Class 11th

When aqueous solution of borax is acidified with hydrochloric acid, a white crystalline solid is formed which is soapy to touch. Is this solid acidic or basic in nature? Explain.

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When aqueous solution of borax is acidified with hydrochloric acid, boric acid is produced. As the name says, boric acid is acidic in nature but weak acid. Unlike protonic acid, boric acid is monobasic acid. It accepts electrons from the hydroxyl group of water and forms [B (OH)₄]^-.

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3. When aqueous solution of borax is acidified with hydrochloric acid, a white crystalline solid is formed which is soapy to touch. Is this solid acidic or basic in nature? Explain.

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Assertion (A): Beryllium carbonate is kept in the atmosphere of carbon dioxide. Reason (R): Beryllium carbonate is unstable and decomposes to give beryllium oxide and carbon dioxide.

(A) Both A and R are correct and A is the correct explanation of R.

(B) Both A and R are correct but A is not the correct explanation of R.

(C) Both A and R are not correct.

(D) A is not correct but R is correct.

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(A) Explanation:

Alkaline earth metals are stable at room temperature except beryllium carbonate. It decomposes to give beryllium oxide and carbon dioxide. It is kept in an atmosphere of carbon dioxide so that equilibrium shifts to the right. The reaction is shown below. BeCO₃→ BeO+CO₂

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In the following questions a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the choices given below each question.

Assertion (A): The carbonate of lithium decomposes easily on heating to form lithium oxide and CO₂⋅

Reason (R): Lithium being very small in size polarises large carbonate ion leading to the formation of more stable Li₂O and CO₂.

(A) Both A and R are correct and R is the correct explanation of A.

(B) Both A and R are correct but R is not the correct explanation of A.

(C) Both A and R are not correct.

(D) A is not correct but R is correct.

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This is a assertion and reason type question as classified in NCERT Exemplar

(A) Lithium beimg small in size, polarises large carbonate ion. Polarisation is the distortion of electron cloud of the anion by the cation. Thus, the carbonate of lithium decomposes easily on heating to form lithium oxide and CO₂. The reaction is shown below.

Li₂CO₃→ Li₂O+CO₂

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Account for the following observations:

(i) AlCl₃ is a Lewis acid (ii) Though fluorine is more electronegative than chlorine yet BF₃ is a weaker Lewis acid than BCl₃

_(iii)_{PbO2 is a stronger oxidising agent than SnO2}_(iv)_{The +1 oxidation state of thallium is more stable than its +3 state}

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(i) ln? AlCl₃, Aluminium is bonded to 3 chlorine atoms through three covalent bonds and six electrons are shared in the structure. To have complete Octet, AlCl₃lacks two electrons & hence act as an electron acceptor substance or Lewis acid.

(ii) Undoubtedly, fluorine has more electronegativity than chlorine, BF₃ is stronger Lewis acid than BCl₃ because of n−p π back bonding in BF₃, both the constituting atoms boron and fluorine are involve p-orbital in back bonding. On moving down the group, the size of halogen atoms increases, back bonding decreases and Lewis ac

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Match the elements given in Column I with the colour they impart to the flame given in Column II.

Column I	Column II
(i) Cs	(a) Apple green
(ii) Na	(b) Violet
(iii) K	(c) Brick red
(iv) Ca	(d) Yellow
(v) Sr	(e) Crimson red
(vi) Ba	(f) Blue

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(i) → (f); (ii) → (d); (iii) → (b) : (iv) → (c) ; (v) → (e); (vi) → (a)

All alkali metal and alkaline earth metals except beryllium and magnesium gives characteristic color when introduced into flame. Due to released energy being absorbed in the visible region, alkali metals and alkaline earth metals gives characteristic color.

(i) Caesium imparts blue color when introduced into flame.

(ii) Sodium imparts yellow color when introduced into flame.

(iii) Potassium imparts violet color when introduced into flame.

(iv) Calcium imparts brick red color when introduced

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Account for the following observations:

(i) AlCl₃ is a Lewis acid (ii) Though fluorine is more electronegative than chlorine yet BF₃ is a weaker Lewis acid than BCl₃

_{(iii) PbO2 is a stronger oxidising agent than SnO2 (iv) The +1 oxidation state of thallium is more stable than its +3 state.}

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As we move down the group in group 13 the participation of s-electrons in bond formation decreases the primary reason behind this is the inert pair effect. In this the p-electrons take part in bond formation and more energy is required to unpair the valence electrons to make them participate in bonding. Due to this the lower oxidation state of elements becomes stable than the higher oxidation state. As for thallium, +1 oxidation state is more stable than +3.

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Match the compounds given in Column I with their uses mentioned in Column II.

Column I	Column II
(i) CaCO₃	(a) Density, ornamental work
(ii) Ca(OH)₂	(b) Manufacture of sodium carbonate from caustic soda
(iii) CaO	(c) Manufacture of high quality paper
(iv) CaSO₄	(d) Used in white washing

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This is a matching type question as classified in NCERT Exemplar

(i) → (c); (ii) → (d); (iii) → (b) : (iv) → (a)

(i) CaCO₃ is used in manufacturing of high quality paper.

(ii) Due to the disinfectant nature of Ca (OH)₂ is used in white wash.

(iii) CaO is used in the manufacture of sodium carbonate from caustic soda.

(iv)CaSO₄ is used in dentistry, ornamental work and for making statues.

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In the following questions more than one option of column I and II may be correlated.

1. Match the elements given in Column I with the properties mentioned in Column II.

Column I	Column II
(i) Li	(a) Insoluble sulphate
(ii) Na	(b) Strongest monoclinic base
(iii) Ca	(c) Most negative E^o value among alkali metals
(iv) Ba	(d) Insoluble oxalate
	(e) 6s² outer electronic configuration

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This is a matching type question as classified in NCERT Exemplar

(i) → (c); (ii) → (b); (iii) → (d) : (iv) → (a); (e)

(i) Lithium has the highest negative reduction potential value. Due to the small size of lithium it has a small atomic size, the highest ionization enthalpy Due to this, the reducing power of lithium is the highest.

(ii) Sodium is a stronger monoacidic base due to lower first ionization enthalpy of sodium. Also sodium forms sodium hydroxide Therefore 1 mole of it replaces one mole of hydrogen ions from acids.

(iii) Calcium oxalate is an ionic compound because its hydration enthalpy is low. It is highly ins

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Which of the following are the correct reasons for anomalous behaviour of lithium?

(i) Exceptionally small size of its atom

(ii) Its high polarising power

(iii) It has high degree of hydration

(iv) Exceptionally low ionisation enthalpy

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