1. Indicate the colour changes in the sample solutions with the given indicators and classify the sample solutions into acids, bases and salts. (AS 1) 4 Marks
On the basis of the results. The classification is as follows:
1) Acids: HCl, H2SO4, HNO3, CH3COOH
2) Bases: NaOH, KOH, Mg(OH)2, Ca(OH)2
3) Salts: NaCl
2. Distinguish between acids and bases. (AS 1) 4 Marks
3. List out the materials used in an experiment to prove when acid reacts with metal evolves hydrogen gas. Describe the experimental process. (AS 3) 4 Marks
A: Materials required: Test tube, delivery tube, glass trough, candle, soap water, dil. HCl, Zinc granules and stand.
i) Set the apparatus as shown in the figure.
ii) Take about 10 ml of dil. HCl in a test tube and add a few Zinc granules to it.
iii) We observe a gas is evolved from the Zinc granules.
iv) Pass the gas being evolved through the soap water.
v) We observe some bubbles formed in the soap solution.
vi) Bring a burning candle near the gas filled bubble.
vii) The candle turn of with a pop sound.
viii) The pop sound indicates that the gas evolved in Hydrogen.
2 HCl + Zn → ZnCl2 + H2 ↑
Acid + Metal Salt + Hydrogen
ix) Repeat this experiment with H2SO4, HNO3 etc.
x) From the above experiment we can conclude that Hydrogen gas is produced when acid reacts with metals.
4. Write down the process and materials used in the experiment of the reaction of carbonates and metal hydrogen carbonates with acids produces corresponding salts, carbon dioxide gas and water.
A: Required Materials: Two test tubes, two holed rubber stopper, delivery tube, Thistle funnel cork, stand, dilute HCl, Sodium carbonate, Sodium hydrogen carbonate, Ca(OH)2 solution.
i) Take two test tubes and label them as A and B.
ii) Take about 0.5 gm of Sodium carbonate (Na2CO3) in test tube A and about 0.5 gm of Sodium hydrogen carbonate (NaHCO3) in test tube B.
iii) Add about 2 ml of dilute HCl to both the test tubes.
iv) Pass the gas produced in each case through lime water.
v) A milky white precipitate is formed. Hence the gas produced is CO2.
vi) The reactions occurring in the above activities.
Na2CO3 + 2 HCl 2 NaCl + H2O + CO2
(s) (aq) (aq) (l) (g)
NaHCO3 + HCl NaCl + H2O + CO2
(s) (aq) (aq) (l) (g)
vii) Pass the gas evolved through lime water.
Ca(OH)2 + CO2 CaCO3 + H2O
(aq) (g) (white precipitate) (l)
Conclusion: From above activity we conclude that when metal carbonates and hydrogen carbonates react with acids they give corresponding salt, carbon - dioxide and water.
Metal carbonate + Acid Salt + Carbondioxide + Water.
Metal Hydrogen carbonate + Acid Salt + Carbondioxide + Water.
5. Describe an experimental procedure with the help of a diagram to show that "every compound which has hydrogen is not an acid." (AS 3) 4 Marks
i) Prepare solutions of glucose, alcohol, hydrochloric acid and sulphuric acid etc.
ii) Connect two different coloured electrical wires to graphite rods separately in a 100 ml beaker as shown in the figure.
iii) Connect free ends of the wire to 230 V AC plug and complete the circuit by connecting a bulb to one of the wires.
iv) Now pour some dilute HCl in the beaker and switch on the current.
v) We observe that the bulb glows.
vi) Repeat the activity with dilute sulphuric acid, glucose and alcohol.
vii) We observe that the bulb glows only in Sulphuric acid solution, but not in glucose and alcohol solutions.
viii) Glowing of bulb indicates that there is flow of electric current through the solution.
ix) Acid solutions have ions and the moment of these ions in solution helps for flow of electric current through the solution.
x) The positive ion present in HCl solution is H+. This suggests that acids produce hydrogen ions (H+) in solution, which are responsible for their acidic properties.
xi) In glucose and alcohol solution the bulb did not glow indicating the absence of H+ ions, they contain Hydrogen.
xii) Hence glucose and alcohol are not categorized as acids.
