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InterviewSolution
This section includes InterviewSolutions, each offering curated multiple-choice questions to sharpen your knowledge and support exam preparation. Choose a topic below to get started.
| 8151. |
According to Newlands' law of octaves, the number of elements between two similar elements is |
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Answer» 6 |
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| 8153. |
According to Newlands' classification of elements, the properties of element B are similar to element A. (i) How many elements are there between A and B? (ii) Starting from A, what is the position of B? |
| Answer» SOLUTION :(i) There are 6 elements between A and B. (II) TAKING POSITION of A as Ist, position of B is 8th. | |
| 8154. |
According to Mendeleef's periodic law, the properties of elements are periodic function of |
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Answer» ATOMIC masses |
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| 8155. |
According to modern periodic law, the physical and chemical properties of elements are the periodic functions of their ? |
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Answer» DENSITY |
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| 8157. |
According to Mendeleev's perodic law, the properties of elements are a periodic function of their |
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Answer» ATOMIC numbers |
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| 8158. |
According to Mendeleev's periodic law, theproperties of elements are a periodic function oftheir atomic numbers. |
| Answer» Solution :False . According toMendeleev. speriodic LAW , the properties of ELEMENTSARE aperiodic function of their atomic MASSES . | |
| 8159. |
According to Mendeleev's periodic law, the elements were arranged in the periodic table in the order of …. |
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Answer» INCREASING ATOMIC NUMBER. |
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| 8160. |
According to Mendeleev's Periodic Law, the elements were arranged in the Periodic Table in the order of |
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Answer» increasing atomic number |
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| 8161. |
According to Mendeelev's periodic Law, the elements were arranged in the periodic table in the order of |
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Answer» INCREASING ATOMIC number |
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| 8162. |
According to Lewis theory, neutralisation is the |
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Answer» transfer of PROTON from acid to BASE |
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| 8163. |
According to Lewis acid-base concept, which is a correct statement ? |
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Answer» SPECIES in which central atom has completed octet cannot act as acid |
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| 8164. |
According to Le Chatelier's principle, |
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Answer» an increase in pressure always causes a change in position of equilibrium for any reaction |
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| 8165. |
According to law of conservation of mass |
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Answer» The MASS of PRODUCT REMAINS constant |
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| 8166. |
According to Joule's iaw of heating, mention the factors on which heat produccd in a resistor depends. According to this law write the formula used talculate the heat produced. |
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Answer» SOLUTION :Direetly proportional to the SQUARE of CURRENT for a given resistance Directly proportional to resistance for a given current, and Directly proportional to the time for which the current flows through the RESISTOR `H - I^(2)RT` |
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| 8167. |
According to _________ atomic model positive charge is thinly spread throghout the atom |
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Answer» BOHR's |
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| 8169. |
