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Chemistry X | Acid, Bases and Salts: NCERT Solved Questions

August 31st, 2015

Acid, Bases and Salts: NCERT Solved Questions

Question 1. You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution respectively. If you are given only red litmus paper, how will you identify the contents of each test tube ?


We will dip the red litmus paper in all the test tubes, the test tube in which red litmus changes to blue., contains, basic solution. Now dip the so changed blue litmus paper in other two test tubes, the test tube in which blue litmus changes to red is acidic solution and the third test tube will contain distilled water.

Question 2. Why should curd and sour substances not be kept in brass and copper vessels ?


Curds and other sour substances contain acids which react with brass and copper to form toxic substances which are not suitable for health and consumption. So, it is advisable not to store curds and other sour substances in brass or copper vessels.

Question 3. Which gas is usually liberated when an acid reacts with a metal ? Illustrate with an example. How will you test the presence of the gas ?


Usually hydrogen gas is liberated when an acid reacts with a metal. For example, when zinc granules react with dilute sulphuric acid, zinc, sulphate and hydrogen are produced.

Zn (s) + H2S04 (aq) clip_image002 ZnS04 (aq) + H2 (g)

Hydrogen gas burns with a ‘pop’ sound.

Question 4. A 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.


Metal compound A reacts with dilute hydrochloric acid to form a gas which extinguishes burning candle means produced gas is carbon dioxide. Other product is calcium chloride, so compound A is carbonate or hydrogen carbonate of calcium. We can present the reaction as follows:

Question 5. Why do HCl, HNO3 etc. show acidic character in aqueous solutions while solutions of compounds like C2H5OH and glucose do not show acidic character ?


HCl, HNO3 show acidic character in aqueous solutions because they produce H+ (aq) ions, but solutions of C2H5OH and glucose do not produce H+ ions, so they do not show acidic character.

Question 6. Why does an aqueous solution of an acid conduct electricity ?


An aqueous solution of an acid conduct electricity because in aqueous solution acid produces cations and anions.

Question 7. Why does dry HCl gas not change the colour of dry litmus paper ?


H+ions are responsible for acidic character of HC1 and change of litmus paper. H+ ions are formed in the presence of water only. That’s why, dry HCl gas cannot change the colour of dry litmus paper.

Question 8. While diluting the acid why is it recommended that acid should be added to water and not water to the acid ?


Mixing water and acid is an exothermic reaction. When water is added to acid due to small amount of water, evolved heat will change it to vapour and acid will spill out and may cause injury. So, it is advised to mix acid to water, not water to acid.

Question 9. How is the concentration of hydronium ions (H3O+) affected when a solution of an acid is diluted ?


when a solution of an acid is diluted, the concentration of hydronium ions (H30+) is decreased.

Question 10. How is concentration of hydroxide ions (OH) affect when excess base is dissolved in a solution of sodium hydroxide ?


When excess base is dissolved in a solution of sodium hydroxide concentration of hydroxide ions (OH) is increased.

Question 11. You have two solutions A and B. pH of solution A is 6 and pH of solution B is 8. Which solution has more hydrogen ion concentration ? Which of the above solution is acidic and which one is basic ?


Solution having more hydrogen ion concentration – Solution A.

Acidic solution – Solution A.

Basic solution – Solution B.

Question 12. What effect does the concentration of H+ (aq) have on the acidic nature of the solution ?


Acidic nature of a solution is directly proportional to the H+ (aq) ion concentration. If H+ (aq) ion concentration of one solution is higher than the other, it will be more acidic than the other.

Question 13. Do basic solution also have H+ (aq) ions ? If yes, then why are they basic ?


Yes, basic solution also have H+ (aq) ions. If a solution has H+ (aq) ions and (OH) ions concentration is neutral and when (OH) ions > H+ ions, solution is basic.

Question 14. Under what soil conditions do you think a farmer would spread or treat the soil of his fields with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate).


Quick lime, slaked lime and chalk are basic in nature, so soil should be treated using these substances when the soil is acidic in nature

Question 15. What is the common name of compound CaOCl2 ?


The common name of compound CaOCl2 is bleaching powder.

Question 16. Name the substance which on treatment with chlorine yields bleaching powder ?