6. Acids produce ions only in aqueous solution. How can you justify your answer with an experiment? (AS 3) 4 Marks
i) Take about 1.0 gm of solid NaCl in a clean and dry test tube.
ii) Add some concentrated Sulphuric acid to the test tube. We observe a gas is evolved.
iii) The reaction is 2 NaCl + H2SO4 → 2 HCl ↑ + Na2SO4.
iv) Test the gas evolved successfully with dry and wet blue litmus paper.
v) We observe that there is no change in the colour of dry litmus paper because dry HCl is not an acid. But HCl aqueous solution is an acid because wet blue litmus paper turned into red.
vi) The HCl gas evolved at delivery tube dissociates in the presence of water to produce hydrogen ions. In the absence of water dissociation of HCl molecules do not occur.
vii) The dissociation of HCl in water is shown below.
HCl + H2O → H3O+ + Cl- (aq)
Hence acids give H3O+ ions in water.
7. Explain a test to know whether the acid (or base) is strong or weak. (AS 3) 4 Marks
i) Take two beakers A and B.
ii) Fill the beaker A with dil. CH3COOH, and beaker B with dil. HCl
iii) Arrange the apparatus as shown in the figure and pass electricity through the solution in separate beakers.
iv) We notice that the bulb glows brightly in HCl solution, while the intensity of the bulb is low in acetic acid solution.
v) This indicates that there are more ions in HCl solution and fewer ions on present in acetic acid solution.
vi) More ions in HCl solution means more H3O+ ions therefore it is a strong acid. Where as Acetic acid has fewer H3O+ ions and it is weak acid.
vii) Carry out the same experiment by taking bases, like dil. NaOH and dil NH4OH instead of acids.
viii) We observe that NaOH is strong base and NH4OH is a weak base.
8. If the pH values of solutions X, Y and Z are 13, 6 and 2 respectively. Then
a) Which solution is a strong acid? Why?
b) Which solution contains ions along with molecules of solution?
c) Which solution is a strong base? Why?
d) Does the pH value of solution increase or decrease when a base is added to it? Why? (AS 1) 4 Marks
A: a) Z - has least pH value (2). So it is the strongest acid.
b) X - has highest pH value (13). So, this solution contains ions along with molecules of solution.
c) X - has highest pH value (13). So, it is the strongest base.
d) When a base is added to solution its pH value increases due to its OH ions concentration gradually increases.
9. In the following table the salts which are formed by Acids and bases and pH values are given. Observe the following table and answer the questions given below:
i) Name the salt with acidic nature.
ii) What is the nature of Na2CO3 salt?
iii) Which acid and base neutralise each other to form NaCl salt?
iv) Which are the neutral salts? (AS 4) 4 Marks
A: i) The salt having acidic nature is NH4Cl.
ii) Na2CO3 salt has basic nature.
iii) Neutralization of HCl, NaOH each other the salt NaCl form up.
iv) NaCl and KNO3 are the neutral salts.
10. Discuss briefly the examples showing the importance of pH in daily life. (AS 4) (AS 6) 2 Marks
A: i) Living organisms can survive in a narrow of pH change.
ii) Tooth decay starts when the change in pH value of mouth.
iii) In our stomach produces HCl acid which control the digestion of food in our stomach.
iv) Plants require a specific pH range for their healthy growth.
iv) Animals and plants use chemical solutions having certain pH value for their self defence.
11. Why does tooth decay start when the pH in the mouth is less than 5.5. How do you prevent the decay? (AS 6) 2 Marks
A: Tooth decay starts when the pH of the mouth is less than 5.5.
