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NCERT Solutions for Class 10 Science CBSE - Topperlearning

Science textbook of Class 10th deals with the disciplines such as Physics, Chemistry, Biology and Environmental Science as integrated. However, as per the examination point of view, we can divide this svience into three parts Physics, Chemistry and Biology. Environment Science part is covered in the Ncert solutions for 10th science question syllabus.

You can select your desired chapter from the list and start your learning. As previously stated, Environment Science part is covered in the Biology syllabus. So we have total three subjects in Ncedt subject, Physics, Chemistry and Biology. NCERT Solutions for Class 10 Science will introduce you to qusetion basic concepts of the chapters as the questions are given that check your all round understanding of the chapter.

You ncert solutions for 10th science question get ahead of your competitors through these solutions. You also need to pay attention to time management to get good numbers. To divide ncert solutions for 10th science question you should divide each topic according to time. Give more and more time to that topic in which you are weak. We often do not give full time to repeat the topics that come to us.

It is necessary that you understand the chapter first and then proceed. Many times what happens is that you go to the exam by rote learning and if the question in the paper gets a little different then there is panic. In such a situation, if you understand svience chapter concepts, then you will be ready to answer in every way.

The first unit has total five chapters. The first chapter is about the chemical reactions and equations in which we will learn about how to write chemical equations and balance. Also, we will learn about the various types of chemical reactions. In the second chapter, we will learn about the various types of acids, bases and salts and their reactions with metals and non-metals. The third chapter will take us to the world of metals and non-metals where we will learn about their properties and reactions among.

The fourth chapter is about the carbon and its compounds where we will ofr about the properties of carbons and chemical substances containing carbon. In the fifth chapter, we will learn about the classification of elements and their evolution.

The Second unit consists of four chapters that solutikns from sixth to ninth. The sixth chapter is about the various life processes which human need for their survival.

In the seventh chapter, we will talk about the parts of the human body which questin engaged in control and coordination activities. The eighth chapter deals with reproduction activities in unicellular and multicellular organisms. The ninth chapter, we will learn how the offsprings look alike. The third unit is How things works which have four chapters. In the tenth chapter, we will learn about light and its phenomena reflection and refraction in a detailed manner.

The eleventh chapter is about the human eye and some optical phenomena in nature. The twelfth chapter deals with the electricity in which we will learn electric circuit and resistance.

In queetion thirteenth chapter, ncert solutions for 10th science question effects of electric current and its applications. The fourth unit has three chapters in it. The fourteenth chapters talk about the various sources of energy such as conventional and non-conventional sources. The fifteenth chapter is about our environment in which we will learn about the eco-systems, food chains and how human activities contribute in degrading its quality.

The last chapter is about dor conservation of natural resources. In previous classes, students were introduced to physical and chemical changes. The chemical changes signify the chemical reactions. Ncert solutions for 10th science question indicators sciene chemical reactions are explained with some indicators like change in physical state, change in color, change in temperature and evolution of gas.

These are explained with some experimental examples. After that writing of chemical equation has been explained. It is symbolic representation of chemical reactions. Also, it has been explained that how such equations can be more informative.

For example, balancing a chemical equation will signify that the chemical reactions follow law of conservation of mass. Other information like physical states and conditions required for reactions are mentioned. After that various types of chemical reactions are explained are discussed. The types of chemical reactions are �combination ncert solutions for 10th science question, decomposition reaction, displacement reaction, double decomposition reaction.

On basis of energy, exothermic and endothermic reactions are mentioned. Redox reactions are explained which are combination of reduction reaction and oxidation reaction. All types of reactions are explained with suitable example with their respective chemical equation. Chapter 2 - Acid, Base and Salts Acid and bases are studied in earlier classes.

Acids are ncert solutions for 10th science question as substances which are sour in taste and turn blue litmus red. Examples of questioh are sour fruits like, Bases are defined as substances which are bitter in taste and turns red litmus blue. Examples of bases are neem, clove, vinegar. Here, acids and bases are defined chemically.

