CBSE Class 10 Science Acids Bases And Salts Worksheet Set E

Question. Write the name, method of preparation and uses of the following :
(a) \( \text{CaOCl}_2 \), (b) \( \text{CaSO}_4 \cdot \frac{1}{2} \text{H}_2\text{O} \), (c) \( \text{NaHCO}_3 \).
Answer:
(a) \( \text{CaOCl}_2 \) : 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.
\( \text{Ca(OH)}_2 + \text{Cl}_2 \rightarrow \text{CaOCl}_2 + \text{H}_2\text{O} \)
Uses : It is used as bleaching agent in textile industry.
(b) \( \text{CaSO}_4 \cdot \frac{1}{2} \text{H}_2\text{O} \) : It is Calcium sulphate hemihydrate. It is also known as Plaster of Paris.
Plaster of Paris is prepared by heating Gypsum at 373 K.
\( \text{CaSO}_4 \cdot 2\text{H}_2\text{O} \rightarrow \text{CaSO}_4 \cdot \frac{1}{2} \text{H}_2\text{O} + \frac{3}{2} \text{H}_2\text{O} \)
Uses : It is used to join bones, buildings and in dentistry.
(c) \( \text{NaHCO}_3 \) : Its chemical name is sodium hydrogen carbonate (\( \text{NaHCO}_3 \)). Also known as Baking soda.
Preparation :
\( \text{NaCl} + \text{H}_2\text{O} + \text{CO}_2 + \text{NH}_3 \rightarrow \text{NH}_4\text{Cl} + \text{NaHCO}_3 \)
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’ ?
Answer:
(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 \( \text{H}^+ \) 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.
Answer:
(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 (Magnesium 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 (\( \text{K}_2\text{SO}_4 \cdot \text{Al}_2(\text{SO}_4)_3 \cdot 24\text{H}_2\text{O} \)) is used to clean water.

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.
(a) (a)
(b) (b)
(c) (c)
(d) (d)
Answer: (a)
Solutions of compounds like alcohol and glucose do not show acidic character because like acids such as HCl which dissociates into \( \text{H}^+ \) and \( \text{Cl}^- \) ion these solutions do not dissociate into ions. Thus both assertion and reason are true and reason is the correct explanation of the assertion.

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 \( \text{OH}^- \) ions.
(a) (a)
(b) (b)
(c) (c)
(d) (d)
Answer: (c)
Colour of the litmus paper is changed by the hydrogen ions. Dry HCl gas does not contain \( \text{H}^+ \) ions. Acids give hydrogen ions only in the presence of ions. In case of dry litmus paper and dry HCl, water is not present. Therefore, the colour of the litmus paper does not change. Thus assertion is true, but reason is false.

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.
(a) (a)
(b) (b)
(c) (c)
(d) (d)
Answer: (a)
When curd and sour substance are kept in brass and copper vessels, the metal reacts with the acid to liberate hydrogen gas and harmful products are obtained due to which the food gets spoiled. Thus both assertion and reason are true and reason is the correct explanation of the assertion.

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.
(a) (a)
(b) (b)
(c) (c)
(d) (d)
Answer: (c)
Hydrogen gas is released when calcium reacts with water. Calcium starts floating because the bubbles of hydrogen gas which are formed during the reaction stick to the surface of the metal. As a result, calcium starts floating on water. Thus assertion is true, but reason is false.

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.
(a) (a)
(b) (b)
(c) (c)
(d) (d)
Answer: (a)
Tap water conducts electricity as it contains ions whereas distilled water does not contain ions. Thus both assertion and reason are true and reason is the correct explanation of the assertion.