Abhinav studies in the nth standard in a city school. One day his science teacher was discussing oils and fats in the clas. During this discussion Abhinav came to know many facts about oils and fats which he did not know earlier. When Abhinav came back home from school, he asked his mother what type of cooking medium she used to prepare food for the family. The mother replied that she was using vegetable ghee(or vanaspati ghee) for cooking food. Abhinav requested his mother not to use vegetable ghee because it is said to be harmful for health. He asked her to purchase vegetable oil always and use it for cooking food because vegetable oils are said to be good for health. Abhinav's mother agreed to do the same. (a) What is the difference in the physical states of vegetable oils and fats such as vegetable ghee (or vanastpati ghee)? (b) How are vegetable oils and fats different chemically? (c) Name the process by which a vegetable oil is coverted into a fat called vegetable ghee (or vanaspati ghee) in inductry. (d) Why is fat such as vegetable ghee (or vanaspati ghee) not considered good for health? (e) Name the most common animal fat consumed by people? (f) Why is vegetable oils considered to be good for health? (g) What values are displayed by Abhinav in this episode? |
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Answer» Solution :(a) Vegetable oils are in liquid state at the room temperature whereas fats are solids (or semi-solids) at room temperature. (b) Vegetable oils are unsaturated organic compounds (containing unsaturated fatty ACIDS) whereas fats are saturated organic compounds (containing saturated fatty acids). (c) Vegetable oils (like groundnout OIL) can be covered into a fat (like vegetable ghee or vanaspati ghee) by the process of hydrogenation of oils. (d) Fats are not considered good for health because due to the presence of saturated fatty acids, they tend to raise the level of cholesterol in blood in the long run and increase the RISK of heart disease (especially if too much fat is consumed). (e) The most common animal fat consumed by people is butter. (f) Vegetable oils are considered good for health because due to the presence of unsaturated fatty acids, they tend to lower the level of cholesterol in blood and decrease the risk of heart disease. (g) The values displayed by Abhinav are (i) Awareness (or knowledge) that vegetable oils are better for health than fats (ii) APPLICATION of knowledge in real life situations and (III) Concern for the health of his family. |
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| 8170. |
A zinc plate was kept in a glass container having copper sulphate solution. On examining it was found that the blue colour of the solution is getting fader and fader. After a few days when the zinc plate was taken out of the solution, a number of small holes were noticed in it. State the reason and give chemical equation of the reaction involved. |
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Answer» Solution :Zinc is more reactive than copper. Hence, when a zinc plate is kept in a solution of copper sulphate, it SLOWLY displaces copper from the solution and blue colour of the solution KEEPS fading away. Because of zinc GOING into solution as zinc sulphate a number of HOLES are seen in the zinc plate. The reaction is `CuSO_4(aq)_(Blue)+ZN(s) to ZnSO_4(aq)_(Colourl ess)+Cu(s)` |
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| 8171. |
A Zinc rod is left for nearly 20 minutes in Copper sulphate solution. What change would you observe in zinc rod. |
| Answer» SOLUTION : ZINC ROD will CHANGE into Zinc SULPHATE. | |
| 8172. |
(a) You have three unlabelled test tubes containing ethanol, ethanoic acid and soap solution. Explain the method you would use to identify the compoundsin different test tubes by chemical tests using litmus paper and sodium metal. (b) Give the reason of formation of scum when soaps are used with hard water. |
Answer» SOLUTION :(a)  (B) Hard water contains calciumions or MAGNESIUM ions or both. These ions on reacting with soap solution forms insoluble SUBSTANCE called scum. |
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| 8173. |
a) Write two points of difference between electric energy and electric power.b) An electric bulb of 200 Omegadraws a current of 1 ampere. Calculate the power of the bulb the potential different at its ends and the energy in KWh consumed burning it for 5h. |
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Answer» Solution :a) Electric ENERGY: 1) The work done or energy supplied by the source in maintaining the flow of electric current is called electrical energy. It appeare in the form of heat given by `VIt = (Vt)/(R) = VRt ` ii) It is EQUAL to the product of power and TIME ` E = P XX t` iii) Its SI units is joule (J) Electric power : i) The time rate at which electric energy is consumed or disipated by an electrical device is called electric power and is given by `P = vI = (v^2)/(R) = I^2 R` ii)It is equal to rate of doing work by an energy source. `P = w/t` iii) Its SI unit is Watt (W) 1W = `1JS^(-1)` (b)Power of the bulb Power of the bulb,` P = I^2R = (1)^2 xx 200` P= 200 W Energy consumed by bulb in 5h in burning. = Power x Time = 200 x 5 = 1000 wh= 1Kwh. |
