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8501.

A liquid has a pH less than 7 which represent an acidic solution: (i) State the nature of solution, if its pH increases from 7 to 14. (ii) Mention the ion whose concentration increases with the increase in pH value. (iii) Suggest a method that is generally used for measuring the pH value.

Answer»

Solution :(i) There is increase in the strength of alkali, so the nature of solution will be basic.
(ii) Hydroxide ION or HYDROXYL ion or `OH^-` ion
(III) A PAPER impregnated with the universal indicator is GENERALLY used to measure the pH of a solution.
Discussion
8502.

A less reactive metals displaces a more reactive metal from its salt solution.

Answer»

Solution :False - A more reactive METAL DISPLACES LESS reactive metal.
Discussion
8503.

A less reactive metal can displace a more reactive metal from the solution of its salt.(True / False)

Answer»


ANSWER :F
Discussion
8504.

A knife which is used to cut a fruit was immediately dipped into water containing drops of blue litmus solution. IF the colour of the solution is changed to red, what inference can be drawn about the nature of the fruit and why?

Answer»

Solution :The FRUIT may be citrus fruit or its JUICE may CONTAIN an acid, that is why the traces of acid remained in the knife that turned the blue LITMUS RED.
Discussion
8505.

A knife , which is used to cut a fruit, was immediately dipped into water containing drops of blue litmus solution . The colour of the solution changes to red, what is the nature of the fruit ?

Answer»

SOLUTION :The fruit is acidic as it TURNS blue LITMUS solution to RED .
Discussion
8506.

A knife is to be electroplated with nickel . The electrolyte selected is

Answer»

NICKEL NITRATE
nickel
nickel SULPHATE
nickel AMMONIUM sulphate

ANSWER :D
Discussion
8507.

A jeweller made jewellery (ornaments) of 22 carat gold and also charged his customers for the rate of 24 carat gold. His business developed due to this act.What value of the jeweller is reflected in this act?

Answer»

Solution :Jeweller has shown the value of DISHONESTY, unfaithfulness and greediness TOWARDS his CUSTOMERS.
Discussion
8508.

A jeweller made jewellery (ornaments) of 22 carat gold and also charged his customers for the rate of 24 carat gold. His business developed due to this act.Name two metals that can be added to make jewellery

Answer»

Solution : COPPER and SILVER can be added to GOLD to MAKE it strong
Discussion
8509.

A jeweller made jewellery (ornaments) of 22 carat gold and also charged his customers for the rate of 24 carat gold. His business developed due to this act.Why can't we make ornaments of 24 carat gold?

Answer»

Solution :24 carat gold is soft and pure, and it cannot be MOULDED in the shape and DESIGN given to it while MAKING the JEWELLERY with strength. HENCE, it is not advisable to make ornaments of 24 carat gold.
Discussion
8510.

A is an aqueous solution of Acid and B is an aqueous solution of base. These are diluted separately. Then

Answer»

pH of A increases while that of B decreases till neutral
pH of B deceases while that of A increasestill neutral
pH of A and B decreases
pH of A and B increases

SOLUTION :Dilution (addition of WATER) decreases `H^+` ions and increases the pH of solution A WHITE dilution of B decreases `OH^-` ION and decreases pH of solution B.
Discussion
8511.

A is a silvery white metal. A combines with O_(2) to form B at 800^(@)C, the alloy of A is used in making the aircraft. Find A and B.

Answer»

SOLUTION :(i) Silver white metal (A) is Aluminium
(ii) (A) combines with `O_(2)` to FORM aluminium oxide at `800^(@)`C
`4Al + 3O_(2) overset(800^(@)C)to 2Al_(2)O_(3)`
(iii) Duralumin is the ALLOY of Al, which is used to make aircraft
Discussion
8512.

A is a reddish brown metal, which combines with O_(2) at lt 1370 K gives B,a black coloured compound. At a temperature gt 1370 K A gives C which is red in colour. Find A,B and C with reaction.

Answer»

SOLUTION :(i) Reddish brown metal (A) is copper.
(ii) (A) reacts with `O_(2)` at below 1370 K gives copper (II) OXIDE (B), which is black in colour. `2CU + O_(2) underset("below")overset("1370 K")to 2CuO` (copper (II) oxide) (B)
(iii) (A) reacts with `O_(2)` at above 1370 K gives copper (I) oxide(C ), which is ured in colour. `4Cu + O_(2) underset("above")overset("1370 K")to 2Cu_(2)O` (Copper (I) oxide) (C )
Discussion
8513.