Creating Based Questions

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 ?
Answer:
(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 :
\( 2\text{NaCl} + \text{H}_2\text{SO}_4 \rightarrow \text{Na}_2\text{SO}_4 + 2\text{HCl}\uparrow \)
Hydrochloric acid in gaseous state is unionised hence cannot furnish the \( \text{H}^+ \) 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 \( \text{H}^+ \) 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 ?
Answer:
(a) Compound X is sodium hydrogen carbonate, \( \text{NaHCO}_3 \).
(b) \( 2\text{NaHCO}_3 \xrightarrow{\text{Heat}} \text{Na}_2\text{CO}_3 + \text{H}_2\text{O} + \text{CO}_2 \)
(c) \( \text{NaHCO}_3 \) 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 \( \text{NaHCO}_3 \).

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 ?
Answer:
(a) As the soil solution turned universal indicator paper yellow, it indicates that the soil solution is acidic and contains a higher \( \text{H}^+ \) 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.
Answer:
The chemical compound being used by the student is hydrated copper sulphate (\( \text{CuSO}_4 \cdot 5\text{H}_2\text{O} \)) 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, \( \text{CuSO}_4 \) crystals again absorb water from surrounding and turn blue in colour.

Paragraph/Table and Case Study Based Questions

Reshma broke her leg in an accident. She went to see the Dr. Sant Prakash. On examination, Dr. Prakash mixed the white power in water and applied to her leg along with the cotton and gauze. After a while, it turned into white, solid, hard mass. He said that it would support her fractured bone in the right position.

Question. After treatment, the doctor repacked the white powder back into moisture proof, airtight container. Why?
(a) The fungus growth will occur in open
(b) The powder would react to moisture and turn into solid mass
(c) The powder with react to sunlight and turn into solid mass
(d) To prevent the stealing of the powder as it is very expensive
Answer: (b)

Question. What is 'white, solid hard mass' called as?
(a) Talcum powder
(b) Paris of Plaster
(c) Plaster of Paris
(d) Copper sulphate
Answer: (c)

Question. The reaction involved in the formation of white mass is :
(a) Combustion
(b) Oxidation
(c) Mineralisation
(d) Crystallisation
Answer: (d)

Question. The graph shows the porosity and expansion of plaster with respect to water content. At what temperature, the reaction would occur?
(a) 373K
(b) 673K
(c) 273K
(d) 573K
Answer: (a)

Question. Study the following reaction and choose the correct option:
\( \text{CaSO}_4 \cdot \frac{1}{2} \text{H}_2\text{O} + \frac{3}{2} \text{H}_2\text{O} \rightarrow \text{CaSO}_4 \cdot 2\text{H}_2\text{O} \)
(a) Reactant is calcium hemihydrate, product is Gypsum
(b) Reactant is Gypsum, product is calcium hemihydrate
(c) Reactant is Gypsum, product is calcium sulphate hemihydrate
(d) Reactant is calcium sulphate hemihydrate, product is Gypsum
Answer: (d)

Harsha collected various solutions. Using a pH paper, she found out the approximate pH values of the solutions. She labelled the solutions as A, B, C, D and E, and presented their pH values on a line graph. Observe the line graph carefully and answer the following questions.
(Graph indicates: A=1.3, B=7.4, C=2.2, D=14, E=10)

Question. Which of the following could be solution A?
(a) Carrot juice
(b) Sodium hydroxide solution
(c) Water
(d) Gastric juice
Answer: (d)

Question. Which one of the following statements is correct?
(a) Solution C is basic in nature.
(b) Solution B is more acidic than A.
(c) Solution D is more basic than E.
(d) Solution A is neutral in nature.
Answer: (c)

Question. Which of the following could be the solution B?
(a) Blood
(b) Lemon juice
(c) HCl
(d) Coffee
Answer: (a)

Question. What colour had pH strip shown with solution D?
(a) Red
(b) Yellow
(c) Violet
(d) Green
Answer: (c)

Question. Which one of the following arrangements is representing increasing concentration of \( \text{H}^+ \) ions in the solution?
(a) A < B < C < D < E
(b) D < E < B < C < A
(c) A < C < B < E < D
(d) E < D < C < B < A
Answer: (b)