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| 8174. |
a] Write the trend of atomic size and metallic character along a group and a period in the Modern Periodic Table. b]"Elements in the periodic table show periodicity of properties." List any four such properties. |
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Answer» SOLUTION : a) In the MODERN PERIODIC Table both atomic size and metallic character increase down a group and decrease along a period from left to right. B) Four periodic properties are: (0) Atomic size (i) Metallic character (iii) CHEMICAL reactivity (iv) Electropositivity |
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| 8175. |
a) Write the structure and functions of placenta. b) What are the changes that occur in a flower after fertilization. |
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Answer» Solution :a) Placenta is a disc which is embedded in the uterine wall. It contains villi on the embryo.s side of the tissue. On the MOTHER.s side are blood spacer, which surround the villi. This PROVIDES large surface area for glucose and oxygen to pass from mother to the embryo. The waste generated in the embryo is REMOVED by transferring them into the mother.s blood through the placenta. b) Pollen grain develops pollen TUBE containing two male gametes, travels from stigma to style to reach the ovule for fertilization to take place. Male and female gametes fuse in the ovule and after fertilization. zygote divides several TIMES to form an embryo within the ovule. The ovule develops a tough coat and is gradually converted into a seed. The ovary grows rapidly and ripens to form a fruit. Meanwhile, the petals. sepals, stamens, style and stigma may shrivel and fall off. The seed contains a seed coal an embryo with plumule - future shoot. radicle. future root and one or two catyledons which supply food to the germinating seed at a later stage. |
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| 8176. |
(a) Write the name of any three elements present in third period. (b) What will be the total number of shells in each and name the valence shell of each. Write configuration of all of these. |
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Answer» SOLUTION :(a) Na, Mg and Al are the elements present in third period. (b) `{:("Element","TOTAL no. of shells","Name of VALENCE shell","Configuration"),(Na,3,M,2","8","1),(Mg,3,M,2","8","2),(AI,3,M,2","8","3):}` |
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| 8177. |
(i) Write the name given to bases that are highly soluble in water. Give an example. (ii) How is tooth decay related to pH? How can it be prevented? (iii) Why does bee-sting cause pain and irritation? Rubbing of baking soda on the sting area gives relief. How? |
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Answer» Solution :(a) Alkali, Eg. NaOH (SODIUM HYDROXIDE) . (b) Lower the pH, more will be TOOTH decay. Acid reacts with `Ca_(3) (PO_(4))_(2)` and cause tooth decay. It can be prevented by brushing teeth after every meal. (c) It is due to Formic acid. Sodium hydrogen CARBONATE (Baking soda) neutralises Formic acid GIVING relief. |
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| 8178. |
(a) Write the correct sequence of steps followed during journey of oxygen rich blood from lungs to various organs of human body. (b) What happens when the system of blood vessels develop a leak? |
Answer» SOLUTION :(a)  (i) Lungs oxygen to the blood which is carried to the left atrium through the pulmonary VEIN. (ii) While receiving blood the left atrium is in diastole. It now enters systole to PUSH the OXYGENATED blood to left ventricle, through the bicuspid valve (Mitral). (iii) The left ventricle now is in diastole while the left atrium is in systole. (iv) The left ventricle enters systole, thereby opening the semilunar valve to push the blood into the aorta which divides into various arteries to take theoxygenated blood to different body parts. (b) Blood clotting is a phenomenon brought about by blood PLATELETS which prevents excessive loss of blood at the time of injury or leakage from a blood vessel. Platelets rupture to release a substance called thromboplastin. 
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| 8179. |
(a) Write the common name of CaOCl_2 How it is prepared? Write the chemicalequation of the reaction involved in the process. Give any two uses of it. (ii) Write the chemical name of washing soda. How is it prepared? Give the relevant chemical equations. |
