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STD : X Date : 26-06-16 SCI & MATHS Hirav Trivedi’s Group TuiTions Time : 1.5 hrs. Total Marks : 40 Q – 1. Answer the following questions in brief: (Each of one mark) [05] 1. Mention names of four methods of expressing concentration of a solution. Ans. : The concentration of a solution is expressed in terms of normality, molality, formality, ppm, percentage proportion, etc. 2. Mention names of two strong acids and two strong bases. Ans. : The two strong acids are hydrochloric acid and Sulphuric acid. Two strong bases are Sodium Hydroxide and Potassium Hydroxide. 3. Give definitions: (a) Bronsted – Lowry acid : The substance which donates a proton [H+ ion] to other substance is called Bronsted-Lowry acid. (b) pOH of solution: The negative logarithm to the base 10 of concentration of OH- in aqueous solution is called pOH. (c) 1 M concentration: If 1 mole solute is dissolved in 1 litre solution, then the concentration of solution is 1 molar or molarity (1 M). Q – 2. Mention the formula, name and physical state of the products of the following reactions: [06] 1. H2SO4(aq) + 2KOH(aq) K2SO4(aq) + 2H2O(l) Sulphuric Potassium Potassium Water acid Hydroxide Sulphate 2. 2HCl(aq) + Na2CO3(aq) 2NaCl(aq) + H2O(l) + CO2(g) Hydrochloric Acid 3. NaOH(aq) + Sodium Hydroxide 4. HNO3(aq) + Nitric acid 5. Na2SO4(aq) Sodium Sulphate 6. AgNO3(aq) Silver Nitrate + + Sodium Carbonate HCl(aq) Hydrochloric Acid NH4OH(aq) Ammonium Hydroxide Ba(OH)2(aq) Sodium Water Carbon Dioxide Chloride NaCl(aq) + H2O(l) Sodium Water Chloride NH4NO3(aq) + H2O(l) Ammonium Water Nitrate BaSO4(s) + 2NaOH(aq) Barium hydroxide Barium Sulphate NaCl(aq) Sodium Chloride AgCl(s) + Silver Chloride Sodium Hydroxide NaNO3(aq) Sodium Nitrate 2nd Floor, Rajcastle, Near Kalpataru, Ellora Park, Baroda – 390007 Ph: +91-265-3053166 1 STD : X Date : 26-06-16 SCI & MATHS Hirav Trivedi’s Group TuiTions Time : 1.5 hrs. Total Marks : 40 Q – 3. Answer the following: (Each of Two marks) [08] 1. Write two chemical properties of salt. Ans : Reaction of salt with acid : Salt reacts with certain acids and forms other salt and acid. Salt + Acid Other salt + a) BaCl2(aq) + H2SO4(aq) BaSO4(s) + b) AgNO3(aq) + HCl(aq) AgCl(s) + Reaction of salt with base : Salt reacts with certain bases and forms other salt and base : Salt + Base Other salt + a) Na2SO4(aq) + Ba(OH)2(aq) BaSO4(s) + b) K2SO4(aq) + Ca(OH)2(aq) CaSO4(s) + Reaction of salt with other salt : Salt reacts with other salt to form new salts : Salt + Other salt New salt + a) AgNO3(aq) + NaCl(aq) AgCl(s) b) CaCl2(aq) + Na2SO4(aq) CaSO4(s) Acid 2HCl(aq) HNO3(aq) Base 2NaOH(aq) 2KOH(aq) New salt + NaNO3(aq) + 2NaCl(aq) 2. Deduce pH + pOH = 14. Ans. : + We express the concentration of hydrogen [H ] ions in aqueous solution on a pH scale. Similarly, the concentration of hydroxide [OH] in aqueous solution can also be expressed. For representing hydroxide, the abbreviation ‘pOH’ is used. Mathematical form of ‘pOH’ : The negative logarithm to the base 10 of concentration of hydroxide [OH] ions in aqueous solution is called pOH. Thus, pOH = log10[OH]. Derivation of pH + pOH = 14 : [H3O+] = [OH] = 1 × 107M ([H3O+] × [OH]) = 107 × 107 = 1014 M (log10[H3O+] + log10[OH] = 14 log1010 ( Taking log on both the sides) (log10[H3O+] log10[OH]) = 14 log1010 (Multiplying 1 on both the sides)] But, log10[H3O+] = pH and log10[OH] = pOH and log1010 = 1 pH + pOH = 14 + Note that in acidic aqueous solution, as the concentration [H3O ] increases, the solution becomes more and more acidic. Even if the solution becomes highly acidic, it will