Sodium chloride is known as common salt. Its main source is sea water. It is also exists in the form of rocks and is called rock salt. Common salt is an important component of our food. It is also used for preparing sodium hydroxide, baking soda, washing soda etc.
Sodium Hydroxide is prepared by passing electricity through an aqueous solution of sodium chloride also known as brine. This process is known as chloralkali process. It is white translucent solid. Crystals of sodium hydroxide are deliquescent. It is readily soluble in water and gives strong alkaline solution.
Washing Soda is sodium carbonate decahydrate. It is prepared by heating baking soda. Recrystallisation of sodium carbonate gives a compound, which is used for removing permanent hardness of water. It is used in glass, soap and paper industries. It can be used as a cleaning agent for domestic purposes.
Plaster of Paris is is obtained by heating Gypsum upto 373K. On treatment with water it is again converted into gypsum and sets as a hard mass. It is used by doctors for setting fractured bones. It is used for making statues, models and other decorative materials.

Question. What is the chemical formula of plaster of paris?
Answer: \( \text{CaSO}_4 \cdot \frac{1}{2} \text{H}_2\text{O} \)

Question. Name the chemical compound obtained by the recrystallization of sodium carbonate.
Answer: Washing soda

Question. Name the solution that is used to prepare caustic soda.
Answer: Brine solution

Question. Which of these statements is incorrect?
(i) On treatment with water plaster of paris is again converted into gypsum.
(ii) Crystals of sodium hydroxide are deliquescent.
(iii) Sodium chloride is known as common salt.
(iv) Plaster of Paris is calcium sulfate hydrates.
Answer: (iv)
The correct chemical name of plaster of paris is calcium sulfate hemihydrates.

Question.
S. No. I II
1. Tartaric acid Calcium hydroxide
2. Lactic acid Sodium hydroxide
3. Formic acid Ammonia
4. Citric acid Magnesium
(a) What does column I represents ?
(b) What does column II represents ?
(c) Name one source of citric acid.
(d) What is released by ant’s sting ?
Answer:
(a) Column I represents acids.
(b) Column II represents bases.
(c) Oranges are good source of citric acid.
(d) Formic acid is released by ant's sting.

Question.
S. No. Test tubes Nature of Solution
1. I Neutral
2. II Acidic
3. III Basic
4. IV Neutral
(a) State the difference between an acid and base.
(b) What is the color of litmus paper for test tube I ?
(c) Give one example of the solution that could be present in test tube II.
(d) What is the color of litmus paper for test tube III ?
Answer:
(a) Acids release hydronium ions in the solution and bases give hydroxide ions in aqueous solution.
(b) The color of litmus paper for test tube I is green.
(c) Solution of vinegar in water is a example of solution that could be present in test tube II.
(d) The color of litmus paper for test tube III is blue.

Question.
S. No. Name of compound
1. Plaster of Paris
2. Baking Soda
3. Washing soda
4. Slaked lime
(a) Give one use of plaster of paris.
(b) Give chemical formula of baking soda.
(c) State difference between baking soda and washing soda.
(d) Give chemical formula of slaked lime.
Answer:
(a) Plaster of Paris is used for making statues, models and other decorative materials.
(b) The chemical formula of baking soda is \( \text{NaHCO}_3 \).
(c) Sodium hydrogen carbonate (\( \text{NaHCO}_3 \)) is known as baking soda whereas Sodium carbonate (\( \text{Na}_2\text{CO}_3 \)) is known as washing soda.
(d) The chemical formula of slaked lime is \( \text{Ca(OH)}_2 \).

Question.
S. No. Substances pH value
1. Lemon juice 2.0
2. Wine 4.0
3. Detergent 10.0
4. Bleach 12.5
(a) What is the nature of bleach ?
(b) What is color of litmus for lemon juice ?
(c) What is the pH value for neutral solutions ?
(d) Name the substances that would turn red litmus blue.
Answer:
(a) Bleach is basic in nature.
(b) Lemon juice turns blue litmus red.
(c) The pH value for neutral solutions is 7.
(d) Detergent and bleach would turn red litmus blue.

