Read and download free pdf of CBSE Class 10 Science Acids Bases And Salts Worksheet Set B. Students and teachers of Class 10 Science can get free printable Worksheets for Class 10 Science in PDF format prepared as per the latest syllabus and examination pattern in your schools. Standard 10 students should practice questions and answers given here for Science in Grade 10 which will help them to improve your knowledge of all important chapters and its topics. Students should also download free pdf of Class 10 Science Worksheets prepared by school teachers as per the latest NCERT, CBSE, KVS books and syllabus issued this academic year and solve important problems with solutions on daily basis to get more score in school exams and tests
Worksheet for Class 10 Science Chapter 2 Acids Bases Salts
Class 10 Science students should refer to the following printable worksheet in Pdf for Chapter 2 Acids Bases Salts in standard 10. This test paper with questions and answers for Grade 10 Science will be very useful for exams and help you to score good marks
Class 10 Science Worksheet for Chapter 2 Acids Bases Salts
Question. 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.
Question. Why should curd and sour substances not be kept in brass and copper vessels?
Answer Curd and other sour substances contain acids. Therefore, when they are kept in brass and copper vessels, the metal reacts with the acid to liberate hydrogen gas and harmful products, thereby spoiling the food.
Question. 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 Hydrogen gas is usually liberated when an acid reacts with a metal.Take few pieces of zinc granules and add 5 ml of dilute H2SO4. Shake it and pass the
gas produced into a soap solution. The bubbles of the soap solution are formed. These soap bubbles contain hydrogen gas.
H2SO4 + Zn → ZnSO4 + H2 ↑
We can test the evolved hydrogen gas by its burning with a pop sound when a candle is brought near the soap bubbles.
Question. 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 CaCO3 (s) + 2HCl (aq) → CaCl2 (aq) + CO2 (g) + H2O (l)
Calcium Carbonate + Hydrochloric acid → Calcium Chloride + Carbon dioxide + Water
Question. 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
HCl (aq) → H+ + Cl-
H+ + H2O → H3O+
When alcohols and glucose are mixed with water then they do not dissolve to form ions.
Hence they do not show acidic character.
Question. 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.
Question. Why does dry HCl gas not change the colour of the dry litmus paper?
Answer : Dry HCl gas not change the colour of the dry litmus paper because it has no Hydrogen ions (H+) in it.
Question. While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?
Answer : Since the process of dissolving an acid in water is exothermic, it is always recommended that acid should be added to water. If it is done the other way, then it is possible that because of the large amount of heat generated, the mixture splashes out and causes burns.
Question. How is the concentration of hydronium ions (H3O+) affected when a solution of an acid is diluted?
Answer : When an acid is diluted, the concentration of hydronium ions (H3O+) per unit volume decreases. This means that the strength of the acid decreases.
Question. How is the concentration of hydroxide ions (OH−) affected when excess base is dissolved in a solution of sodium hydroxide?
Answer : The concentration of hydroxide ions (OH−) would increase when excess base is dissolved in a solution of sodium hydroxide.
Question. You have two solutions, A and B. The pH of solution A is 6 and pH of solution B is 8. Which solution has more hydrogen ion concentration? Which of this is acidic and which one is basic?
Answer : A pH value of less than 7 indicates an acidic solution, while greater than 7 indicates a basic solution. Therefore, the solution with pH = 6 is acidic and has more hydrogen ion concentration than the solution of pH = 8 which is basic.
Question. 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.
Question. Do basic solutions also have H+ (aq) ions? If yes, then why are these basic?
Answer : Yes, basic solution also has H+ ions. However, their concentration is less as compared
to the concentration of OH- ions that makes the solution basic.
Question. 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 and improper for cultivation, then to increase the basicity of soil, the farmer would treat the soil with quick lime or slaked lime or chalk.
Question. What is the common name of the compound CaOCl2?
Answer : Bleaching Powder.
Question. Name the substance which on treatment with chlorine yields bleaching powder?
