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2251.

Divide the class into two groups. Give 5 g of iron filings and 3 g of sulphur powder in a china dish to both the groups. Group I Mix and crush iron filings and sulphur powder. Group II Mix and crush iron filings and sulphur powder. Heat this mixture strongly till red hot. Remove from flame and let the mixture cool. Groups I and II Check for magnetism in the material obtained. Bring a magnet near the material and check if the material is attracted towards the magnet. Compare the texture and colour of the material obtained by the groups. Add carbon disulphide to one part of the material obtained. Stir well and filter. Add dilute sulphuric acid or dilute hydrochloric acid to the other part of the material obtained. Perform all the above steps with both the elements (iron and sulphur) separately. Can we separate the components of the material obtained ?

Answer»

SOLUTION :The components of the material obtained in CASE of GROUP I can be separated USING a magnet, but not in case of Group II.
Discussion
2252.

A mixtureof ammoniaand water is a ………………

Answer»


ANSWER :SOLUTION
Discussion
2253.

Divide the class into two groups. Give 5 g of iron filings and 3 g of sulphur powder in a china dish to both the groups. Group I Mix and crush iron filings and sulphur powder. Group II Mix and crush iron filings and sulphur powder. Heat this mixture strongly till red hot. Remove from flame and let the mixture cool. Groups I and II Check for magnetism in the material obtained. Bring a magnet near the material and check if the material is attracted towards the magnet. Compare the texture and colour of the material obtained by the groups. Add carbon disulphide to one part of the material obtained. Stir well and filter. Add dilute sulphuric acid or dilute hydrochloric acid to the other part of the material obtained. Perform all the above steps with both the elements (iron and sulphur) separately. Did the material obtained by the two groups look the same ?

Answer»

SOLUTION :The materials obtained by the two GROUPS LOOK different.
Discussion
2254.

A _________ mixture has no distinguishable boundary between its components.

Answer»


ANSWER :HOMOGENOUS
Discussion
2255.

Distribute the following samples to groups A, B, C and D: Few crystals of copper sulphate to group A. One spatula full of copper sulphate to group B. Chalk powder or wheat flour to group C. Few drops of milk or ink to group D. Filter the mixture. Is there any residue on the filter paper ?

Answer»

Solution :Residue will be LEFT on the filter paper in CASE of GROUP C.
Inference :
GROUPS A and B have got solutions.
Group C has got suspension.
Group D has got a colloidal solution.
Discussion
2256.

A mixture contains nitre, common salt and silver chloride as the components. The different separation techniques involved are_____, _______ and _______.

Answer»

SOLUTION :solventextraction , FILTRATION CRYSTALLISATION
Discussion
2257.

A liquid wets the given surface if ______ forces are predominant over ______ forces.

Answer»

SOLUTION :ADHESIVE FORECE,cohesiveforces
Discussion
2258.

Distribute the following samples to groups A, B, C and D: Few crystals of copper sulphate to group A. One spatula full of copper sulphate to group B. Chalk powder or wheat flour to group C. Few drops of milk or ink to group D. Leave the mixtures undisturbed for a few minutes. Is the mixture stable or do the particles begin to settle after some time ?

Answer»

Solution :The PARTICLES SETTLE down after some TIME in case of group C.
The particles do not settle down after some time in groups A, B and D.
Discussion
2259.

A liquid is converted into vapour below its boiling point . What is the process called?

Answer»

SOLUTION :EVAPORATION
Discussion
2260.

Distribute the following samples to groups A, B, C and D: Few crystals of copper sulphate to group A. One spatula full of copper sulphate to group B. Chalk powder or wheat flour to group C. Few drops of milk or ink to group D. Each group should add the given sample in water and stir properly using a glass rod. Are the particles in the mixture visible ?

Answer»

Solution :The PARTICLES of MIXTURE are VISIBLE only in the CASE of group C.
Discussion
2261.

(a) In thegold foil experiment , what observations led Rutherford to conclude that (i) Most of the space inside the atom is hollow (ii) The central protion of the atom is positively charged. (iii) volume occupied by the nucleus is very small as compared to the total volume of the atom (iv) almost the entire mass of the atom concentrated at its centre. (b) If bromine atom is available in the form of two isotopes overset(79)underset(35)Br(49.7%) and overset(81)underset(35)Br (50.3%) calculate the average atomic mass of bromine atom.