Dry slaked lime.

Question 17. Name the sodium compound which is used for softening of hard water.


Washing soda (sodium carbonate) is used for softening of hard water.

Question 18. What will happen if the solution of sodium hydrogen carbonate is heated ? Give the equation of the reaction involved.


On heating NaHCO3 changes to Na2CO3

NaHCO3clip_image002[1] Na2CO3 + H20 + CO2

Question 19. Write an equation to show the reaction between plaster of Paris and water.


CaSO4. clip_image005 H20 + 1clip_image005[1] H20 clip_image002[2] CaS04. 2H20

Objective Questions

Question 20. A solution turns red litmus blue, its pH is likely to be

(a) 1

(b) 4

(c) 5

(d) 10

Answer: (d)

Question 21. A solution reacts with crushed egg shells to give a gas that turns lime water milky, the soultion contains.

(a) NaCl

(b) HCl

(c) LiCl

(d) KCl.

Answer: (d)

Question 22. 10 mL of a solution of NaOH is found to be completely neutralised by 8 mL of a given solution of HCl. If take 20 mL of same solution of NaOH, the amount of HCl solution (the same solution as before) required neutralise it will be

(a) 4 mL

(b) 8 mL

(c) 12 mL

(d) 16 mL.

Answer: (d)

Question 23. Which one of the following types of medicines is used for treating indigestion ?

(a) Antibiotic

(b) Analgesic

(c) Antacid

(d) Antiseptic.

Answer: (c)

Question 24. Write word equations and then balanced equation when

(a) Dilute sulphuric acid reacts with zinc granules

(b) Dilute hydrchloric acid reacts with magnesium ribbon

(c) Dilute sulphuric acid reacts with aluminium powder

(d) Dilute hydrochloric acid reacts with iron filings



(a) Zinc (s) + Sulphuric acid (aq) clip_image002[3] Zinc sulphate (aq) + Hydrogen (g)

Zn (s) + H2S04 (aq) clip_image002[4] ZnS04 (aq) + H2 (g)

(b) Magnesium (s) + Hydrochloric acid (aq) —> Magnesium chloride (aq) + Hydrogen (g)

Mg (s) + 2HC1 (aq) clip_image002[5] MgCl2 (aq) + H2 (g)

(c) Aluminium (s) + Sulphuric acid (aq) clip_image002[6]Aluminium sulphate (aq) + Hydrogen (g)

2A1 (s) + 3H2S04 (aq) clip_image002[7]A12(S04)3 (aq) + 3H2 (g)

(d) Iron (s) + Hydrochloric acid (aq) clip_image002[8] Iron chloride (aq) + Hydrogen (g)

2Fe (s) + 6HC1 (aq) clip_image002[9]2FeCl3 (aq) + 3H2 (g)

Question 25. With the help of a chemical reaction explain how a soda-acid fire extinguisher helps in putting out a fire.


In soda-acid fire extinguisher, which contains a solution of sodium hydrogen carbonate surrounding a glass bottle containing sulphuric acid.

In case of fire, the knob (provided at the top of extinguisher) is pressed, thereby bottle breaks and the two solutions come in contact, thereby liberating carbon dioxide gas.

2 NaHCO3 + H2SO4clip_image013Na2SO4 + 2 H2O + 2 CO2

The liberated carbon dioxide forces a stream of effervescing liquid on the fire. In this way, carbon dioxide surrounds the combustible substances and cut­off the supply of air, thereby it assists to put out the fire.


Question 27. Why does distilled water not conduct electricity whereas rain water does.


Rain water dissolves atmospheric carbon dioxide to form carbonic acid (H2C03) which forms H+ions and due to presence of H+ ions, rain water conducts electricity, but a distilled water cannot.

Question 28. Why do acids do not show acidic behaviour in the absence of water?


Acids show acidic behaviour when they form H+ (aq) ions which are not formed in the absence of water.

Question 29. Five solutions A, B, C, D and E when tested with universal indicator showed pH as 4, 1, 11, 7 and 9 respectively. Which solution is:

(a) neutral ?

(b) strongly alkaline ?

(c) strongly acidic ?

(d) weakly acidic ? weakly alkaline ?