Answer : Calcium hydroxide [Ca(OH)2]
Question. Name the sodium compound which is used for softening hard water.
Answer : Washing soda (Na2CO3.10H2O)
Question. 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.
Question. A solution turns red litmus blue, its pH is likely to be
Answer : D
Question. A solution reacts with crushed egg-shells to give a gas that turns lime-water milky.
The solution contains
Answer : B
Question. 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 of HCl solution (the same solution as before) required to neutralise it will be
(a) 4 mL
(c) 12 mL
(d) 16 mL
Answer : D
Question. Which one of the following types of medicines is used for treating indigestion?
Answer : C
Question. 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.
(a) H2SO4 (aq) + Zn (s) → ZnSO4 (aq) + H2 (g)
(b) 2HCl (aq) + Mg (s) → MgCl (aq) + H2 (g)
(c) 3H2SO4 (aq) + 2Al (s) → Al2SO4 (aq) + 3H2 (g)
(d) 6HCl (aq) + 2Fe (s) → 2FeCl3 (aq) + 3H2 (g)
Question. Compounds such as alcohols and glucose also contain hydrogen but are not categorized as acids. Describe an activity to prove it.
Answer : Two nails are fitted on a cork and are kept it in a 100 mL beaker. The nails are then connected to the two terminals of a 6-volt battery through a bulb and a switch. Some dilute HCl is poured in the beaker and the current is switched on. The same experiment is then performed with glucose solution and alcohol solution.
Observations: It will be observed that the bulb glows in the HCl solution and does not glow in the glucose solution.
Result: HCl dissociates into H+and Cl−ions. These ions conduct electricity in the solution resulting in the glowing of the bulb. On the other hand, the glucose solution does not dissociate into ions. Therefore, it does not conduct electricity.
Conclusion: From this activity, it can be concluded that all acids contain hydrogen but not all compounds containing hydrogen are acids.
That is why, though alcohols and glucose contain hydrogen, they are not categorised as acids.
Question. 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.
Question. Why do acids not show acidic behaviour in the absence of water?
Answer : Acids do not show acidic behaviour in the absence of water because the dissociation of hydrogen ions from an acid occurs in the presence of water only.
Question. 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
(b) strongly alkaline?
(c) strongly acidic?
(d) weakly acidic?
(e) weakly alkaline?
Arrange the pH in increasing order of hydrogen-ion concentration.
(a) Neutral →Solution D with pH 7
(b) Strongly alkaline →Solution C with pH 11
(c) Strongly acidic →Solution B with pH 1
(d) Weakly acidic →Solution A with pH 4
(e) Weakly alkaline →Solution E with pH 9
The pH can be arranged in the increasing order of the concentration of hydrogen ions as: 11 < 9 < 7 < 4 < 1.
Question. 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?
The fizzing will occur strongly in test tube A, in which hydrochloric acid (HCl) is added.
This is because HCl is a stronger acid than CH3COOH and therefore produces hydrogen gas at a faster speed due to which fizzing occurs.
Question. Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd?
Explain your Answer :.
Answer : The pH of milk is 6. As it changes to curd, the pH will reduce because curd is acidic in nature. The acids present in it decrease the pH.
Question. 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?
(a) The milkman shifts the pH of the fresh milk from 6 to slightly alkaline because in alkaline condition, milk does not set as curd easily.
(b) Since this milk is slightly basic than usual milk, acids produced to set the curd are neutralized by the base. Therefore, it takes a longer time for the curd to set.
Question. 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.
Question. What is a neutralization reaction? Give two examples.
Answer : A reaction in which an acid and base react with each other to give a salt and water is termed as neutralization reaction.For Example:
(i) NaOH + HCl → NaCl + H2O
(ii) HNO3 + KOH → KNO3 + H2O
Question. Give two important uses of washing soda and baking soda.
Answer : Two important uses of washing soda are:
→ It is used in glass, soap, and paper industries.
→ It is used to remove permanent hardness of water.