Answer»

SOLUTION :(a) (i) Most o fthe `alpha` particles passed through the foil undeflected
(ii) some `alpha` particles (POSITIVELY charged ) were delfected and a few CAME back in the same dierction . The atom thios is known as nucleus.
(iii) The number of `alpha` aparticles which were delfected back was very small
(iv) since th amss of hte atom is mainly due to positiviley chrged protons (neutons were not known at that time) this means that the ENTIRE mass of the atom is concentrated in the center of the atom
(B) % of Br isotope with massnumber 79 =49.7
% of Br isotope with mass number 81 =50.3
Discussion
2262.

Distribute the following samples to groups A, B, C and D: Few crystals of copper sulphate to group A. One spatula full of copper sulphate to group B. Chalk powder or wheat flour to group C. Few drops of milk or ink to group D. Direct a beam of light from a torch through the beakers of each mixture and observe. Was the path of the beam of light visible ?

Answer»

Solution :The path of LIGHT is VISIBLE in CASE of groups C and D.
Discussion
2263.

(a) (i) Ethyl mercaptan (ii) Strong smell of ethyl mercaptan (b) Diffusion (in gases) (c) The spreading out and mixing of a gas with another gas due to the motion of their particles is called diffusion in gases (d) The leaking cooking gas containing the strong smelling substance ethyl mercaptan spreads and mixes with the surrounding air by the process of diffusion. When the air containing ethyl mercaptan reaches our nose, we can smell it and come to know of the gas leakage. (e) LPG is a highly inflammable gas (which catches fire very easily). If Mrs. Chopra had continued to use the leaking LPG cylinder, then a lot of LPG would have collected in the kitchen after some time. This collected LPG could ignite on coming in contact with gas stove flame causing a big fire in the kitchen. Even the LPG cylinder could catch fire and burst causing a big explosion. This could lead to the loss of life and property. (f) The various values displayed by Vibha in this episode are (i) Good smelling power (so as to smell leaking cooking gas even from a distance) (ii) Knowlege of tshe risks of using a leaking LPG cylinder (iii) Responsible citizen (in calling LPG distributor to rectify gas leakage), and (iv) Desire to protect her family and property (from any related accident).

Answer»

SOLUTION :(a) Fog is a thick cloud of tiny water droplets suspended in air which reduces the visibility. The object engulfed in fog are difficult to see clearly
(b) The white soild used to create artificial fog EFFECT on the stage was 'dry ice' (which is solid carbon dioxide or frozen carbondioxide). Dry ice is an extremely COLD substances
(c) The special property of dry ice is 'sublimation'. When warmed, solid dry ice CHANGES directly into carbon dioxide gas
(d) The purpose of putting dry ice in warm water is to supply heat for the sublimation of dry ice to form extremely cold carbon dioxide gas (for producing gramatic fog effect on stage)
(e) When dry ice is put into a bucket of warm water, then warm water supplies heat to it. By absorbing this heat, dry ice (or solid carbon dioxide) sublimes to form extremely cold carbon dioxide gas. This cold carbon dioxide gas mixes with air on stage and cools it. When air GETS cooled, then the water vapour present in air condenses t form fog. This thick fog looks like moving smoke and creates a special effect on stage
The various values displayted by Anhad in this episode are (i) Awareness of the formation of fog. (ii) Knowledge of sublimation of dry ice (solid carbon dioxide) (iii) Ability to apply knowledge in everyday situations, and (iv) Helping nature (in creating special effect on stage).
Discussion
2264.

Distinguish between calcination and roasting.

Answer»

SOLUTION :N/A
Discussion
2265.

A hydrocarbon 'X' can have only three chain isomers and one of the isomers consists of same alkyl groups attached to central carbon atom with single bonds.Identify the preceding and succeding homologue of 'X' .

Answer»

Solution :(i) identification of hydrocarbon'X'
(ii) valen'cy of carbon atom'.
(iii) relation between valency of carbon atom and the number of single bonds it can FORM.
(iv) identification of hydrocarbon on the basis of number of chain isomer.
(v) Prediction of molecular formula from the STRUCTURE of hydrocarbon: .
(vi) Identification of PRECEDING and succeeding HOMOLOGUES of hydrocarbon.
Discussion
2266.

Discuss with examples the factors affecting the rate of evaporation.

