Science

a) Derive the expression for the heat produced due to a current I flowing for a time interval t through a resistor R having a potential difference V across its ends. With which name is this relation known? b) How much heat will an instrument of 12W produce in one minute if it is connected to a battery of 12V? c) The current passing through a room heater has been halved. What will happen to the heat produced by it? d) What is meant by the heating effect of current? Give two applications of the heating effect of current. e) Name the material which is used for making the filaments of an electric bulb.

Answer a) The amount of work done when an electric charge Q moves against a potential difference V is: W = Q V = W = Q V = W = Q V = W = Q V (1) We all know that current I = Q/T. IT = Q (2)...

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A silvery-white metal X taken in the form of ribbon, when ignited, burns in air with a dazzling white flame to form a white powder Y. When water is added to powder Y, it dissolves partially to form another substance Z. (a) What could metal X be? (b) What is powder Y? (c) With which substance metal X combines to form powder Y? (d) What is substance Z? Name one domestic use of substance Z. (e) Write a balanced chemical equation of the reaction which takes place when metal X burns in air to form powder Y.

(a) Magnesium, Mg because magnesium undergoes oxidation in the presence of oxygen. (b) Magnesium oxide, MgO (c) Oxygen (of air), O2 (d) Magnesium hydroxide, Mg(OH)2; Used as an antacid to relieve...

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A solid substance P which is very hard is used in the construction of many buildings, especially flooring. When substance P is heated strongly, it decomposes to form another solid Q and a gas R is given out. Solid Q reacts with water with the release of a lot of heat to form a substance S. When gas R is passed into a clear solution of substance S, then a white precipitate of substance T is formed. The substance T has the same chemical composition as starting substance P. (a) What is substance P? Write its common name as well as a chemical formula. (b) What is substance Q? (c) What is gas R? (d) What is substance S? what is its clear solution known as? (e) What is substance T? Name any two natural forms in which substance T occurs in nature.

(a) Calcium carbonate (limestone), CaCO3 (b) Calcium oxide, CaO (c) Carbon dioxide, CO2 (d) Calcium hydroxide, Ca(OH)2; Lime water. (e) Calcium carbonate; Limestone and Marble.

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When metal X is treated with a dilute acid Y, then a gas Z is evolved which burns readily by making a little explosion. (a) Name any two metals which can behave like metal X. (b) Name any two acids which can behave like acid Y. (c) Name the gas Z. (d) Is the gas Z lighter than or heavier than air? (e) Is the reaction between metal X and dilute acid Y exothermic or endothermic? (f) By taking a specific example of metal X and dilute acid Y, Write a balanced chemical equation for the reaction which takes place. Also, indicate physical states of all the reactants and products.

(a) Zinc and Iron. (b) Dilute hydrochloric acid and dilute sulphuric acid. (c) Hydrogen. (d) Lighter than air. (e) Exothermic. (f) Suppose metal X is zinc (Zn) and acid Y is dilute hydrochloric acid...

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When water is added gradually to a white solid X. A hissing sound and a lot of heat is produced forming a product Y. A suspension of Y in water is applied to the walls of a house during whitewashing. A clear solution of Y is also used for testing carbon dioxide gas in the laboratory. (a) What could be solid X? Write its chemical formula. (b) What could be product Y? Write its chemical formula. (c) What is the common name of the solution of Y which is used for testing carbon dioxide gas? (d) Write a chemical equation of the reaction which takes place on adding water to solid X. (e) Which characteristics of chemical reactions are illustrated by this example?

Answer: (a) Calcium oxide, CaO. (b) Calcium hydroxide, Ca(OH)2 (c) Lime water. (d) CaO + H2O →  Ca(OH)2 (e) Change in temperature.

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When the solution of substance X is added to a solution of potassium iodide, then a yellow solid separates out from the solution. (a) What do you think substance X is likely to be? (b) Name the substance of which the yellow solid consists. (c) Which characteristic of chemical reactions is illustrated by this example? (d) Write a balanced chemical equation for the reaction which takes place. Mention the physical states of all the reactants and products involved in the chemical equation.

