CBSE NCERT SOLUTIONS: 2013-03-10

Thursday, March 14, 2013

Corrosion and rancidity

Corrosion: It is the process in which metals are slowly eaten up by the action of air moisture or chemicals. For example rusting is a form of corrosion in which iron is eaten up by the action of air and moisture and a reddish brown coating of iron oxide is formed as shown in the following chemical reaction.

Rancidity: When the substance containing oils and fats are exposed to air they get oxidised and become rancid due to which their smell, taste and colour change. This process is known as rancidity. For example when a when butter is kept open for a long time then its smell and taste gets changed.

Chemical Equations

Chemical Equations: It is the symbolic representation of a chemical reaction where the reactant entities are given on the left hand side and the product entities on the right hand side of the equation. In complete chemical equation all reactants and products are written along with their physical state. A chemical equation must be balanced so that it can follow the law of conservation of mass. For example

Identify the substances that are oxidised and the substances that are reduced in the following reactions.

3. Identify the substances that are oxidised and the substances that are reduced in the following reactions.

Answer:
(i)The substance oxidised is sodium and the substance reduced is oxygen gas.
(ii) The substance oxidised is Hydrogen gas and the substance reduced is copper oxide.

Give an example of a double displacement reaction other than the one given in Activity 1.10.

2. Give an example of a double displacement reaction other than the one given in Activity 1.10.

Answer:

Why does the colour of copper sulphate solution change when an iron nail is dipped in it?

1. Why does the colour of copper sulphate solution change when an iron nail is dipped in it?

Answer:When an iron nail dipped in the copper sulphate solution than iron displaces copper from the copper sulphate because iron is more reactive than copper. Therefore the colour of the copper sulphate solution changes.
The reaction involved is

Why is the amount of gas collected in one of the test tubes in Activity 1.7 double of the amount collected in the other? Name this gas.

2. Why is the amount of gas collected in one of the test tubes in Activity 1.7 double of the amount collected in the other? Name this gas.

Answer:
The chemical reaction involved in the electrolysis of water is

From the above reaction it is clear that the amount of hydrogen gas and the oxygen gas formed are always in the ratio of 2:1. Therefore the volume of gas collected in the first test tube is double the volume of the gas collected in second test tube.

A solution of a substance ‘X’ is used for white washing. (i) Name the substance ‘X’ and write its formula. (ii) Write the reaction of the substance ‘X’ named in (i) above with water.

1. A solution of a substance ‘X’ is used for white washing.
(i) Name the substance ‘X’ and write its formula.
(ii) Write the reaction of the substance ‘X’ named in (i) above with water.

Answer:

(i)The substance ‘X’ which is used in white washing is calcium oxide or quick lime and its formula is CaO.
(i)The reaction involved is

Write the balanced equation for the following chemical reactions. (i) Hydrogen + Chlorine Hydrogen chloride (ii) Barium chloride + Aluminium sulphate Barium sulphate + Aluminium chloride

2. Write the balanced equation for the following chemical reactions.
(i) Hydrogen + Chlorine Hydrogen chloride
(ii) Barium chloride + Aluminium sulphate Barium sulphate + Aluminium chloride
(iii) Sodium + Water Sodium hydroxide + Hydrogen
Answers:

Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride.

3. Write a balanced chemical equation with state symbols for the following reactions.
(i) Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride.
(ii) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water.
Answers:

Why should a magnesium ribbon be cleaned before burning in air?

1. Why should a magnesium ribbon be cleaned before burning in air?

Magnesium ribbon must be cleaned before burning in air so that the the layer of magnesium oxide (which is formed due to reaction of magnesium with air) can be removed in order to get the desired chemical reaction.

Explain the following terms with one example each. (a) Corrosion (b) Rancidity

Question 20. Explain the following terms with one example each.
(a) Corrosion
(b) Rancidity
Answer:
Corrosion: It is the process in which metals are slowly eaten up by the action of air moisture or chemicals. For example rusting is a form of corrosion in which iron is eaten up by the action of air and moisture and a reddish brown coating of iron oxide is formed as shown in the following chemical reaction.

Oil and fat containing food items are flushed with nitrogen. Why?

Question 19. Oil and fat containing food items are flushed with nitrogen. Why?
Answer: Oil and fat containing food items flushed with nitrogen because nitrogen acts as an antioxidant and it prevent them from being oxidised.

A shiny brown coloured element ‘X’ on heating in air becomes black in colour. Write the name the element ‘X’ and the black coloured compound formed.