(f) arrange the pH in increasing order of hydrogen ion concentration.


Solution Showing pH

(a) Neutral 7

(b) Strongly alkaline: 11

(c) Strongly acidic: 1

(d) Weakly acidic: 4

(e) Weakly alkaline: 9

(f) pH in increasing order of hydrogen ion concentration: 11 <9<7<4< 1.

Question 30. Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCl) is added to tube A while acetic acid (CH3COOH) is added to test tube B. In which test tube will the fizzing occur more vigorously and why ?


The fizzing will occur more vigorously in test tube A because HCl is a strong acid and it produces more number of H+ ions.

Question 31. Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd ? Explain your Answer


When milk changes to curd its pH will decrease due to the formation lactic acid.

Question 32. A milkman adds a small amount of baking soda to fresh milk.

(a) Why does he shift the pH of the fresh milk from 6 to slightly alkaline ?

(b) Why does the milk take a long time to set as curd.


(a) Addition of baking soda (alkaline in nature) makes milk more alkaline, i.e., pH of milk increase about

(b) The pH required for fermentation of milk is about 5-6 and we know that on addition of baking sour milk makes it alkaline {i.e., pH>7). Hence, milk takes a long time to set as curd.

Question 33. Plaster of Paris should be stored in moisture-proof container. Explain why ?


Plaster of Paris changes to a hard substance reacting with water. That’s why, it is stored in a moisture- proof container.

Question 34. What is a neutralization reaction ? Give two examples.


Neutraliztion is the interaction of an acid and base with the formation of salt
Example :

HCl (aq) + NaOH (aq) clip_image002[10] NaCl (aq) + H20 (I)

H2S04 (aq) + Ca (OH)2 (aq) clip_image002[11] CaS04 (aq) + 2H20 (I)

Question 33. Give two important uses of washing soda and baking soda.


Uses of washing soda :

(i) It is used in the manufacture of soap, glass and paper.

(ii) It is used in the production of sodium compound.

Uses of baking soda :

(i) It is an important ingredient of baking powder.

(ii) It is also used as antacid.


Biology X – Control and Coordination – Questions and Answers

November 24th, 2014

Control and Coordination Class 10 Questions Answers

Control and Coordination is a very important topic in Biology of Class 10th CBSE. Here are NCERT Control and Coordination Questions and Answers given for Biology of Class 10th.

1.    What is the difference between a reflex action and walking?



Reflex Action Walking
  1. Reflex action is the sudden action in response to something in the environment
  1. Walking is the mechanism of electrical impulse which travels in the nerve cells & transmits to the concerning muscles with the result of that the muscles shrink and we start walking.
  1. It is controlled by the spinal cord.
  1. It is controlled by the brain.
  1. It occurs in a fraction of second

(iii) It occurs in responding by the brains through nerve cells so it takes time.


2.    What happens at the synapse between two neurons?

Ans.    In between two nerve cells or neurons the free tips dendrites come closer to the free ends of distal axon fibres. When the impulse travels the chemical compound is released which is filled in the gap between the synapse. The impulse travels through this compound into other neuron and after that this compound is drawn. Thus, the impulse is transmitted from one place or organ to another organ.

3.    Which part of the brain maintains posture and equilibrium of the body?

Ans.    Cerebellum a part of hind brain maintains the posture and equilibrium of the body.

4.    How do we detect the smell of an agarabatti (incense stick)?

Ans.    The cerebrum which is a part of the fore brain is responsible for the detection of smell of an agarbatti.

5.    What is the role of the brain in reflex action ?

Ans.    In reflex action we do something without thinking about it or without feeling in control of our reactions. The nerves of input are in the spinal cord on their way to the brain. Thus, the information through input nerves or sensory nerves go to the brain. The brain keeps the information of what the reflex action is doing.

The movement of the plant (shoot and root) due to the influence of sunlight is called phototropism. In this movement the cells of that part which are in direct contact of light shrink due to the transfer of wall from these cells to the cells of opposite side. Thus, the plant part bend towards sunlight. It is called positive phototropic. It does not have the effect of sensation by electrical-chemical means.

