein from colourless to pink.
Fresh milk has a pH of 6 and when it changes into curd the pH value will decrease because the fresh milk when converted to curd it produces lactic acid, as the production is acid the value will be lesser than 7 which causes for acidity. Acidity will increase on this conversion and tastes sour.
(c) For neutral substances like water The pH value will always be 7. A green colour will be observed when a drop of universal indicator added to the test tube contacting water and shows the neutrality of water.
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