Sunday, July 5, 2020

What is an ester ? Describe an activity to form an ester.









SOLUTION:(a)Carbon has 4 electrons in its valence shell. To attain stability, it should either gain 4 electrons or lose 4 electrons. It cannot lose 4 electrons as it involves a lot of energy. Also, it cannot gain 4 electrons because the  nucleus  cannot  hold  on  to  the  four  extra  electrons  added. Therefore,  to  complete  the  octet,  it  shares  4  electrons  with  other atoms.  That  is  why,  carbon  forms  compounds  mainly  by  covalent bonding.

(b)Covalent compounds have covalent bonding in them. The bonds are formed by sharing of electrons. There are no ions in such compounds. There are weak forces of attraction between the molecules. So, they have low melting and boiling points


SOLUTION:(a)Carbon has 4 electrons in its valence shell. To attain stability, it should either gain 4 electrons or lose 4 electrons. It cannot lose 4 electrons as it involves a lot of energy. Also, it cannot gain 4 electrons because the  nucleus  cannot  hold  on  to  the  four  extra  electrons  added. Therefore,  to  complete  the  octet,  it  shares  4  electrons  with  other atoms.  That  is  why,  carbon  forms  compounds  mainly  by  covalent bonding.

(b)Covalent compounds have covalent bonding in them. The bonds are formed by sharing of electrons. There are no ions in such compounds. There are weak forces of attraction between the molecules. So, they have low melting and boiling points


(c) As ester is a compound having the general formula RCOOR’ where R and  R’  are  alkyl  groups.For  example,  ethyl  ethanoate,  CH3COOC2H5which is obtained by the combination of ethanoic acid with ethanol.


Activity to form an esterMaterials required : Beaker, test tube , wire gauze, tripod stand, burner, ethanoic acid, ethanol.

Procedure:(1)Take 1 mL ethanol, 1 mL glacial acetic acid and a few drops of conc.H2SO4 in a clean and dry test tube.
SOLUTION:
(2)Warm in a water bath for about 5 minutes as shown in Figure.
(3) Pour the contents of the test tube in a beaker containing  about  50  mL  of  water  and  smell  the resulting mixture. A sweet smell of the ester is noticed.

Both soap and detergent are some type of salts. What is the difference between them ? Describe in brief the cleansing action of soap. Why do soaps not form lather in hard water ? List two problems that arise due to the use of detergents instead of soaps

Both soap and detergent are some type of salts. What is the difference between them ? Describe in brief the cleansing action of soap. Why do soaps not form lather in hard water ? List  two    problems  that  arise  due  to  the  use  of  detergents instead of soaps
soaps are sodium or potassium salts of long chain fatty acids while detergentsare ammonium or sulphonate salts of long chain carboxylic acids.soap molecule has two parts. The ionic end of soap dissolves in water while thecarbon  dissolves  in  oil.  Most  dirt  is  oily  in  nature.

Soap  molecules  form  anacelle around dirt cip whose outer parts are directed towards water. On addingexcess water, the dirt along oil th the soap molecules is washed away. This ishow the cleansing action of soaps is described.Hard water contains chlorides and sulphates of calcium and magnesium whichreact with soap to form insoluble scum.

Therefore soap is not able to perform itscleansing action.Detergents  are  not  biodegradable  substances.  Thus,  they  may  cause  waterpollution.Detergents are highly basic in nature.They may affect the skin.

Questions CBSE 10th class

Questions CBSE 10th class
Q1.(a)  What  Is  homologous  series?  State  any  two characteristics of a homologous series.
(b) (i)  How are carboxylic acids different from mineral acids from the the ionisation point of view?