Bases are chemically those ncwrt which generate OH- ions in aqueous solutionIf not they are weak acids. After that, various chemical and olfactory indicators are discussed; this indicates the presence of acids or base in the solution.

Bases are said to be strong if whole of them get dissociated in water to form OH- ions. For example, Methyl orange is a chemical indicator. It turns red in acidic solution and yellow in basic solution. Olfactory indicators are indicators which changes odor after coming in contact with acid and base. For example, smell of clove vanishes when kept in contact with acid. After ncert solutions for 10th science question acids and bases reactions are discussed with metals, metal oxides and metal carbonates.

Reactions between acids and bases are also discussed. They are known as neutralization reactions. Salt is one of the products formed by acid, base reaction.

The various types of salts are discussed based on the strength of acid or base. The pH scale Indicates if the solution is acidic, basic our neutral. It is an scale from So, is acidic, ncert solutions for 10th science question is neutral, basic solution.

Universal indicator is a mixture of several indicators. Chloro-alkali process is performed of salt solution.

The various chemical substances are formed after reactions, directly or in-directly are used for various process. Their formation and uses are explained in this chapter. Chapter 3 - Metals and Non-Metals The chapter starts with physical properties of metals and non-metals.

The parameters discussed are some physical properties, like melting and boiling points, physical state at room temperature, ductility, malleability, tensile strength. The metals and non �metals are differentiated on the basis of physical properties. But there are some expectations based on physical properties. For example iodine is non-metal but has lustrous appearance as metal.

Mercury is metal but liquid at room temperature. There are more such exceptions. Therefore, classification of metals and non-metals, are based on chemical properties. Chemical reactions of metals with oxygen gas, water, acids and other metal salts are discussed.

The reactions sokutions their condition depends upon the reactivity series. The metals on top of reactivity series are sodium and Potassium. They perform vigorous reactions. Nature of metallic oxides is discussed. Generally Metal oxides are basic in nature. But, some of them like aluminum oxide and zinc oxide can be both acidic and basic and hence known as amphoteric oxides.

After that how such reactions takes place is discussed. Ionic bond formation is discussed. Such bond formation can be represented in two forms.

Electrons are loosed by metals and gained by non-metals. One get positively charged and another get negatively charged. They get attracted ncert solutions for 10th science question a strong bond is formed.

The first one is electronic configuration. The bond formation is discussed through Bohr model. Another method is Lewis structure or electron-dot structure. The metals and non-metals are written ncert solutions for 10th science question their symbol and dots.

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He observed that when the elements were arranged in increasing order of their atomic masses, there was a periodic recurrence in their physical and chemical properties. It was much accurate than previous models. It also had some demerits. Finally, modern periodic came into existence. Atomic number was considered to be criteria for classification. Elements with same group have same number of outermost electron. Elements in same period have same number of outermost shell.

A particular increase to decrease in certain pattern can be predicted. Many such trends are studied in this chapter. Such processes are digestive system, respiration system, circulation system etc.

All these things are important to leave. The thing is to consume food through digestive system, perform oxidation of food which involves the process of respiration, and transportation of food and water which is done through circulation. This chapter starts with process of nutrition. The process in which an organism takes in food, utilizes it to get energy, for growth, repair and maintenance, etc. Other modes of nutrition are autotrophic and heterotrophic nutrition which are discussed in chapter.

Autotrophic nutrition is done by plants by photosynthesis. Heterotrophic nutrition is done by animals. Different types of Heterotrophic nutrition are discussed. Parasitic Nutrition, saprophytic Nutrition and Holozonic Nutrition are different types of heterotrophic nutrition.

Cellular nutrition is done by unicellular organisms which has been discussed in this chapter. Next topic is nutrition by human beings. It starts with mouths which include salivary glands, tongue and teeth. The food goes to stomach through oesophagus. The food goes to stomach. Liver secretes greenish yellow liquid called bile juice. Pancreas lies behind the lower portion of stomach.