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Answer» Solution :(a) The common name of `CaOCl_2` is Bleaching powder. By passing chlorine into DRY slaked lime `(Ca(OH)_2)`. `Ca(OH)_2+Cl_2 to CaOCl_2+ H_2O` Two uses: (i) Used for bleaching COTTON and linen in the textile industry and wood pulp in paper industry etc. (II) It is used for disinfecting drinking WATER. (b) Washing soda:- `Na_2CO_3. 10 H_2O` By HEATING baking soda, sodium carbonate is obtained, its recrystallisation gives washing soda. `2NaHCO_3 to^(Heat) Na_2CO_3+H_2O+CO_2` `Na_2CO_3+10H_2O toNa_2CO_3. 10 H_2O` |
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| 8180. |
(a) Write the chemical reactions taking place when : (i) Manganese dioxide is heated with aluminium powder (ii) Steam is passed over red hot iron (c ) Magnesium reacts with hot water. (b) The oxide X_(2)O_(3) is unaffacted by water. Name a method by which metal X can be obtained from its ore. Give one reason as to why have you chosen this method. |
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Answer» Solution :(i) `3MnO_(2)(s) + 4Al(s) overset("heat")rarr3Mn(s) + 2Al_(2)O_(3)(s)` (ii)`3FE(s) + 4H_(2)O(g) rarrunderset("Iron (II, III) oxide")(Fe_(3)O_(4)(s) + 4H_(2)(g))` (iii)`Mg(s) + underset(("Stream"))(2H_(2)O(g))overset("heat")rarrMg(OH)_(2)(aq)+H_(2)(g)` (b) Since the metal oxide `X_(2)O_(3)` is not affected by water, this means that the metal is of low reactivity. It can be ISOLATED by Alumino thermic PROCESS i.e. by reacting with metal like aluminium. For example, the metal Cr(X = Cr) can be obtained from its oxide `Cr_(2)O_(3)` by heating with aluminium. `Cr_(2)O_(3)(s) + 2Al(s) overset("heat")RARR Al_(2)O_(3)(s) + 2Cr(s)` |
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| 8181. |
a] Write the chemical name of absolute alcohol. b] Identify A, B, X, and Y in the reaction sequence: i] CH_3CH_2OH overset(KMnO_4 + KOH)(rarr) A + H_2O ii] CH_3CHOH +A overset("conc". H_2SO_4)(rarr) B + H_2O iii] B + NaOH to X + CH_3CH_2OH iv] A + NaHCO_3 rarr CO_2 + Y + H_2O. |
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Answer» Solution :a] Ethanol. B] `A: CH_3 COOH, B: CH_3COOCH_2CH_3,` X and Y are the same compound, `CH_3 COONA.` |
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| 8182. |
(a) Write the chemical formula of hydrated copper sulphate and anhydrous copper sulphate. Give an activity to illustrate how these two are inter convertible. (b) Write chemical names and formulae of Plaster of paris and gypsum. |
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Answer» SOLUTION :(a) Hydrated copper sulphate- `CuSO_4. 5H2O` Anhydrous coppper sulphate- `CuSO_4` Activity (i) Heat a few crystals of copper sulphate in a DRY BOILING tube. (ii) Add 2-3 drops of water on the sample of copper sulphate obtained after heating. After heating, water is removed and salt turns white. If crystals are moisten again with water, blue colour reappears. Water of crystallization is fixed number of water molecules present in one formulae unit ofa salt. FIVE water molecules are present in one FORMULA unit of copper sulphate. (b) Calcium sulphate hemihydrate: `CaSO_4. 1//2 H_2O` Calcium sulphate dihydrate: `CaSO_4. 2 H_2O`. |
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| 8183. |
(a) Write the balanced chemical equations for the extraction of copper metal from its ore. What is the reducing agent used ? (b) Which reducing agent can be used in the extraction of metals placed at the top of the reactivity series ? Give the name of the process also. (c ) What is the chemical substance formed as green coating when copper reacts with atmospheric gases in moist condition ? (d) What is galvanisation ? |
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Answer» Solution :(a) Copper is isolated from its sulphide ore known as copper glance `(Cu_(2)S)` by heating with excess of air or oxygen. `2Cu_(2)S(s) + 3O_(2)(g) overset("heat")rarr 2Cu_(2)O(s) + 2SO_(2)(g)` `2Cu_(2)O(s) + Cu_(2)S(s) overset("heat")rarr6Cu(s)+SO_(2)(g)` CUPROUS oxide `(Cu_(2)O)` acts as reducing agent and this process is known as auto-reduction. (b) These metals (K, Na, MG, etc.) can be isolated by carrying out the process of electrolysis (electrolytic reduction) for their molten salts. (c ) The green coating is of basic copper CARBONATE. It is formed as follows : `2Cu + underset(("PRESENT in air"))(H_(2)O + CO_(2)+O_(2))rarrunderset("Basic copper carbonate")(Cu(OH)_(2).CuCO_(3))` |
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| 8184. |
(a) Write the balanced chemical equations for the extraction of copper metal from its ore. What is the reducing agent used ? (b) Which reducing agent can be used in the extraction of metals placed at the top of the reactivity series ? Give the name of the process also. (c ) What is the chemical substance formed as green coating when copper reacts with atmospheric gases in moist conditions ? |