Q.  b  (ii)  Describe  an  activity  to  find  out  how  ethanoic  acid reacts with sodium carbonate. Name the gas evolved.How can it be tested?
Q2.An  organic  compound  A  on  heating  with  concentrated H2SO4  form  compound  B  which  on  addition  of  one  mole  of hydrogen in presence of Ni forms a compound C.One mole of compound  C  on  combustion  forms  two  moles  of  CO2  in  3 moles of H2O.Identify the compounds A,B and C and write the chemical equations of the reactions involved
Q3. (a)  Why  does  carbon  form  compounds  mainly  by  covalent bonding ? (b) Why do covalent compounds have low melting and boiling points
Q3. (c) What is an ester ? Describe an activity to form an ester.
Q4. (a) Give reasons for the following:(i) Unsaturated hydrocarbons show addition reaction.(ii)  Conversion  of  ethanol  to  ethanoic  acid  is  an  oxidation reaction.(iii)  Alcohol  supplied  for  industrial  purpose  is  mixed  with copper sulphate
Q4.  (b)  chemical  equation  to  represent  the  preparation  of ethane from ethanol.(c)  State  the  role  of  concentrated  sulphuric  acid  in  an esterification reaction.
Q5. Both soap and detergent are some type of salts. What is the difference between them ? Describe in brief the cleansing action of soap. Why do soaps not form lather in hard water ? List  two    problems  that  arise  due  to  the  use  of  detergents instead of soaps.

Q6. (a) Give a chemical test to distinguish between saturated and unsaturated hydrocarbon.(b) Name the products formed when ethane burns in air. Write the balanced chemical equation for the reaction showing the types of energies liberated

Q6. (c) Why is reaction between methane and chlorine in the presence of sunlight considered a substitution reaction ?
Q7. A compound A(C2H4O2) reacts with Na metal to form a compound B and evolves a gas which burns with a pop sound. Compound A on treatment with an alcohol C in the presence of an  acid  forms  a  sweet  smelling  compound,  D(C2H4O2).On addition of NaOH to D gives back B and C.Identify A,B,C and D. Write the reactions involved

Soaps and detergents class 10th cbse notes














 a) Soaps :-  Soaps are long chain sodium or potassium salts of carboxylic acids.      Eg:- Sodium stearate – C17H35COONa  
    Structure of soap molecule :-  A soap molecule has two parts. A long hydrocarbon part which is hydrophobic (water repelling) and soluble in oil and grease and a short ionic part which is  hydrophyllic (water attracting) and insoluble in oil and grease.
                                                              

   Cleansing action of soap :-   When soap is dissolved in water it forms spherical structures called micelles. In each micelle the soap molecules are arranged radially such that the HC part is towards the centre and the ionic part is towards the outside. The HC part dissolves the dirt, oil and grease and forms an emulsion at the centre of the micelles which can be washed away by water.


Chemical properties of Carbon Compounds Class 10th notes CBSE

Chemical properties of Carbon Compounds


Carbon is a fascinating element. It is known to form almost ten million different compounds most of which are chemical compounds that are organic in nature. Let us learn a bit about the chemical properties of carbon compounds.


















Combustion Reactions:


When Carbon and its compounds burn in the presence of Oxygen (or air), they give CO2, heat and light.The process of burning carbon and its compounds in excess of oxygen for the release of heat and light (energy) is known as combustion.

Following are some of the examples of the combustion reaction of organic compounds:

C + O2 ⇨ CO2 + Heat + Light

C3H8 + 5O2 = 3CO2 + 4H2O.+ Heat + Light

(C3H8 is the molecular formula for Propane, a common gas present in LPG which we burn for cooking in our kitchens).

In General, saturated hydrocarbons burn with a clear blue flame, whereas unsaturated hydrocarbons burn with a yellow flame producing soot (carbon).

Combustion of hydrocarbons may be of two types: Complete combustion and incomplete combustion.

Complete combustion of hydrocarbons occurs in excess of oxygen(air), producing CO2 and H2O as the only final chemical products.Heat and light (clear blue flame) as a form of energy is generated.

Incomplete combustion occurs when there is insufficient Oxygen(air) and the hydrocarbon is in excess.This reaction burns with a sooty or smokey flame and produces products which are CO(g) and/or C(s) and H2O.

Oxidation Reactions:


In a combustion reaction, carbon compounds are oxidized in the presence of oxygen. Though combustion is generally an oxidation reaction, not all oxidation reactions are combustion reactions. Oxidation is also carried out by using oxidizing agents (Oxidants).