It secretes pancreatic juice which contains many digestive enzymes. All such processes are discussed in this digestive system. Next is respiration. The process of respiration involves: a Gaseous exchange i. Breathing: Intake of oxygen from the atmosphere and release of CO 2. And b Cellular respiration: Breakdown of simple food in order to release energy inside the cell. Both are discussed. The human respiration system is discussed with some special attention.

Pharynx ,bronchio lungs, diaphragm are different elements of human respiratory system. Mechanisam of process involves inhale and exhale. Both are explained. Circulation involves the process of transportation of food and other materials from one place to another. The blood is pumped through heart and transported through veins. So, all of them are discussed. Different components of blood are discussed-Red blood cells and White blood cells. Four chambers of heart are discussed.

In plants, We have discussed earlier how plants take in simple compounds such as CO 2 and photosynthesise energy stored in their chlorophyll-containing organs, namely leaves. The other kinds of raw materials needed for building plant bodies will also have to be taken up separately. For plants, the soil is the nearest and richest source of raw materials like nitrogen, phosphorus and other minerals. The absorption of these substances therefore occurs through the part in contact with the soil, namely roots.

It has been discussed in details. The biological process involved in the removal of these harmful metabolic wastes from the body is called excretion. Different organisms use varied strategies to do this. It is discussed in details for human beings. The excretory system of human beings includes a Ncert Solutions For Class 10th Science Chapter 2 Questions pair of kidneys, a pair of ureters, an urinary bladder and urethra. Chapter 7 - Control and Coordination System Earlier, we had started with a notion we all have, that if we see something moving, it is alive.

Some of these movements are in fact the result of growth, as in plants. A seed germinates and grows, and we can see that the seedling moves over the course of a few days, Control and coordination are the functions of the nervous system and hormones in our bodies. The responses of the nervous system can be classified as reflex action, voluntary action or involuntary action. The nervous system uses electrical impulses to transmit messages.

The nervous system gets information from our sense organs and acts through our muscles. Chemical coordination is seen in both plants and animals.

Hormones produced in one part of an organism move to another part to achieve the desired effect. A feedback mechanism regulates the action of the hormones. Chapter 8 - How do organisms reproduce? Reproduction, unlike other life processes, is not essential to maintain the life of an individual organism. It involves creation of a DNA copy and additional cellular apparatus by the cell involved in the process.

Various organisms use different modes of reproduction depending on their body design such as fission, fragmentation, regeneration, budding, spore formation and vegetative propagation. Sexual reproduction involves two individuals for the creation of a new individual.

Modes of sexual reproduction allow for greater variation to be generated. Reproduction in flowering plants involves transfer of pollen grains from the anther to the stigma which is referred to as pollination followed by fertilisation. The male reproductive system in human beings consists of testes which produce sperms, vas deferens, seminal vesicles, prostate gland, urethra and penis. The female reproductive system in human beings consists of ovaries, fallopian tubes, uterus and vagina.

Sexual reproduction in human beings involves the introduction of sperm in the vagina of the female. Fertilisation occurs in the fallopian tube.

Chapter 9 - Heredity and Evolution We have seen that reproductive processes give rise to new individuals that are similar, but subtly different.

We have discussed how some amount of variation is produced even during asexual reproduction. Heredity and evolution deals with the fact � the long-term consequences of the accumulation of variations. The fact of sex determination in newborn individual is completely solved. Evolution can be worked out by the study of not just living species, but also fossils.

Complex organs may have evolved because of the survival advantage of even the intermediate stages. Changes in the non-reproductive tissues caused by environmental factors are not inheritable indicates about different traits like Acquired and Inherited. Speciation may take place when variation is combined with geographical isolation.

Evolutionary relationships are traced in the classification of organisms. Study of the evolution of human beings indicates that all of us belong to a single species that evolved in Africa and spread across the world in stages. Chapter 10 - Light: Reflection and Refraction Light is source of energy which generates sensation of vision in human beings.