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Answer» Solution :(a) COPPER is isolated from its SULPHIDE ORE known as copper glance `(Cu_(2)S)` by heating with excess of air or oxygen. `2Cu_(2)S(s) + 3O_(2)(g) overset("heat")rarr 2Cu_(2)O(s) + 2SO_(2)(g)` `2Cu_(2)O(s) + Cu_(2)S(s) overset("heat")rarr6Cu(s) + SO_(2)(g)` Cuprous oxide `(Cu_(2)O)` acts as reducing agent and this process is known as auto-reduction. These metals (K, Na, Mg etc.) can be isolated by carrying out the process of ELECTROLYSIS (electrolytic reduction) from their MOLTEN salts. (c ) The green coating is of basic copper carbonate. It is formed as follows : `2Cu + underset(("Present in air"))ubrace(H_(2)O + CO_(2)+O_(2)) rarrunderset("Basic copper carbonate")(Cu(OH)_(2).CuCO_(3))` |
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| 8185. |
(a) Write one equation each for decomposition reaction when energy is supplied in the form of : (i) heat ,(ii) light. (b) Account for the following : (i) Paint is applied on iron articles. (ii) Oil and fat containing food items are flushed withnitrogen . (iii) When an iron nail kept in copper sulphate solution, blue colour of the solution fades and iron nail becomes brownish . |
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Answer» Solution :(a) (i) `CaCO_(3)(S) overset Delta rarrCaO(S)+CO_(2)(g)` (II) `2AgBr overset("Sunlight")rarr2Ag+Br_(2)` (b) (i) To protect the iron articles from corrosion . When iron articles are exposed to moist air , corrosion takes place . When the surface is covered by paint, it is not exposed to moist air . (ii) To flush out any air or oxygen present in the packet . In the absence of oxygen , food items will not get rancid. (iii) Since iron is more reactive than copper , it displaces copper from copper sulphate solutionand the blue colour of solution fades . Dueto the DEPOSITION of copper on iron nail , iron nail becomes brownish. |
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| 8186. |
(a) Write method will you use to reduce the following ? Explain by giving a suitable example. (i) Oxides of less reactive metals (ii) Oxides of moderately reactive metals (iii) Oxides of highly reactive metals. (b) The reaction between metal 'X' and Fe_(2)O_(3) is highly exothermic and is used to join railway tracks. (i) Identify metal 'X' and name the reaction. (ii) Write the chemical equation of its reaction with Fe_(2)O_(3). |
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Answer» Solution :(a) (i) Oxides of less REACTIVE metals can be reduced either by auto-reduction or upon HEATING. For example, `2Cu_(2)O + Cu_(2)S overset("heat")rarr6Cu + SO_(2)` `2HgO overheat("heat")rarr 2Hg + O_(2)` (ii) Oxides of moderately reactive metals can be reduced with coke. This is known as smelting. For example, `ZnO + C overset("heat")rarrZn + CO` `PbO + C overset("heat")rarr Pb + CO` (iii) Oxides of highly reactive are reduced by electrolytic reduction. `Al_(2)O_(3) ("molten")rarr underset(("cathode"))(2Al^(3+)) +underset(("Anode"))(3O^(2-))` At cathode : `Al^(3+) + 3e^(-) rarrAl`. At anode : `O^(2-) rarr O(1//2O_(2))+2e^(-)` (b) (i) The metal 'X' is aluminium. The reaction is known as thermit reaction. (ii) `Fe_(2)O_(3) + 2Al overset("heat")rarr Al_(2)O_(3) + 2FE` |
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| 8187. |
a. Write electron dot diagram for chlorine (At No. 17) and Calcium (At No 20) show the formation of Calcium chloride by transfer of electrons. |
Answer» SOLUTION : `CatoCa^(2+)+2E^(-)` `2Cl+2e^(-)to2Cl^(-)` 
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| 8188. |
(a) Write chemical equations. (i) When carbon dioxide gas is passed through lime water. (ii) When excess of carbon dioxide gas is passed through line water. (b) List two natural forms of calcium carbonate. |
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Answer» Solution :(a) (i) `Ca(OH)_(2)(AQ)+CO_(2)(g)rarrCaCO_(3)(S)+H_(2)O(L)` (ii) `Ca(OH)_(2)(aq)+CO_(2)(g)rarrCaCO_(3)(s)+H_(2)O(l)` `CaCO_(3)(s)+H_(2)O(l)+CO_(2)(g)rarrCa(HCO_(3))_(2)(aq)` (b) Aragonite and calcite |
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| 8189. |
(a) With the help of labelled ray diagram show the path followed by a narrow beam of monochromatic light when it passes through a glass prism. (b) What would happen if this beam is replaced by a narrow beam of white light? |
Answer» Solution :(a) A labelled ray DIAGRAM of a narrow BEAM of monochromatic light when it passes through a glass prism is shown here.  (b) If monochromatic beam is replaced by a beam of white light then on entry into the glass prism it is SPLITTED into seven coloured beams which travel differently. In the emergent light the violet colour beam is DEVIATED the most and red colour beam is deviated the least. As a result we OBTAIN a spectrum of white light. |