Answer: (a) Lead Nitrate (b) Lead Iodide (c) Formation of precipitate (d)Pb(NO3)2 (aq) + 2KI (aq) → PbI2 (s) + 2KNO3 (aq)

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The chemical equations are balanced to satisfy one of the following laws in chemical reactions. This law is known as (a) Law of conservation of momentum (b) Law of conservation of mass (c) Law of conservation of motion (d) Law of conservation of magnetism

Answer: Option (b) is the correct response. When the mass of atoms of different elements in the reactants side equals the mass of atoms in the products side, the equations are balanced.

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One of the following is an endothermic reaction. This is: (a) Combination of carbon and oxygen to form carbon monoxide (b) Combination of nitrogen and oxygen to form nitrogen monoxide (c) Combination of glucose and oxygen to form carbon dioxide and water(d) Combination of zinc and hydrochloric acid to form zinc chloride and hydrogen

Answer: Option (b) is the correct response. Nitrogen monoxide is formed when nitrogen and oxygen are heated to extremely high temperatures in an endothermic reaction.

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The chemical reaction between the two substances is characterised by a change in colour from orange to green. These two substances are most likely to be: (a) Potassium dichromate solution and sulphur dioxide (b) Potassium permanganate solution and sulphur dioxide (c) Potassium permanganate solution and lemon juice (d) Potassium dichromate solution and carbon dioxide

Answer: Option (a) is the correct response. The reaction of potassium dichromate with sulphur dioxide is characterised by a colour shift. By passing sulphur dioxide through acidified potassium...

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One of the following does not happen during a chemical reaction This is : (a) Breaking of old chemical bonds and formation of new chemical bonds (b) Formation of new substances with entirely different properties (c) Atoms of one element change into those of another element to form new products(d) A rearrangement of atoms takes place to form new products

Answer: Option (c) is the correct response. Atoms of one element do not convert into another to generate products; however, bonds between these atoms break and products are formed, and atoms are...

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Answer the following questions: (a) What do you understand by exothermic and endothermic reactions? (b) Give one example of an exothermic reaction and one of an endothermic reaction. (c) Which of the following are endothermic reactions and which are exothermic reactions? (i) Burning of natural gas (ii) Photosynthesis (iii) Electrolysis of water (iv) Respiration (v) Decomposition of calcium carbonate

Answer: (a)An exothermic reaction occurs when energy is discharged from the system into the environment. An endothermic reaction occurs when energy is taken from the environment in the form of heat....

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(a) State the various characteristics of chemical reactions. (b) State one characteristic of each of the chemical reactions which take place when: (i) Dilute hydrochloric acid is added to sodium carbonate (ii) Lemon juice is added gradually to potassium permanganate solution (iii) Dilute sulphuric acid is added to barium chloride solution (iv) Quicklime is treated with water (v) Wax is burned in the form of a candle

Answer: (a) A chemical reaction is a process that occurs when reactants react to generate new material. It is defined by the evolution of a gas, color change, precipitate formation, temperature...

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(a) What is meant by a chemical reaction? Explain with the help of an example. (b) Give one example each of a chemical reaction characterized by: (i) Evolution of a gas (ii) Change in colour (iii) Formation of a precipitate (iv) Change in temperature (v) Change in the state.

Answer: (a) By undergoing particular reactions and rearrangements, a chemical reaction produces new compounds. On the left, there will be reactants, and on the right, there will be products. Methane...

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Translate the following statement into a chemical equation and then balance it: ‘Barium chloride solution reacts with aluminium sulphate solution to form a precipitate of barium sulphate and aluminium chloride solution’.

Answer: The balanced chemical equation for the reaction of Barium chloride with Aliminium sulphate solution to form a precipitate of barium sulphate and aluminium chloride solution is as follows:...

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(a) Substitute formulae for names and balance the following equations: Calcium carbonate reacts with hydrochloric acid to produce calcium chloride, water, and carbon dioxide gas. (b) Write a balanced chemical equation with state symbols for the following reaction: Sodium hydroxide solution reacts with a hydrochloric acid solution to produce sodium chloride solution and water.

Answer: (a) Balanced chemical equation for the reaction of calcium carbonate with hydrochloric acid: CaCO3 + 2HCl → CaCl2 + H2O + CO2 (b) Balanced chemical equation for the...

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(a) Potassium chlorate (KClO3) on heating forms potassium chloride and oxygen. Write a balanced equation for this reaction and indicate the evolution of gas. (b) Rewrite the following information in the form of a balanced chemical equation: Magnesium burns in carbon dioxide to form magnesium oxide and carbon.

