Recent questions tagged chemistry-10

Description : What are metalloids? Explain by giving examples. -Chemistry-10

Last Answer : Metalloids are elements which show some properties of metals and some properties of non-metals. Examples: Silicon, boron, arsenic, antimony, germanium, tellurium, polonium.

Description : What happens when baking soda is heated? -Chemistry-10

Last Answer : Sodium hydrogen carbonate (also known as sodium bicarbonate or bicarbonate of soda) has the chemical formula NaHCO3. When it is heated above about 80°C it begins to break down, forming sodium carbonate, water and carbon dioxide. This type of reaction is called a thermal decomposition.

Description : Why is plaster of paris stored in a moisture proof container? -Chemistry-10

Last Answer : Plaster of Paris in contact with moisture (water) changes to solid hard mass, gypsum. Therefore, it gets wasted. Hence it should be stored in moisture proof containers.

Description : (i) Substances oxidised is Na as it gains oxygen and oxygen is reduced. (ii) Substances reduced is Cu as hydrogen is oxidised as it gains oxygen. -Chemistry-10

Last Answer : During this reaction, the sodium is gaining oxygen and is being oxidized. Oxygen is getting reduced. During this reaction, copper oxide is losing oxygen and is being reduced. The hydrogen is gaining oxygen and is being oxidized.

Description : Identify the substances that are oxidised and the substances which are reduced in the following reactions. (i) 4Na(s) + O2(g) → 2Na2O(s) (ii) CuO (s) + H2(g) → Cu (s) + H2O(l) -Chemistry-10

Last Answer : (i) Substances oxidised is Na as it gains oxygen and oxygen is reduced. (ii) Substances reduced is Cu as hydrogen is oxidised as it gains oxygen.

Description : Give an example of a double displacement reaction other than the one given in Activity 1.10 -Chemistry-10

Last Answer : Sodium hydroxide and hydrochloric acid react to form sodium chloride and water.

Description : An iron nail is dipped in the solution of copper sulphate for about 30 minutes. State the change in colour observed. Give reason for the change. -Chemistry-10

Last Answer : When an iron nail is dipped in copper sulphate solution, the displacement reaction takes place. The colour of copper sulphate solution fades due to the formation of light green solution of iron sulphate.

Description : Why does the colour of copper sulphate solution change when an iron nail is dipped in it ? -Chemistry-10

Last Answer : When an iron nail is dipped in copper sulphate solution, the displacement reaction takes place. The colour of copper sulphate solution fades due to the formation of light green solution of iron sulphate.

Description : Why is the amount of gas collected in one of the test tubes in text book Activity 1.7 (i.e., electrolysis of water) double of the amount collected in the other? Name this gas. -Chemistry-10

Last Answer : In Activity 1.7, water is electrolysed to give H2 gas at one electrode and O2 gas at the other electrode. 2H2O(l) → 2H2(g) + O2(g) Thus two molecules of water on electrolysis give two ... oxygen gas or in other words the amount of hydrogen gas collected would be double than that of oxygen gas.

Description : A solution of a substance ‘X’ is used for white washing. (i) Name the substance ‘X’ and write its formula. (ii) Write the reaction of the substance ‘X’ named in (i) above with water. -Chemistry-10

Last Answer : (i) The substance whose solution in water is used for white washing is calcium oxide (or quick lime). Its formula is CaO.

Description : Write a balanced chemical equation with state symbols for the following reactions : -Chemistry-10

Last Answer : (i) BaCl2 (aq) + Na2SO4 (aq) → BaSO4(s) + 2NaCl (aq) (ii) NaOH (aq) + HCl(aq) → NaCl(aq) + H2O(l)

Description : Write the balanced equation for the following chemical reactions. (i) Hydrogen + Chlorine → Hydrogen chloride (ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride (iii) Sodium + Water → Sodium hydroxide + Hydrogen -Chemistry-10

Last Answer : (i) H2 + Cl2 → 2HCl (ii) 3 BaCl2 + Al2(SO4)3 → BaSO4 + 2 AlCl3 (iii) 2Na + 2H2O → 2NaOH + H2↑

Description : Why should a magnesium ribbon be cleaned before burning in air ? -Chemistry-10

Last Answer : Magnesium gets covered with a layer of magnesium oxide when kept in air for a long time. This layer hinders the burning of magnesium. Hence, it is to be cleaned before burning.

Description : 15. An object 2 cm high is placed at a distance of 64 cm from a white screen. On placing a convex lens at a distance of 32 cm from the object it is found that a distinct image of the object is formed on the screen. What is the focal length of the conve -Chemistry-10

Last Answer : Since, object-screen distance is double of object-lens separation, the object is at a distance of 2f from the lens and the image should be of the same size of the object.

Description : 14. An object 2 cm in size is placed 30 cm in front of a concave mirror of focal length 15 cm. At what distance from the mirror should a screen be placed in order to obtain a sharp image? What will be the nature and the size of the -Chemistry-10

Last Answer : Answer. hope this helps you

Description : 13. A ray of light, incident obliquely on a face of a rectangular glass slab placed in air, emerges from the opposite face parallel to the incident ray. State two factors on which the lateral displacement of the emergent ray depends. [Foreign] -Chemistry-10

Last Answer : Lateral displacement depends on the: angle of incidence, thickness of slab, and refractive index of the material. (any two)

Description : 12. Draw ray diagrams to represent the nature, position and relative size of the image formed by a convex lens for the object placed: -Chemistry-10

Last Answer : Answer. hope this helps you

Description : 10. Which kind of mirrors are used in the headlights of a motor-car and why? [Foreign] -Chemistry-10

Last Answer : Answer. Concave mirror, to get the parallel beam of light.

Description : 11. Explain with the help of a diagram, why a pencil partly immersed in water appears to be bent at the water surface. [Delhi] -Chemistry-10

Last Answer : Answer. Light from different points on the pencil, immersed in water refracts and appears to come from a point above the original position.

Description : 7. Redraw the given diagram and show the path of the refracted ray: [All India(C)] -Chemistry-10

Last Answer : Answer. hope this helps you

Description : 6. “The refractive index of diamond is 2.42”. What is the meaning of this statement in relation to speed of light? [Delhi] -Chemistry-10

Last Answer : Answer. hope this helps you

Description : 5. The refractive indices of four media A, B, C and D are given in the following table: -Chemistry-10

Last Answer : (i) Minimum change is seen as light moves between 1.50 and 1.52, i.e. B and C. (ii) Maximum change when light moves between 1.33 and 2.40, i.e. A and D.

Description : 4. If a light ray IM is incident on the surface AB as shown, identify the correct emergent ray. [Delhi (C)] -Chemistry-10

Last Answer : Answer. Ray NQ, as it has to be parallel to ray OS.

Description : 3. Draw the ray diagram in each case to show the position and nature of the image formed when the object is placed: -Chemistry-10

Last Answer : Answer. Nature of image: Real, inverted and same size image is formed at the centre of curvature. Nature of image: Virtual, enlarged and erect image is formed behind the mirror. Nature of image: ... image: Virtual, erect and diminished image is formed between O and F on the same side of object.

Description : 2. An object 50 cm tall is placed on the principal axis of a convex lens. Its 20 cm tall image is formed on the screen placed at a distance of 10 cm from the lens. Calculate the focal length of the lens. [All India] -Chemistry-10

Last Answer : this is the answer for the respected question

Description : 1. A concave lens has focal length of 20 cm. At what distance from the lens a 5 cm tall object be placed so that it forms an image at 15 cm from the lens? Also calculate the size of the image formed. [Delhi] -Chemistry-10

Last Answer : Answer. hope this helps youu