Two important uses of baking soda are:
→ It is used as baking powder. Baking powder is a mixture of baking soda and a mild acid known as tartaric acid. When it is heated or mixed in water, it releases CO2 that makes bread or cake fluffy.
→ It is used in soda-acid fire extinguishers.
Question. An aqueous solution ‘A’ turns phenol-phthalein solution pink. On addition of an aqueous solution ‘B’ to ‘A’ and ‘B’.
(a) A is strongly basic and B is a weak base.
(b) A is strongly acidic and B is a weak acid.
(c) A has pH greater than 7 and B has pH less than 7.
(d) A has pH less than 7 and B has pH greater than 7.
Answer : D
Question. When you add a few drops of acetic acid to a test-tube containing sodium bicarbonate powder, which one of the following is your observation ?
(a) No reaction takes place.
(b) A colourless gas with pungent smell is released with brisk effervescence.
(c) A brown coloured gas is released with brisk effervescence.
(d) Formation of bubbles of a colourless and odourless gas.
Answer : D
Question. A student requires hard water for an experiment in his laboratory which is not available in the neighbouring area. In the laboratory there are some salts, which when dissolved in distilled water can convert it into hard water. Select from the following groups of salts, a group, each salt of which when dissolved in distilled water will make it hard.
(a) Sodium chloride, potassium chloride
(b) Sodium sulphate, potassium sulphate
(c) Sodium sulphate, calcium sulphate
(d) Calcium sulphate, calcium chloride
Answer : D
Question. You have four test tubes, A, B, C and D containing sodium carbonate, sodium chloride, lime water and blue litmus solutions respectively. Out of these the material of which test tube/test tubes would be suitable for the correct test of acetic/ethanoic acid ?
(a) Only A
(b) A and B
(c) B and C
(d) A and D
Answer : D
Question. For demonstrating the preparation of soap in the laboratory which of the following combination of an oil and a base would be most suitable ?
(a) Mustard oil and calcium hydroxide
(b) Castor oil and calcium hydroxide
(c) Turpentine oil and sodium hydroxide
(d) Mustard oil and sodium hydroxide.
Answer : D
Question. A student took four test tubes P, Q, R and S and filled about 8 ml. of distilled water in each. After that he dissolved an equal amount of Na2SO4 in P, K2SO4 in Q, CaSO4 in R and MgSO4 in S. On adding an equal amount of soap solution and shaking each test tube well, a good amount of lather will be obtained in the test tubes :
(a) P and Q
(b) P and R
(c) P, Q and S
(d) Q, R and S
Answer : A
Question. If you take some distilled water in a test-tube, add an equal amount of acetic acid to it, shake the test-tube well and leave it undisturbed on the test-tube stand, then after about 5 minutes, what would you observe ?
(a) There is a layer of water over the layer of acetic acid.
(b) A precipitate is settling at the bottom of the testtube.
(c) Bubbles of colourless gas are coming out of the test-tube.
(d) There is a clear, colourless transparent solution in the test-tube.
Answer : D
Question. Which of the following is used for dissolution of gold ?
(a) Hydrochloric acid
(b) Sulphuric acid
(c) Nitric acid
(d) Aqua regia
Answer : D
Question. Which of the following is not a mineral acid ?
(a) Hydrochloric acid
(b) Citric acid
(c) Sulphuric acid
(d) Nitric acid
Answer : B
Question. Which among the following is not a base ?
Answer : D
Question. Which of the following gives the correct increasing order of acidic strength ?
(a) Water < Acetic acid < Hydrochloric acid
(b) Water < Hydrochloric acid < Acetic acid
(c) Acetic acid < Water < Hydrochloric acid
(d) Hydrochloric acid < Water < Acetic acid
Answer : A
Question. Sodium hydrogen carbonate when added to acetic acid evolves a gas. Which of the following statements are true about the gas evolved ?
(i) It turns lime water milky.
(ii) It extinguishes a burning splinter.
(iii)It dissolves in a solution of sodium hydroxide.
(iv)It has a pungent odour.
