What produces more severe burns
[question] Question. What produces more severe burns, boiling water or steam? [/question] [solution] Solution: Steam will produce more severe burns than boiling water. It is because, 1 g of steam at 373 K (100°C) contains 2260 J of heat energy more in the form of latent heat of vaporization as compared to water at 373 K (100°C ). Thus steam produces more severe burns. [/solution]...
Read More →A capsule of medicine is in the shape of a sphere of diameter 3.5 mm.
[question] Question. A capsule of medicine is in the shape of a sphere of diameter $3.5 \mathrm{~mm}$. How much medicine (in $\mathrm{mm}^{3}$ ) is needed to fill this capsule? $\left[\right.$ Assume $\left.\pi=\frac{22}{7}\right]$ [/question] [solution] Solution: Radius $(r)$ of capsule $=\left(\frac{3.5}{2}\right) \mathrm{mm}=1.75 \mathrm{~mm}$ Volume of spherical capsule $=\frac{4}{3} \pi r^{3}$ $=\left[\frac{4}{3} \times \frac{22}{7} \times(1.75)^{3}\right] \mathrm{mm}^{3}$ $=22.458 \mathrm{...
Read More →Twenty seven solid iron spheres,
[question] Question. Twenty seven solid iron spheres, each of radius r and surface area S are melted to form a sphere with surface area S'. Find the (i) radius r' of the new sphere, (ii) ratio of S and S'. [/question] [solution] Solution: (i)Radius of 1 solid iron sphere $=r$ Volume of 1 solid iron sphere $=\frac{4}{3} \pi r^{3}$ Volume of 27 solid iron spheres $=27 \times \frac{4}{3} \pi r^{3}$ 27 solid iron spheres are melted to form 1 iron sphere. Therefore, the volume of this iron sphere wil...
Read More →A dome of a building is in the form of a hemisphere. From inside,
[question] Question. A dome of a building is in the form of a hemisphere. From inside, it was white-washed at the cost of Rs $498.96$. If the cost of white-washing is Rs $2.00$ per square meter, find the (i) inside surface area of the dome, (ii) volume of the air inside the dome. $\left[\right.$ Assume $\left.\pi=\frac{22}{7}\right]$ [/question] [solution] Solution: (i) Cost of white-washing the dome from inside $=$ Rs $498.96$ Cost of white-washing $1 \mathrm{~m}^{2}$ area $=$ Rs 2 Therefore, C...
Read More →Some of the most profound statements on the nature of science have come from Albert Einstein, one of the greatest scientists of all time.
[question] Question Some of the most profound statements on the nature of science have come from Albert Einstein, one of the greatest scientists of all time. What do you think did Einstein mean when he said: "The most incomprehensible thing about the world is that it is comprehensible"? [/question] [solution] Solution Naturally, the entire physical world is complicated. The biological world has its own complexities. Moreover, space, time and mass are involved in different orders of magnitudes. D...
Read More →What do you mean by a precipitation reaction?
[question] Question. What do you mean by a precipitation reaction? Explain by giving examples. [/question] [solution] solution: A reaction in which an insoluble solid (called precipitate) is formed is called a precipitation reaction. For example, In this reaction, calcium carbonate is obtained as a precipitate. Hence, it is a precipitation reaction. Another example of precipitation reaction is In this reaction, barium sulphate is obtained as a precipitate. [/solution]...
Read More →What produces more severe burns,
[question] Question. What produces more severe burns, boiling water or steam? [question] [solution] Solution: Steam will produce more severe burns than boiling water. It is because, 1 g of steam at 373 K (100°C) contains 2260 J of heat energy more in the form of latent heat of vaporization as compared to water at 373 K (100°C ). Thus steam produces more severe burns. [/solution]...
Read More →In the refining of silver,
[question] Question. In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved. [/question] [solution] solution: [/solution]...