Tooth enamel made up of Calcium Phosphate is the hardest substance in the body. It does not dissolve in Water, but is corroded when the pH in the mouth is below 5.5
Bacteria present in the mouth produce acids by degradation of sugar and food particles remaining in the mouth. The best way to prevent this is to clean the mouth after eating food. Using tooth pastes, which are generally basic neutralise the excess acid and prevent tooth decay.
12. The flow of acid rain in to river/tank make the survival of aquatic life in a river/tank is difficult. Why? (AS 6) 2 Marks
A: Living organisms can survive only in a narrow range of pH change. When pH of rain water is less than 5.6, it is called acid rain. When acid rain flows into the rivers, it lowers the pH of the river water, the survival of aquatic life in such rivers becomes difficults.
13. Explain the role of pH in our digestive systems. (AS 1, AS 6) 2 Marks
A: Our stomach produces HCl acid. It helps in the digestion of food, without harming the stomach. During indigestion the stomach produce too much acid and this causes pain and irritation. To get rid of this pain, people use bases called antacids. These antacids neutralise the excess acid in the stomach.
14. Why does a bee sting causes pain and itching? What is the remedy for it? (AS 6) 2 Marks
A: Bee sting leaves an Methonoic acid which causes pain and irritation. Use of a mild base like baking soda on the sting area gives relief.
15. Why does it make the cake soft and spongy? (AS 1) 2 Marks
A: Baking Powder mainly contains NaHCO3 and its other components are acidic Ca(H2PO4)2 and starch. NaHCO3 produces CO2 which rises through bubling the dough into smooth and spongy cake or bread.
NaHCO3 + H+ → CO2 + H2O + Sodium Salt of acid.
16. Substance 'X' turns blue litmus into red. Substance 'Y' turns red litmus into blue. If the reaction takes place between X and Y guess what are the substances to be formed? Give reasons.(AS 2) 2 Marks
A: 'X' turns blue litmus into red so it is an Acid. Similarly 'Y' turns red litmus into blue. So, it is base. So when X reacts with Y that means an acid react with base which form salt and water. So, the products formed are salt and water because it is a neutralization reaction.
acid + base → salt + water
17. The gas 'X' which is obtained at the anode during the electrolysis of Sodium chloride solution. Produces a compound 'Y' on reacting with dry Calcium hydroxide. The compound 'Y' is used for disinfecting drinking water to make it free of germs. Name 'X', 'Y' and write the chemical equation for the reaction between them. (AS 2) 2 Marks
A: i) X is chlorine and Y is bleaching powder.
ii) Chemical equation is
Ca(OH)2 + Cl2 → CaOCl2 + H2O
Dry slaked lime + Chlorine → Bleaching powder + water.
18. What are the uses of Bleaching powder? (AS 6) 2 Marks
A: i) It is used for bleaching cotton and linen in the textile industry for bleaching wood pulp in paper industry and for bleaching washed clothes in laundry.
ii) Used as an oxidizing agent in many chemical industries.
iii) Used for disinfecting drinking water to make it free of germs.
iv) Used as a reagent in the preparation of Chloroform.
19. What are the uses of Washing Soda? (AS 6) 2 Marks
A: i) Sodium carbonate (Washing soda) is used in glass, soap and paper industries.
ii) It is used in the manufacture of sodium compounds such as Borax.
iii) Sodium carbonate can be used as a cleaning agent for domestic purposes.
iv) It is used for removing permanent hardness of water.
20. What are the uses of Baking Soda? (AS 6) 2 Marks
A: i) Baking soda is added for faster cooking.
ii) It is used in the manufacture of baking powder.
iii) It is used as an ingredient in antacids.
iv) It is also used in soda-acid fire extinguishers.
v) It acts as a mild antiseptic.
21. Which substance is called as Plaster of paris?
How it is prepared? Give its important uses. (AS 1, AS 6) 4 Marks
A: i) Calcium sulphate hemi hydrate is called Plaster of paris. The formula of Plaster of paris is CaSO4. H2O.
ii) Gypsum is heated at 373 K to form Plaster of paris.