Oxidizing agents, also referred as Oxidants are substances that oxidize other substances while undergoing reduction themselves.

Alcohols undergo oxidation in presence of Oxidants like alkaline potassium permanganate (KMnO4) to form carbolic acids.

Example: Ethanol undergoes oxidation to produce Acetic acid when heated by an Oxidizing agent like alkaline KMnO4.

Addition reactions:


Unsaturated organic compounds, like alkenes and alkynes, contain multiple bonds (C=C, C≡C) between their carbon atoms.They undergo addition reactions to become saturated in nature.

The formation of larger molecules by addition of more radicals is known as addition reaction.During an addition reaction of unsaturated organic compounds, a reagent takes place at the double bonded or a triply bonded carbon atoms.

For example; ethene is converted into ethane when heated with the catalyst nickel.

CH2=CH2 + H2 + (Nickel catalyst) ⇨ CH3−CH3

Nickel acts as a catalyst, which basically regulates (increase/decrease) the rate of a given reaction, without itself undergoing any chemical change.

When ethene undergoes an addition reaction with chlorine, it gives dichloroethane.

addition reaction ethene and chlorine

Chlorine is a halogen, whose atoms partially break the carbon-carbon double bond in the alkene to a single bond and add itself across it.

Substitution Reaction:


A Substitution reaction is one in which an atom or a group of atoms(functional group)  in the compound are replaced by another atom (or group of atoms). Substitution reactions are single displacement reactions.

Alkanes, which have only single bonds between their carbon atoms, are saturated hydrocarbons.They are chemically least reactive.They are also called paraffin, as they have no affinity (minimum affinity)towards chemical changes (parum=little; affins=affinity).However, under suitable conditions, they undergo substitution reactions.

For example, under the presence of Sunlight, Methane reacts with chlorine gas to produce chloromethane and hydrogen chloride.

CH4 + Cl2 + Sunlight ⇨ CH3Cl + HCl

Sunlight (UV Light) breaks down the chlorine into free radicles, which initiates the substitution reaction.

Versatile nature of Carbon CBSE 10 NOTES

Versatile Nature of Carbon

 carbon - definition

1. Carbon is an  element with atomic number 6 with  symbol C.
2. Carbon shows hybridization hence its valence is 4 and it is called as tetravalent.
3. Carbon is most commonly obtained from coal deposits, although it usually must be processed into a form suitable for commercial use.
4. Three naturally occurring allotropes of carbon are known to exist: amorphous, graphite and diamond.
5. Carbon present in saturated form eg. Alkane where it contain single bond.
6. Carbon in unsaturation shows double and triple bond eg. Alkene and Alkyne.








But what makes Carbon such an interesting element can be directly attributed to its two unique properties, i.e. tetra-valency and catenation. It is because of these properties that the element has the capacity to form a large number of compounds. Not only is carbon the fourth most abundant element in the universe, it has so far more than three million compounds know to us till date.

The following is a deeper understanding of how these unique properties of tetra-valency and catenation result in a highly versatile nature of carbon:
Tetra-valency of Carbon

Carbon has the atomic number of 6, meaning each carbon atom has a total of six electrons. Two are in the completed inner orbit, while four electrons are found in the atom’s outermost orbit. This basically means that carbon has four valence electrons (outer electrons that are available for forming bonds with other atoms). Because of this arrangement within the atom’s orbits, carbon is called tetravalent.

The carbon’s four valence electrons can be shared by other atoms (that have electrons to share), thus forming what we call covalent bonds (shared electrons bonds). The carbon atom also has the ability to form a bond with other carbon atoms to create covalent bonds forming long strings of carbon atoms, bonded to each other like links in a chain.

Silicon (Si), another element in group 14 of the periodic table, also has four valence electrons and can make large molecules called silicones. But due to its higher atomic number (in comparison to Carbon), its atoms are too large to fit together into as great a variety of molecules as carbon atoms can.

What makes carbon unique is its ability in forming covalent bonds which are very strong in nature. The small size of the carbon atom makes the compounds of Carbon exceptionally stable. Hence carbon as an element has the ability to form a variety of stable compounds, which can exist freely in nature.