Read More →Ice at 273 K is more effective in cooling,
[question] Question. Ice at 273 K is more effective in cooling, than water at the same temperature, why? [/question] [solution] Solution: At 0° both ice and water exist together. But the particle in water at 0°C have more energy as compared to particle in ice at the same temperature since during the change of state from ice to water, heat energy equal to latent heat of fusion has been absorbed. In the other words, ice, at 0°C is more effective in cooling a substance than water at 0°C. [/solution...
Read More →Find the volume of a sphere whose surface area is 154 cm2.
[question] Question. Find the volume of a sphere whose surface area is $154 \mathrm{~cm}^{2} .\left[\right.$ Assume $\left.\pi=\frac{22}{7}\right]$ [/question] [solution] Solution: Let radius of sphere be r. Surface area of sphere $=154 \mathrm{~cm}^{2}$ $\Rightarrow 4 \pi r^{2}=154 \mathrm{~cm}^{2}$ $\Rightarrow r^{2}=\left(\frac{154 \times 7}{4 \times 22}\right) \mathrm{cm}^{2}$ $\Rightarrow r=\left(\frac{7}{2}\right) \mathrm{cm}=3.5 \mathrm{~cm}$ Volume of sphere $=\frac{4}{3} \pi r^{3}$ $=\l...
Read More →What is the difference between displacement and double displacement reactions?
[question] Question. What is the difference between displacement and double displacement reactions? Write equations for these reactions. [/question] [solution] solution: In a displacement reaction, a more reactive element replaces a less reactive element from a compound. $\mathrm{A}+\mathrm{BX} \longrightarrow \mathrm{AX}+\mathrm{B} ;$ where $\mathrm{A}$ is more reactive than B In a double displacement reaction, two atoms or a group of atoms shift places to form new compounds. $\mathrm{AB}+\math...
Read More →Give two reasons to justify
[question] Question. Give two reasons to justify. (a) Water at room temperature is a liquid. (b) An iron almirah is solid at room temperature. [/question] [solution] Solution: (a) (i) Intermolecular forces are less. (ii) Intermolecular spaces and kinetic energy is more. Thus, the molecules of water can interchange their spaces and hence water is in liquid state at room temperature. (b) (i) Intermolecular forces are very large. (ii) Intermolecular spaces, as well as, kinetic energy are very small...
Read More →Write one equation each for decomposition reactions
[question] Question. Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity. [/question] [solution] solution: (a) Thermal decomposition (b) Decomposition by light (c) Decomposition by electricity [/solution]...
Read More →What is the physical state of water at
[question] Question. What is the physical state of water at (a) 25°C (b) 0°C (c) 100°C [/question] [solution] Solution: (a) At 25°C, water is in liquid state. (b) At 0°C, water is in solid state, provided heat is removed from it. (c) At 100°C, water is in gaseous state, provided heat is supplied to it. [/solution]...
Read More →A hemispherical tank is made up of an iron sheet 1 cm thick.
[question] Question. A hemispherical tank is made up of an iron sheet $1 \mathrm{~cm}$ thick. If the inner radius is $1 \mathrm{~m}$, then find the volume of the iron used to make the tank. $\left[\right.$ Assume $\left.\pi=\frac{22}{7}\right]$ [/question] [solution] Solution: Inner radius $\left(r_{1}\right)$ of hemispherical tank $=1 \mathrm{~m}$ Thickness of hemispherical tank $=1 \mathrm{~cm}=0.01 \mathrm{~m}$ Outer radius $\left(r_{2}\right)$ of hemispherical tank $=(1+0.01) \mathrm{m}=1.01...
Read More →Arrange the following substances in the increasing order of forces
[question] Question. Arrange the following substances in the increasing order of forces of attraction between the particles – water, sugar and oxygen. [/question] [solution] Solution: Oxygen, water and sugar. [solution]...
Read More →Why are decomposition reactions called the opposite of combination reactions ?
[question] Question. Why are decomposition reactions called the opposite of combination reactions ? Write equations for these reactions. [/question] [solution] solution: Decomposition reactions are those in which a compound breaks down to form two or more substances. These reactions require a source of energy to proceed. Thus, they are the exact opposite of combination reactions in which two or more substances combine to give a new substance with the release of energy. $\mathrm{AB}+$ Energy $\lo...