Answer»

Solution :The four factors affecting the RATE of evaporation are : 1. surface area 2. Temperature, 3.Humidity and 4. Wind.
1.Surface area: Eavaporation is a surface phenomenon. The escaping particles from liquid state of vapiur state depends on the surface area. Therefore, the rate of evaporation increases with the INCREASE in the surface area.
Example : We spread wet clothes for DRYING. Spreadingwet clothes increases thesurface area of clothes. The rate of evaporation increase and wet clothes get dried easily.
2.Temperature: With the increase in temperature, the number of particles with larger kinetic energy increases and they escape from liquid to vapourstate overcoming intermolecular forces.
Example: We clothes dry faster inthe after noon sunshine.
3. Humidity: Humidity is the amount of water vapour present inair. The air around us CONTAIN water vapour at a given temperature. If the amount of water vapour inthe air is high, it cannot contain more water vapour and hence the rate of evaporationdecreases.
Example: We perspire on a hot day. Perspiration evaporates into the atmosphere. If the air is more humid, sweat cannot evaporate and we feel uncomfortable.
4. Wind: The rate of evaporation increases with an increase in wind speed.
Example: If the wind speed is more, more particles of liquid from the surface are carried away. Thus the wet clothes dry faster on a WINDY day.
Discussion
2267.

(a) How will you separate the components of ink using chromatography ? Explain with the help of a labelled diagram. (b) Which method out of evaporation and crystallisation is a better technique to separate sugar from sugar solution ? Give reason also.

Answer»

Solution :(a) Take a thin strip of filter paper.
Draw a line on it using a pencil, 3 cm above the lower edge.
Put a small drop of ink at the CENTRE of this line.
Lower the filter paper in a jar containing water so that the drop of ink on the filter paper is just above the water level. Leave it undisturbed.
As the water rises in the filter paper, the ink particles also RISE along with it.
Different colours are obtained on the filter paper.
The coloured components of ink which are more soluble rise FASTER.
(b) The process of crystallisation is a better technique than the process of EVAPORATION to separate sugar from sugar solution.
In evaporation, sugаr may char on heating.
Some impurities may go with the filtrate, which on evaporation would contaminate sugar.
Discussion
2268.

Discuss three important uses of graphite.

Answer»

SOLUTION :N/A
Discussion
2269.

A house wife churned full cream with a milk churner (i) What will she observe after churning the milk ?(ii) What could be the possible reason for the observation ?

Answer»

Solution :(i) Churning of milk is a centrifugation process. As a result, lighter PARTICLES of cream or butter will move upwards and collect at the top. HEAVIER residual particles will remain at the BOTTOM. This is very common process used to separate cream from milk on butter from yogurt.
(ii) The SEPARATION is BASED on the principle that lighter particles move upwards while denser particle downwards upon centrifugation.
Discussion
2270.

Discuss the change inenergy and arrangement of moleculs on increasing of ice from -5^(@)C to10^(@) C at 1 atm pressure.

Answer»

Solution :When ice is heated at `-5^(@)`C, its TEMPERATURE increases upto `0^(@)` C, i.e the kinetic energy of the MOLECULES increases. At `0^(@)C`, the ice starts melting. During this process the energy supplied is utilised to increase the potential energy of the molecules keeping kinetic energy CONSTANT, and the arrangement of molecules changes, Once the process ENDS, the heat supplied is again used to increase the temperature of water by increasing the kineticenergy. However, from `0^(@)C` to `4^(@)C` , the molecules of water come closer and above `4^(@)C`, the molecules move further away.
Discussion
2271.

A group of students took an old shoe box and covered it with a black paper from all sides. They fixed a source of light (a torch) at one end of the box by making a hole in it and made another hole on the other side to view the light. They placed a milk sample contained in a beaker/tumblerin the box as shown in the Figure. They were amazed to see that milk taken in the tumbler was illuminated. They tried the same activity by taking a salt solution but found that light simply passed through it ? (a) Explain why the milk sample was illuminated? Name the phenomenon involved. (b) Same results were not observed with a salt solution. Explain. (c) Can you suggest two more solutions which would show the same effect as shown by the milk solution?

Answer»

Solution :(a) MILK sample is a colloidal sol also called emulsion. It got ILLUMINATED because of the scattering of light on passing through it. The phenomenon is known as Tyndall effect.
(b) The SALT solution is a true solution and not a colloidal solution. It will not show any Tyndall effect.
(c ) A solution of sulphur in WATER and a solution of STARCH in water.
Discussion
2272.

Discuss the action of hydrogen chloride on ammonia.

Answer»

SOLUTION :N/A
Discussion
2273.

A group of students in a school were supposed to demonstrate some experiments in a science exhibition to be conducted on the National Science Day. As a part of planning for the above activity. They gatered in the science laboratory and were discussing their ideas. Smith took a beaker of water and a piece of charcoal. He asked his friends to predict whether it will float or sink in the water. Most of them said that it would float and it actually did. He then asked them whether anybody could make it sink in the water. After a few secondsof silence, Andy came forward and said he could do it by boiling the beaker containing water and charcoal. Then all of them were astonished to see the charcoal slowly sinking in the water. Predict the principle involved in the above experiment.