In this chapter first reflection of light is discussed. Reflection is governed by its laws. The chapter is concerned with laws of reflection. Here we are basically concerned with the spherical mirrors. After that image formation by spherical mirrors are discussed.

The different types of spherical mirror, convex and concave are taught. The various terms related with spherical mirrors like centre of curvature, radius of curvature etc, focus, pole etc are discussed with ray diagrams. Uses of spherical mirror has been discussed in chapter.

Mirror formula is the way to relate object distance, image distance and focal length of mirror. Magnification is the ratio of size of image by size of object. This is related to ratio of image distance and object distance. Distances are majored from pole of mirror. Sign convention is kept in mind to find relative distances of image and object. Refraction is the phenomena of bending of light when light travels from one medium to another.

The phenomena of refraction can be understood easily by the concepts of refractive index and optical density. This is better explained by an example of rectangular glass slab. This example is dealt. After that concept of Lens is explained. It is transparent medium bounded by refractive index. Types of Lens �converging and diverging is discussed. Example of converging lens double convex lens and diverging double concave lens.

Image formation and terminology is discussed for both convex and concave lens. Lens formula relates focal length of lens with image distance and object distance. Magnification is related with image and object distance. Sign convention is kept in mind. Power of lens is also discussed. Numerical based on lens formula and mirror formula are to be solved.

Chapter 11 - Human Eye and colorful world Human eye, its components, are discussed. The process of by which human eye can see objects is discussed. The ability of the eye to focus on both near and distant objects, by adjusting its focal length, is called the accommodation of the eye. The smallest distance, at which the eye can see objects clearly without strain, is called the near point of the eye or the least distance of distinct vision.

For a young adult with normal vision, it is about 25 cm. Defects of vision is discussed with their corrective measures using suitable ray diagrams. The common refractive defects of vision include myopia, hypermetropia and presbyopia. Myopia short-sightedness � the image of distant objects is focussed before the retina is corrected by using a concave lens of suitable power. Hypermetropia far-sightedness � the image of nearby objects is focussed beyond the retina is corrected by using a convex lens of suitable power.

The eye loses its power of accommodation at old age. The splitting of white light into its component colours is called dispersion. Scattering of light causes the blue colour of sky and the reddening of the Sun at sunrise and sunset.

Chapter 12 - Electricity Electricity is required for many thing around us. What is electricity? It is phenomena related to flow of charge. The concept of electric current and electric potential difference voltage is taught. Flow of electrons moving through a conductor constitutes an electric current.

Conventionally, the direction of current is taken opposite to the direction of flow of electrons. The SI unit of electric current is ampere. To set the electrons in motion in an electric circuit, we use a cell or a battery. A cell generates a potential difference across its terminals.

It is measured in volts V. Resistance is a property that resists the flow of electrons in a conductor. It controls the magnitude of the current. Ohms Law, which establish relationship between potential difference and current is discussed. Concept of resistance and resistivity is studied. Resistance is property of any conductor to resist flow of current. The resistance of a conductor depends directly on its length, inversely on its area of cross-section, and also on the material of the conductor.

Resistance of conductor having unit length and cross section is defined specific resistance. Series and parallel combination of resistors are discussed. In series current is same and in parallel potential difference is same across resistors. The unit of power is watt W. One watt of power is consumed when 1 A of current flows at a potential difference of 1 V.

The commercial unit of electrical energy is kilowatt hour kWh. Chapter 13 - Magnetic effects of Current In this chapter, relationship between magnetism and electricity is discussed. At first some basics of magnetism is discussed with magnetic field lines.

A compass needle is a small magnet. Its one end, which points towards north, is called a north pole, and the other end, which points towards south, is called a south pole. Magnetic Field lines are used to represent a magnetic field. A field line is the path along which a hypothetical free north pole would tend to move.

