To a small amount of copper oxide in a beaker, when we add dilute hydrochloric acid slowly with stirring, the change in the colour of the solution is due to the formation of :
(a)Copper(II) oxide, which is black in colour.
(b)Copper(I) chloride, which is blue in colour.
(c)Copper(II) chloride, which is blue-green in colour.
(d)Copper(I) oxide, which is black in colour.
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(C)/ Copper (II) chloride, which is blue-green in colour.
(a) What are amphoteric oxides ? (b) Categorise the following based on their nature : $\ce{ZnO}$, $\ce{Na2O}$, $\ce{CO2}$
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(a) Metal oxides which can react with both acids as well as bases to produce salt and water. (1) (b) $\ce{ZnO}$ – Amphoteric oxide $\ce{Na2O}$ - Basic oxide $\ce{CO2}$ - Acidic oxide (1)
Four solutions, namely fructose, ethanol, hydrochloric acid and sodium hydroxide filled in four separate beakers are connected one by one in an electric circuit with a bulb. The solutions in which the bulb will glow when current is passed are :
(a)ethanol and hydrochloric acid
(b)fructose and ethanol
(c)fructose and sodium hydroxide
(d)hydrochloric acid and sodium hydroxide
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(D)/ hydrochloric acid and sodium hydroxide (1 Mark)
Give reasons for the following : (a) Dry $\ce{HCl}$ gas does not change the colour of a dry blue litmus paper. (b) Copper sulphate crystals turn white on heating.
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(a)Because $\ce{HCl}$ does not ionize in dry state/does not give $\ce{H+}$ ions in dry state. (1 Mark) (b)Because of loss of 5 molecules of water of crystallization. (1 Mark)
Attempt either (a) or (b) : (a) Give reasons : (i) For dilution of an acid, acid is added into water and not water into acid. (ii) Dry $\ce{HCl}$ gas does not turn blue litmus red whereas dilute $\ce{hydrochloric}$ $\ce{acid}$ does. (iii) Blue colour of $\ce{Copper(II)}$ $\ce{sulphate}$ crystals turns white on heating.
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(a) (i) When acid is added to water, it does not cause excessive local heating/ does not splash out and cause burns. (1) (ii) Because dry $\ce{HCl}$ does not ionize/produce $\ce{H+}$ ions whereas in dilute $\ce{HCl}$, $\ce{H+}$ ions are present. (1) (iii) Because of loss of 5 molecules of water of crystallisation. (1)
How is a universal indicator obtained ? How is the wide range of pH of solution tested by it ?
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• Universal indicator is obtained by mixing several indicators. (1 Mark) • Universal indicator shows different colours at different concentrations of hydrogen ions in a solution. (1 Mark)
How is tooth decay related to $\text{pH}$ ? How can it be prevented ?
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• Tooth decay starts when pH of mouth is lower than 5.5. (1 Mark) • It can be prevented by cleaning the mouth after eating. / By using toothpastes as they are basic in nature. (1 Mark) (any other preventive method)
The pH plays an important role in our daily life. Strength of acids and bases depends on the number of $\ce{H+}$ ions and $\ce{OH-}$ ions produced by these respectively. pH scale helps in predicting the strength of acids and bases by measuring hydrogen ion concentration in a solution. Answer the following : (a) What type of indicator is used to predict how strong an acid or base is ? (b) Three solutions A, B and C showed pH as 3, 5 and 7. Which solution has the highest concentration of $\ce{H+}$ ions ? (c) What are strong acids and weak acids ? OR (c) (i) Under what condition is rainwater called acid rain ? (ii) In the following acids, identify weak acids : Nitric acid, hydrochloric acid, acetic acid, sulphuric acid, formic acid.
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(a) Universal indicator (1 Mark) (b) A/ (pH = 3) (1 Mark) (c) • Strong acids give more $\ce{H+}$ ions in water. (1 Mark) • Weak acids give less $\ce{H+}$ ions in water. (1 Mark) (c) (i) When pH < 5.6 (1 Mark) (ii) Weak acid: acetic acid, formic acid (½ + ½ = 1 Mark)
Explain chlor-alkali process with chemical equation. Name the products formed at anode and cathode.
