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NCERT Activity Chapter 02 Acid Bases and Salt Class 10 Chemistry Activity 2.1 Indicator Acid Base Red litmus No Change Blue Blue Litmus Red No change Phenolphthalein Colourless Pink Methyl Orange Pink Yellow Indictors are substance which change colour in acidic or basic media. Activity 2.2 There are some substances whose odour changes in in acidic or basic media. These are called olfactory indicators. Like onion vanilla, onion and clove. These changes smell in basic solution. Activity 2.3 Take about 5 mL of dilute sulphuric acid in a test tube and add few pieces of zinc granules to it. => You will observe bubbles of hydrogen gas on the surface of zinc granules. Zn + H2SO4 --> ZnSO4 + H2 => Pass the Hydrogen gas through the soap solution. Bubbles formed in the soap solution as Hydrogen gas it does not get dissolved in it
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ReplyDelete1. Mrs. Sharma has gone to the jewelers to buy gold jewellery. She asks the jeweler if the jewellery is made of pure gold. The jeweler assure her that it is 10% gold and nothing has been mixed in it. Mrs. Sharma is happy and buys the necklace.
ReplyDeleteRead the above passage and answer the following questions:
(a) Was the jeweler right in saying that the necklace is made of 100% gold?
(b)What values are promoted by the jeweler?
(c) What precautions should you take while purchasing gold jewellery?
(d)Why does Government insist on purchasing Hallmarked jewellery? [Value Based Questions]
Ans: (a) No, he was wrong. Pure gold is very soft and is therefore not suitable for making jewellery.
It is alloyed with either silver or copper to make it hard. But sometimes jewelers mix a large quantity of copper and silver in gold to earn more profit.
(b) Untrustworthiness, cleverness.
(c) We should always purchase the gold jewellery from a branded shop with proper receipt and Hallmark certificate.
(d) Government insists on purchasing Hallmarked jewellery as it contains the gold and its alloyed metal (i.e. copper or silver) in a fixed ratio.
2. Describe with labelled diagram, the Froth Floatation Process used to separate the gangue from a Sulphide ore.
Ans: Sulphide ore is mixed with water and pine oil. The mixture is agitated (shaken vigorously) with the help of stirrer in the blast of air. Froth is formed, sulphide ore gets attracted towards pine oil in the froth which is skimmed off, dried and concentrated sulphide ore is obtained. Gangue is left behind at the bottom of water.
3. Give reasons for the following:
(a)Metals generally do not form compounds with hydrogen.
(b) A piece of zinc placed in blue copper sulphate solution decolourize it.
(c) Alumina is dissolve in molten cryolite for electrolysis to obtain aluminium metal.
Ans:
(a) Metals are good reducing agents and H2 is weak oxidizing agent therefore, metals do not
react with hydrogen to form hydrides.
(b) Zn + CuSO4 ¾¾® ZnSO4 + Cu
It is due to formation of ZnSO4 (aq) which is colourless.
(c) It increases electrical conductivity and molten cryolite acts as a solvent.
4. What is the purpose of the soft iron core used in making an electromagnet?
Ans: The purpose of soft iron core used in making an electromagnet that:
(i) It is temporary magnetized.
(ii) It retains magnetism as long as current flow is maintained.
(iii) It will ensure an uniform and stronger field.
5. During the reaction of some metals with dilute hydrochloric acid, following observations were made:
(i) Silver metal doesn’t show any change.
(ii) The temperature of reaction mixture rises when aluminium (Al) is added.
(iii) The reaction of sodium metal is found to be highly explosive.
(iv) Some bubbles of a gas are seen when lead (Pb) is reacted with the acid.
(v) A gas produced when sodium carbonate is added to the acid.
Explain these observations giving suitable reasons.
Ans: (i) Silver is very less reactive metal. So it does not react with dilute HCl.
(ii) The reaction of Al with dilute HCl is exothermic i.e. heat is produced in the reaction, so the temperature of the reaction mixture rises.
(iii) Sodium is a very reactive metal. It react vigorously with the evolution of heat too.
(iv) Bubbles are seen due to the evolution of H2 gas.
Pbs + 2HCl ----> PbCl2 + H2
(v) CO2 gas is produced when Na2CO3 reacts with dilute HCl.
Na 2CO3 + 2HCl --> 2NaCl + H 2O + CO2
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ReplyDeleteBrain Development
Whn an object is placed 20cm from concave mirror a real image magnified 3 times is formed.Find where must the object be placed to give a virtual image 3 times the height of the object? this question is frm reflection of light class 10. plzzz solve it
ReplyDeletewhn an object is placed 20cm frm the concave mirror a real image magnified 3 times is formed.Find where must the object be placed to give a virtual image 3 times the height of the object. this question is frm reflection of light class 10. plzzz solve it
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ReplyDelete(a)
ReplyDeleteMagnification, m=-3 (Image is real)
Object distance, u=-20cm
Magnification, m=-v/u
-3=- v/(-20)
v=-60 cm
Thus the image is located at a distance of 60cm in front of the mirror.
Now using the mirror formula,
1/v +1/u=1/f
1/(-60) + 1/(-20)=1/f
f=-15 cm
(b)
m=h2 /h1=- v/u=3
v=-3u
Using mirror formula,
1/(-3u) +1/u=1/-15
u=-10 cm
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