Answer»

Solution :Charcoal is porous in NATURE and AIR is present in the PORES of charcoal. So in the FIRST case it floats on the water. In the SECOND case, on bonding air escapes from its pores and hence, its density becomes more thus, it sinks in the water.
Discussion
2274.

Discuss in brief about the properties of Coordinate covalent compounds.

Answer»

Solution :The compounds containing coordinate covalent bonds are called coordinate covalent compounds.
i. Physical state - These compounds exist as GASES, liquids or solids.
ii. Electrical conductivity - Like covalent compounds, coordinate compounds also do not contain charged particles (ions), so they are bad conductors of ELECTRICITY.
iii. Melting point - These compounds have melting and boiling points higher than those of purely covalent compounds but lower than those of purely Ionic compounds.
IV. SOLUBILITY - Insoluble in polar solvents like water but are soluble in non-polar solvents like benzene, `CCl_(4)`, and toluene.
v. Reactions - Coordinate covalent compounds undergo molecular reactions which are slow.
Discussion
2275.

A greater value of K_(c ) indicates a higher rate of the ____ reaction.

Answer»
Discussion
2276.

Discuss ant two uses of carbon monoxide.

Answer»

SOLUTION :N/A
Discussion
2277.

A glass tumbler containing hot water is kept in the freezer compartment of a refrigerator (temperature lt 0^(@) C). If you could measure the temperature of the content of the tumbler , which of the following graphs would correctly represent the change in its temperature as a function of time.

Answer»

Solution :The graph (a) gives the correct REPRESENTATION. The temperature of water in the tumbler kept in the freezer compartment GETS lowered with time till water changes into ICE. At this STAGE, the temperature becomes `0^(@)C` and remains contstant till the entire water in the tumbler has frozen. If the tumbler is still in the freezer, the temperature will fall below `0^(@)C` (negative sign) with PASSAGE of time.
Discussion
2278.

Discuss any three uses of wood charcoal.

Answer»

SOLUTION :N/A
Discussion
2279.

(a) Four samples of carbon dioxide (CO_(2)) were prepared by using different methods. Each sample on analysis was found to contain 27.27% carbon by mass. Name the law which is in agreement with this observation. (b) Explain why the number of atoms in one mole of hydrogen gas is double the number of atoms in one mole of helium gas.

Answer»

Solution :Carbon dioxide consists of elements carbon and oxygen. Since the percentage of carbon in each sample is fixed, that of oxygen must be also fixed. This is ACCORDING to law of CONSTANT proportions.
(b) HYDROGEN GAS is diatomic in nature `(H_(2))` while helium gas is monoatomic (He). As a result, the number of atoms in one MOLE of hydrogen. `(2xxN_(A))` are expected to be double as compared to number of atoms in one mole of helium `(N_(A))`.
Discussion
2280.

State the kind of chemical reactions in the following examples : (i) Digestion of foodin stomach (ii)Combustion of coal in air (iii) Heating of limestone.

Answer»


ANSWER :t
Discussion
2281.

Fog and cloud are both colloidal in nature. How do they differ ?

Answer»

SOLUTION :Both fog and CLOUD are the EXAMPLES in which liquid (water) is the dispersed phase and gas (air) is the dispersion medium. The only difference between them is that clouds are formed in the upper atmosphere while fog gets formed in the REGION close to earth.
Discussion
2282.

Diffusion means

Answer»

The phenomenon of intermixing of PARTICLES of mattersdue to the RANDOM motioni of their atoms.
The capacity of suction FORCE on the particles of matter.
The phenomena of MERGING of particles of matters into one another.
The process of conversion of particles of matter in gaseous state.

Answer :A::C
Discussion
2283.

A few substances are arranged in the increasing order of forces of attraction between their particles. Which one of the following represents a correct arrangement ?

Answer»

Water, AIR, wind
Air, SUGAR, oil
Oxygen, water, sugar
Salt, juice, air

Solution :It is the CORRECT SEQUENCE.
Discussion
2284.

Differerntaiting electrnos enter anti penuiltimate shell in transition elements

Answer»


ANSWER :FALSE
Discussion
2285.

Differentiate graphite and diamond.

Answer»

SOLUTION :
Discussion
2286.

A few drops of 'Dettol' when added to water the mixture turns turbid Why?