The direction of the magnetic field at a point is given by the direction that a north pole placed at that point would take. The denser magnetic field lines indicate more magnetic field strength. After that, magnetic field due to current carrying conductor is discussed. A metallic wire carrying an electric current has associated with it a magnetic field whose direction is given by right hand thumb rule.

An electromagnet consists of a core of soft iron wrapped around with a coil of insulated copper wire. A current-carrying conductor when placed in a magnetic field experiences a force. Phenomena related to this are explained. This is the basis of an electric motor. An electric motor is a device that converts electric energy into mechanical energy. Working and construction of electric motor is discussed.

Electricity generation through magnet is discussed. The phenomenon of electromagnetic induction is the production of induced current in a coil placed in a region where the magnetic field changes with time. The magnetic field may change due to a relative motion between the coil and a magnet placed near to the coil. If the coil is placed near to a current-carrying conductor, the magnetic field may change either due to a change in the current through the conductor or due to the relative motion between the coil and conductor.

A generator converts mechanical energy into electrical energy. It works on the basis of electromagnetic induction. Two types of generators are discussed. DC generator generates direct current as a cell. AC generators generates Alternating Current whose direction keep on changing after a time period.

Domestic circuiting is discussed. In our houses we receive AC electric power of V with a frequency of 50 Hz. The different aspects is discussed. The concept of live wire, neutral wire and earth wire is discussed. Earth wire, insulated green which provide, passage for leakage of current. Chapter 14 - Sources of Energy Our energy requirements increase with our standard of living.

In order to fulfil our energy requirements, we try to improve the efficiency of energy usage and also try and exploit new sources of energy. The chapter is all about different sources of energy. Three types of sources of energy are discussed. The first one is conventional sources of energy. These are sources of energy we keep on using from long years. It include fossil fuels, thermal power plant and hydroelectric power plant.

These are discussed with advantages and disadvantages. After that, energy sources conventionally used, but improvised due to technology has been discussed. For example, cow dung used initially had low calorific value, and combustion of it causes lot of pollution. But, with help of technology, it can converted into Bio-gas, which is an efficient and pollution free fuel.

Similarly, with the help of technology, wind energy can be harnessed by placing many wind mills in a large field creating a wind farm.

Charcoal obtained from wood is better fuel than wood. All these things are discussed. The third category is Non-conventional sources of energy.

In this category, we have energy sources like solar energy, in which energy is generated through solar cell and solar panel, or by solar cooker. Energy from ocean can be generated through waves, tides or through temperature difference between upper and lower level of ocean.

Energy can also be obtained from earth crust, known as geo-thermal energy. The solution which turns red litmus to blue will be a basic solution. The blue litmus paper formed here can now be used to test the acidic solution. The solution which turns the blue litmus paper to red will be the acidic solution.

Question 1 Why should curd and sour substances not be kept in brass and copper vessels? Answer: Curd and sour substances should not be kept in brass and copper vessels because these and other sour food-stuffs contain acids which can react with the metal of the vessel to form poisonous metal compounds which can cause food poisoning and affect our health adversely. Question 2 Which gas is usually liberated when an acid reacts with a metal?

Illustrate with an example. How will you test for the presence of this gas? Answer: i Hydrogen H 2 gas is liberated when an acid reacts with a metal. Take some zinc granules in the test tube. Add about 5 mL dilute hydrochloric acid slowly. Soon the reaction between zinc and hydrochloric acid starts and hydrogen gas is evolved.

When passed through soap solution, it gets trapped into bubbles. Bring a burning candle near the soap bubble filled with gas. The soap bubble bursts and hydrogen gas burns with a pop sound. Question 3 Metal compound A reacts with dilute hydrochloric acid to produce effervescence.

The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride. Answer: As the end product is calcium chloride and the gas formed is carbon dioxide, the metal compound A must be calcium carbonate. Therefore, the reaction between calcium carbonate and hydrochloric acid is.

Question 1 Why do HCl, HNO 3 , etc show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character? HCl, HNO 3 , etc. Therefore, alcohol and glucose do not show acidic character. Question 2 Why does an aqueous solution of an acid conduct electricity?

