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» Checking dimensional correctness for v²= 2 g h LHS = v² = [L T ^-1]² = [L² T ^-2] RHS = 2 g h = 2 [L T ^-1][L] = [L² T^-2]              »LHS = RHS So, the LHS= RHS.  HENCE, the given formula is dimensionally correct.  » Checking dimensional correctness for v = u+ at LHS = v = [L T ^-1]  RHS = u + at=  [L T ^-1] + [L T^-2][T]                       = [L T^-1]              »LHS = RHS So, the LHS= RHS.  HENCE, the given formula is dimensionally correct. 

Ques : Three oxides of lead on analysis were found to contain lead as under: (i) 3.45 g of yellow oxide contains 3.21 g of lead. (ii) 1.195 g of brown oxide contains 1.035 g of lead. (iii) 1.77 g of red oxide contains 1.61 g of lead. Show that these data illustrate law of multiple proportions. Ans : The amounts of lead and oxygen in three oxides are : (i) Yellow oxide : Mass of lead = 3.21 g Mass of oxygen = 3.45 - 3.21                              = 0.24 g  (ii) Brown oxide : Mass of lead = 1.035 g                             Mass of oxygen = 1.195 - 1.035                                                          = 0.160 g (iii) Red oxide: Mass of lead = 1.61 g                          Mass of oxygen = 1.77 – 1.61                                                       = 0.16 g Let us fix the mass of lead as 1 g and calculate the different weights of oxygen which combine with 1 g of lead in these oxides. (i) Yellow oxide      Mass of oxygen which combines with 3.21 g of lead = 0.24 g    

Ques : Phosphorus and chlorine form two compounds The first compound contains 22.54% by mass of phosphorus and 77.46% by mass of chlorine. In the second compound the percentages are 14.88 for phosphorus and 85.12 for chlorine. Show that these data are consistent with the law of multiple proportions. Ans : In the first compound,        Percentage of phosphorus = 22.54         Percentage of chlorine = 77.46 Thus, 22.54 g of phosphorus combines with 77.46 g chlorine. In the second compound,        Percentage of phosphorus = 14.88        Percentage of chlorine = 85.12 Thus, 14.88 g of phosphorus combine with 85.12 g of chlorine. Let us fix the mass of phosphorus as 1 g and find the different masses of chlorine which combine with 1 g of phosphorus in two compounds. In the first compound,      Mass of chlorine which combines with 22.54 g of phosphorus = 77.46 g     The mass of chlorine which combines with 1 g of phosphorus = 77.46 / 22.54 = 3.44 g In the second compound,      Mass of chlorin

Ques : 2.0 gram of a metal burst in oxygen give 3.2 gram of its oxide. 1.42 gram of the same metal heat in steam give 2.27 gram of its oxide which toys shown by this data?  Ans : In the first compound, 3.2 gram of metal oxide contained 2.0 gram of metal 100 gram of metal oxide contained metal =2.0/3.2 × 100= 62.5 g :· % metal in first compound= 62.5% In the second compound, 2.27 gram of metal oxide contains metal = 1.42 gram 100 gram of metal oxide contains the metal= 1.42/2.27×100=62.55 gram :· % metal in first compound= 62.55% Thus, the percentage of metal in metal oxide obtained from to experiment is nearly same. Hence, the above data illustrate the law of constant composition.  <<   Previous                                                       Next   >>

  Ques 1: Which of the following pairs will give displacement reactions?   (a) sodium chloride solution and copper metal (b) magnesium chloride solution and aluminium metal (c) ferrous sulphate solution and silver metal (d) silver nitrate solution and copper metal. Ans 1: (d) silver nitrate solution and copper metal   Ques 2: Which of the following methods is suitable for preventing an iron frying pan from  rusting? (a) Applying grease (b) Applying paint (c) Applying a coating of zinc (d) All of the above. Ans 2: (c) Applying a coating of zinc (We can also apply grease and paint to prevent iron from rusting. However, in case of iron frying pan, grease and paint cannot be applied because when the pan will be heated and washed again and again, the coating of grease and paint would get destroyed. The process of layering of zinc surface on the utensils or on the metals are known as galvanisation.) Ques 3: An element reacts with oxygen to give a compound with a high melti

                                  Page 18:   Ques 1: You have been provided with 3 test tubes. One of them contains distilled  water and the other 2 contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the  contents of each test tube?  Ans 1: If the colour of red litmus paper gets changed to blue, then it is a base and if there  is no colour change, then it is either acidic or neutral. Thus, basic solution can be  easily identified. Let us mark the three test tubes as A, B, and C. A drop of the solution in A is put  on the red litmus paper. Same is repeated with solution B and C. If either of them changes colour to blue, then it is basic. Therefore, out of three, one is eliminated.  Out of the remaining two, any one can be acidic or neutral. Now a drop of basic  solution is mixed with a drop of each of the remaining two solutions separately and then the nature of the drops of the mixtures is checked. If the c

