Q1. The diagram shows the reaction between metal and dil. acid. What is the reason for different behaviour of Mg in test tube B ?
a. Mg is lighter element than dil. HCI.
b. Mg reacts with dil. HCl to produce H2 gas which helps in floating.
c. Mg reacts with dil. HC1 to produce N2 gas which helps in floating.
d. Mg reacts with dil. HCI to produce CO2 gas which helps in floating.
Ans: B
Q2. A blue litmus paper was first dipped in dil. HCl and then in dil. NaOH solution. It was observed that the colour of the litmus paper
a. changed first to red and then to blue
b. changed to red
c. remained blue in both the solutions
d. changed first to red and then to blue
d. changed first to red and then to blue Explanation: Blue paper turn in red indicate the sample is acidic. Blue paper that does not change color indicates the sample is a base. HCl is acidic and NaOH is base, So, dil. HCl turns blue litmus red which becomes blue again in NaOH.
Q3. 5 mL of acetic acid was added to equal volume of water and the mixture was shaken well for one minute and allowed to settle. The correct representation of the observation made would be as given in test tube (1)
a. III b. I c. II d. IV
IV Explanation: Acetic acid dissolves in water forming clear solution.
Q4. On putting few drops of an unknown liquid on pH strip, the colour of pH strip changed to green. The liquid taken is likely to be
a. pH paper shows green colour with water us neutral.
b. dilute sodium hydroxide solution
c. dilute hydrochloric acid
d. lemon juice
Q5What happens when a solution of an acid is mixed with a solution of a base in a test tube?
(i) The temperature of the solution increases
(ii) The temperature of the solution decreases
(iii) The temperature of the solution remains the same
(iv) Salt formation takes place
(a) (i) only (b) (i) and (iii) (c) (ii) and (iii) (d) (i) and (iv)
Ans: (d) (i) and (iv) When acid is mixed with a solution of base it results in a neutralization reaction. Neutralization is an exothermic reaction which results in the formation of salt.
Q6. A scientist in a chemistry lab wants to make salt of pH5.5 using acid and base. The table shows the acid and base present in the lab.
1 HCL
2 NaOH
3 H2CO3
4 NH4OH
5 CH3COOH
Which of the acid and base he should use for the reaction?
a. CH3COOH and NaOH
b. HCL and NaOH
c. H2CO3 and NaOH
d. HCL and NH4OH
Ans: (c) HCl and NH4OH The salt having pH 5.5 is acidic. So, to prepare an acidic salt, a strong acid (HCl) and a weak base (NH4OH) is required.
Q7. Equal volumes of hydrochloric acid and sodium hydroxide solutions of same concentration are mixed and the pH of the resulting solution is checked with a pH paper. What would be the colour obtained?
Which of the following will turn phenolphthalein pink?
(a) NaOH(aq) (b) HCl(aq) (c) CH3COOH(aq) (d) H2O
Ans: (a) NaOH(aq)
Phenolphthalein solution is a colourless indicator which gives pink colour in basic solution.
Phenolphthalein solution remains colourless in acidic solution as well as in neutral solution.
Q8. Common salt besides being used in kitchen can also be used as the raw material for making:
(i) washing soda (ii) bleaching powder (iii) baking soda (iv) slaked lime
(a) (i) and (ii) (b) (i), (ii) and (iv) (c) (i) and (iii) (d) (i), (iii) and (iv)
Ans: (c) (i) and (iii) The common salt obtained is an important raw material for various other materials of daily use, such as sodium hydroxide, baking soda, washing soda and many more.
Q9Ayush is putting in the test tube containing water whereas Piyush is putting water in the lest tube containing . Which of the two is likely to face danger?
(a) Piyush (b) Ayush (c) None of the two (d) Both Ayush and Piyush
Ans: (a) Piyush Piyush is likely to face danger. Addition of water to concentrated sulphuric acid is an exothermic reaction and can lead to explosions. Water should not be poured into a container containing an acid
Q10. Anand took four colourless solutions P, Q, R and S, and performed the following tests. What is the definite conclusion that Anand can reach?
(a) Both P and S are salt solutions.
(b) Both Q and S are basic solutions.
(c) Both Q and R are salt solutions.
(d) Both P and R are neutral solutions.
Ans: (d) Both P and R are neutral solutions. Since there is no change in the colour of solution P and R with any of the indicators so they are neutral solutions.
Answer the following Questions:
. Q1. Case Study - 1 Sohan went door to door posing as a goldsmith. He promised to bring back the glitter of old and dull gold ornaments. An unsuspecting lady gave a set of gold bangles to him, which he dipped in a particular solution. The bangles sparkled like new but their weight was reduced drastically. The lady was sad but after a futile argument, the man beat a hasty retreat.
(a) What is used for dissociation of gold? [1]
(b) Why the weight of the bangle was reduced drastically? [1]
(c) Aqua-regia is a strong oxidising agent. (True or False). [2]
OR
(c) What is the other name of the solution (in Latin) used by that man posing as the goldsmith? Why is it so called?
