Try segregating the things around
[question] Question. Try segregating the things around you as pure substances or mixtures : (a) distilled water (b) curd (c) diamond (d) ice-cream (e) kerosene oil (f) cooking oil (g) steel (h) graphite (i) raw rubber (j) vulcanized rubber (k) solder wire (l) glass (m) iron nail. [/question] [solution] Solution: (i) Pure substances : distilled Water, glass, iron nail, graphite, diamond, raw rubber. (ii) Mixture : curd, ice cream, kerosene oil, cooking oil, steel, vulcanized rubber, solder wire. ...
Read More →The diameter of a sphere is decreased by 25%.
[question] Question. The diameter of a sphere is decreased by $25 \%$. By what per cent does its curved surface area decrease? [/question] [solution] Solution: Let the diameter of the sphere be d. Radius $\left(r_{1}\right)$ of sphere $=\frac{d}{2}$ New radius $\left(\mathrm{r}_{2}\right)$ of sphere $=\frac{d}{2}\left(1-\frac{25}{100}\right)=\frac{3}{8} d$ $\operatorname{CSA}\left(S_{1}\right)$ of sphere $=4 \pi r_{1}^{2}$ $=4 \pi\left(\frac{d}{2}\right)^{2}=\pi d^{2}$ CSA $\left(S_{2}\right)$ o...
Read More →Why does an aqueous solution
[question] Question. Why does an aqueous solution of an acid conduct electricity? [/question] [solution] solution: Acids dissociate in aqueous solutions to form ions. These ions are responsible for conduction of electricity. [/solution]...
Read More →Why do $\mathrm{HCl}, \mathrm{HNO}_{3}$, etc., show acidic character in aqueous solution
[question] Question. Why do $\mathrm{HCl}, \mathrm{HNO}_{3}$, etc., show acidic character in aqueous solution while solutions of compounds like alcohol and glucose do not show acidic character? [/question] [solution] solution: $\mathrm{HCl}$ and $\mathrm{HNO}_{3}$ dissociate in the presence of water to form hydrogen or hydronium ions. Although aqueous solutions of glucose and alcohol contain hydrogen, these cannot dissociate in water to form hydrogen or hydronium ions. Hence, they do not show ac...
Read More →No physicist has ever “seen” an electron. Yet, all physicists believe in the existence of electrons.
[question] Question No physicist has ever “seen” an electron. Yet, all physicists believe in the existence of electrons. An intelligent but superstitious man advances this analogy to argue that ‘ghosts’ exist even though no one has ‘seen’ one. How will you refute his argument? [/question] [solution] Solution Although an electron was never ‘seen’ its impacts were observed and its practical evidence was tested and proven. For example, electricity. With respect to spirits and ghosts, though there a...
Read More →Classify the following as chemical
[question] Question. Classify the following as chemical or physical changes : • Cutting of trees • Melting of butter in a pan • Rusting of almirah • Boiling of water to form steam • Passing of electric current through water and the water breaking down into hydrogen and oxygen gases • Dissolving common salt in water • Making a fruit salad with raw fruits, and • Burning of paper and wood. [/question] [solution] Solution: Physical changes : Cutting of trees, melting of butter in a pan, boiling wate...
Read More →Metal compound A reacts with dilute hydrochloric acid to produce effervescence.
[question] Question. Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride. [/question] [solution] solution: $\mathrm{CaCO}_{3}(\mathrm{~s})+2 \mathrm{HCl}(\mathrm{aq}) \rightarrow \mathrm{CaCl}_{2}(\mathrm{~s})+\mathrm{CO}_{2}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(\ell)$...
Read More →What type of mixtures are separated
[question] Question. What type of mixtures are separated by the technique of crystallisation? [/question] [solution] Solution: The crystallisation method is used to purify solid mixtures. [/solution]...
Read More →Which gas is usually liberated when an acid reacts with a metal?
[question] Question. Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas ? [/question] [solution] solution: Hydrogen gas is usually liberated when an acid reacts with a metal. Example, Step 1- Take few pieces of zinc granules and add $5 \mathrm{ml}$ of dilute $\mathrm{H}_{2} \mathrm{SO}_{4}$. Step 2 - Shake it and pass the gas produced into a soap solution. The bubbles are formed in the soap solution. These s...
Read More →Though India now has a large base in science and technology, which is fast expanding,
[question] Question Though India now has a large base in science and technology, which is fast expanding, it is still a long way from realizing its potential of becoming a world leader in science. Name some important factors, which in your view have hindered the advancement of science in India. [/question] [solution] Solution Here are some significant factors that have hindered scientific development in India: lack of infrastructure and funding for high-quality scientific research work education...
Read More →Name the technique to separate,
[question] Question. Name the technique to separate, (i) Butter from curd, (ii) Salt from sea-water, (iii) Camphor from salt. [/question] [solution] Solution: (i) Centrifugation (ii) Evaporation (iii) Sublimation [/solution]...
Read More →Why should curd and sour substances
[question] Question. Why should curd and sour substances not be kept in brass and copper vessels? [/question] [solution] solution: Curd and other sour substances contain acids. Therefore, when they are kept in brass and copper vessels, the metal reacts with the acid to liberate hydrogen gas and harmful products, thereby spoiling the food. [/solution]...
Read More →How will you separate a mixture containing kerosene
[question] Question. How will you separate a mixture containing kerosene and petrol (difference in their boiling points is more than 25°C), which are miscible with each other? [/question] [solution] Solution: The process of distillation is used for the separation of components of a mixture containing two miscible liquids that boil without decomposition and have sufficient difference in their boiling points (that is greater than 25°C). [/solution]...
