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:

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)

Acids Bases and Salts Question List

Concepts
1) What are Acids?
2)What are Bases?
3)What are Acid-Base Indicators?
4)Olfactory indicators?
5)pH scale?
6)Reaction of acid with a metal?
7)Reaction of base with a metal?
8)How do metal carbonates and Metal Hydrogencarbonates React with metals? 
9)Reaction of acids and bases together
10)What is Neutralisation reaction?
11)Reaction of metallic oxide with acid.
12)Why Acidic and basic solutions conduct electricity?
13) Water of crystallisation
14) Some very important salts with their chemical name and formula

In text Questions page number 18

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?

In text Questions page number 22

Question 1. Why should curd and sour substances not be kept in brass and copper vessels?

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?

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.

In text Questions page number 25

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?

Question 2. Why does an aqueous solution of an acid conduct electricity?

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?

Question 5. How is the concentration of hydronium ions (H₃O⁺) affected when a solution of an acid is diluted?

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

In text Questions page number 28

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? 

Question 2. What effect does the concentration of H⁺(aq) ions have on the nature of the solution?

Question 3. Do basic solutions also have H⁺(aq) ions ? If yes, then why are these basic?

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)?

In text Questions page number 33

Question 1. What is the common name of the compound CaOCl₂?

Question 2. Name the substance which on treatment with chlorine yields bleaching powder.

Question 3. Name the sodium compound which is used for softening hard water.

Question 4. What will happen if a solution of sodium hydrocarbonate is heated? Give the equation of the reaction involved.

Question 5. Write an equation to show the reaction between Plaster of Paris and water.

Exercise Solution

Question 1.  A solution turns red litmus blue; its pH is likely to be(a) 1 (b) 4 (c) 5 (d) 10

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

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

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

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.

Question 6. Compounds such as alcohols and glucose also contain hydrogen but are not categorised as acids. Describe an Activity to prove it.

Question 7. Why does distilled water not conduct electricity, whereas rain water does?

Question 8. Why do acids not show acidic behaviour in the absence of water?

Question 9. 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.

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?

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.

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?

Question 13. Plaster of Paris should be stored in a moisture-proof container. Explain why?

Question 14. What is a neutralization reaction? Give two examples.

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

Chemical reactions and equations

Concepts

Chemical Equations
Balanced Chemical equation
Combination Reaction
Decomposition reaction
Displacement Reaction
Double displacement reaction
Precipitation Reaction
Oxidation Reaction
Reduction Reaction
Redox Reaction or Oxidation-Reduction reaction
Corrosion
Rancidity 

In text questions page number 6

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

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

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.

In text questions page number 10

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.

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.

In text questions page number 13

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

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

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

Text Book Exercise

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

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

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.

Question 4. What is a balanced chemical equation? Why should chemical equations be balanced?

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.

Question 6. Balance the following chemical equations. 
 

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

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)

Question 9. What does one mean by exothermic and endothermic reactions? Give examples.

Question 10. Why is respiration considered an exothermic reaction? Explain.

Question 11. Why are decomposition reactions called the opposite of combination reactions? 
Write equations for these reactions.

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

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

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.

Question 15. What do you mean by a precipitation reaction? Explain by giving examples.

Question 16. Explain the following in terms of gain or loss of oxygen with two examples each. 
(a) Oxidation
(b) Reduction

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.

Question 18. Why do we apply paint on iron articles?

Question 19. Oil and fat containing food items are flushed with nitrogen. Why?

Question 20. Explain the following terms with one example each.

 

types of reactions

Combination Reaction: If in a Chemical equation, two or more reactants combine to form a single product then it is known as combination reaction.

Decomposition reaction: If in a chemical reaction a single substance decomposes to form two or more substances then it is known as decomposition reaction.

Displacement Reaction: If in a chemical equation, more reactive elements displaces a less reactive element from its compound then it is known as displacement reaction.

Double displacement reaction: If in a chemical reaction exchange of ions takes place then it is known as double displacement reaction

Precipitation Reaction: A white coloured substance which is insoluble in water also known as precipitate is formed during a chemical reaction then the reaction is known as precipitation reaction

In this reaction Barium sulphate is a white colour precipitate.
Oxidation Reaction: It is a chemical reaction in which gain of oxygen or loss of hydrogen takes place. For example in the following reaction copper is oxidised to become copper oxide.

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

Redox Reaction or Oxidation-Reduction reaction: The chemical reaction in which both oxidation and reduction takes place is known as Redox reaction. For example in the following reaction Hydrogen is oxidised to become water and copper oxide is reduced to become copper.

what is a chemical equation and balanced chemical equation

What is a chemical equation?

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

What is a balanced chemical equation ?

Balanced Chemical equation: 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.