(a) (i) and (ii)
(b) (i), (ii) and (iii)
(c) (ii), (iii) and (iv)
(d) (i) and (iv)
Answer : B
Question. If a few drops of a concentrated acid accidentally spills over the hand of a student, what should be done ?
(a) Wash the hand with saline solution.
(b) Wash the hand immediately with plenty of water and apply a paste of sodium hydrogen carbonate.
(c) After washing with plenty of water apply solution of sodium hydroxide on the hand.
(d) Neutralise the acid with a strong alkali.
Answer : B
Question. One of the constituents of baking powder is sodium hydrogen carbonate, the other constituent is :
(a) Hydrochloric acid
(b) Tartaric acid
(c) Acetic acid
(d) Sulphuric acid
Answer : B
Question. Which of the following phenomena occur, when a small amount of acid is added to water ?
(i) Ionisation, (ii) Neutralisation,
(iii) Dilution, (iv) Salt formation.
(a) (i) and (ii)
(b) (i) and (iii)
(c) (ii) and (iii)
(d) (ii) and (iv)
Answer : B
Question. Which one of the following can be used as an acid– base indicator by a visually impaired student?
(c) Vanilla essence
(d) Petunia leaves
Answer : C
Question. Which of the following substance will not give carbon dioxide on treatment with dilute acid ?
(c) Baking soda
Answer : D
Question. Match the following
Column I Column II
(a) Bleaching powder (i) Preparation of glass
(b) Baking soda (ii) Production of H2 and Cl2
(c) Washing soda (iii) Decolourisation
(d) Sodium chloride (iv) Antacid
Answer : (a) (iii), (b) (iv), (c) (i), (d) (ii)
Question. Fill in the blanks
(a) The pH of the gastric juices released during digestion is .................. .
(b) When acid reacts with a metal, .................. gas is evolved.
(c) On heating gypsum, it loses water molecules and form .................. .
(a) Less than 7, (b) H2 (hydrogen), (c) CaSO4. 1/2H2O (Plaster of paris).
Assertion and Reasoning Based Questions
Directions : In the following questions, a statement of assertion is followed by a statement of reason. Mark the correct choice as :
(a) If both assertion and reason are true and reason is the correct explanation of assertion.
(b) If both assertion and reason are true, but reason is not the correct explanation of assertion.
(c) If assertion is true, but reason is false.
(d) If assertion is false but reason is true.
Question. Assertion : Solutions of compounds like alcohol and glucose do not show acidic character.
Reason : They do not show acidic character because they do not dissociate into ions.
Answer : A
Question. Assertion : Dry HCl gas does not change the colour of the dry litmus paper.
Reason : It is because dry HCl does not contain the OH– ions.
Answer : C
Question. Assertion : Curd and sour substances should not be stored in copper vessels.
Reason : Curd and other sour substances should not be kept in brass and copper vessels as they contain acids.
Answer : A
Question. Assertion : Calcium starts floating when added in water.
Reason : Calcium starts floating because the bubbles of oxygen gas which are formed during the reaction stick to the surface of the metal.
Answer : C
Question. Assertion : Tap water conducts electricity but distilled water does not conducts electricity.
Reason : Tap water contains ions whereas distilled water does not contain ions.
Answer : A
Question : Name the acid along with its'chemical formula present in ant sting.
Answer : The acid present in ant sting is methanoic acid (formic acid). The chemical formula is HCOOH. Explanation: When an ant stings, it leaves formic acid (Methanoic acid) which causes pain and irritation. To get relief from the sting, mild base like baking soda on the stung area gives relief.
Question : A solution ‘X’ gives orange colour when a drop of it falls on pH paper, while another solution ‘Y’ gives bluish colour when a drop of it falls on pH paper. What is the nature of both the solutions? Determine the pH of solutions ‘X’ and ‘Y’.
Answer : Comparing with the pH chart, we find that orange colour corresponds to pH value of about 4 and blue colour to pH value of about 10. (1) X is therefore acidic and pH is around 4. (2) Y is basic having a pH of about 10.