Fig: Reflex are in Human Body

6.    What are plant hormones ?

Ans.    Plant hormones are also known as phytohormones which are chemical substances produced in the cells Of root and shoot tips. These chemicals are responsible for controlling growth of the plant body. e.g. ethylene, cytokinin, etc.

7.    How is the movement of leaves of the sensitive plant different from the movement of a shoot towards light?

Ans.    In sensitive plants like Mimosa pitdica (Touch me not), there is electrical-chemical means to convey the information of touch from cell to cell. Plant cells change shape by changing the amount of water in them resulting in swelling or shriking.

This type of movements in sensitive plant is totally different from the movement of a shoot towards light in the following way.

The sensitive plant

The movement of the plant (shoot and root) due to the influence of sunlight is called phototropism. In this movement the cells of that part which are in direct contact of light shrink due to the transfer of wall from these cells to the cells of opposite side. Thus, the plant part bend towards sunlight. It is called positive phototropic. It does not have the effect of sensation by electrical-chemical means.

8.    Give an example of a plant hormone that promotes growth.

Ans.     Auxin

9.    How do auxins promote the growth of a tendril around a support?

Ans.    In weak plants like pea, the cells of the tip of the tendril produce auxins. The side part of the tendril which comes in contact with the support, transfers its auxins along with water towards opposite side due to which the cells elongate and turgid and the whole tendril bends, clinging to the support or around the support.

10.    Design an experiment to demonstrate hydrotropism.

Ans.    AIM: To demonstrate hydrotropism.

Material: A trough, soil water and germinating seeds or baby plants, perforated card board sheet equal to the diameter of trough.


Take a trough.

2. Fix the perforated card board sheet in the trough vertically.

3. Half fill one part of trough with soil and the other half or second part of the trough with water.

4. Now fix the germinating seed or baby plants in the soil.

5. Keep the whole apparatus in the sun in open place for few days.

Observations : After a few days, the following changes are observed.

1. The roots bend towards water.

2. The shoot part bends away from water.

Result: The experiment confirms that:

1. Water has positive effect on roots which is called positive hydrotropism.

2. Water has negative effect on shoot (stem and other aerial parts) which is called as negative



1.    Appartatus should be placed at open place in the sun so that plants may get all the necessary conditions.

2.    Perforations in the carboard sheet should neither be too big nor too small. Water should be diffused slowly.

11.    How does chemical coordination take place in animals?

Ans.     The chemical coordination in animals takes place by the hormones which are secreted by several endocrine glands. The hormones after secretion reaches into blood and after that through blood, it (hormone) reaches to the various parts of the body. Take an example of Adrenaline which is secreted by Adrenal gland and through blood it reaches to its target heart. As a result, the heart beats faster in order to supply more oxygen to the muscles and the target organs get more oxygen and satisfies its need of oxygen to work.

12.    Why is the use of iodised salt advisable ?

Ans.    Thyroid glands present in the neck region secrete thyroxin hormone. It is secreted in presence of iodine. So, iodised salt is advisable to every body.

13.    How does our body respond when adrenaline is secreted into the blood?

Ans.    Adrenaline hormone is secreted directly into the blood and carried to different parts of the body. It helps in the oxidation of carbohydrates, fats and proteins to produce energy. It goes to heart which increases the heart beats. Thus, the blood is pumped rapidly which supplies blood quickly to the target organ and thus organ gets large amount of energy and works.

14.    Why are some patients of diabetes treated by giving injections of insulin?

Ans.    In case of some patients, the cells of pancreas do not produce insulin when sugar level in blood is high. In such a case, they are given insulin injections to decrease the sugar level in the blood.

Section B

1.    Which of the following is a plant hormone?

(a) Insulin     (b) Thyroxin     (c) Oestrogen     (d) Cytokinin

Ans.    (d) Cytokinin is a plant hormone which helps in cell division.

2.    The gap between two neurons is called a

(a) dendrite     (b) synapse     (c) axon         (d) impulse

Ans.    (b) In a human body, one neuron is connected with another via nerve endings and dendrites then a gap is created which is called synapse.

3.    The brain is responsible for

(a) thinking     (b) regulating the heart beat    (c) balancing the body     (d) all of the above

Ans.    (b) Brain controls thinking, regulating the heart beat and balances the body.