Answer: (a) Balanced chemical equation for heating of potassium chlorate: 2KClO3 (s) → 2KCl (s) + 3O2 (g) (b) Balanced chemical equation for burning of magnesium in carbon...

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Carbon monoxide reacts with hydrogen under certain conditions to form methanol. Write a balanced chemical equation for this reaction indicating the physical states of reactants and products as well as the conditions under which this reaction takes place.

Answer: Carbon dioxide reacts with hydrogen under certain conditions to form methanol. The reaction for the same is as follows: CO(g) + 2H2(g) → CH3OH Conditions for the reaction to take place:...

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(a) Explain, with example, how the physical states of the reactants and products can be shown in a chemical equation. (b) Balance the following equation and add state symbols:

    \[\mathbf{Zn}\text{ }+\text{ }\mathbf{HCl}~\to ~\mathbf{ZnC}{{\mathbf{l}}_{\mathbf{2}}}~+\text{ }{{\mathbf{H}}_{\mathbf{2}}}\]

(c) Convey the following information in the form of a balanced chemical equation: “An aqueous solution of ferrous sulphate reacts with an aqueous solution of sodium hydroxide to form a precipitate of ferrous hydroxide and sodium sulphate remains in solution.”

Answer: (a) In a chemical reaction, the physical state of the reactants and products can be indicated by using the letters in the round brackets. If it is solid, it will be (s), liquid, it will be...

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a) What is a balanced chemical equation? Why should chemical equations be balanced? b) Aluminium burns in chlorine to form aluminium chloride (AlCl3). Write a balanced chemical equation for this reaction. c) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas. Write a balanced chemical equation for this reaction.

Answer: (a) By balancing the total number of atoms of each element in reactants and products, a chemical equation can be created. To follow the Law of Conservation of Mass, a chemical equation must...

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(a) What are the various ways in which a chemical equation can be made more informative? Give examples to illustrate your answer. (b) Write a balanced chemical equation from the following information: An aqueous calcium hydroxide solution (lime water) reacts with carbon dioxide gas to produce a solid calcium carbonate precipitate and water.

Answer: (a) Ca(OH)2 (aq)+ CO2 (g)—3000°C →CaCO3(s)+H2O(l) A chemical equation can be informative by 1) The chemical states of substances present in the reaction are denoted by (s) for solids,...

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When hydrogen is passed over copper oxide, copper and steam are formed. Write a balanced equation for this reaction and state which of the chemicals are: (i) Elements (ii) Compounds (iii) Reactants (iv) Products (v) Metals (vi) Non-metals

Answer: H2 + CuO→  Cu + H2O (i) H2 and Cu are elements (ii) CuO and H2O are compounds (iii) H2 and CuO are reactants (iv) Cu and H2O are products (v) Cu is the metal (vi) H2 is...

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(a) What is a chemical equation? Explain with the help of an example. (b) Giving examples, state the difference between balanced and unbalanced chemical equations. (c) Balance the following chemical equations:

    \[~\left( \mathbf{i} \right)\text{ }\mathbf{N}{{\mathbf{H}}_{\mathbf{3}~}}\to \text{ }{{\mathbf{N}}_{\mathbf{2}~}}+\text{ }{{\mathbf{H}}_{\mathbf{2}}}\left( \mathbf{ii} \right)\text{ }\mathbf{C}\text{ }+\mathbf{C}{{\mathbf{O}}_{\mathbf{2}}}\to \text{ }\mathbf{CO}\]

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  Solutions: Answer: (a) Chemical equations are symbols for chemical reactions in which the reactants and products are stated as chemical formulae. The left side of a chemical equation contains...

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(a) Give one example of a chemical reaction. (b) State two characteristics of the chemical reaction which takes place when dilute sulphuric acid is poured over zinc granules. (c) Give two characteristics of the chemical reaction which occurs on adding potassium iodide solution to lead nitrate solution.

Answer: (a) By undergoing specific reactions and rearrangements, a chemical reaction produces new compounds. On the left, there will be reactants, and on the right, there will be products. The...

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A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggests that the genetic make-up of the tall parent can be depicted as

(a) TTWW (b) TTww (c) TtWW (d) TtWw Solution: The correct answer is (c) TtWW TtWW could be a result of the tall parent's genetic makeup. Half of the progenies are short, implying that the parent...

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