'A' is a blue coloured crystalline salt. On heating it loses blue colour and to give 'B'. When water is added, 'B' gives back to 'A'. Identify A and B, write the equation.

Answer»

Solution : (i) Blue COLORED crystalline salt is copper sulphate pentahydrate (A)
(II) On heating Copper sulphate pentahydrate it loses blue colour and to GIVE anhydrous copper sulphate (B).
(iii) When water is added to the anhydrous copper sulphate (B) gives back to copper sulphate pentahydrate (A).
(iv) `underset(" coppersulphatepentahydrate(bluecolour )")(CuSO_4. 5H_2 O )underset("COOLING ") overset("Hearting ") hArrunderset("Anhydrouscoppersulphate( coloruless )") (CuSO_4 + 5H_2 O`
Discussion
8514.

(a) In the modern periodic table, which are the metals among the first ten element? (b) What is the significance of atomic number in the modern classification of elements? Explain with the help of an example.

Answer»


SOLUTION :NA
Discussion
8515.

(a) In the following reactions, name the reactants, which undergo oxidation and reduction: (i) CuO(S)+H_(2)(g)rarrCu(S)+H_(2)O(g) (ii) CuO(S)+ZnO(S)+Cu(S) (b) State one industrial application of reduction.

Answer»

SOLUTION :(a) (i) The reactants copper OXIDE and hydrogen. Copper oxide undergoes reduction and hydrogen `(H_(2))` undergoes oxidation.
(II) The reactants are copper oxide and zinc . Zincundergoes oxidation and copper oxide undergoes reduction.
(b) Calcium carbonate is REDUCED in industries to GET `CaO and CO_(2)`.
Discussion
8516.

(a) Identify the compound of calcium which is used for plastering fractured bones. With the help of chemical equation shwo how is it prepared and whether special precautions shoud be taken during the preparation of this compound Or Sweet tooth may lead to 'tooth decay'. Explain why ? What is the role of tooth paste in preventing cavity

Answer»

SOLUTION :(a) For ANSWER CONSULT SECTION 2.16
For answer, consult section 2.7.
Discussion
8517.

(a) Identify the bond between H and F in HF molecule. (b) What property forms the basis of identification? (c ) How does the property vary in periods and in groups?

Answer»

Solution :(a)The nature of bond in HF molecule is ionic:
(b) Electronegativity.
( c ) Along the PERIOD, from left to RIGHT in the periodic table the electronegativity increases because of the increase in the NUCLEAR charge which in turn attracts the electrons more strongly. On moving down a group, the electronegativity of the elements decreases because of the increased NUMBER of energy levels.
Discussion
8518.

A hydrogen fuel cell uses hydrogen and

Answer»

NITROGEN
oxygen
carbon
sulphur

ANSWER :B
Discussion
8519.

A hydrocarbon on combustion gives CO_(2) and H_(2)O in a volume ratio of 2 : 1 , under similar conditions of temperature and pressure. What is theemperical formula of the hydrocarbon?

Answer»

SOLUTION :(i) relation between theratio of the VOLUMES and ratio of the number of moles
(ii) determination of the empirical formula based on themolar ratio of the product
(iii) CH
Discussion
8520.

A hydrocarbon involving only single covalent bonds is called_____ (unsaturated/saturated.)

Answer»

SOLUTION :SATURATED
Discussion
8521.

A hydrocarbon is

Answer»

a compound containing CARBON, hydrogen and OXYGEN.
is SODIUM hydrogen carbonate.
a compound containing carbon and hydro GEN only.
a derivative of benzene.

Solution :a compound containing carbon and hydro gen only.
Discussion
8522.

A hydrocarbon decolourizes KMnO_5solution but does not form any precipitate with either ammoniacal AgNO_3 or Cu_2Cl_2.What will be the change on adding a few drops of bromine solution to a test tube filled with this hydrocarbon?

Answer»

SOLUTION :BROMINE will be decolourised
Discussion
8523.

A hydrocarbon decolourizes KMnO_4solution but does not form any precipitate with either ammoniacal AgNO_3 or Cu_2Cl_2. Does the hydrocarbon belong to alkane, alkene or alkyne family?

Answer»

SOLUTION :ALKENE
Discussion
8524.

A hydrocarbon decolourizes KMnO_4solution but does not form any precipitate with either ammoniacal AgNO_3 or Cu_2Cl_2.What is the type of bonds between two C atoms-single, double or triple?

Answer»

SOLUTION :DOUBLE BOND (C=C)
Discussion
8525.