Example: saturated hydrocarbons like Propane and Ethane.

Catenation


The linkage of atoms of the same elements to form longer chain is called CATENATION.

Carbon due to its tetravalent nature has the unique property to form bonds with other atoms of carbon forming a long chain. Because of its property of catenation, carbon can form a

  •     Straight chain
  •     Branched chain
  •     Cyclic ring

The astounding compound-forming ability of the element comes from the capacity of its atoms bind to each other not only in straight chains but in complex branchings, like the branches of a tree. They can join in a “head-to-tail” structures to make rings of carbon atoms. The element has practically no limit to the number or complexity of the branches or the number of rings that can be attached to them, thus making it unique as there is no limit to the number of different molecules that can be formed.

Carbon atoms have the ability to share not only a single electron with another atom forming a single bond, but it can also share two or three electrons, forming a double or triple bond.This characteristic of carbon allows it to form a high number of possible bond combinations at different places, making a huge number of different possible molecules. What is important to remember is that a molecule that differs from even a single atom or bond position, becomes a molecule of a different compound with different physical and chemical properties.
Examples
  •     Methyl iodide (CH3-I) and Methylene iodide(CH2-l2), both differ only in the single bond and double bond aspect, but the properties vary distinctly and have different uses.
  •     Methyl iodide (CH3-I) is used as a pre-plant biocide to control insects like a pesticide, while Methyl iodide (CH2-l2) is used as an optical contact liquid, for determining the refractive index of certain gemstones.

CBSE Class 10 Science Chapter 4 – Carbon and Its Compounds Revision Notes

More About Carbon







The origin of the name ‘carbon’ is a Latin word ‘carbo’ which means charcoal. This may come as a surprise to you, but it is the fourth most abundant element in the entire universe. And it is the second most abundant element in our bodies, the first being oxygen. As a matter of fact, all organic substances in the world contain carbon in some form or element, which is why it is the base for the entire branch of organic chemistry.


The atomic number of carbon is 6, which represents the number of electrons. It is represented by the symbol C and is a non-metal. It has 6 protons, 6 neutrons and obviously 6 electrons. A carbon atom is considered to be special and unique because it can bond with other carbon atoms to an almost unlimited degree. It is because its atom is very small in size and can conveniently fit in as a part of larger molecules. Each of its atoms has four electrons in its outer shell called valence electrons and can form for chemical bonds with other atoms and molecules.

Physical Properties of Carbon


The physical properties of this element vary according to its allotropes. The two major allotropes are diamond and graphite. These two have almost opposing physical properties.

  •     Whereas diamond is transparent and has no colour, graphite is opaque and black
  •     Diamond is the hardest substance known to man, graphite is soft and spongy in texture
  •     Now diamond cannot conduct electricity at all, graphite is a very good conductor of electricity
  •     Both allotropic elements are solid, non-gaseous
  •     Also both diamond and graphite are insoluble in water
  •     It does not melt when heated, it sublimes which is it turns to gaseous form


Uses of Carbon in daily life


Now you may not even notice but carbon is used in so many daily activities. Some of the most important uses are:

  •     It makes up for 18% of the human body. Sugar, glucose, proteins etc are all made of it. The food we eat contains an important source of energy which we call carbohydrates. Carbohydrates are nothing but elements of carbon itself.
  •     Carbon in its diamond form is used in jewellery. But diamonds are also used for industrial purposes. It is the hardest substance known to man and so has many uses in manufacturing processes.
  •     Amorphous carbon is used to make inks and paints. It is also used in batteries.
  •     Graphite is used as the lead in your pencils. It is also used in the production of steel.
  •     One of the most important uses is carbon dating. We can actually use carbon to measure the age of things. Scientists use a rare form of carbon called Carbon-14 to measure the age of fossils, bones etc. The release of this carbon-14 is recorded to estimate the life of the said organic substance. This is how scientists find the age and period of dinosaur bones and fossils!

So as you can see from the facts given above carbon is an interesting element with uncountable uses. This is why a detailed study of it is essential in Chemistry.