Uses of Plaster of paris:
iii) Plaster of paris is used as Plaster for supporting fractured bones in the right position.
iv) Plaster of paris is used for making statues, moulds, black board chalks, toys, materials for decoration and for making surfaces smooth.
22. Explain about pH scale.
Write a short note on pH scale. (AS 1) 4 Marks
A: i) A scale for measuring Hydrogen ion concentration in a solution is called pH scale.
ii) pH value of a solution is simply a number which indicates the acidic or basic nature of a solution.
iii) The range of pH value is from 0 to 14.
iv) For acidic solutions pH range is 0 to 7. For acidic solution pH < 7.
v) For basic solutions, the pH range is 7 to 14. For basic solution pH > 7.
iv) For neutral solution, pH is equal to 7. For neutral solution pH = 7.
vii) As pH increases from 7 to 14, it represents a decrease in H3O ion concentration or an increase in OH ion concentration in the solution.
23. By observing the given pH scale answer the following.
i) What is the pH of Vinegar?
ii) Is gastric juice a strong acid or weak acid?
iii) Which of the body fluid is basic in nature?
iv) Which of the above liquid have strong basic character? (AS4) 4 Marks
A: From the above pH scale
i) The pH of Vinegar is 3.
ii) The pH of gastric juice is 1. So, it is a strong acid.
iii) The body fluid that is basic in nature is blood (pH > 7)
iv) NaOH solution is the strong base because it has highest pH value.
24. Bases which are soluble in water are called as? (AS 1) 1 Mark
25. What are the uses of Hydrochloric acid? (AS 6) 1 Mark
A: HCl is used as cleaning agent for steel, floor and toilets. It is also used in preparation of medicines, cosmetics etc.
26. What is the reaction of Plaster of pairs with water? (AS 1) 1 Mark
A: Plaster of paris is a white powder and on mixing with water, it sets into hard solid mass due to the formation of Gypsum.
CaSO4. H2O + 1 H2O → CaSO4. 2 H2O
(Plaster of paris) (Gypsum)
27. What are the salts obtained from common salt? (AS 1) 1 Mark
A: The various salts obtained from common salt are Sodium hydroxide (NaOH), Baking soda (NaHCO3), Washing soda (Na2CO3), bleaching powder (CaOCl2) and many more.
28. What is the change you observe in Litmus paper with acid? (AS 3) 1 Mark
A: In acidic medium, blue litmus turns red and red litmus remains unchanged.
29. What is the change you observe in litmus paper with base? (AS 3) 1 Mark
A: In the presence of base, red Litmus turns blue and blue litmus remains unchanged.
30. How do you decide the strength of acid or base? (AS 1) 1 Mark
A: The strength of acid or base can be decided on the basis of no. of H3O+ ions or OH-ions produced in a solution.
Short Answer Questions
1. Which colour can be given by phenolphthalein in the presence of HCl? (AS 3) 1 Mark
2. Which colour can be given by phenolphthalein in the presence of KOH solution? (AS 3) 1 Mark.
A: Pink colour.
3. Which colour can be shown by methyl orange in the presence of NH4OH solution. (AS 3) 1Mark
A: Pale yellow colour.
4. Which colour can be shown by methyl orange in the presence of H2SO4. (AS 3) 1 Mark
A: Red Colour.
5. Give two examples for factory indicators? (AS 1) 1 Mark
A: Clove oil, Vanilla essence.
6. When acids reacts with metals gives Hydrogen gas, how can you identify this gas? (AS 3) 1 Mark
A: In a burning stick H2 gas burns with pop sound.
7. Write balanced Chemical reaction between Zn and NaOH? (AS 1) 1 Mark
A: 2 NaOH + Zn →Na2ZnO2 + H2
8. What are the products formed when carbonates react with acid? (AS1) 1 Mark
A: Salts, water and CO2.
9. Write a chemical reaction between HCl and NaHCO3? (AS1) 1 Mark
A: NaHCO3 + HCl → NaCl + H2O + CO2
10. Which precipitate is formed When CO2 gas is passed through lime water? (AS1) 1 Mark
11. What is the final product formed when excess of CO2 gas is passed through lime
water? (AS 1) 1 Mark
A: Calcium Hydrocarbonate [Ca(HCO3)2].