Question : The pH of soil A is 7.5 while that of soil B is 4.5. Which of the two soils should be treated with chalk and why?
Answer : Chalk or CaCO3 is basic in nature. As the soil B having pH 4.5 is acidic, it should be treated with powdered chalk to reduce its acidity by increasing its pH. Soil A is slightly alkaline.
Question : Blue litmus solution is added to two test tubes A and B containing dilute HCl and NaOH solution respectively. In which test tube a colour change will observed? State the colour change and give its reason.
Answer : Colour change will be observed in Test tube A containing dil HCl. It will change the colour of blue litmus to red. Test tube contains dil HCl which is an acid and acids turn the colour of blue litmus to red as they contain H+ ions.
Question : What types of ions are formed:
(a) when an acid is dissolved in water
(b) when a base is dissolved in water ?
Answer : When an acid is dissolved in water, it forms hydrogen or H+ ions whereas it forms hydroxide or OH- ions when a base is dissolved in water.
Question : State the effect of concentration of H+(aq) ions on the nature of the solution. Do basic solutions also have H+(aq) ions ? If yes, then why are these basic?
Answer : The solution becomes more acidic when the concentration of H+ (aq) ions increases. Yes, basic solutions also have H+ (aq) ions. They are basic as the concentration of OH– ions is more than that of H+ ions in the solution.
Question. Identify the acid and base which form sodium hydrogen carbonate. Write chemical equation in support of your answer. State whether this compound is acidic, basic or neutral. Also write its pH value.
The acid and base that forms sodium hydrogen carbonate are as follows :
Acid – H2CO3
Base – NaOH
The chemical equation for its formation will be :
NaOH + H2CO3 → NaHCO3 + H2O
Sodium Hydrogen Sodium
Hydroxide Bicarbonate Hydrogen
Question. The pH of a salt used to make tasty and crispy pakoras is 14. Identify the salt and write a chemical equation for its formation. List its two uses.
The salt commonly used to make tasty and crispy
pakoras is baking soda i.e., sodium hydrogen carbonate (NaHCO3).
Chemical equation for its formation :
NaCl + H2O + CO2 + NH3 → NH4Cl + NaHCO3
Uses of Baking Soda :
(a) It is used in fire extinguisher.
(b) It is also used as ingredient of antacid.
Question. Complete the following chemical equations :
(a) CH3COOH + Na2CO3 →
(b) CH4 + O2 →
(c) 2C2H5OH + Na →
(a) 2CH3COOH +Na2CO3 → 2CH3COONa + H2O + CO2↑
(b) CH4 + 2O2 Δ→ CO2↑ + 2H2O
(c) 2C2H5OH + 2Na → 2C2H5ONa + H2↑
Question. What happens when an acid reacts with a base ?
Explain by taking the example of hydrochloric acid and sodium hydroxide. Give equation of the chemical reaction which takes place. What is the special name of such a reaction ?
When an acid reacts with a base, then a salt and water are formed. When hydrochloric acid reacts with sodium hydroxide solution, then a neutralisation reaction takes place to form sodium chloride and water.
NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)
Such a reaction is termed as neutralisation reaction.
Question. What happens when chlorine is passed over slaked lime at 313 K ? Write chemical equation of the reaction involved and state two uses of the product obtained.
Bleaching powder is formed.
Ca(OH)2 + Cl2 → CaOCl2 + H2O
(a) It is used as bleaching agent in paper and textile industries.
(b) It is used as disinfectant in purification of drinking water.
Question. How following metals react with acids : magnesium,zinc, iron and copper?
(a) Magnesium react vigorously with acids.
(b) Zinc reacts less vigorously with acids than magnesium.
(c) Iron react slowly.
(d) Copper does not react at all.
Question. Which gas is usually liberated when an acid rea cts with a metal ? Illustrate with an example. How will you test for the presence of this gas ?