A hydrocarbon decolourizes KMnO_4solution but does not form any precipitate with either ammoniacal AgNO_3 or Cu_2Cl_2.Is the hydrocarbon saturated or unsaturated?

Answer»

SOLUTION :UNSATURATED
Discussion
8526.

A human hormone reducing blood flow to the digestive systems and skin during stress is

Answer»

THYROXIN
Adernaline
GROWTH hormone
Insulin

SOLUTION :Adernaline
Discussion
8527.

(a) How would the tendency to lose electrons change as you go(i) from left to right across a period?(ii) down a group? (b)An element X (2,8, 2) combines separately with (NO_3)^- , (SO_4)^(2-) and (PO_4)^(3-)radicals. Write the formulae of the three compounds so formed. To which group of the periodic table does the element ‘X' belong? Will it form covalent or ionic compound? Why?

Answer»

Solution : (a) (i) TENDENCY to lose electrons decreases.(ii) INCREASES.
(b) The three compounds are `X(NO_3)_2, XSO_4` and `X_3(PO_4)_2`
Valence electrons of element X is 2. Therefore, element X belongs to group 2. It will form ionic compounds because X LOSES 2 electrons to achieve the electronic CONFIGURATION of inertgas and forms a positively charged ion.
Discussion
8528.

(a) How will you bring about following reactions? Write the concerned chemical equations (i) Ethanol to Ethene (ii) Ethanol to Ethanoic acid (b) Give one example with chemical equation for the following reactions : (i) Substitution reaction (ii) Combustion reaction

Answer»

Solution :(i) `CH_(3)CH_(2)OH overset("CONC."H_(2)SO_(4))UNDERSET("443K")to CH_(2)=CH_(2)+H_(2)O`
(ii) `CH_(3)CH_(2)OHoverset("Alkaline" KMnO_(4))rightarrowCH_(3)COOH`
(b) (i) `CH_(4)+CI_(2)overset"Sunlight"rightarrowCH_(3)CI+HCI`
(ii) `CH_(4)+O_(4)rightarrowCO_(2)+H_(2)O+"light"+"ENERGY"`
Discussion
8529.

(a) How were the positions of isotopes of an element decided in the modern periodic table? (b) How were the positions of cobalt and nickel resolved in the modern periodic table? (c) Where should hydrogen be placed in the modern periodic table?Give reason for your answer.

Answer»


SOLUTION :NA
Discussion
8530.

(a) How many elements are known till date ? (b) List the triads that Dobereiner could identify? (c) Which scientist believed that no more elements will be discovered in future? (d) What was the nationality of Mendeleev? In which year was his Periodic Table published? (e) How many periods and groups are there in the Modem Periodic Table?

Answer»

Solution :(a) 118 elements are known till date.
(B) Triads identified by Dobereiner are:
`{:(Li, Ca, CI),(Na, Sr, Br),(K, BA, I):}`
(c) John NEWLANDS.
(d) Mendeleev was a Russian. His Periodic Table was published in the year 1872.
(e) There are 7 periods and 18 groups in the MODEM Periodic Table.
Discussion
8531.

How would the tendency to gain electrons change as you go from left to right across a peroid?

Answer»

SOLUTION :a] As we move from left to right along a period, electronegative CHARACTER increases. This is because of increase in the number of protons which increases the positive charge on the nucleus. THUS, the attractive force between the nucleus and valence electrons increases thereby increasing the TENDENCY of atoms to gain electrons. This increases electronegativity
b] Out of N and F, F is more electronegative since it is PLACED to the right of N in the same period of the periodic table.
Discussion
8532.

(a) How does the supply of air affect combustion of saturated hydrocarbons? (b) What is indicated by: (i) sooty flame (ii) blue flame of a bunsen burner? (c ) Why are holes provided at the bottom of a bunsen burner?

Answer»

Solution :(a) If air SUPPLY is not sufficient, saturated hydrocarbons give YELLOW SOOTY flame.
(b) (i) Yellow sooty flame-Burning of UNSATURATED hydrocarbons such as ethene and ethyne/incomplete combustion (any one),
(ii) Blue falme-Burning of saturated hydrocarbons/completecombustion.
(c ) Holes let the supply of air to be adjusted for complete combustion.
Discussion
8533.

(i) How does the electronic configuration of an atom relates to its position (period and group) in the modern periodic table ? (ii) Would you place the two isotopes of chlorine, Cl -35 and Cl -37, in different slots because of their different atomic masses or in the same slot because their chemical properties are the same ? Justify your answer.