4.    What is the function of receptors in our body? Think of situations where receptors do not work properly. What problems are likely to arise?

Ans.    All information from our environment is detected by the specialised tips of some nerve cells. These receptors are usually located in our sense organs, such as the inner ear, the nose, the tongue, and so on. So olfactory receptors will detect smell. If the receptor is not working properly, the environmental effects will be received by the receptors but the respond from the spinal cord and brain is not coming in due time to the effectors with the result of that the effector will be effected.

5.    Draw the structure of a neuron and explain its function.

Ans.    The dendrites of a neuron receive the environmental information from the receptor. This information travels in the whole body of neuron and then reaches to the synapse where the chemical compound is secreted out +o fill the gap of synapse when the information is passed out into the other neuron, the chemical compound is withdrawn. Thus, information reaches from the receptor to brain and spinal cord.

Structure of Neuron

6.    How does phototropism occur in plants ?

Ans.    The movement in plant due to light is known as phototropism. In this case, the plant parts move with effect of sunlight. The shoot-stem and the other parts related to it in the air show positive phototropism while the whole root system shows negative phototropism.

7.    Which signals will get disrupted in case of spinal cord injury?

Ans.    In case of spinal cord injury the reflex action will get disturbed due to which when we keep our palm on a flame, then we will not take our hand away from it because of defect in reflex action.

8.    How does chemical coordination occur in plants?

Ans.    Phytohormones are chemical compounds which are produced in the cells of the tips of main stem a branches. These hormones are diffused from the originating cells to the neighbouring cells through diffusion. They are responsible for cell elongation, cell multiplication, opening of flowers etc. Thus, chemical coordination occurs in plants.

9.    What is the need for a system of control and coordination in an organism?

Ans.    In multicellular organisms, all the activities concerning to any part of the body are controlled by spin cord and brain. All the cell of all the parts of the body are connected with them through nerves. There a thick network of nerves in the whole body. These nerves are of two types i.e. sensory nerves carry impulses from the receptor to brain and spinal cord and the response is carried to the effector through motor nerves. All these activities are possible by control and coordination. Brain and spinal cord control over the activities while nerves are the coordinating devices.

10.    How are involuntary actions and reflex actions different from each other?


Reflex actions

Involuntary actions

  1. It is controlled by spinal cord.

(i) It is controlled by brain

  1. It is very quick.

(ii) It takes some time.

  1. There is no need of thinking.

(iii) Brain takes the judgment and then respond accordingly.

  1. Response is given to the concerned organ just after receiving the stimulus.

(iv) There is need of thinking and not the environmental stimulus for response.

11.    Compare and contrast nervous and hormonal mechanisms for control and coordination in animals.


Nervous Coordination

Homonal Coordination

  1. In this type there is a network of nerves which connects the cells of all the body organs to the central nervous system.

(i) In this type, there is no such system in the body.

  1. The coordination is controlled by brain and spinal cord.

(ii) There is no controlling organ for this coordination.

  1. There is no secretion of such type.

(iii) Hormones quantity affect the organ and the system.

  1. All type of functions are controlled by the nerves and the central nervous system.

(iv) Special hormone is responsible for particular function.

  1. There is no such effect of this system.

(v) Hormone’s quantity affect the organ and the system.

  1. The whole system is fixed at its own place in the body.

(vi) Endocrine glands are situated at various places in the body.

  1. The stimuli and the responses travel in the nerves.

(vii) Blood carries the hormones to the concerning body organs.

  1. The system functions according to the environmental stimuli.

(viii) The hormones have no effect of external environment.

12.    What is the difference between the manner in which movement takes place in a sensitive plant and the movement in our legs?


Movement in sensitive plants

Movements in les of human beings

  1. The leaves of sensitive plants are sensitive to touch.

(i) No special organs in leg for such action.

  1. They have electrical-chemical means to convey the information of touch.

(ii) The chemical meant to convey actions in this movement.

  1. There is no special tissue in plants for the conduction of information.

(iii) It is controlled by brain and spinal cord.

  1. The cells change their shape by changing the amount of water in them.

(iv) There is no effect of the amount of water on movement of muscles.