12. Name the type of reaction held between NaOH and HCl? (AS 1) 1 Mark
A: Neutralization reaction.
13. When copper oxide reacts with dil. HCl gives blueish − green compound. Name the compound formed? (AS 1) 1 Mark
A: (CuCl2) Copper Chloride.
14. Which property exhibited by Non − metal oxides? (AS 1) 1 Mark
A: Acidic property.
15. What are the articles and solutions to be used in the experiment, which proves the electrical conductivity of Aqueous acid solution? (AS 3) 1 Mark
A: 230 volts AC. Plug, bulb, conducting wires, graphite rods, beakers, dil. HCl (or) dil. H2SO4 (or) dil.HNO3.
16. Compounds contains H+ ion can exhibit which property? (AS 1) 1 Mark
A: Acid property.
17. Compounds having OH- ions can exhibit which property? (AS 1) 1 Mark
A: Basic property.
18. To obtain dry HCl. in the laboratory, which type of delivery tube is used? (AS 3) 1Mark
A: Guard tube.
19. Which substance is used in guard tube to obtain dry HCl gas? (AS 1) 1 Mark
A: (CaCl2) Calcium Chloride.
20. Water soluble bases are called by which name? (AS 1) 1 Mark
21. What happens when strong acids mixed with water? (AS 3) 1 Mark
A: Produces heat.
22. pH indicates what? (AS 1) 1 Mark
A: pH indicates concentration of the H+ ions in the solution.
23. What is the pH value for strong acids? (AS 1) 1 Mark
A: From 0 to 2.
24. The Concentration H+ ions of a solution is 10-6.What is the pH of the solution? (AS1) 1 Mark
25. The concentration of OH- ions in a solution is 10-12. Then what will be the concentration of H+ ions? (AS 1) 1 Mark
26. The concentration of H+ ions in a solution is 10-7, Then the solution exhibits which property (AS 1) 1 Mark
27. pH of the solution is 13, then what will be its property? (AS 1) 1 Mark
A: Strong base.
28. What will the pH range of Acid rain? (AS 6) 1 Mark
A: Less than 5.6 pH value.
29. At what pH tooth decay takes place? (AS6 ) 1 Mark
A: Less than 5.5 pH value.
30. What is the nature of tooth paste? (AS1) 1 Mark
A: Basic property.
31. Food materials in the mouth under go degradation by Bacteria and produces which substance? (AS 1) 1 Mark
32. What is the weak base used in the Antacid? (AS 6) 1 Mark
A: Milk of Magnesia (Magnesium Hydroxide)
33. Which substance is injected into our body when Honey - bee bites? (AS 6) 1Mark
A: Methanoic acid (Formic acid - HCOOH)
34. Which substance can give relief from the pain caused by Honey - bee bites? (AS 6) 1 Mark
A: Rubbing with Baking Soda on the area effected by Honey-bee bites.
35. Write Chemical formulae of the following salts? (AS 1) 2 Marks
a. Potassium sulphate b. Calcium Sulphate c. Aluminium Sulphate.
A: a. K2SO4 b. CaSO4 c. Al2 (SO4)3.
36. Identify the salts having same positive or negative radicals belonging to a family. (AS 1) 2 Marks
e.g.: NaCl, Na2SO4, KCl, K2SO4
A: NaCl, KCl are belongs to family of chloride salts. NaCl, Na2SO4 are belongs to family of Sodium salts. Na2SO4, K2SO4 are belongs to a family of sulphate salts.
37. Give example for acidic, basic and neutral salts? (AS 1) 2 Marks
A: NaCl is neutral salt
CH3COONa is basic salt
NH4Cl is Acidic salt.
38. What is the pH of KCl aqueous solution and exhibits which property? (AS 1) 2 Marks
A: KCl belongs to strong acid and strong base salt. So, its pH is 7. It exhibits neutral property.