Hydrogen gas is usually liberated when an acid reacts with a metal.Take few pieces of zinc granules and add 5 ml of dilute H2SO4. Shake it and pass the gas produced into a soap
solution. The bubbles of the soap solution are formed.
These soap bubbles contain hydrogen gas.
Zn + 2H2SO4 → Zn(SO4)2 + 2H2
Zinc Sulphuric acid Zinc Sulphate
We can test the evolved hydrogen gas by burning it with a pop sound when a candle is brought near the soap bubbles.
Question. (a) What is produced if an acid is added to a base ?
(b) Why does dry HCl gas not change the colour of dry litmus paper ?
(c) What colour does phenolphthalein indicator turn when added to an alkali (such as sodium hydroxide) ?
(a) Salt and water.
(b) Dry HCl gas does not change the colour of dry litmus paper because it has no hydrogen ions (H+ ions) in it which can impart acidic properties to it.
Question. Why should curd and sour substances not be kept in brass and copper vessels ?
Answer : Curd and other sour substances not be kept in brass and copper vessels as they contain acids. When these substances are kept in brass and copper vessels, the metal reacts with the acid to liberate hydrogen gas and harmful products. As a result, food gets spoiled.
Question. You have been provided with three test-tubes. One of these test-tubes contains distilled water and the other two contain an acidic and a basic solution respectively.If you are given only blue litmus paper, how will you identify the contents of each test-tube ?
Answer : Acidic solution will turn blue litmus red. This red litmus will turn blue in basic solution. Distilled water will have no effect on any type of litmus paper.
Question. A group of students measured the pH of some substances they found in their homes. Their results are given in the following table :
(a) What would the students have used to measure the pH ?
(b) Which solution is the most acidic ?
(c) Which solution is the most alkaline ?
(d) Which solutions are neutral ?
(e) Which solution can be used to treat wasp stings ?
(f) Which solution can be used to treat bee stings ?
(a) Universal indicator paper is used to measure the pH.
(b) Lemon juice with pH = 2.5 is the most acidic.
(c) Household ammonia with pH = 12 is the most alkaline.
(d) Salt solution and sugar solution with pH = 7 are neutral.
(e) Vinegar (acid) can be used to treat wasp stings since it injects an alkaline liquid into the skin.
(f) Baking soda can be used to treat bee stings since, it injects methanoic acid into the skin.
Question. 1 g of solid sodium chloride is taken in a clean and dry test tube and 2 ml of conc. sulphuric acid is added to it. If the gas evolved is tested first with dry and then with wet blue litmus paper, in which case will the litmus paper change colour ? Give reason for your answer. What inference can be drawn about the nature of the evolved gas ? Support your answer with chemical equation for the reaction.
Wet blue litmus paper will change the colour because hydrogen ions are produced by HCl in the presence of water. It has acidic nature and the reaction involved is :
HCl + H2O → H3O+ + Cl–
Question. (a) For the preparation of cakes, baking powder is used. If at home your mother uses baking soda instead of baking powder, how will it affect the taste of the cake and why ?
(b) How is baking soda be converted into baking powder ?
(c) What makes the cake soft and spongy ?
(a) The cake will have a bitter taste because of the formation of Na2CO3 or sodium carbonate while baking or heating the cake.
(b) By adding tartaric acid baking soda can be converted to baking powder.
(c) The CO2 gas liberated makes the cake soft and spongy.
Question. (a) If you are asked to report your observations about the following two properties of acetic acid, what would you report ?
(ii) Effect on litmus
(b) If you take a pinch of sodium hydrogen carbonate powder in a test-tube and add drop-by-drop acetic acid to it, what would you observe immediately ? List any two main observations.
(a) (i) Smells like vinegar.
(ii) Turns blue litmus red.
(b) (i) Brisk effervescence will be observed.
(ii) Evolution of colourless gas.
Long Answers Type Questions
Question. In the following schematic diagram for the preparation of hydrogen gas as shown in figure what would happen if following changes are made ?
(a) In place of zinc granules, same amount of zinc dust is taken in the test tube.