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| 8190. |
(a) Why does an aqueous solution of an acid conduct electricity ? (b) How does the concentration of hydrogen ions [H_(3)O]^(+) change when the solution of an acid is diluted with water ? (c ) Which has a higher pH value , a concentrated or dilute solution of hydrochloric acid ? (d) what happens when hydrochloric acid reacts with (i) sodium bicarbonate placed in a test tube ? (ii) zinc metal in a test tube ? |
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Answer» Solution :(a) An awueous solution of an acid conducts electricity because in wate, an acid (e.g.HCl) DISSOCIATED to give ions. Since the current is carried by the MOVEMENT of ions, an awueous solution of acid conducts electricity. (b) Upon dilution, more of acid dossociates into ions. Therefore, concentration of `[H_(3)O]^(+)` ions increases upon dilution. (C ) Although more `[H_(3)O]^(+)` ions are formed upon dilution, but the number of ions per unit VOLUME decrease. Therefore pH will increase upon dilution. (d) (i) Carbon dioxide gas would evolve accompanied by drisk effervescene. `NaHCO+_(3)(s) +HCl(aq)to NaCl(aq)+CO_(2)(g)+H_(2)O(aq)` (ii) Hydrogen gas would evolve accompanied by brisk effervescent. `ZN(s)+2HCl(aq)toZnCl_(2)(aq)+H_(2)(g)` |
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| 8191. |
Why does an aqueous solution of an acid conduct electricity ? |
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Answer» Solution :a) The presence of hydrogen (`H^(+)`) or hydronium(`H_(3)O^(+)`) ions in the aqueous solution of an acid are responsible for conducting ELECTRICITY b) Plaster of Paris is prepared by heating gypsum to a temperature of `100^(@)C` the FOLLOWING reaction TAKES place : `CaSO_(4). 2H_(2)O to CaSO_(4). (1)/(2)H_(2)O + 1 (1)/(2)H_(2)O` On mixing with water it converts to a hard mass to form gypsum again i,e the reverse reaction takes place. |
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| 8192. |
a) Why do stars twinkle b) State two properties of the image formed by the eye lens on the retina. |
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Answer» Solution :(a) Stars twinkle due to atmospheric REFRACTION of starlight as the stars are very far away. They behave as almost point sources of light as on account of atmospheric refraction. The path rays of light coming from the star GOES on varying slightly the apparent position of the star fluctuates and the AMOUNT of starlight entering the eyc flickers. So sometimes the star APPEARS BRIGHTER and at some other time fainter, thus the stars twinkle. (b) i) Image on the retina is real and inverted. ii) Diminished in size. |
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| 8193. |
Write equations for the reactions. (i) Iron with steam (ii) Calcium and potassium with water |
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Answer» SOLUTION :In the formation of ionic compounds, positive ions and negative ions precipitate. These are closely packed and the ionic compounds exist as crystalline solids. They have strong inter - ionic process of attraction and have high metling and boiling points. i) `3Fe + 4H_(2)O to FC_(2)O_(4)+H_(2)` ii) `Ca+2H_(2)O toCa(OH)_(2)+ H_(2)` `2K + 2H_(2)O to 2KOH+H_(2)` |
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| 8194. |
Why are we not able to see the things clearly when we come out of a drak room? |
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Answer» Solution :a) When we are in dark, pupil size is bigger, as we come out of dark ROOM, its size needs to BECOME smaller. For that time interval person is unable to see. b) During sunrise, the light rays coming from the sun have to travel a greater distance in the earth.s ATMOSPHERE before reaching our eyes. In this journey, the shorter wave LENGTH of lights are scattered out and only LONGER wavelength are able to reach our eyes. Since blue colour had a shorter wavelength and red colour has longer wave length, the red colour is able to reach our eyes after the atmospheric scattering of light. Therefore the sun appear reddish early in the morning. |
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| 8195. |
a] Why are sodium and chlorine placed in the same period in the Modern Periodic Table? b] Why do elements placed in the same group of the periodic table have similar chemical properties? c] Who proposed the modern periodic law? On which fundamental property of an atom is it based? |