Ques 1: A solution turns red litmus blue, its pH is likely to be   (a) 1  (b) 4  (c) 5  (d) 10 Ans 1: (d) Bases turn red litmus blue and acids turn blue litmus red. Basic solution has a pH  value more than 7 to 14. P H 14 is the most basic in nature. Since the solution turns red litmus blue, its pH is likely to be 10.  Ques 2: A solution reacts with crushed egg-shells to give a gas that turns lime-water milky. The solution contains   (a) Na Cl  (b) HCl  (c) L i Cl (d) K Cl Ans 2: (b) The solution contains HCl.  Egg shells contains Calcium carbonate. When C a CO 3 reacts with H Cl it releases CO 2 which turns lime water milky.  Ques 3: 10 mL of a solution of Na OH is found to be completely neutralised by 8 mL of a given  solution of HCl. If we take 20 mL of the same solution of Na OH, the amount of HCl  solution (the same solution as before) required to neutralise it will be   (a) 4 mL  (b) 8mL (c) 12 mL  (d) 16 mL Ans 3: (d) 16 mL of HCl solution will be required.  

                                  Page 6: Qu es 1: Why should a magnesium ribbon be cleaned before burning in air ? Ans  1: Magnesium is very reactive metal like (Na, C a, etc.). When it expose to air it reacts with oxygen to form a layer magnesium oxide (Mg O) on its surface.                  Mg + O 2→ 2 Mg O This layer of magnesium oxide is quite stable and prevents further reaction of magnesium with oxygen. The magnesium ribbon is cleaned by sand paper to remove this layer so that the underlying metal can be used for the reaction. Ques 2: Write the balanced equation for the following chemical reactions.  (i) Hydrogen + Chlorine → Hydrogen chloride (i i) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride  (i i i) Sodium + Water → Sodium hydroxide + Hydrogen Ans  2: (i) H 2  + Cl 2 →2 H  (i i) B a Cl 2 + Al 2 (SO 4) 3 →3 B a SO 4 + 2 Al Cl 3 (i i i) Na + H 2 O → Na OH Ques 3: Write a balanced chemical equation with state symbols for the following react

Ques 1 : Which of the statements about the reaction below are incorrect?              2 P b O  +  C → 2 P b + CO (a) Lead is getting reduced. (b) Carbon dioxide is getting oxidised. (c) Carbon is getting oxidised. (d) Lead oxide is getting reduced. (i) (a) and (b) (i i) (a) and (c) (i i i) (a), (b) and (c) (i v) all Ans 1: (i)(a) and (b) Ques 2: The above reaction is an example of a:              Fe 2 O 3 +2 Al →Al 2 O 3  + 2 Fe (a) combination reaction. (b) double displacement reaction. (c) decomposition reaction. (d) displacement reaction. Ans 2: (d) The given reaction is an example of a displacement reaction. Ques 3: What happens when dilute hydrochloric acid is added to iron filings? Tick the correct answer. (a) Hydrogen gas and iron chloride are produced. (b) Chlorine gas and iron hydroxide are produced. (c) No reaction takes place. (d) Iron salt and water are produced. Ans 3: (a) Hydrogen gas and iron chloride are produced. The reaction is as  follows

Ques 1. On turning a corner a motorist rushing and 44 m/s finds a child on the road ahead. He instantly stops the engine and applies the brakes so as to stop it will in one metre of the child calculate time required to stop it. Ans . 4.5 sec   Ques 2.  An object is thrown vertically upwards with some speed. It crosses two points p, q which are separated by h metre. If TP is the time between p and highest point and coming back at t q is the time between q and highest point and coming back, relate acceleration due to gravity,  t p, t q and h.  Ans . g =8h/(t p²-t q²)  Ques 3. A body covers 12 metre in 2 seconds and 20 metre in 4 second. Find what distance the body will cover in 4 seconds after 5 th second.  Ans. 136 metre Ques 4. Two bodies are released from the same height at an interval of 1 second. How long after the first body begins to fall will the two bodies be 10 metre apart? Ans. 1.5 second Ques 5. A particle experiences constant acceleration for 20 sec

               1. Introduction Atoms are the basic component of matter. It consists of many sub atomic particles. In 1897, the experiments on electric discharge through gases carried out by the English physicist J. J. Thomson (1856 – 1940) revealed that atoms of different elements contain negatively charged  constituents (electrons) that are identical for all atoms. However, atoms on a whole are electrically neutral. Therefore, an atom must also contain some positive charge to neutralise the negative charge of the electrons.The first model of atom was proposed by J. J. Thomson in 1898.  According to this model, the positive charge of the atom is uniformly distributed throughout the volume of the atom and the negatively charged  electrons are embedded in it like seeds in a watermelon. This model was picturesquely called plum pudding model of the atoms. The distribution of the electrons and positive charges are very different from that proposed in this model. We know that condensed mat