Answer»

SOLUTION :The MIXTURE TURNS TURBID, because of EMULSION.
Discussion
2287.

a. Explain what is sublimation. b. Which of the following shows phenomenon of sublimation? Solid water, solid carbon dioxide, solid ammonium chloride.

Answer»

SOLUTION :a. Generally when a solid is heated ti converts to liquid and on further heating it converts into gas. However, there are some SUBSTANCES which on heating change from solid to gas witout undergoing liquid state. This change of solid state directly to GASEOUS state and vice versa is called sublimation.
b. Solid CARBON DIOXIDE andsolid ammonium chloride show sublimation.
Discussion
2288.

Differentiate between white phosphorous and red phosphorous.

Answer»

SOLUTION :N/A
Discussion
2289.

(a) Explain how, nitrogen, oxygen and argon gases are separted from air. (b) Draw a flow diagram of the processed involved in obtaining gases like nitrogen, oxygen and argon from air.

Answer»
Discussion
2290.

(a) Explain Bohr and Bury rules for distrubution of electrons into different shells. (b) Draw the electronic structure of element X with atomic number 17 and element y with atomic number 16?

Answer»

Solution :(a) Fro Bohr and Bury rules , consult section 4.9
(b) For electronic structure of ELEMENTS X nd Y , consult section4.9 (Table : Electronic configruation of FIRST 20 elements)
Discussion
2291.

Differentiate between rhombic sulphur and monoclinic sulphur.

Answer»

SOLUTION :N/A
Discussion
2292.

(a) Enumerate any two differences between simple distillation and fractional distillation. (b) Draw a labelled diagram showing the process of fractional distillation.

Answer»

Solution :(a) (i) Simple distillation can be used if the liquids to be separated differ in their boiling points by more than `25^(@)C`. If the DIFFERENCE is LESS, than FRACTIONAL distillation can be used.
(ii) A fractionating COLUMN is NEEDED for fractional distillation but not for simple distillation.
(b) For process of fractional distillation.
Discussion
2293.

Differentiate between homogeneous and heterogeneous mixtures with examples.

Answer»

SOLUTION :EXAMPLES of Homogeneous mixtures :
1. Solid solution : Alloys
2. Liquid solution : Sea water, sugar solution in water
3. Gaseous solution : Air
Examples of HETEROGENEOUS mixtures :
1. Solid + Solid : Iron filings and sulphur
2. Solid + liquid : Pastes
3. Solid + gas : Smoke
4. Liquid + liquid : milk EMULSIONS
5. Liquid + gas : Soap BUBBLES
Discussion
2294.

a. Dry ice is obtained when a gas is compressed at high pressure. Name the gas and state what happens to it when the pressure is released. b. Suggest a method to liquefy atmospheric gases. c. What type of clothes should we wear in summer?

Answer»

SOLUTION :a. Name of the gas: Carbon dioxide If the pressure is released, dry ice converts directly into gaseous STATE.
B. Atmospheric GASES can be liquefied by applying HIGH pressure at low temperature.
c. We should wear cotton clothes in summer.
Discussion
2295.

List the difference between homogenous and heterogenous mixture.

Answer»

SOLUTION :
Discussion
2296.

A drop of water when spilled on floor spreads out . What is this due to ?

Answer»

SOLUTION :FLUIDITY of WATER
Discussion
2297.

Differentiate between an element and a compound. Categorise the following substances into elements and compounds.Sodium chloride, iodine, water, 24 carat gold, oxygen gas, carbon.

Answer»

Solution :For distinction between element and COMPOUND.
Elements : Iodine, 24 carat gold, CARBON.
COMPOUNDS : SODIUM chloride, water, oxygen GAS.
Discussion
2298.

(a) Draw a well labelled diagram to show the process of separatation using separating funnel. (b) Give one example of mixture that can be separated by separating funnel. ( c) Is air a mixture or a compound ? Give two points to support your answer.

Answer»

Solution :(b) GROUNDNUT OIL and WATER.
( c) Air is a mixture.
(i) The COMPONENTS of air can be separated by physical method. By LIQUEFACTION and evaporation processes.
(ii) The components of air are not in the same proportion everywhere.
Discussion
2299.

Differentiate between Acids and Bases.

Answer»

SOLUTION :
Discussion
2300.

(a) Draw a flow sheet diagram to show the process of obtaining constituent gases from air. (b) Which gas condenses first ? Why ?

Answer»

Solution :(a) For flow sheet Diagram.
(b) NITROGEN `(N_(2))` condenses first because its boiling point is the least `(-196^(@)C)` among all the gases present in air.
Discussion