Archives

Question. Two solutions A and B have pH values of 3.0 and 10.5 respectively. Which of these will turn :
(a) Blue litmus solution to red and
(b) Phenolphthalein from colourless to pink ?
Justify your answer in each case.
Answer: (a) Solution A with pH 3.0 (acidic) will turn blue litmus to red. (b) Solution B with pH 10.5 (basic) will turn phenolphthalein to pink.

Question. Write one point of difference between each of the following :
(a) A hydrated salt and an anhydrous salt
(b) Washing soda and soda ash
(c) Baking soda and Baking powder
Answer: (a) Hydrated salt contains water of crystallization, anhydrous salt does not. (b) Washing soda is \( \text{Na}_2\text{CO}_3 \cdot 10\text{H}_2\text{O} \), soda ash is \( \text{Na}_2\text{CO}_3 \). (c) Baking soda is \( \text{NaHCO}_3 \), baking powder is a mixture of baking soda and an edible acid like tartaric acid.

Question. (a) Define indicator. Name two indicators obtained from plants.
(b) Write balanced chemical equation for the reaction that takes place when sodium oxide reacts with water. How will this solution behave towards phenolphthalein and red litmus paper ?
(c) State what happens when sodium hydroxide solution reacts with dilute hydrochloric acid. What is this reaction called ?
Answer: (a) Indicators are substances that change colour in acidic or basic solutions. Examples: Litmus, Turmeric. (b) \( \text{Na}_2\text{O} + \text{H}_2\text{O} \rightarrow 2\text{NaOH} \). It turns phenolphthalein pink and red litmus blue. (c) Salt and water are formed. It is called neutralisation.

Question. The two colours seen at the extreme ends of the pH chart are :
(a) Red and blue
(b) Red and green
(c) Green and blue
(d) Orange and green
Answer: (a)

Question. Four students A, B, C and D determine the pH of water, lemon juice and dil. sodium bicarbonate solution. They recorded their observations and arranged them in descending order of pH values as follows :
(a) (A)
(b) (B)
(c) (C)
(d) (D)
Answer: (d)
(D) sodium bicarbonate solution, water, lemon juice.

Question. A solution of \( \text{FeSO}_4 \) in water is :
(a) colourless
(b) blue
(c) light green
(d) brown
Answer: (c)

Question. While demonstrating decomposition reaction in laboratory the teacher heated ferrous sulphate crystals in a hard glass dry boiling tube.
(a) What change in the colour of ferrous sulphate crystals you will observe ?
(b) What type of smell of the gases coming out of the boiling tube would you feel ?
Answer: (a) Green color changes to reddish brown. (b) Pungent smell of burning sulphur.

Question. For preparing soap in the laboratory we require an oil and a base. Which of the following combinations of an oil and a base would be best suited for the preparation of soap ?
(a) Castor oil and calcium hydroxide
(b) Turpentine oil and sodium hydroxide
(c) Castor oil and sodium hydroxide
(d) Mustard oil and calcium hydroxide
Answer: (c)

Question. In the neighbourhood of your school, hard water required for an experiment is not available. Select from the following groups of salts available in your school, a group each member of which, if dissolved in distilled water, will make it hard :
(a) Sodium chloride, calcium chloride
(b) Potassium chloride, sodium chloride
(c) Sodium chloride, magnesium chloride
(d) Calcium chloride, magnesium chloride
Answer: (d)

Question. A student adds a spoon full of powdered sodium hydrogen carbonate to a flask containing ethanoic acid. List two main observations, he must note in his note book, about the reaction that takes place. Also write chemical equation for the reaction.
Answer: (1) Brisk effervescence due to evolution of \( \text{CO}_2 \) gas. (2) The flask becomes cold. Equation: \( \text{CH}_3\text{COOH} + \text{NaHCO}_3 \rightarrow \text{CH}_3\text{COONa} + \text{H}_2\text{O} + \text{CO}_2 \)