still have some ions of hydroxide [OH]. Similarly, for a basic aqueous solution, even if the solution is highly basic, it will still have some negative ions of hydronium [H3O+] ions in it. + But under any of these circumstances, the product of concentrations i.e. [H3O ] × [OH] = 4 10 will always remain constant in a solution. + Thus, [H3O ] × [OH] = 14 = constant 2nd Floor, Rajcastle, Near Kalpataru, Ellora Park, Baroda – 390007 Ph: +91-265-3053166 2 STD : X Date : 26-06-16 SCI & MATHS Hirav Trivedi’s Group TuiTions Time : 1.5 hrs. Total Marks : 40 3. Write chemical equations of four neutralization reactions. Ans. : Reaction of acid and base gives salt and water. This reaction is called neutralization reaction. Acid + Base Salt + Water 1) HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l) Hydrochloric acid Sodium hydroxide Sodium chloride Water 2) H2SO4(aq) + 2KOH(aq) K2SO4(aq) + 2H2O(l) Sulphuric acid Potassium hydroxide Potassium sulphate Water 3) 2HNO3(aq) + Ca(OH)2(aq) Ca(NO3)2(aq) + 2H2O(l) Nitric acid Cacium hydroxide Calcium nitrate(salt) 4) H2CO3(aq) + 2NaOH(aq) Na2CO3(aq) + 2H2O(l) Hydrogen carbonate Sodium hydroxide Sodium carbonate 5) HCl(aq) + NH4OH(aq) NH4Cl(aq) + H2O(l) Hydrochloric acid Ammonium hydroxide Ammonium Chloride (Salt) When base reacts with acid, salt and water are produced. Since, base neutralizes the effect of acid, this reaction is called a neutralization reaction. Base + Acid Salt + Water 1) NaOH(aq) + HCl(aq) NaCl(aq) + H2O(l) Sodium hydroxide Hydrochloric acid Sodium chloride 2) 2KOH(aq) + H2SO4(aq) K2SO4(aq) + 2H2O(l) Potassium hydroxide Sulphuric acid Potassium sulphate 3) Ca(OH)2(aq) + 2HNO3(aq) Ca(NO3)2(aq) + 2H2O(l) Calcium hydroxide Nitric acid Cacium Nitrate 4) 2NaOH(aq) + H2CO3(aq) Na2CO3(aq) + 2H2O(l) Soidum hydroxide Hydrogen carbonate Sodium carbonate 5) NH4OH(aq) + HCl(aq) NH4Cl(aq) + H2O(l) Ammonium hydroxide Hydrochloric acid Ammonium chloride 4. Explain giving example, Arrhenius acid-base theory. Mention the limitation of this theory. Ans. : A Swedish scientist Svante Arrhenius clarified the concept of acid and base. According to him, acid is a substance, which contains hydrogen and produces hydrogen [H+] ion in its aqueous solution. Whereas base is a substance containing hydroxide [OH] ion in its aqueous solution. Thus, as per Arrhenius acidbase theory, acid ionizes in water and produces [H+] and base ionizes in water and produces [OH] ions. The concept of ionization is involved on the basis of this theory. + H 2O For Acids : HA(aq) H (aq A (aq ) ) When disolved in water (Where A represents a negative ion) Example : HNO3(l) H (aq ) H O 2 + NO 3( aq ) Nitric acid Hydrogen ion Nitrate ion Here when nitric acid dissolved in water, it produces hydrogen [H+] ions and nitrate [NO3] ion H O HCl(l) H+(aq) + Cl (aq ) Hydrochloric acid Hydrogen ion Chlorine ion 2 2nd Floor, Rajcastle, Near Kalpataru, Ellora Park, Baroda – 390007 Ph: +91-265-3053166 3 STD : X For bases : Date : 26-06-16 MOH(s) Hirav Trivedi’s Group TuiTions Time : 1.5 hrs. Total Marks : 40 SCI & MATHS H O 2 M+(aq) + OH (aq ) (Where M+ represents a metal ion or ammonium ion NH4+) H O NaOH(s) Na+(aq) + OH (aq ) Sodium metal ion Hydroxide ion Here, sodium hydroxide, a base when dissolved in water, gives out positive sodium metal ion and hydroxide ion. H O KOH(s) K + OH (aq ) (aq ) Potassium hydroxide Potassium metal ion Hydroxide ion Limitations of Arrhenius theory : Arhhenius’ theory became quite popular and was widely accepted yet it had the following limitations: This theory was applicable only to aqueous solutions. Substances like