39. What will be the pH of NaHCO3 salt solution and exhibits which property? (AS 1) 2 Marks
A: NaHCO3 belongs to stronger base (NaOH) & weak acid (H2CO3) salt. So, it exhibits basic property. Its pH is above 7.
40. What is the name of large crystals of sodium chloride salt with impurities? (AS1) 1 Mark
A: Rock salt.
41. What are the products formed by the Electrolysis of aqueous NaCl solution? (AS 1) 2 Marks
Electrolysis of Aqueous NaCl gives NaOH, H2 and Cl2 gases.
42. How the bleaching powder is prepared? Write the Chemical reaction for it? (AS 1) 2 Marks
A: Ca(OH)2 + Cl2 → CaOCl2 + H2O
Action of Chlorine ore dry slaked lime produces bleaching powder.
43. What are the uses of bleaching powder? (AS 6) 1 Mark
A: 1. For bleaching the cloths & wood pulp in paper industry.
2) It is used as oxidising agent in chemical industries.
3) Used for disinfecting drinking water.
4) Used as a reagent in the preparation of chloroform.
44. Write main reaction for the preparation of chloroform? (AS 1) 1 Mark
A: NaCl + H2O + CO2 + NH3→ NH4Cl + NaHCO3
45. What are the uses of baking soda? (AS 6) 1 Mark
A: 1. It is used in cooking food materials.
2. It acts as antacid.
3. It acts as mild antiseptic.
46. Write Chemical formula for washing soda? (AS 1) 1 Mark
A: Na2CO3 . 10 H2O
47. How can you prepare Sodium carbonate? (AS 1) 1 Mark
A: On heating NaHCO3 gives Na2CO3
2 NaHCO3 → Na2CO3 + H2O + CO2
48. What are the uses of Na2CO3 - Washing soda? (AS 6) 1 Mark
A: 1) It is used in glass, paper and soap industries.
2) It is used as cleaning agent.
3) It is used for removing permanent hardness of water.
49. Why blue CuSO4 crystals on heating loses its colour? (AS 1) 1 Mark
A: On loosing crystalline water molecules, it will become colourless.
50. How Colourless CuSO4 Crystals regain its colour? (AS 1) 1 Mark
A: By adding few drops of water on colourless crystals, regains its blue colour by converting into hydraded CuSO4. 5 H2O
51. What is formula of gypsum? (AS 1) 1 Mark
A: CaSO4. 2 H2O
52. What is the name of half hydrated calcium sulphate? (AS 1) 1 Mark
A: Plaster of paris
53. How can you prepare plaster of paris? (AS 1) 2 Marks
A: On Carefull heating of gypsum at 373 K, it loses water molecules partially to became hemi hydrated calcium sulphate called plaster of paris.
54. How plaster of paris get into hard mass? (AS 1) 2 Marks
A: On mixing with water, it sets into hard solid mass due to formation of gypsum.
55. How can you get half water molecule in plaster of paris? (AS 1) 1 Mark
A: Two formula units of CaSO4 shares one water molecule So, it will be written as
CaSO4 . H2O
56. During the electrolysis of Brine solution what are gases evolved at cathode and anode? (AS 1) 1 Mark
A: H2 gas at cathode and Cl2 gas at anode evolves.
57. In chloro alkali process, what are substances formed at cathode? (AS 1) 1 Mark
A: The compounds H2 & NaOH are formed at cathode.
58. What are uses of Cl2 gas? (AS 6) 1 Mark
A: 1) It is used in the preparation of PVC, CFC, bleaching powder and pesticides.
59. What are the uses of HCl? (AS 6) 1 Mark
A: 1) For cleaning the steel
2) In the preparation of NH4Cl, medicines and cosmetics.
60. Write the uses of NaOH. (AS 6) 1 Mark
A: 1) It is used in de - greasing the metals.
2) It is used in the preparation of soaps, detergents, artificial threads.