Question. Which of the following sets of materials can be used for conducting a saponification reaction for the preparation of soap ?
(a) \( \text{Ca(OH)}_2 \) and neem oil
(b) \( \text{NaOH} \) and neem oil
(c) \( \text{NaOH} \) and mineral oil
(d) \( \text{Ca(OH)}_2 \) and mineral oil
Answer: (b)

Question. A student takes four test tubes marked P, Q, R and S of 25 ml capacity and fill 10 ml of distilled water in each. He dissolves one spoon full of four different salts in each as—KCl in P, NaCl in Q, \( \text{CaCl}_2 \) in R and \( \text{MgCl}_2 \) in S. He then adds about 2 ml of a sample of soap solution to each of the above test-tubes. On shaking the contents of each of the test-tubes, he is likely to observe a good amount of lather (foam) in the test tubes marked :
(a) P and Q
(b) R and S
(c) P, Q and R
(d) P, Q and S
Answer: (a)

Question. What do you observe when you drop a few drops of acetic acid to a test-tube containing :
(a) phenolphthalein
(b) distilled water
(c) universal indicator
(d) sodium hydrogen carbonate powder
Answer: (a) Remains colourless. (b) Miscible, forms a clear solution. (c) Turns orange/yellow. (d) Brisk effervescence.

Question. (a) Define a universal indicator. Mention its one use.
(b) Solution A gives pink colour when a drop of phenolphthalein indicator is added to it. Solution B gives red colour when a drop of methyl orange is added to it. What type of solutions are A and B and which one of the solutions A and B will have a higher pH value ?
(c) Name one salt whose solution has pH more than 7 and one salt whose solution has pH less than 7.
Answer: (a) It is a mixture of indicators that shows different colours at different pH. Use: To determine pH strength. (b) A is basic, B is acidic. A will have higher pH. (c) \( \text{Na}_2\text{CO}_3 \) (pH > 7), \( \text{NH}_4\text{Cl} \) (pH < 7).

Question. The pH value of a sample of hydrochloric acid is 2. pH value of this sample when diluted by adding water will be :
(a) less than 2 but more than 0
(b) more than 2 but less than 7
(c) more than 7
(d) no change in pH.
Answer: (b)

Question. A student added a drop of universal indicator to one ml of the given solution and found that a green colour is produced. pH value of the solution will be in the range of :
(a) 0-3
(b) 4-6
(c) 7-9
(d) 10-12
Answer: (c)

Question. Aqueous solution of which of the following is colourless ?
(a) \( \text{FeSO}_4 \)
(b) \( \text{ZnSO}_4 \)
(c) \( \text{Al}_2(\text{SO}_4)_3 \)
(d) Both (b) and (c)
Answer: (d)

Question. Which of the following solution is coloured ?
(a) \( \text{ZnSO}_4 \)
(b) \( \text{FeSO}_4 \)
(c) \( \text{Al}_2(\text{SO}_4)_3 \)
(d) \( \text{Na}_2\text{SO}_4 \)
Answer: (b)

Question. You are provided with three test tubes A, B and C which contain distilled water, acidic solution and basic solution respectively. If you are given blue litmus paper only, how will you identify the contents of each test tube ?
Answer: Dip blue litmus in all three. The one that turns red is acidic. Take the red litmus and dip in remaining two. The one that turns blue is basic. The one with no effect is distilled water.

Question. (a) The blue colour of crystals of a substance changed on heating in a closed test tube but the colour was regained after sometime on cooling. Name the substance and write its chemical formula. Explain the phenomenon involved.
(b) Write name and chemical formula of two such compounds whose one formula unit is associated with 10 and 2 water molecules respectively.
Answer: (a) Copper sulphate (\( \text{CuSO}_4 \cdot 5\text{H}_2\text{O} \)). On heating, it loses water of crystallization. On cooling, it absorbs moisture. (b) Washing soda (\( \text{Na}_2\text{CO}_3 \cdot 10\text{H}_2\text{O} \)) and Gypsum (\( \text{CaSO}_4 \cdot 2\text{H}_2\text{O} \)).