Question 17. A shiny brown coloured element ‘X’ on heating in air becomes black in colour. Write the name the element ‘X’ and the black coloured compound formed.
Answer: The shiny brown coloured element 'X' is copper and the black coloured compound formed is Copper oxide. The reaction involved is

Why do we apply paint on iron articles?

Question 18. Why do we apply paint on iron articles?
Answer: Iron articles are painted to prevent them from rusting. After painting iron surface does not come in contact with moisture and air which cause rusting.

Explain the following in terms of gain or loss of oxygen with two examples each. (a) Oxidation (b) Reduction

Question 16. Explain the following in terms of gain or loss of oxygen with two examples each.
(a) Oxidation
(b) Reduction
Answer:
Oxidation Reaction: It is a chemical reaction in which gain of oxygen or loss of hydrogen takes place. For example in the first reaction copper is oxidised to become copper oxide and in second Magnesium is oxidised to become Magnesium Oxide.

Reduction Reaction: It is a chemical reaction in which loss of oxygen or gain of hydrogen takes place. For example in the first reaction copper oxide is reduced to become copper and in second Zinc Oxide is reduced to become Zinc.

What do you mean by a precipitation reaction? Explain by giving examples.

Question 15. What do you mean by a precipitation reaction? Explain by giving examples.
Answer:The chemical reaction in which a white coloured substance which is insoluble in water (precipitate) is formed then it is known as precipitation reaction

In this reaction Barium sulphate is a white colour precipitate and it is insoluble in water.

What is the difference between displacement and double displacement reactions? Write equations for these reactions.

Question 13. What is the difference between displacement and double displacement reactions? Write equations for these reactions.
Answer:

In displacement reaction a more reactive element replaces a less reactive element from its compound while in double displacement reaction exchange of ions takes place for example

In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.

Question 14. In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.
Answer:

Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.

Question 12. Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.
Answer:

Why are decomposition reactions called the opposite of combination reactions?

Question 11. Why are decomposition reactions called the opposite of combination reactions?
Write equations for these reactions.
Answer:In Decomposition reaction a single substance decomposes to form two or more substances which is exact opposite of Combination reaction in which two or more reactants combine to form a single product that is why decomposition reactions called the opposite of combination reactions. For examples
Decomposition reaction:

Combination Reaction:

Why is respiration considered an exothermic reaction? Explain.

Question 10. Why is respiration considered an exothermic reaction? Explain.
Answer:Respiration is considered as an exothermic reaction because in respiration oxidation of glucose takes place which produces large amount of heat energy. This is shown in following chemical equation.

Potassium bromide (aq) + Barium iodide (aq) → Potassium iodide (aq) + Barium bromide(s) (b) Zinc carbonate(s) → Zinc oxide(s) + Carbon dioxide(g)

Question 8. Write the balanced chemical equation for the following and identify the type of reaction in each case.
(a) Potassium bromide (aq) + Barium iodide (aq) → Potassium iodide (aq) + Barium bromide(s)
(b) Zinc carbonate(s) → Zinc oxide(s) + Carbon dioxide(g)
(c) Hydrogen(g) + Chlorine(g) → Hydrogen chloride(g)
(d) Magnesium(s) + Hydrochloric acid(aq) → Magnesium chloride(aq) + Hydrogen(g)
Answer:

What does one mean by exothermic and endothermic reactions? Give examples.

Question 9. What does one mean by exothermic and endothermic reactions? Give examples.
Answer:
Exothermic Reaction: A chemical reaction in which heat is given out is known as exothermic reaction. For example

Endothermic Reaction: A chemical reaction in which heat energy is absorbed is known as endothermic reaction. For example

Write the balanced chemical equations for the following reactions. (a) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water

Question 7. Write the balanced chemical equations for the following reactions.
(a) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
(b) Zinc + Silver nitrate → Zinc nitrate + Silver
(c) Aluminium + Copper chloride → Aluminium chloride + Copper
(d) Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride
Answer:

Balance the following chemical equations.

Question 6. Balance the following chemical equations.

Answer:Balanced chemical equations are

Translate the following statements into chemical equations and then balance them.

Question 5. Translate the following statements into chemical equations and then balance them.
(a) Hydrogen gas combines with nitrogen to form ammonia.
(b) Hydrogen sulphide gas burns in air to give water and sulpur dioxide.
(c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.
(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.

Answers:

What is a balanced chemical equation? Why should chemical equations be balanced?