Answer: The aqueous solution of an acid conducts electricity due to the presence of charged particles called ions in it. Question 3 Why does dry HCl gas not change the colour of the dry litmus paper? Question 4 While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid? Answer: While diluting an acid it is recommended that the acid should be added to water and not water to the acid because if water is added to concentrated acid to dilute it, then a large amount of heat is evolved at once.

Answer: When a given amount of an acid is added to water, there is a fixed number of hydronium ions per volume of the solution. On dilution, the number of hydronium ions per volume decreases and concentration decreases. Question 6 How is the concentration of hydroxide ions OH � affected when excess base is dissolved in a solution of sodium hydroxide?

Answer: The concentration of hydroxide ions will increase when excess base is dissolved in a solution of sodium hydroxide, but it happens to a limited extent only after which the concentration becomes almost constant. Question 1 You have two solutions A and B. The pH of solution A is 6 and pH of solution B is 8. Which solution has more hydrogen ion concentration? Which of this is acidic and which one is basic? Answer: A pH value of less than 7 indicates an acidic solution, while greater than 7 indicates a basic solution.

Since solution A has more hydrogen ion concentration, solution A is acidic and solution B is basic. If yes, then why are these basic? But these are far less in number than OH � ions that is responsible for their basic nature.

Question 4 Under what soil condition do you think a farmer would treat the soil of his fields with quick lime calcium oxide or slaked lime calcium hydroxide or chalk calcium carbonate? Answer: If the soil is too acidic having low pH then it is treated with materials like quick lime calcium oxide or slaked lime calcium hydroxide or chalk calcium carbonate. Question 1 What is the common name of the compound CaOCl 2?

Answer: Bleaching powder. Question 2 Name the substance which on treatment with chlorine yields bleaching powder. Answer: Slaked lime Ca OH 2. Question 3 Name the sodium compound which is used for softening hard water.

Answer: Sodium carbonate. Question 4 What will happen if a solution of sodium hydrogen carbonate is heated. Give the equation of the reaction involved? Answer: Solution of sodium hydrogen carbonate on heating gives sodium carbonate and carbon dioxide gas is evolved. Question 5 Write an equation to show the reaction between plaster of Paris and water. Question 1 A solution turns red litmus blue, its pH is likely to be a 1 b 4 c 5 d 10 Answer: d Question 2 A solution reacts with crushed-egg shells to give a gas that turns lime water milky.

Question 4 Which one of the following types of medicines is used for treating indigestion? Question 6 Compounds such as alcohol and glucose also contain hydrogen but are not categorised as acids. Describe an activity to prove it. The bulb does not glow in this case also.

This shows that alcohols and glucose are not acids. Question 7 Why does distilled water not conduct electricity, whereas rainwater does? Answer: Distilled water does not conduct electricity because it does not contain any ionic compound like acids, bases or salts dissolved in it.

Rainwater, while falling to the earth through the atmosphere, dissolves an acidic gas carbon dioxide from the air and forms carbonic acid H 2 CO 3. Hence, due to the presence of carbonic acid which provides ions to rainwater, the rainwater conducts electricity. Question 8 Why do acids not show acidic behaviour in the absence of water?

The acid produces hydrogen ions only in the presence of water. So in the absence of water, an acid will not form hydrogen ions and hence will not show its acidic behaviour. Which solution is a Neutral b Strongly alkaline c Strongly acidic d Weakly acidic e Weakly alkaline Arrange the pH in increasing order of hydrogen ion concentration. Question 10 Equal lengths of magnesium ribbons are taken in test tubes A and B.

In which test tube will the fizzing occur more vigorously and why? Answer: Fizzing will occur more vigorously in test tube A. Being strong acid, the hydrochloric acid solution contains a much greater amount of hydrogen ions in it due to which the fizzing will occur more vigorously in test tube A containing hydrochloric acid. The fizzing is due to the evolution of hydrogen gas which is formed by the action of acid on the magnesium metal of magnesium ribbon.

