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प्रश्न
Why does table salt, NaCl, sometimes appear yellow in colour?
Why is common salt sometimes yellow instead of being pure white?
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उत्तर
- The yellow colour of sodium chloride is due to metal excess defect.
- In metal excess defects, anionic vacancies are created due to the diffusion of Cl– to the surface of the crystal and thereafter after unpaired electrons occupy anionic sites.
- These sites are called F-centres. The electrons at F-cetres then absorb energy from the visible region for the excitation, which makes the crystal appear yellow.
संबंधित प्रश्न
If NaCl is doped with 10−3 mol % of SrCl2, what is the concentration of cation vacancies?
Yellow colour of NaCl crystals in sodium vapour is due to ____________.
The following diagram shows:
Which of the following will have metal deficiency defect?
Which of the following is a non-stoichiometric defect?
Pink colour of LiCl crystals is due to ______.
Why does white ZnO (s) becomes yellow upon heating?
Match the types of defect given in Column I with the statement given in Column II.
| Column I | Column II |
| (i) Impurity defect | (a) NaCl with anionic sites called F-centres |
| (ii) Metal excess defect | (b) FeO with Fe3+ |
| (iii) Metal deficiency defect | (c) NaCl with Sr2+ and some cationic sites vacant |
A sample of ferrous oxide has actual formula Fe0.93O1.00. In this sample what fraction of metal ions are Fe2+ ions? What type of nonstoichiometric defect is present in this sample?
The appearance of colour in solid alkali metal halides is generally due to ______.
If NaCl is doped with 10–3 mol % of SrCl2 calculate the concentration of cation vacancies.
Non-stoichiometric defects refer to ______