Read More →“Politics is the art of the possible”. Similarly, “Science is the art of the soluble”. Explain this
[question] Question “Politics is the art of the possible”. Similarly, “Science is the art of the soluble”. Explain this beautiful aphorism on the nature and practice of science. [/question] [solution] Solution Politicians make everything possible to win votes. And science is a systematized study of observation. Researchers and scientist study these observations and then work out certain laws from them. In this universe, there are several natural phenomena taking place and all of them can be desc...
Read More →To make a saturated solution,
[question] Question. To make a saturated solution, 36 g of sodium chloride is dissolved in 100 g of water at 293 K. Find its concentration at this temperature. [/question] [solution] Solution: Concentration $=\frac{\text { Mass of solute }}{\text { Mass of solution }} \times 100$ Here, mass of solute = 36 g and mass of solvent = 100 g Therefore, Mass of solution $=100+36=136 \mathrm{~g}$ Thus, concentration $=\frac{36}{136} \times 100=26.47 \%$ [/solution]...
Read More →Differentiate between homogeneous
[question] Question. Differentiate between homogeneous and heterogeneous mixtures with examples. [/question] [solution] Solution: Homogeneous mixture They contain physically distinct parts and have non-uniform compositions. Mixtures of sodium chloride and iron fillings, salt and sulphur, and oil and water are examples of heterogeneous mixtures. Suspensions and colloids are also heterogeneous mixtures. Heterogeneous mixture : They contain physically distinct parts and have non-uniform composition...
Read More →Explain the following terms with one example each.
[question] Question. Explain the following terms with one example each. (a) Corrosion (b) Rancidity [/question] [solution] solution: (a) Corrosion- Corrosion is defined as a process where materials, usually metals, deteriorate as a result of a chemical reaction with air, moisture, chemicals, etc. For example, iron, in the presence of moisture, reacts with oxygen to form hydrated iron oxide. $4 \mathrm{Fe}+3 \mathrm{O}_{2}+\mathrm{nH}_{2} \mathrm{O} \rightarrow 2 \mathrm{Fe}_{2} \mathrm{O}_{3} \c...
Read More →Oil and fat containing food items are flushed with nitrogen.
[question] Question. Oil and fat containing food items are flushed with nitrogen. Why? [/question] [solution] solution: Nitrogen is an inert gas and does not easily react with these substances. On the other hand, oxygen reacts with food substances and makes them rancid. Thus, bags used in packing food items are flushed with nitrogen gas to remove oxygen inside the pack. When oxygen is not present inside the pack, rancidity of oil and fat containing food items is avoided. [/solution]...
Read More →List the points of differences between
[question] Question. List the points of differences between homogeneous and heterogeneous mixtures] [/question] [solution] Solution: Homogeneous mixture : (i) The composition of a homogeneous mixture is the same throughout. For example, if you make a solution of sugar in water and taste it by taking a spoonful of solution either from the surface or from somewhere underneath the surface, it tastes equally sweet. (ii) A homogeneous mixture has no distinct boundaries, i.e., it consists of only one ...
Read More →Why do we apply paint on iron articles?
[question] Question. Why do we apply paint on iron articles? [/question] [solution] solution: Iron articles are painted because it prevents them from rusting. When painted, the contact of iron articles from moisture and air is cut off. Hence, rusting is prevented. Their presence is essential for rusting to take place. [/solution]...
Read More →What is meant by a pure substance?
[question] Question. What is meant by a pure substance? [question] [solution] Solution: A pure substance is one that cannot be separated into different constituents by physical or chemical process. A pure substance is one that contains particles of only one type of a substance. [/solution]...
Read More →A shiny brown-coloured element ' $X$ ' on heating in air becomes black in colour.
[question] Question. A shiny brown-coloured element ' $\mathrm{X}$ ' on heating in air becomes black in colour. Name the element ' $\mathrm{X}^{\prime}$ and the black coloured compound formed. [/question] [solution] solution: $' X^{\prime}$ is copper $(\mathrm{Cu})$ and the black-coloured compound formed is copper oxide $(\mathrm{CuO})$. The equation of the reaction involved on heating copper is given below. [/solution]...
Read More →Explain the following in terms of gain
[question] Question. Explain the following in terms of gain or loss of oxygen with two examples each. (a) Oxidation (b) Reduction [/question] [solution] solution: (a) Oxidation is the gain of oxygen. For example, In equation (i), $\mathrm{H}_{2}$ is oxidized to $\mathrm{H}_{2} \mathrm{O}$ and in equation (ii), $\mathrm{Cu}$ is oxidised to $\mathrm{CuO}$. (b) Reduction is the loss of oxygen. For example, In equation (i), $\mathrm{CO}_{2}$ is reduced to $\mathrm{CO}$ and in equation (ii), $\mathrm...
Read More →Name A, B, C, D, E and F in the following diagram
[question] Question. Name A, B, C, D, E and F in the following diagram showing change in its state [/question] [solution] Solution: A : Fusion B : Vaporization C : Condensation D : Solidification E : Sublimation F : Desublimation/deposition. [/solution]...
Read More →“Every great physical theory starts as a heresy and ends as a dogma”.
[question] Question “Every great physical theory starts as a heresy and ends as a dogma”. Give some examples from the history of science of the validity of this incisive remark [/question] [solution] Solution Solution: In our daily lives, a common observation is that light travels in a straight line. It was heresy when Huygens advocated his theory of waves. However, it quickly became a dogma that could be explained effectively on the grounds of wave theory as interference patterns, refraction, e...
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