Answer»

Solution :In the periodic table elements are placed acrording to their atomic number. If an element has only ONE shell in its electronic CONFIGURATION it is placed in the first period, if the element has two shells then it is placed in the sccond period and so on. Vertical column in the periodic tuble in group all the elements have same number or VALENCE CLECTRON.
No. C1 35 and CI - 37 will be placed in same sior. The moderan periodie table is based on atomic numbers not atomic mass since, both CI-35 and Cl - 37 have same atomic numbers hence they are placed in same slot.
Discussion
8534.

(a) How does the atomic radius change as you go(i) from left to right in a period?(ii) down a group in the periodic table?(b) Two elements X and Y have atomic numbers 12 and 16 respectively. Write the electronicconfiguration for these elements. To which period of the Modern Periodic Table do these twoelements belong? What type of bond will be formed between them and why?

Answer»

SOLUTION :(a) (i) ATOMIC radius decreases.(ii) Atomic radius increases.

They will form ionic BOND because X is a metal and Y is a non-metal. X loses two ELECTRONS which will be gained by Y.
Discussion
8535.

a) How does electropositivity of elements get affected as we move: (i) down a group (ii) across a period? b] Which atomic property increases as we move across a period and down a group?

Answer»

Solution :a] Electropositivity of elements (i) INCREASES down a GROUP and (ii) decreases as we move from left to right across a period.
B] The atomic number and hence the number of electrons (and PROTONS) increases both across a period and down a group.
Discussion
8536.

a)what ismeantby analagousorgans ? b)Definevariationin relationto a specieswhyis variationbeneficialto thespecies .

Answer»

Solution :(a) Evolutionary relationships can be traced by STUDYING FOSSILS, by studying homologous and ANALOGOUS organs, by comparing the embryo or of different ANIMALS and by comparing the DNA.s ot dilterent species.
(b) Variation are difterences that occur between the ORGANISMS of same species in spite of the same basic features.
Variation in species promotes survival of an organisin m the changing environment by increasing the adaptability.
Discussion
8537.

(a) How are the following related ? (i) Number of valence electrons of the different elements present in the same group. (ii) Number of the shells of the elements in the same period. (b) How do the following change ? (i) Number of shells of the elements as we go down a group. (ii) Number of valence electrons of elements on moving from left to right in a period. (iii)Atomic radius in moving from left to right along a period. (iv) Atomic size down a group.

Answer»

Solution :(a) (i) Number of valence electrons of the elements PRESENT in a group do not change.
(II) The elements present in the same PERIOD have same number of SHELLS.
(b) (i) The number of shells of elements in a group gradually increase downwards.
(ii) The number of valence electrons of the elements in moving from left to RIGHT along a period gradually increase
(iii) Atomic radius decreases from left to the right.
(iv) Atomic size increases down a group.
Discussion
8538.

(a) How are carboxylic acids different from mineral acids from ionisation point of view? (b) Describe an activity to show how ethanoic acid reacts with sodium carbonate. Name the gas evolved. How can it be tested? (c) State the principle on which the cleasing action of soap is based.

Answer»

Solution :(a) Carboxylic acids (organic acids) are less ionised in solution as compared to MINERAL acids `(Na_(2)CO_(3))` solution `H_(2)SO_(4)etc.)` due to this reason, these are weaker acids than the mineral acids.
(b) Take a SMALL volume of ethanoic acid in a tube. add a few drops of sodium carbonate `(Na_(2)CO_(3))` solution prepared in water to the tube. A clourless gas with brisk effervescence will evolve. when the gas is passed through lime water, it will become millky.
`Na_(2)CO_(3)(aq)+2CH_(3)COOH(aq)to2CH_(3)COONa(aq)+H_(2)O(l)+CO_(2)(G)`
`underset("Lime water")(CA(OH)_(2)(aq))+CO_(2)(g)tounderset(("Milky"))(CaCO_(3)(s))+H_(2)O(l)`
(c) The cleansing action of soap is based on its tendency to act as a bridge between water ad oil drops containing dirt particles. As a result, oil and water get mixed. they form a stable emulsion also called micelle. This helps in removing oil drops containing dirt particles from clothes. the clothes become clean.
Discussion
8539.

A hot saturated solution of copper sulphate forms crystals as it cools. Why?