Question 4. What is a balanced chemical equation? Why should chemical equations be balanced?
Answer: If in a chemical equation the total number of atoms in the reactant side are equal to the total number of atoms in the product side then the chemical reaction is said to be balanced. For example

The chemical reaction should be balanced show that it can follow the law of conservation of mass.

The above reaction is an example of a (a) combination reaction. (b) double displacement reaction. (c) decomposition reaction. (d) displacement reaction.

The above reaction is an example of a
(a) combination reaction.
(b) double displacement reaction.
(c) decomposition reaction.
(d) displacement reaction.
Answer: (d)

What happens when dilute hydrochloric acid is added to iron fillings? Tick the correct answer.

Question 3. What happens when dilute hydrochloric acid is added to iron fillings? Tick the correct answer.
(a) Hydrogen gas and iron chloride are produced.
(b) Chlorine gas and iron hydroxide are produced.
(c) No reaction takes place.
(d) Iron salt and water are produced.
Answer: (a)

Which of the statements about the reaction below are incorrect? 2PbO(s) + C(s) → 2Pb(s) + CO

Question 1. Which of the statements about the reaction below are incorrect?
2PbO(s) + C(s) → 2Pb(s) + CO
(a) Lead is getting reduced.
(b) Carbon dioxide is getting oxidised.
(c) Carbon is getting oxidised.
(d) Lead oxide is getting reduced.
(i) (a) and (b)
(ii) (a) and (c)
(iii) (a), (b) and (c)
(iv) all
Answer: (i)

Wednesday, March 13, 2013

Reaction of acid with a metal

Reaction of acid with a metal: When an acid reacts with a metal then Hydrogen gas is evolved along with corresponding salt.

Some very important salts with their chemical name and formula

Some very important salts with their chemical name and formula.

Water of crystallisation

Water of crystallisation: It is the definite number of molecules of water that is chemically attached to each formula unit of a salt in its crystalline form. For example washing soda (Na₂CO₃.10H₂O) or Gypsum (CaSO₄.2H₂O).

Why Acidic and basic solutions conduct electricity?

Why Acidic and basic solutions conduct electricity?: Acidic and basic solutions in water conduct electricity because they produce hydrogen and hydroxide ions respectively.

Reaction of metallic oxide with acid

Reaction of metallic oxide with acid: When metallic oxide reacts with acid they produce salt along with water. For example

Neutralisation reaction

Neutralisation reaction: When acid and base react with each other to produce salt and water then such reaction is known as neutralisation reaction. For example

Reaction of acids and bases together

Reaction of acids and bases together: Whenever acids and bases react with each other they produce salt with water. For example

How do metal carbonates and Metal Hydrogencarbonates React with Acids?

How do metal carbonates and Metal Hydrogencarbonates React with Acids?
When Metal carbonates and Metal Hydrogencarbonates react with acid they form corresponding salt with carbon dioxide and water as shown in following chemical equation

Reaction of base with a metal

Reaction of base with a metal: When a base reacts with a metal then Hydrogen gas is evolved along with corresponding salt. Salt is composed of metal and oxygen and has negative ion.

Acids Bases Acid-Base Indicators Olfactory indicators pH scale

Concepts: Acids, Bases and Salts

Acids: Those substances which when dissolved in water then produce H⁺ (aq) or Hydronium (H₃O⁺) ions. They are sour in taste and change the colour of blue litmus to red. For example HCl, H₂SO₄, HNO₃etc.

Bases: Bases are generally metallic oxide or metallic hydroxide. When they are dissolved in water they produce OH^-(aq) ions. They are bitter in taste and change the colour of red litmus to blue. For example CuO, NaOH, KOH etc.

Acid-Base Indicators: Indicators are basically dyes or mixtures which are used to detect whether the substance is acidic or basic with the help of their colour changing property. They are of two type, natural indicators and synthetic indicators. The examples of natural indicators are Litmus and turmeric. The examples of synthetic indicators are methyl orange and phenolphthalein.

Olfactory indicators: Those substances whose odour changes in acidic or basic medium are known as olfactory indicators. Some of the examples of olfactory indicators are vanilla, onion and clove.

pH scale: It is the measure of acidic or basic strength of an aqueous solution. The pH value of an acidic solution lies between 0 to 7. The pH value of a basic solution lies between 7 to 14. The pH value of a neutral substance is always 7.

Write an equation to show the reaction between Plaster of Paris and water.