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Answer» Solution :a) Since they have the same number of electron shells. b) Since they have the same number of VALENCE electrons, which decides the chemical properties of an element. c) MOSELEY proposed the modern periodic law. It is based on the ATOMIC number - the number of PROTONS in an atom which decides its electronic CONFIGURATION and hence its properties. |
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| 8196. |
(a) Why cannot a chemical change be normally reversed ? (b) Why is it always essential to balance a chemical equation ? (c) Why do diamond and graphite, the two allotropic forms of carbon evolve different amounts of heat on combustion ? (d) Can rusting of iron take place in distilled water ? |
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Answer» Solution :(a) In a chemical change, the products are quite different from the reactants. Therefore, it cannot be normally reversed. (B) A chemical equation has to be balanced to meer the requirement of the law of conservation of mass. According to the law, the total mass of the reacting SPECIES taking part in the reaction is the same as that of the products FORMED. Since there is a DIRECT relationship between the mass of the different species and their number, it is always essential to balance a chemical equation. (c) Because they differ in the arrangement of carbon atoms present and have different shapes. The attractive forces among the atoms in the two cases are not same. That is why they evolve different amount of heat. `C("diamond") + O_(2)(g) to CO_(2)(g) + 393*5 kj` ltBrgt `C("graphite") + O_(2)(g) to CO_(2)(g) + 395*4 kj` Please note that diamond and graphite are the two allotropic forms of carbon. For details, consult chapter 4. (d) No, rusting of iron cannot take place in distilled water because it neither contains dissolved oxygen not carbon dioxide. Both are essential for the rusting of iron. |
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| 8197. |
(a) Why are metals not generally found in their free state ? (b) If a strip of aluminium with scratched surface is dipped in an aqueous solution of copper sulphate for little time, the surface of the strip becomes brownish. What is the reason for this ? Write the balanced chemical equation for the reaction. |
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Answer» Solution :(a) Metals in general are of reactive nature. Due to the high temperature prevailing below the surface of the earth, they generally EXIST in COMBINED STATES with other elements (metals and non-metals). (b) Aluminium displaces copper from the aqueous copper sulphate solution since it is PLACED above copper in the activity series. Copper forms a BROWNISH coating over the surface of the metal. `2Al(s) + 3CuSO_(4)(aq) rarr Al_(2)(SO_(4))_(3)(aq) + 3Cu(s)` |
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| 8198. |
(a) Why are ionic compounds usually hard crystalline solids ? (b) Give two methods to prevent rusting of iron. (c ) Name the ores of the metals (i) mercury (ii) zinc. |
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Answer» Solution :(a) In ionic compounds, the cations and anions are closely packed in space and have strong forces of interaction. They exist as crystals which are quite HARD. (b) (i) Coating the surface of iron with zinc (galvanisation) (ii) Painting the surface of iron with a rust PROOF paint. (c ) Mercury : CINNABAR or mercury (II) sulphide (HGS) Zinc : Zinc blende or zinc (II) sulphide (ZnS) |
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| 8199. |
A white powder is added while baking bread and cakes to make them soft and fluffy. Write the name of the powder. Name its main ingredients. Explain the function of each ingredient. Write the chemical reaciton taking place when the powder is heated. |
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Answer» Solution :Baking powder Baking soda and an EDIBLE acid like tartaric acid. Baking soda `(NaHCO_3)` is used to release `CO_2` gas when HEATED to make them fluffy. Tartaric acid is used to AVOID the bitter taste by reacting with the `Na_2CO_3` FORMED. |
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A white powder having an odour of chlorine is used to remove yellowness of white clothes in laundries . Name this powder . How is it prepared ? Write the chemical reaction involved in its preparation . |
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Answer» Solution :The white powder is BLEACHING powder , `CaOCl_2` . It is prepared by passing `Cl_2` gas over DRY SLAKEDLIME. `UNDERSET("Slaked lime ")(Ca(OH)_2) + Cl_2 to underset("Bleaching powder ")(CaOCl_2)` |
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