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Sanjay Singh Sanjay Singh
Teacher of chemistry
Feb 13, 2012 | Closed

CBSE Xth Board chemistry examination (Session V)


  • Explain why: Bleeding due to a small cut can be stopped by rubbing alum Asked by: Garima
  • Due to its astringent properties, alum crystals or blocks (potassium alum) can be used to prevent bleeding from small cuts.
  • How does one chemically differentiate between a carboxylic acid and an alcohol? Asked by: Adarsh Rao
  • You can simply test it by litmus paper .
  • What are structural isomers Asked by: kanika
  • Those isomers which have the same molecular formula but they differ in the arrangement of the groups. Structural isomers have different IUPAC names and may or may not belong to the same functional group
  • what happens when a small piece of sodium is dropped into ethanol ? Asked by: vikash
  • when sodium is dropped into ethanol, sodium ethoxide along with hydrogen gas is formed. 2C2H5OH + 2Na ---->2C2H5ONa + H2
  • what is periodicity ? what is the cause of periodicity ? Asked by: vikash
  • Periodicity refers to how the Periodic Table is organized. Elements are grouped in a logical ways that puts elements with similar properties in the same groups and periods. The cause for the periodicity is: When elements are placed in the order of their increasing atomic number, the elements having the same number of valence shell electrons is repeated in such a way, so as to fall under the same group. Since, the electronic configuration of the valence shell electrons is same they show similar properties. Members of the same group have similar electronic configuration of the valence shell and thus show same valency.
  • why does the size of the atom progressively become smaller from na to cl ? Asked by: vikash
  • While going from sodium to chlorine we move from left to right in a group . From moving left to right the electrons in the valence shell keep on increasing which causes increase in nuclear pull of the electrons towards the nucleus and hence the atomic size increases.
  • thank u sir .... what are oxidising agent? Asked by: pooja kuril
  • An oxidizing agent is referred to as a chemical compound that readily transfers oxygen atoms or a substance that gains electrons in a redox chemical reaction.
  • name two elements whose atom are readily converted to unipositive ion. Asked by: vikash
  • Li and Na
  • what is alcohol ? write the molecular formula , condensed formula and structural formula of ethyl alcohol. Asked by: vikash
  • An alcohol is an organic compound in which the hydroxyl functional group (-OH) is bound to a carbon atom. molecular formula=C2H6O(where 2, 6 are in subscript) condensed formula=CH3CH2OH or C2H5OH(all numbers are in subscripts) If still you have any problem you can go to our website www.topperlearning.com
  • Write two properties of carbon which lead to the huge number of carbon compounds we see around us? Asked by: vikash
  • 1. Catenation- the ability of carbon to form bonds with other carbon atoms. 2. Tetravalency- Because of the valency of carbon=4, it is able to form bonds with four other atoms.
  • Write a chemical equation to represent the reaction of ethanol with acidified solution of potassium dichromate. Asked by: vikash
  • 2K2Cr2O7 + 16H+ + 3CH3CH2OH --> CH3COOH + 4Cr+3 + 4K+ + 11 H2O
  • Why is balancing a chemical reaction important? Asked by: trisha
  • Firstly, It is important because one is usually interested in finding of how efficient the processes are i.e what are the yields of the products obtained, and only by knowing the stoichiometry one can know the expected yields of products and the correct ratio of reactants. And secondly, to show the principle of conservation of matter it is important to balance a chemical reaction.
  • how many structural isomers can you pentane ? Asked by: pooja kuril
  • There are three structural isomers possible for pentane: n-pentane, 2-methylbutane, 2,2-dimethylpropane
  • What are the limitations of modern periodic table? Asked by: Mansi
  • 1. It does not give any idea about isotopes since the table is based on atomic numbers of elements and has no mention for position of isotopes. 2. The position of hydrogen is not correctly defined.
  • What are halogens? Asked by: Mansi
  • The halogens are a series of non- metal elements from Group 17 of the periodic table and comprises fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). Halogens are highly reactive,because of highly electronegative nature of their atoms due to their high effective nuclear charge.
  • How does baking powder differ from baking soda ? Asked by: vikash
  • Baking powder is sodium bicarbonate and potassium bitartarate. Baking soda is sodium bicarbonate.Baking powder is actually baking soda with a starch (often corn starch) and and acid like cream of tartar. Baking soda is alkaline and baking powder is acidic.
  • Define with suitable examples Gold number Asked by: GARIMA