Question 5. Write an equation to show the reaction between Plaster of Paris and water.
Answer: When plaster of paris reacts with water it produce gypsum as shown in the following chemical reaction

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

Question 3. Name the sodium compound which is used for softening hard water.
Answer: Washing Soda (Na₂CO₃.10H₂O) is hydrated sodium carbonate which is used for softening hard water.

What will happen if a solution of sodium hydrocarbonate is heated? Give the equation of the reaction involved.

Question 4. What will happen if a solution of sodium hydrocarbonate is heated? Give the equation of the reaction involved.
Answer: When sodium hydrogen carbonate is heated then sodium carbonate and water is formed along with the evolution of carbon dioxide gas.

What is the common name of the compound CaOCl2

Question 1. What is the common name of the compound CaOCl₂?
Answer: Bleaching Powder.

Question 2. Name the substance which on treatment with chlorine yields bleaching powder.
Answer: When calcium hydroxide is treated with chlorine gas it yields bleaching powder. It is shown in the following chemical reaction.

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)

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 acidic in nature which is not suitable for agriculture then the farmer would treat the soil with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate).

Do basic solutions also have H+(aq) ions ? If yes, then why are these basic?

Question 3. Do basic solutions also have H⁺(aq) ions ? If yes, then why are these basic?
Answer: Yes the basic solution also has H⁺(aq) ions but it is less than the concentration of (OH^-)ions.

What effect does the concentration of H+(aq) ions have on the nature of the solution?

Question 2. What effect does the concentration of H⁺(aq) ions have on the nature of the solution?
Answer: If the concentration of H⁺(aq) ions is increased(>10^-7) then the solution become acidic and if the concentration of H⁺(aq) ions is decreased(<10^-7) then the solution become basic in nature.

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

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: The pH value of a solution varies from 0 to 14. The pH value is 0 for a very strong acid and the pH value is 14 for a very strong base. The pH value is 7 for a neutral solution. Hence A is acidic and B is basic in nature. The concentration of hydrogen ion decreases from pH value of 0 to 14 therefore A has more hydrogen ion concentration.

How is the concentration of hydroxide ions (OH-) affected when excess base is dissolved in a solution of sodium hydroxide?

Question 6. How is the concentration of hydroxide ions (OH^-) affected when excess base is dissolved in a solution of sodium hydroxide?
Answer: When excess base is dissolved in the solution of sodium hydroxide then the concentration of hydroxide (OH^-) ions increases.

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

Question 5. How is the concentration of hydronium ions (H₃O⁺) affected when a solution of an acid is diluted?
Answer: When the solution of an acid is diluted then its strength decreases as there is decrease in the concentration of hydronium (H₃O⁺) ions.

While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?

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: The process of adding water to an acid is highly exothermic. If it is not done in the proper way then may the mixture splash out and causes serious burns. Therefore it is recommended that acid should be added to water carefully.

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

Question 3. Why does dry HCl gas not change the colour of the dry litmus paper?
Answer: The colour of litmus paper changes only in the presence of ions like hydrogen (H⁺) or hydronium (H₃O⁺) ions. HCl can produce these ions only in the form of aqueous solution. Hence dry HCl gas does not change the colour of dry litmus paper.

Why does an aqueous solution of an acid conduct electricity?

Question 2. Why does an aqueous solution of an acid conduct electricity?
Answer: The presence of hydrogen (H⁺) or hydronium (H₃O⁺) ions in the aqueous solution of an acid are responsible for conducting electricity.

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

Question 1. Why do HCl, HNO₃, etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character?
Answer: When HCl or HNO₃ are mixed with water then they dissolve in water to form H⁺ or H₃O⁺ ions which shows their acidic character. For example just see the following reactions

When alcohols and glucose are mixed with water then they do not dissolve to form ions. Hence they do not show acidic character.

Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example

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: When acids react with metal generally hydrogen gas is produced. We can test it by bringing burning candle near to it then it will produce pop sound.

Metal compound A reacts with dilute hydrochloric acid to produce effervescence

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:

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

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 as curd and sour substances are acidic in nature and react with the metallic surface of the brass and copper to form some toxic compound which may be unfit for health.

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?

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?

Answer: If the colour of red litmus does not change then it is acid. If the colour of red litmus changes to blue then it is base. If there is slight change in the colour of red litmus (such as purple) then it is distilled water.

Give two important uses of washing soda and baking soda.

Question 15. Give two important uses of washing soda and baking soda.
Answer:

(a) Two important uses of washing soda

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

(ii) It is used to remove the permanent hardness of water.