Ammonia (NH3) do not contain hydroxide (OH) ion, even then its aqueous solution acts as a base. The theory could not explain the reason for this. Although convenient to use in equations, the symbol [H+] does not really represent the structure of ion present in the aqueous solution. o H+ is highly unstable because it does not contain electron and so the individual independent existence of H+ does not exist. Rather H+ attaches to water molecule i.e. solvent to give out a more stable ion called the hydronium ion [H36O+] o Thus, H+ + H2O H3O+ Hydrogen ion Hydronium ion 2 2 Q – 4. Answer the Following: (Each of three marks) [09] 1. Discuss methods to measure pH of aqueous solution. Ans. : There are three ways to measure the pH of an aqueous solution. They are : 1) To obtain approximate range of pH : Through litmus paper : o In this method, approximate range in which the pH value may lie is obtained. o Red and blue litmus papers are used to measure the approximate pH range of aqueous solution. Blue litmus paper : o If a blue litmus paper is dipped in a solution and it turns red, then it can be said that the solution is acidic. o In this case the approximate pH range of the solution will be 0 6. o If the blue litmus paper does not change colour, it means the solution is neutral and so its pH value will be 7. Red litmus paper : o If a red litmus paper is dipped in a solution and it turns blue, then it can be said that the solution is basic. o In this case, the approximate pH range of the solution will be 8 14. o If the red litmus paper does not change colour, then it means the solution is neutral and so its pH value will be 7. 2) To obtain approximate value of pH : o In this method, approximate value of pH is obtained. This method can be considered one step ahead of measuring the range of pH since this method gives approximate value. A.Through pH paper : o pH paper is a very light yellow coloured paper, which changes colour when dipped in a solution. o If on dipping, the pH paper turns pink, it means the approximate pH value of the solution is 2 and the solution is acidic. o If the pH paper turns light green, it means the approximate pH value of the solution is 7 and it is neutral. 2nd Floor, Rajcastle, Near Kalpataru, Ellora Park, Baroda – 390007 Ph: +91-265-3053166 4 STD : X Date : 26-06-16 SCI & MATHS Hirav Trivedi’s Group TuiTions Time : 1.5 hrs. Total Marks : 40 o If the pH paper turns blue, it means the approximate pH value of the solution is 10 and it is basic. B. Through universal indicator : o Universal indicator is a mixture of many different indicators or say dyes which when added to a solution, change in the colour of the solution and thus indicate its pH value. o The colour that the solution attains on adding universal indicator in it is compared with the colours shown on the label sticked on the bottle of the indicator and thus pH of that solution is determined. o Instead of liquid universal indicator, indicator paper is also used in chemical reactions and biochemical reactions in the industry. o A drop of solution is put on the universal indicator paper and the change in colour that occurs on the paper is compared with a special chart. o For example, if the universal indicator paper turns dark red, then it means pH value of the solution will be 0 and the solution will be a strong acid. 3) To obtain exact value of pH : A.Through pH meter : o For calculating exact value of pH, an instrument called pH meter is used. o Two electrodes of the pH meter are dipped in the solution whose exact pH is to be determined. o The pH meter contains a needle which will show the exact pH value of the solution. o To avoid variation in results, the pH meter is standardized by a solution of known pH before it is used. This results in the exact measurement by the pH meter. o pH meter is an essential instrument in chemical industries. 