Question. A student was given a solution to find its pH. His teacher declared his recorded pH as wrong. Student explained to his teacher, all the steps done by him while finding pH of sample. Mark the step taken by student in which he committed mistake.
(a) collection of apparatus.
(b) clearing of all apparatus
(c) making pH paper wet and then dip it in sample.
(d) recording observation.
Answer: (c)

Question. A student was provided with four samples of solutions as shown in figures (I), (II), (III), and (IV). He determined pH value of each solution by using pH paper. The correct sequence of colour change of pH paper observed by the student will be : (I: Dil sodium bicarbonate, II: Lemon juice, III: Water, IV: Dil hydrochloric acid)
(a) indigo, light red, green, red
(b) red, indigo, green, light red
(c) indigo, red, green, yellow
(d) green, red, yellow, indigo
Answer: (a)

Question. What do we observe on pouring acetic acid on red blue litmus papers ?
(a) Red litmus remains red and blue litmus turns red.
(b) Red litmus turns blue and blue litmus remains blue.
(c) Red litmus turns blue and blue litmus turns red.
(d) Red litmus becomes colourless and blue litmus remains blue.
Answer: (a)

Question. While preparing soap a small quantity of common salt is generally added to the reaction mixture of vegetable oil and sodium hydroxide. Which one of the following may be the purpose of adding common salt ?
(a) To reduce the basic nature of the soap
(b) To make the soap neutral
(c) To enhance the cleansing power of the soap
(d) To favour the precipitation of the soap
Answer: (d)

Question. A student takes about 4 ml of distilled water in four test tubes marked P, Q, R and S. He then dissolves in each test tube an equal amount of one salt in one test tube, in namely sodium sulphate in P, potassium sulphate in Q, calcium sulphate in R and magnesium sulphate in S. After that he adds an equal amount of soap solution in each test tube. On shaking each of these test tubes well, he observes a good amount of lather (foam) in the test tubes marked
(a) P and Q
(b) Q and R
(c) P, Q and S
(d) P, R and S
Answer: (a)

Question. When you add sodium hydrogen carbonate to acetic acid in a test tube, a gas liberates immediately with a brisk effervescence. Name this gas. Describe the method of testing this gas.
Answer: Carbon dioxide (\( \text{CO}_2 \)). Test: Pass the gas through lime water; it turns milky.

Question. A student adds 2 ml of acetic acid to a test tube containing 2 mL of distilled water. He then shakes the test tube well and leaves it to settle for some time. After about 5 minutes he observes that in the test tube there is :
(a) a clear transparent colourless solution
(b) a clear transparent pink solution
(c) a precipitate settling at the bottom of the test tube
(d) a layer of water over the layer of acetic acid.
Answer: (a)

Question. Hard water is not available for an experiment. Some salts are given below : (I) Sodium chloride (II) Sodium sulphate (III) Calcium chloride (IV) Calcium sulphate (V) Potassium chloride (VI) Magnesium sulphate. Select from the following a group of these salts, each member of which may be dissolved in water to make it hard.
(a) I, II, V
(b) I, III, V
(c) III, IV, VI
(d) II, IV, VI
Answer: (c)

Question. State reason for the following :
(a) dry HCl gas does not change the colour of the dry blue litmus paper.
(b) alcohol and glucose also contain hydrogen, but do not conduct electricity.
(c) Conc. of \( \text{H}_3\text{O}^+ \) ion is affected when a solution of an acid is diluted.
Answer: (a) Absence of moisture prevents formation of \( \text{H}^+ \) ions. (b) They do not ionize in water. (c) Concentration decreases per unit volume.

Question. Four students studied reactions of zinc and sodium carbonate with dilute hydrochloric acid and dilute sodium hydroxide solutions and presented their results as follows. The (\( \surd \)) shows evolution of gas and (–) shows no reaction. The right set is :
(a) (a)
(b) (b)
(c) (c)
(d) (d)
Answer: (a)