(b) Two important uses of baking soda

(i) It is used for making baking powder.

(ii) It is used in soda- fire extinguishers.

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

Question 13. Plaster of Paris should be stored in a moisture-proof container. Explain why?
Answer: The Plaster of Paris should be stored in a moisture-proof container as it absorbs water from moisture and turn into hard substance (Gypsum) as shown in following chemical equation.

What is a neutralisation reaction? Give two examples.

Question 14. What is a neutralisation reaction? Give two examples.
Answer: When acid and base react with each other to produce salt and water then such reaction is known as neutralisation reaction. For example

A milkman adds a very small amount of baking soda to fresh milk. (a) Why does he shift the pH of the fresh milk from 6 to slightly alkaline?

Question 12. A milkman adds a very 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 this milk take a long time to set as curd?
Answer:

He shifts the pH of the fresh milk from 6 to alkaline so that in basic form it will not spoil easily.

This milk takes a long time to set as curd because the lactic acid produced reacts with the baking soda.

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

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:When milk is turned into curd then its pH value will decrease due to the production of lactic acid in curd which is acidic in nature.

Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCl) is added to test tube A, while acetic acid (CH3COOH) is added to test tube B

Question 10. Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCl) is added to test tube A, while acetic acid (CH₃COOH) is added to test tube B. In which test tube will the fizzing occur more vigorously and why?
Answer: In both the test tubes hydrogen gas is formed. The HCl is strong acid then acetic acid so more hydrogen gas is formed in test tube A which results in vigorous fizzing.

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

Question 8. Why do acids not show acidic behaviour in the absence of water?
Answer: The acidic behaviour of a substance is due to the presence of H+(aq) ions. As acids do not dissociate to produce H+(aq) ions in the absence of water so they do not show acidic behaviour.

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

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?
(e) weakly alkaline?
Arrange the pH in increasing order of hydrogen-ion concentration.
Answer: (a) neutral -> D
(b) strongly alkaline -> C
(c) strongly acidic -> B
(d) weakly acidic -> A
(e) weakly alkaline -> E
The arrangement of pH in increasing order of hydrogen-ion concentration is 11<9<7<4<1

Why does distilled water not conduct electricity, whereas rain water does?

Question 7. Why does distilled water not conduct electricity, whereas rain water does?
Answer: Distilled water cannot conduct electricity because it does not contain ions while rain water conducts electricity as it contains ions due presence of dissolved salts in it.

Compounds such as alcohols and glucose also contain hydrogen but are not categorized as acids. Describe an Activity to prove it.

Question 6. Compounds such as alcohols and glucose also contain hydrogen but are not categorized as acids. Describe an Activity to prove it.
Answer: As shown in figure insert two nails on the wooden or rubber cork and place it in a beaker. Now connect these iron nails with a bulb, a 6 volt battery and a switch using a wire. Now pour some alcohol or glucose such that the nails will dip into it. Now turn the switch on, you will see that the bulb will not glow. Now empty the beaker and add some HCl aqueous solution at this time the bulb will glow. This proves that an acid can conduct electricity while alcohols and glucose cannot, even when they are containing hydrogen.

Above diagram shows that an acid solution can conduct electricity.

Write word equations and then balanced equations for the reaction taking place when – (a) dilute sulphuric acid reacts with zinc granules. (b) dilute hydrochloric acid reacts with magnesium ribbon. (c) dilute sulphuric acid reacts with aluminium powder. (d) dilute hydrochloric acid reacts with iron filings.

Question 5. Write word equations and then balanced equations for the reaction taking place when –
(a) dilute sulphuric acid reacts with zinc granules.
(b) dilute hydrochloric acid reacts with magnesium ribbon.
(c) dilute sulphuric acid reacts with aluminium powder.
(d) dilute hydrochloric acid reacts with iron filings.
Answer: Write word equations and then balanced equations for the reaction taking

10ScienceCh2Q Exercise 1to4

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. The solution contains
(a) NaCl (b) HCl (c) LiCl (d) KCl
Answer: (b)

Question 3. 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 HCl solution (the same solution as before) required to neutralise it will be
(a) 4 mL (b) 8 mL (c) 12 mL (d) 16 mL
Answer: (d)

Question 4. Which one of the following types of medicines is used for treating indigestion?
(a) Antibiotic
(b) Analgesic
(c) Antacid
(d) Antiseptic
Answer: (c)