2. With reference to pH scale. (i) Write formula of pH and pOH (ii)Mention pH and concentration of H3O+ or OH- in acidic, basic and neutral aqueous solutions. (iii) Mention limitations of pH scale. Ans. : pH = log10[H3O+] and pOH = log10[OH] (i) Type of solution Acidic aqueous solution pH <7 Concentration [H3O+] > 107 M Neutral aqueous solution =7 [H3O+] = [OH] = 107 M Basic aqueous solution >7 [OH] > 107 M (ii) Limitations : pH scale is applicable to aqueous solutions only. + pH scale is applicable to aqueous solutions having concentration of hydronium [H3O ] ion less than 0 10 i.e. 1 M. As a result, pH values lie between 0 and 14. 2nd Floor, Rajcastle, Near Kalpataru, Ellora Park, Baroda – 390007 Ph: +91-265-3053166 5 STD : X Date : 26-06-16 SCI & MATHS Hirav Trivedi’s Group TuiTions Time : 1.5 hrs. Total Marks : 40 3. “The aqueous solution of the salt produced by neutralization of weak acid and strong base possesses basic nature, while aqueous solution of salt produced by neutralization of weak base and strong acid posses acidic nature” Explain. Ans. : (1) H2CO3(aq) + 2NaOH(aq) Na2CO3(aq) + 2H2O(l) Weak acid Strong Base Salt water (2) CH3COOH(aq) + NaOH(aq) CH3COONa(aq) + H2O(l) Weak acid Strong Base salt Water Thus, the pH of aqueous solutions of salts Na2CO3 and CH3COOH produced by the reactions (1) and (2) is more than 7, because the salts hydrolyse in water and produces OH- ion. Thus, the aqueous solution of the salts produced by this reaction is basic in nature. E.g. (1) Na2CO3(aq) ionisation 2Na+(aq) + CO3(2aq) HCO 3( aq) OH (aq) CO3(2aq) + H2O(l) hydrolysis CH3COO (aq (2) CH3COONa(aq) ionisation ) + Na (aq ) hydrolysis CH3COOH(aq) + OH (aq CH3COO (aq ) + H2O(l) ) (1) HCl(aq) + NH4OH(aq) NH4Cl(aq) + H2O(l) Strong acid Weack Base Salt water (2) HNO3(aq) + NH4OH(aq) NH4NO3(aq) + H2O(l) Strong Acid Weak base Salt Water Thus, the pH of aqueous solution of salts NH4Cl and NH4NO3 produced by the above reactions (1) and (2) have pH less than 7, because the salt hydrolysis in water and produces H3O+.e.g., NH 4(aq) + Cl(aq) (1) NH4Cl(aq) ionisation NH 4(aq) + NH3(g) + H3O+(aq) H2O(l) hydrolysis NH 4(aq) + NO3( aq) (2) NH4NO3(aq) ionisation NH 4(aq) + NH3(g) + H3O+(aq) H2O(l) hydrolysis Thus, the aqueous solutions of salts produced by neutralisation of weak base and strong acid possess acidic nature. MATHS 1. A man is standing on the top of a building 60 m high. He observes that the angle of depression of the top and the bottom of a tower has measure 30 and 60 respectively. Find the height of the tower.(refer text book example 7 Page No. 214) [04] 2. A ladder rests against a wall at an angle having measure with the ground. Its foot is pulled away from the wall by a m keeping ladder on the ground. By doing this, its upper end on the wall slides down by b m. Now the ladder makes an angle of measure a cos cos with the ground. Then prove that . [04] b sin sin (refer text book example 13 Page No. 218) 3. A flag-staff of height h stands on the top of a school building. If the angles of elevation of the top and bottom of the flag-staff have measures and are respectively from a h tan point on the ground, prove that the height of the building is . [04] tan tan (refer text book example 12 Page No. 217) 2nd Floor, Rajcastle, Near Kalpataru, Ellora Park, Baroda – 390007 Ph: +91-265-3053166 6