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• When electricity is passed through brine, it decomposes to form sodium hydroxide (alkali) and chlorine, hence this process is called chlor-alkali process. (1 Mark) $\ce{2NaCl(aq) + 2H2O(l) ->[Electricity] 2NaOH(aq) + H2(g) + Cl2(g)}$ (1 Mark) • At anode: $\ce{Cl2}$ (½ Mark) • At cathode: $\ce{H2}$ (½ Mark)
Attempt either (a) or (b) : OR (b) Write the preparation of the following compounds with balanced chemical equation : (i) $\ce{NaOH}$ by chlor-alkali process (ii) Baking Soda (iii) Plaster of Paris
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(b) (i) $\ce{2NaCl(aq) + 2H2O(l) ->[electricity] 2NaOH(aq) + H2(g) + Cl2(g)}$ (ii) $\ce{NaCl + H2O + NH3 + CO2 -> NaHCO3 + NH4Cl}$ (iii) $\ce{CaSO4.2H2O ->[373K] CaSO4.1/2H2O + 1/2H2O}$ (Deduct ½ mark if no/ incorrect balancing in each case)
Attempt either subpart (a) or (b) : (a) During electrolysis of brine solution, a gas (A) is liberated at the anode. When the gas (A) is passed through slaked lime, a compound (B) is formed which is used for disinfecting drinking water. (i) Write the names of (A) and (B). (ii) Write the chemical equation involved. (iii) Write one use of compound (B) other than disinfecting water.
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(a) (i) (A): Chlorine (½ Mark) (B): Calcium oxychloride / Bleaching powder (½ Mark) (ii) $\ce{Ca(OH)2 + Cl2 -> CaOCl2 + H2O}$ / (1 Mark) $\ce{2Ca(OH)2+2Cl2 -> Ca(ClO)2 +CaCl2 +2H2O}$ (iii)For bleaching cotton, linen in textile industry / for bleaching wood pulp in paper factories / for bleaching washed clothes in laundry/as an oxidizing agent in chemical industry. (1 Mark)
What happens : (I) If a drop of red litmus solution is added to the aqueous solution of substance 'Z'? (II) If $\ce{CO2}$ gas is passed through ammoniacal solution of aqueous $\ce{NaCl}$ ?
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(a) X - Chlorine gas Y -Hydrogen gas (b) $\ce{2NaCl(aq) + 2H2O(l) -> 2NaOH(aq) + Cl2(g) + H2(g)}$ (Deduct ½ marks for no/incorrect balancing)
Write the preparation of Baking soda. How does it help in making cakes soft and spongy ?
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• Baking soda is prepared by passing carbon dioxide and ammonia gas through aqueous solution of sodium chloride. (1) / $\ce{NaCl + H2O + NH3 + CO2 -> NaHCO3 + NH4Cl}$ • Baking soda on heating releases $\ce{CO2}$ gas which makes cakes soft and spongy (1) / $\ce{2NaHCO3 -> Na2CO3 + H2O + CO2(g)}$
(a) Name the acid present in ant’s sting. (b) Give reason : (i) While diluting an acid, it is recommended that the acid should be added to water. (ii) Baking soda is used as an antacid.
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(a) Methanoic acid/ Formic acid/ $\ce{HCOOH}$. (1 Mark) (b) (i) When acid is added to water, it does not cause excessive local heating/ does not cause splash out and burns. (1 Mark) (ii) Baking soda, being alkaline in nature, neutralises excess acid in stomach and provides relief. (1 Mark)
Define the following terms : (i) Olfactory indicator (ii) Water of crystallization
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(i) The substances whose odour changes in acidic or basic media. (1 Mark) (ii) The fixed number of water molecules present in one formula unit of a salt. (1 Mark)
Attempt either subpart (a) or (b) : OR (b) Define the following terms with an example : (i) Olfactory indicators (ii) Water of crystallisation (iii) Basic salt
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(b) (i)Substances whose odour changes in acidic or basic media. (½ Mark) Example: Onion, vanilla, clove (any one) (½ Mark) (ii)The fixed number of water molecules present in one formula unit of a salt. (½ Mark) Example: $\ce{CuSO4 . 5H2O}$, $\ce{CaSO4 . 2H2O}$, $\ce{FeSO4.7H2O}$, $\ce{Na2CO3.10H2O}$ (any one or any other) (½ Mark) (iii)The salt formed by reaction between strong base and weak acid. (½ Mark) Example: $\ce{Na2CO3}$, $\ce{NaHCO3}$ (any one or any other) (½ Mark)
(a) A compound ‘A’ is used in soda-lime fire-extinguisher and decomposes on heating to form compound ‘B’. Compound ‘B’ is used for removing permanent hardness of water. Identify ‘A’ and ‘B’. (b) Write chemical formula of Plaster of Paris. At what temperature gypsum is heated to obtain Plaster of Paris ?
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A $\rightarrow$ Sodium hydrogen carbonate/ baking soda/ $\ce{NaHCO3}$ B $\rightarrow$ Sodium carbonate/ washing soda/ $\ce{Na2CO3}$
(a) Give the chemical name and formula of Plaster of Paris. (b) Write the chemical equation of its preparation. (c) Give any two uses of it.
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(a) • Calcium sulphate hemihydrate (½ Mark) • $\ce{CaSO4.1/2H2O}$ (½ Mark) (b) $\ce{CaSO4.2H2O ->[373K] CaSO4.1/2H2O + 3/2H2O}$ (1 Mark) (c) Plaster of Paris is used for • making toys (½ Mark) • to support fractured bones in right position. (½ Mark) (or any other two uses)