Question 11 fresh milk has a pH of 6. How do you think the pH will change as it turns into curd? Explain your answer. Answer: pH of milk falls below 6 as it turns into curd due to the formation of lactic acid during this process. Lactic acid present in it reduces its pH value. Question 12 A milkman adds a very small amount of baking soda to fresh milk.

Answer: a Milk is made slightly alkaline so that it may not get sour easily due to the formation of lactic acid in it. Question 13 Plaster of Paris should be stored in a moisture proof container. Explain why? Answer: Plaster of Paris should be stored in a moisture proof container because the presence of moisture can cause slow setting of plaster of Paris by bringing about its hydration.

This will make the plaster of Paris useless after sometime. Question 14 What is a neutralisation reaction? Give two examples. Answer: The reaction between an acid and a base to form salt and water is called a neutralisation reaction. Question 15 Give two important uses of washing soda and baking soda. Answer: Uses of washing soda : i Washing soda is used in glass, soap and paper industries. Uses of baking soda : i Baking soda is used as an antacid in medicines to remove acidity of the stomach.

One of them contains distilled water and the other two contain an acidic solution and a basic solution respectively. Solution: The contents of each test tube would be identified by change in colour of red litmus paper.

For example, when we wet the red litmus paper with the basic solution, it changes into blue colour. Put the changed blue litmus paper in the solution which turns the blue to red will be the acidic solution. The solution, which has no effect on any litmus paper, will be neutral and hence it will be distilled water. Question 2 Why should curd and sour substances not be kept in brass and copper vessels?

Solution: Curd and other sour foodstuffs contain acids, which can react with the metal of the vessel to form poisonous metal compounds which can cause food poisoning and damage our health.

Question 3 Which gas is usually liberated when an acid reacts with a metal? Solution: When an acid reacts with metal, a salt and hydrogen gas is formed. Question 4 Metal compound A reacts with dilute hydrochloric acid to produce effervescence. Solution: The gas that extinguishes a burning candle is carbon dioxide, which is formed by the action of dilute hydrochloric acid on a metal carbonate and produces effervescence.

Now, since one of the compounds formed is calcium chloride, it shows that the metal compound is calcium carbonate. Thus, the metal compound A is calcium carbonate CaCO 3.

Calcium carbonate reacts with dilute hydrochloric acid to form calcium chloride, carbon dioxide and water. This can be written as:. The compounds such as glucose and alcohol also contain hydrogen but they do not show acidic character. Question 6 Why does an aqueous solution of acid conduct electricity?

Solution: The aqueous solution of an acid conducts electricity due to the presence of charged particles called ions in it. Question 7 Why does dry HCl gas not change the colour of the dry litmus paper? Solution: Dry HCl gas does not contain any hydrogen ions in it, so it does not show acidic behaviour. Question 8 While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?

Solution: Diluting an acid should be done by adding concentrated acid to water gradually with stirring and not by adding water to concentrated acid. The heat is evolved gradually when a concentrated acid is added to water for diluting an acid and the large amount of water is easily absorbed. If, however, water is added to concentrated acid to dilute it, a large amount of heat is evolved at once. The heat generated may cause the mixture to splash the acid on our face or clothes and cause acid burns.

Question 10 How is the concentration of hydroxide ions OH- affected when excess base is dissolved in water? Solution: When the solution of a base is diluted by mixing more water in it, the concentration of hydroxide ions OH � ions per unit volume decreases. Question 11 You have two solutions A and B. Solution: The pH of a solution is inversely proportional to its hydrogen ion concentration.

This means that the solution having lower pH will have more hydrogen ion concentration. In this case, solution A having a lower pH of 6 will have more hydrogen ion concentration. Solution A is acidic and solution B is basic. Solution: Acids produce hydrogen ions in water. So, when an acid is added to water, the concentration of hydrogen ions in water increases.

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