(b) Instead of dilute sulphuric acid, dilute hydrochloric acid is taken.
(c) In place of zinc, copper turnings are taken.
(d) Sodium hydroxide is taken in place of dilute sulphuric acid and the tube is heated.
(a) If in place of zinc granules, same amount of zinc dust is taken, hydrogen gas will evolve with greater speed.
(b) If instead of dilute sulphuric acid, dilute hydrochloric acid is taken, almost same amount of gas is evolved.
(c) Hydrogen gas is not evolved.
(d) If sodium hydroxide is taken, sodium zincate is formed and hydrogen gas will be evolved.
Zn + 2NaOH → Na2ZnO2+ H2
Question. For making cake, baking powder is taken. If at home your mother uses baking soda instead of baking powder in cake.
(a) How will it affect the taste of the cake and why ?
(b) How can baking soda be converted into baking powder ?
(c) What is the role of tartaric acid added to baking soda ?
(a) Baking soda is sodium hydrogen carbonate. On heating, it is converted into sodium carbonate which is bitter to taste. Thus, if baking soda is used the taste of cake changes.
NaHCO3 → Na2CO3 + H2O + CO2
(b) Baking powder is a mixture of baking soda, cream of tartar (a dry acid), and sometimes corn starch.
Therefore, baking soda can be converted into baking powder by the addition of appropriate amount of tartaric acid to it.
(c) Tartaric acid is added to neutralise the sodium carbonate formed on heating by the decomposition of NaHCO3. If it is not added, the cake would taste bitter due to the presence of sodium carbonate in it. Also, CO2 produced during the reaction causes cake to rise making them soft and spongy.
Question. Write the name, method of preparation and uses of the following :
(a) CaOCl2, (b) CaSO4. 1/2H2O, (c) NaHCO3.
(a) CaOCl2 : Its chemical name is Calcium oxychloride.
It is also known as bleaching powder.
Preparation : Bleaching powder is produced by the action of chlorine on dry slaked lime.
Ca(OH)2 + Cl2 → CaOCl2 + H2O
Uses : It is used as bleaching agent in textile industry.
(b) CaSO4.1/2 H2O : It is Calcium sulphate hemihydrate.
It is also known as Plaster of Paris.
Plaster of Paris is prepared by heating 1/2H2O Gypsum at 373 K.
CaSO4. 2H2O → CaSO4. 1/2 H2O + 3/2 H2O
Uses : It is used to join bones, buildings and in dentistry.
(c) NaHCO3 : Its chemical name is sodium hydrogen carbonate (NaHCO3). Also known as Baking soda.
NaCl + H2O + CO2 + NH3 → NH4Cl + NaHCO3
Uses : It is used in food industry and bakery, as an antacid and mild antiseptic.
Question. (a) What is ‘pH’ scale ? Explain. How the pH of a neutral solution can be changed to acidic or basic ?
(b) Why is calcium sulphate hemihydrate called ‘Plaster of Paris’ ?
(a) The strength of an acid or a base is expressed in terms of hydronium ion concentration. This is expressed on a scale known as ‘pH’ scale. It is a 14 point scale; i.e., it has values ranging from 0 to 14, indicating the value of negative logs of H+ ion concentration of the solution. In the pH scale pH=7 means neutral solution, pH less than 7 means acidic solution and pH more than 7 means basic solution.
pH of a neutral solution can be changed by adding acid or base. If a small amount of acid is added, its pH decreases and solution becomes acidic. If few drops of base is added, its pH increases and solution becomes basic.
(b) Plaster of Paris gets its name from large gypsum deposits in Montmartre in Paris. We know that Plaster of Paris, which is chemically calcium sulphate hemihydrate is obtained by heating gypsum. So, the origin of the name ‘Plaster of Paris’ is the fact that the source material gypsum is found in large deposits at Montmartre in Paris.
Question. Write uses of (a) Acids (b) Bases (c) Salts.