  • It is defined as the minimum amount of lyophilic colloid in milligrams which prevents the coagulation of 10 ml gold sol against 1 ml of 10% NaCl solution. More is the gold number less is the protective power of the lyophilic colloid.For various colloids: Gelatin 0.005-.01 Haemoglobin 0.03-0.07 Egg Albumin 0.15-0.25
  • are aliphatic compounds the same as saturated compounds? Asked by: jhalak
  • Aliphatic compounds are not the same as saturated compounds , aliphatic compounds include both saturated and unsaturated compounds
  • what is the product formed when cane sugur reacts with conc.H2SO4 Asked by: karan
  • sugar charcoal is obtained on reacting cane sugar with conc. sulphuric acid.
  • Give the chemical test to identify this compound. Write the chemical equation. Asked by: vikash
  • You forgot to give the compound to be identified.
  • 1. Gases with high critical temperature are readily adsorbed. Why? Asked by: GARIMA
  • Gases with high critical temperature are readily adsorbed because they have strong Van der Waals forces.
  • A lens is placed inside water.Mention the condition wherein the lens will not be visible to us? Asked by: Vivek
  • you should ask this question in physics chat on thursday
  • how to learn reaction easily in carbon and its compound Asked by: jay
  • You should practice the chemical reactions of Alkanes and alkenes for alkynes you will observe various similarities with that of alkenes. In case of alcohols and carboxylic acid practice esterification and other reactions as much as you can but the important thing is you should write down the reactions on the paper.Practice these reactions and after finishing one topic say alkane make a flow chart or list of the various reactions that you learnt in that topic.
  • What are the examples of catalysts? Asked by: Mansi
  • Sulfuric Acid is used to dehydrate Ethanol to Ethylene. Manganese dioxide, used to decompose Hydrogen Peroxide to Oxygen and Water. Zeolite, iron oxide
  • a substance with initial concentration 'a' follows 0 order kinetics with the rate constant 'k' molLinverse1 sec inverse 1. In how much time will the reaction go to completion? Asked by: GARIMA
  • t(time for completion) = [Ao]/k = (Initial concentration)/(Rate constant)
  • how ios the rate law written for ist order ; zero order ; 2nd order & 3rd order reaction Asked by: GARIMA
  • For zero order: Differential Rate Law: r = k For first order: Differential Rate Law: r = k [A] For second order : Differential Rate Law: r = k [A]^ 2
  • 21. The trans isomer of complex CoCl2(en)2 is optically inactive .Why? Asked by: GARIMA
  • The trans isomer of this complex has a superimposable mirror image which makes it optically inactive.
  • will iron nail will be rusted in distilled water and why? Asked by: vishnu
  • Yes distilled water will rust an iron nail and will rust it faster as compared to water as distilled water contains higher levels of OXYGEN and would rust it more.
  • What are the uses of ethyl alcohol? Asked by: Mansi
  • It is used as alcoholic beverages, in medical wipes and antibacterial hand sanitizer, general purpose solvent, used as a base chemical for other organic compounds like ethyl halides, ethyl esters, di ethyl ether, acetic acid.
  • How to remembr d reactns????????? Asked by: Anil Kumar
  • To remember the reactions you must be aware of the reactivity series of elements in organic reactions and in organic reactions you must be aware of the movement of electrons.To get good hold over the reactions you must practice it as much as you can.
  • What is “occlusion” Asked by: GARIMA
  • An occlusion occurs when an adsorbed impurity gets physically trapped inside the crystal as it grows i.e when a impurity is surrounded by the material of interest, but not actually incorporated into the crystal lattice.
  • how is a rate law & rate expression written? Asked by: GARIMA
  • Rate law is an equation that gives relation between the reaction rate with concentrations or pressures of reactants and constant parameters. For a reaction A+B--->C+D The expression for rate law is: Rate = k [A][B]
  • what are the key points which should be kept in mind during writing a chemistry exam Asked by: mai
  • First of all if the question is a numerical then write all the formulae and the units for all. Secondly, balance all the reactions and write their state also like gas or aq.
  • Could you explain the mechanism of Aldol condensation? Also pl. elucidate on what one must study for solid states. Asked by: Priti
  • The aldol condensation reaction proceeds via a carbanion intermediate. The mechanism of base-catalyzed aldol condensation is: 1. Firstly the base removes an α hydrogen. 2. Then the carbanion undergoes nucleophilic addition with the carbonyl group of a second molecule of ethanal, which leads to formation of the condensation product. 3. A reaction with water protonates the alkoxide ion. If the aldol is heated in basic solution, the molecule can be dehydrated to form an α β-unsaturated aldehyde.

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