Answer»

Solution :The capability of a solution to maintain a CERTAIN CONCENTRATION of solute is temperature dependent. When a saturated solution of copper sulphate at above room temperature is allowed to cool, the solution BECOMES super-saturated and in the absence of stirring or the return of the previous solution temperature, the solute STARTS to precipitate out. i.e., crystal formation occurs.
Discussion
8540.

A homogeneous mixture of a metal with other metals

Answer»


ANSWER :ALLOY
Discussion
8541.

A hole is the reason of conduction in which type of semiconductors

Answer»

<P>p type
n type
Both
None

Answer :A
Discussion
8542.

A heat producing device should be used in an electric circuit. This device should have

Answer»

HIGH resistance and LOW melting point
low resistance and high melting point
high resistance and high melting point
low REISTANCE and low melting point

Solution :high resistance and high melting point
Discussion
8543.

A group of students measured the pH of some substances they found in their homes. Their results are given in the following table: (a). What would the student have used to measure the pH? (b). Which solution is the most acidic? (c). Which solution is the most alkaline? (d). Which solutions are neutral? (e) Which solution can be used to treat wasp stings? (f) Which solution can be used to treat bee stings?

Answer»

Solution :(a) Universal INDICATOR paper (b) Lemon juice (c) HOUSEHOLD ammonia
(d). SALT solution and sugar solution (e) Vinegar (F) Baking SODA
Discussion
8544.

A group of elements in the Periodic Table are given pelow (Boron is the first member of the group and Thallium is the last). Boron Aluminium Gallium Indium Thallium Answer the following questions in relation to the above group of elements :Will the elements in the group to the right of thisBoron group be more metallic or less metallic in character ? Justify your answer.

Answer»

Solution :LESS METALLIC, because metallic character decreases from left to RIGHT in the periodic table.
Discussion
8545.

A group of elements in the Periodic Table are given pelow (Boron is the first member of the group and Thallium is the last). Boron Aluminium Gallium Indium Thallium Answer the following questions in relation to the above group of elements : Which element has the most metallic character ?

Answer»

SOLUTION :THALLIUM
Discussion
8546.

A groupof atomschemicallybondedtogether is a (an ) :

Answer»

MOLECULE
ATOM
SALT
Element

Answer :A
Discussion
8547.

A green stemmed rose plant denoted by GG and a brown stemmed rose plant denoted by gg are allowed to undergo a cross with each other. (a) List your observationsregarding (i) Colour of stem in their F1 progeny. (ii) Percentage of brown stemmed plants in F2 progency if F1 plants are self pollinated. (iii) Ratio of GG and Gg in the F2 progeny. (b) Based on the findings of this cross, what conclusion can be drawn?

Answer»

Solution :(a) (i)
So all F1 progency have green stem.
(ii) `F1 xx F2=F2`

Only `25%` POPULATION will have brown stem.
(iii) Ratio of GG : Gg in F2 is 1 : 2.
(b) We can CONCLUDE that .G. gene is DOMINANT over .g. and hence most of the population is green stemmed. Also, EVEN in Heterozygous condition (Gg), G is expressed.
Discussion
8548.

A green coating develops on the copper vessel in the rainy season. Why ?

Answer»

SOLUTION :COPPER reacts with moist carbon dioxide in the air in rainy SEASON and a green coating is formed. This is DUE to the formation of copper carbonate.
Discussion
8549.

A green coloured hydrated metallic salt on heating loses its water of crystallisation and gives the smell of burning sulphur. Identify the salt and write down the reaction involved.

Answer»

SOLUTION :GREEN VITRIOL: `FeSO_4.7H_2O`
`FeSO_4 .7H_2O to^(DELTA)FeSO_4+7H_2O`
`2FeSO_4(s)to^(Delta)Fe_2O_3(s)+SO_2(G)+SO_3(g)`
Discussion
8550.

a. Give two methods to prevent the rusting of iron b. Name the ores of the following metals. 1. Mercury and 2. Zinc. c. Explain with the help of diagram, how copper metal can be refined? Label the important arrangement in the experiment set up.

Answer»

Solution :a. (i) Painting
b. glavanisation
b. (i) Cinnabar
(ii) Zinc Blend

c. Impure copper is taken as anode, whereas pure copper is taken as cathode. Copper sulphate solution `(CuSO_(4))` is taken as electrolyte. When ELECTRIC current is PASSED, impure copper changes to IONS which gains electrons at cathode and change into pure copper. Impurities are left behind as anode mud.
`Cu(s)TOCU^(2+)(aq)+2e`
Al anode`""`impure
`Cu^(2+)(aq)+2e^(-)toCu(s)`
Al cathode `""` pure
Discussion