Ans: (a) Aqua regia is used for dissolving gold. Aqua regia is a mixture of concentrated nitric acid and concentrated hydrochloric acid in the ratio of 1 : 3
b)As the gold from the bangles was dissolved in aqua-regia, their weight was reduced drastically. (c) True. Aqua Regia is a strong oxidising agent due to the formation of NOCl (Nitrosyl chloride) and chlorine produced by reaction of two acids. OR Goldsmith used a solution known as Aqua regia, which is known as royal water in Latin. This mixture was given its name (literally, royal water") by the alchemists because of its ability to dissolve gold. It is a red or yellowish liquid.
Q2. The primary reason behind the formation of the toxic foam is high phosphate content in the wastewater because of detergents used in dyeing industries, dhobi ghat and households. Yamuna’s pollution level is so bad that parts of it have been labelled ‘dead’ as there is no oxygen in it for aquatic life to survive. Study the passage and answer the questions that follow:
(i) Give an idea about the pH value of the water of river Yamuna if the reason of froth is high content of detergents dissolved in it. What does it tell us about the concentration of hydroxide ion and hydronium ion? [2]
(ii) The table provides the pH value of four solutions P, Q, R and S Solution pH value P 2 Q 9 R 5 S 11
Arrange the solutions in increasing order of their hydronium ion concentration. [2] OR
(ii) What is the effect of high content of phosphate ion in river Yamuna? [2]
Ans: (i) Detergents being basic increase the pH of water above 7. It will have high concentration of hydroxide ion (OH–) and low concentration of hydronium ion (H3O+). (ii) Higher the pH , lower is the hydronium ion concentration. So, S < Q< R< P OR (ii) Phosphate ion increases the growth of algae which ultimately decrease the level of dissolved oxygen.
Q3. (a) Write the chemical name of Na2CO3.10H2O and Na2CO3. (b) Write the significance of 10H2O. (c) Mention the term used for water molecules attached with a salt. (d) With the help of a chemical equation, explain the method of preparation of both Na2CO3.10H2O and Na2CO3. Also, list two uses of Na2CO3.10H2O.
Ans:Na2CO3.10H2O - Sodium carbonate decahydrate. Na2CO3 - Anhydrous sodium carbonate 10H2O - Water of crystallization which impacts shape and colour to the crystals. Preparation: NaCl + H2O + CO2 + NH3 → NH4CI +NaHCO3 2NaHCO3 +Heat→ Na2CO3 + H2O + CO2 Na2CO3 + 10H2O → Na2CO3.10H2O Uses: (i) Used in glass, soap and paper industries. (ii) Used in the manufacture of borax. (iii) Used as a cleansing agent for domestic Purpose.
Q4. (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?
Ans: (a) The cake will have a bitter taste because of the formation of Na2CO3 / sodium carbonate while baking / heating. (b) By adding tartaric acid. (c) The liberated CO2 gas.
Q5. The pH of a solution is a measure of its hydrogen ion (H+) concentration. It is measured generally using pH scale. The values on pH scale ranges from 0 to 14. A pH of 1 is very acidic and corresponds to a high concentration of H+ ions. A pH of 14 is very basic and corresponds to a low concentration of H+ ions. The pH of a neutral solution is 7. The table given below shows the pH and H+ ion concentration of some common aqueous solutions. The leftmost column shows the number of moles of H+ ions in 1 mole of liquid. The pH and Hydrogen ion (H+) Concentration of Some Solutions H+ Concentration (moles) pH Solution 10–1 1 10–2 2 Gastric (stomach) juice, cola, lemon juice 10–3 3 Vinegar 10–4 4 Tomato juice 10–5 5 Black coffee, rain water 10–6 6 Urine 10–7 7 Pure water 10–8 8 Sea water 10–9 9 Baking soda 10–10 10 10 –11 11 Milk of magnesia 10–12 12 Household bleach 10–13 13 Oven cleaner 10–14 14 (i) How is the hydrogen ion concentration and pH related to each other? (ii) On the basis of above table, arrange the following in the decreasing order of H+ concentration. Pure water, tomato juice, milk of magnesia, sea water (iii) A solution of pH 2 is filled in two separate beakers. A few drops of methyl orange and phenolphthalein are added into separate solutions. How will the colour of the indicators change? OR (iii) Two solutions X and Y have pH values of 3.0 and 9.5 respectively. Which of these will turn litmus solution from blue to red and which will turn phenolphthalein from colourless to pink?
