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Practice each question, then open the answer or worked solution.
What are metallic/interstitial hydrides? How do they differ from molecular hydrides?
Metallic hydrides are those compounds which are formed when the transition element reacts with hydrogen. Eg. CaH₂, LiBH₄
Molecular hydrides are formed by the combination of an element which is having comparable higher electronegativity with hydrogen. Eg. H₂O, B₂H₆
Name the classes of hydrides to which H2O, B2 H6 and NaH belong.
Solution;
H2O – Electron rich hydride
B2H6 – Electron deficient hydride.
NaH – Ionic hydride.
Solution coming soon.
If the same mass of liquid water and a piece of ice is taken, then why is the density of ice less than that of liquid water?
On freezing water expands and the volume of ice for the same mass of water will be more than that of the water. We can say that the density of ice is lower than water and hence floats on water.
Complete the following equations:
(i) PbS (s) + H2O2 (aq) →
(ii) CO (g) + 2H2 (g) →
(i) PbS (s) + H2O2 (aq) → PbSO4 + 4H2O
(ii) CO (g) + 2H2 (g) → CH3OH
Give reasons:
(i) Lakes freeze from top towards bottom.
(ii) Ice floats on water.
(i) The density of ice is less than water. Coldwater starts expanding and becomes less dense than what it should be when the temperature drops to 4°C. As a result, cold water being less dense floats on to the surface and when it comes to the chilly freezing weather conditions outside, it gets frozen.
(ii) the density of ice is lower than water and hence ice floats on water.
What do you understand by the term ‘auto protolysis of water’? What is its significance?
Auto protolysis of water is self ionisation of water. It is one of the chemical properties of water. Here, two same molecules react to give ions involving proton transfer.
Discuss briefly de-mineralisation of water by ion exchange resin.
Demineralised water is obtained by ion exchange resin by passing it through an anion exchange and cation exchange resin. Those resins have large SO3H and COOH groups.
The water is passed through cation exchanger which removes cations like Na+ and Mg+
Now, this water coming out from cation exchanger is acidic, therefore it is passed through the anionic exchanger which removes anions like OH-, NO3-, etc. by exchanging with OH- ions.
In the end, the H+ and OH- thus produced, combine amongst themselves to produce water
This is demineralisation of water by ion exchange resin.
Molecular hydrides are classified as electron-deficient, electron precise and electron-rich compounds. Explain each type with two examples.
Molecular hydrides are classified into electron-deficient, electron precise and electron-rich compounds.
B2H6 is an electron-deficient hydride. These have an incomplete octet. They are formed generally by the group 13 elements like B, Al, etc.
An electron-precise hydride is a type of hydride which has the exact number of electrons required to form normal covalent bonds, no excess no deficient. These are formed generally by group 14 elements like Si and C which have 4 valence electrons.
Eg. CH4, SiH4, etc.
How is heavy water prepared? Compare its physical properties with those of ordinary water.
Heavy water, which is deuterium oxide (D2O) is mainly prepared by electrolysis of ordinary water.
1. The molecular mass of ordinary water is 18.015 and that of heavy water is 20.027
2. The melting point of ordinary water is 273.0 and that of heavy water is 276.8
3. The boiling point of ordinary water is 373.0 and that of heavy water is 374.4
4. Density at 298K of ordinary water is 1.000 and that of heavy water is1.106
Write one chemical reaction for the preparation of D2O2
When D2SO4 reacts with BaO2, D2O2 is formed along with barium sulphate (BaSO4).
D2SO4 + BaO2 → D2O2 + BaSO4