Read More →(a) Naphthalene balls disappear with time
[question] Question. (a) Naphthalene balls disappear with time without leaving any solid why? (b) We can get the smell of perfume sitting several meters away. [/question] [solution] Solution: (a) Naphthalene is volatile solid and has a tendency to sublime, therefore, it changes into vapours completely which disappear into the air and no solid is left. (b) This is because perfumes contain volatile solvent which carries pleasant smelling vapours. They diffuse quite fast and can reach to people sit...
Read More →Why is respiration considered an exothermic reaction ?
[question] Question. Why is respiration considered an exothermic reaction ? Explain. [/question] [solution] solution: Energy is required to support life. Energy in our body is obtained from the food we eat. During digestion, large molecules of food are broken down into simpler substances such as glucose. Glucose combines with oxygen in the cells and provides energy. The special name of this combustion reaction is respiration. Since energy is released in the whole process, it is an exothermic pro...
Read More →Convert the following temperature to the kelvin scale.
[question] Question. Convert the following temperature to the kelvin scale. (i) 25°C (ii) 373°C [/question] [solution] Solution: (i) 25 + 273 = 298K (ii) 373 + 273 = 646K [/solution]...
Read More →How many litres of milk can a hemispherical bowl of diameter 10.5 cm hold?
[question] Question. How many litres of milk can a hemispherical bowl of diameter $10.5 \mathrm{~cm}$ hold? $\left[\right.$ Assume $\left.\pi=\frac{22}{7}\right]$ [/question] [solution] Solution: Radius $(r)$ of hemispherical bowl $=\left(\frac{10.5}{2}\right) \mathrm{cm}=5.25 \mathrm{~cm}$ Volume of hemispherical bowl $=\frac{2}{3} \pi r^{3}$ $=\left[\frac{2}{3} \times \frac{22}{7} \times(5.25)^{3}\right] \mathrm{cm}^{3}$ $=303.1875 \mathrm{~cm}^{3}$ Capacity of the bowl $=\left(\frac{303.1875}...
Read More →What does one mean by exothermic and endothermic reactions?
[question] Question. What does one mean by exothermic and endothermic reactions? Give examples. [/question] [solution] solution: Chemical reactions that release energy in the form of heat, light, or sound are called exothermic reactions. Example: Reaction of sodium and chlorine to yield common salt $\mathrm{Na}(\mathrm{s})+\frac{\mathbf{1}}{\mathbf{2}} \mathrm{Cl}_{2}(\mathrm{~s}) \rightarrow \mathrm{NaCl}(\mathrm{s})+411 \mathrm{~kJ}$ of energy In other words, combination reactions are exotherm...
Read More →Convert the following temperature to the Celsius scale
[question] Question. Convert the following temperature to the Celsius scale (i) 293 K (ii) 470 K [/question] [solution] Solution: (i) 293 - 273 = 20°C (ii) 470-273 = 197°C [/solution]...
Read More →The diameter of the moon is approximately one-fourth of the diameter of the earth.
[question] Question. The diameter of the moon is approximately one-fourth of the diameter of the earth. What fraction of the volume of the earth is the volume of the moon? [/question] [solution] Solution: Let the diameter of earth be $d$. Therefore, the radius of earth will be $\frac{d}{2}$. Diameter of moon will be $\frac{d}{4}$ and the radius of moon will be $\frac{d}{8}$. Volume of moon $=\frac{4}{3} \pi r^{3}=\frac{4}{3} \pi\left(\frac{d}{8}\right)^{3}=\frac{1}{512} \times \frac{4}{3} \pi d^...
Read More →What type of clothes should
[question] Question. What type of clothes should we wear in summer? [/question] [solution] Solution: We should wear light coloured cotton clothes in summer. Light colour because it reflects heat. Cotton clothes because it has pores in it, which absortbs sweat and allows the sweat to evaporate faster thereby giving cooling effect. [/solution]...
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