Ans: (i) pH is inversely proportional to the hydrogen ion concentration. (ii) The decreasing order of H+ concentration is Tomato juice > Pure water > Sea water > Milk of magnesia (iii) The solution of pH 2 is acidic in nature. So, the colour change is Methyl orange: red; phenolphthalein: colourless OR (iii) X will turn blue litmus to red because it is acidic in nature having pH value less than 7. Y will turn phenolphthalein from colourless to pink because it is basic in nature having pH value greater than 7
Q6. In an industrial process used for the manufacture of sodium hydroxide, a gas ‘A’ is formed as a by-product. The gas ‘A’ reacts with lime water to give a compound ‘B’ which is used as a bleaching agent in the chemical industry. Identify ‘A’ and ‘B’. Also give the chemical equations of the reactions involved
. Ans: A — Cl2 (Chlorine gas) B — CaOCl2 (Calcium oxychloride) 2NaCl + 2H2O → 2NaOH + Cl2 + H2 Cl2 + Ca(OH)2 → CaOCl2 + H2O
Q7. A chemical compound ‘X’ is used in the soap and glass industry. It is prepared from brine. (i) Write the chemical name, common name and chemical formula of ‘X’. (ii) Write the equation involved in its preparation. (iii) What happens when it is treated with water containing Ca or Mg salts?
Ans: (i) Chemical Name – Sodium Carbonate decahydrate Common Name – Washing Soda Chemical Formula - Na2CO3 .10H2O (ii) NaCl + H2O + CO2 + NH3 ⎯⎯→ NH4Cl + NaHCO3 2NaHCO3 ⎯⎯⎯→ Heat Na2CO3 + H2O + CO2 Prepared by: M. S. KumarSwamy, TGT(Maths) Page - 8 - Na2CO3 + 10H2O ⎯⎯→ Na2CO3 .10H2O (iii) It helps in removing permanent hardness./ It forms insoluble Ca or Mg salts in the form of scum.
Q8. A teacher provided acetic acid, water, lemon juice, aqueous solution of sodium hydrogen carbonate and sodium hydroxide to students in the school laboratory to determine the pH values of these substances using pH papers. One of the students reported the pH values of the given substances as 3, 12, 4, 8 and 14 respectively. Which one of these values is not correct? Write its correct value stating the reason.
Ans: The pH value of water given is incorrect. Its correct value is 7 since it is neutral in nature.
Q9.Sahil took five solutions A, B, C, D and E and 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.
Ans: Given pH for the solutions are A = 4, B = 1, C = 11, D = 7, E = 9. Hydrogen ions concentration increases with decrease in pH value and thus strength of acid increases with decrease in pH value from 7 to 0. On the other hand, hydroxide ion’s concentration decreases with increase in pH value and thus strength of bases increases with increase in pH value from 7 to 14. While neutral solution has pH value = 7. Therefore, (a) Solution D is neutral having pH value equal to 7. (b) Solution C is strongly alkaline as its pH value is equal to 11 (c) Solution B is strongly acidic as its pH value is equal to 1 (d) Solution A is weakly acidic as its pH value is equal to 4 (e) Solution E is weakly alkaline as its pH value is equal to 9 Hence arrangement of given pH value in increasing order of hydrogen ion concentration: C (11) < E (9) < D (7) < A (4) < B (1) 30.
Q10. 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.
Ans: Acid - H2CO3 Base - NaOH NaOH + H2CO3 → NaHCO3 + H2O Compound is basic in nature. pH value - ranges between 7 to 10
Q11. Manoj performed an experiment to understand that heat is produced when a few drops of concentrated sulphuric acid is slowly added into a beaker containing water. For this, he took 10 mL water in a beaker and added a few drops of concentrated H2SO4 to it. Then, he swirled the beaker slowly. During the process, a vigourous reaction takes place. It is an exothermic process. - (a) Why is it recommended that the acid should be added to water and not water to the acid? (b) How will the concentration of hydrogen ions gets affected if an acid is diluted? (c) What is this process called? Define the process. OR If we have hydrochloric acid and acetic acid of equal concentration, which will be a stronger acid and why?
Ans: (a) Dilution of concentrated acid is an exothermic process. If water is added to a concentrated acid, the heat generated may cause the mixture to splash out and cause burns. When the acid is added to water slowly with constant stirring, the mixture will not splash out. (b) Concentration of H+ decreases with increase in dilution. (c) Dilution of the acid. Dilution of an acid or base means mixing an acid or base with water. This is done to decrease the concentration of ions (H3O + /OH- ) per unit volume. OR Hydrochloric acid will be a stronger acid, because it produces more H+ ions.
Q12. A metal carbonate X on reacting with an acid gives a gas which when passed through a solution Y gives the carbonate back. On the other hand, a gas G that is obtained at anode during electrolysis of brine is passed on dry Y, it gives a compound Z, used for disinfecting drinking water. Identify X, Y, G, and Z. (5)
Ans: The gas that is evolved at anode during the electrolysis of brine is chlorine. Hence, G is chlorine. When chlorine gas is passed over dry slaked lime - Ca(OH)2 , it produces bleaching powder which is used for disinfecting drinking water. Hence, Y is slaked lime (calcium hydroxide) and Z is calcium oxy-chloride (bleaching powder). Since Y and Z are calcium salts, therefore X is also a calcium salt. Since, X is a metal carbonate, it is calcium carbonate. Carbonates react with acids to produce carbon dioxide gas which when through a solution of slaked lime (Y) forms insoluble calcium carbonate. X Calcium carbonate Y Slaked lime (Calcium hydroxide) G Chlorine Z Calcium oxy-chloride (Bleaching powder)
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