(a) Uses of acid :
(i) Hydrochloric acid is used in many industries like cleaning boilers from inside, cleaning sink and sanitary etc.
(ii) Nitric acid is used for making fertilizers,cleansing of ornaments of gold and silver.
(iii) Sulphuric acid is used in cells, car battery etc.It is known as King of Chemicals.
(b) Uses of bases :
(i) Sodium hydroxide is used to make soaps, in paper industry and in textile industry.
(ii) Calcium hydroxide is used to remove acidity of soil. It is an important constituent of lime and pesticides.
(iii) Milk of magnesia (Magneisum hydroxide) is used as an antacid.
(c) Uses of salts :
(i) Calcium carbonate is used to make floors.
(ii) In metallurgy for extraction of iron and in making of cement.
(iii) Silver nitrate is used in photography, Ammonium nitrate is used as explosive and in making fertilizers.
(iv) Alum(K2SO4.Al2SO4.24H2O) is used to clean water.
Question. (a) Yellow stain of an Indian style vegetable curry on a white cloth turns reddish brown on application of soap on the cloth. What is the reason behind ?
(b) What is the colour of litmus solution when it is neither acidic nor basic ?
(a) The yellow stain contains turmeric (used as ingredient in most of the Indian curries) which is a natural indicator and it changes its colour from yellow to reddish brown when soap,which is basic in nature and is applied on the moist or wet cloth.
(b) Litmus solution is purple in colour when it is neither acidic nor basic.
Question. In a reaction of sodium chloride and sulphuric acid, hydrochloric acid is obtained as a gaseous product however, the evolved gas fails to turn the blue litmus paper red. What could be the reason ? But, if the litmus paper to be used is made moist prior hand, the evolved gas turns the moist litmus paper to red colour. Explain the observations.
Answer : The reaction can be shown as follows :
2NaCl + H2SO4 → Na2SO4 + HCl ↑
Sodium chloride Sodium sulphat e Hydrochloric acid
Hydrochloric acid in gaseous state is unionised hence cannot furnish the H+ ions, hence there is no reaction and colour change with litmus paper. On the other hand, when exposed to moist litmus paper, the hydrochloric acid gas reacts with water molecules present on paper and furnishes H+ ions which then react with litmus paper and changes its colour to red.
Question. A chemical compound X is prepared using sodium chloride as starting material. The compound X is used for faster cooking. It is also found as an ingredient in medicine to treat indigestion.
(a) Identify the compound X.
(b) Give an equation for the chemical reaction which takes place upon heating X during cooking.
(c) Which quality of compound X makes it suitable for treating indigestion ?
(a) Compound X is sodium hydrogen carbonate,NaHCO3.
Heat→ Na2CO3 + H2O + CO2
Sodium hydrogen carbonate Sodium carbonate
(c) NaHCO3 is a mild non-corrosive base and can be used to neutralise acid. Indigestion caused by increased acidity in stomach can be reduced by consuming medicine containing NaHCO3.
Question. A soil sample solution was analysed with universal pH indicator paper and the colour of the paper turned yellowish.
(a) What is the nature of soil ?
(b) What type of substance should the farmer add to the soil in order to get a suitable soil for farming ?
(a) As the soil solution turned universal indicator paper yellow, it indicates that the soil solution is acidic and contains a higher H+ ion concentration.
(b) The farmer should add some basic additives to soil such as slaked lime (calcium hydroxide) or quick lime (calcium oxide) to enhance the productivity of the soil.
Question. A student prepared a special ink using some basic chemical compound. The colour of the ink is blue.The imprints marked on white paper using this ink turn invisible when the paper is heated slightly and the imprints reappear when the paper is kept outside for some time. Explain the observations.
The chemical compound being used by the student is hydrated copper sulphate (CuSO4.5H2O) which is blue in colour. On heating it loses its water of crystallization and becomes white in colour, hence white colour on white paper becomes invisible. When the paper is left exposed to atmosphere, CuSO4 crystals again absorb water from surrounding and turn blue in colour.
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