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प्रश्न
How is potassium dichromate prepared from chrome iron ore?
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उत्तर
Potassium dichromate is prepared from chromite ore (FeCr2O4) in the following steps.
Step (1): Preparation of sodium chromate
4FeCr2O4 + 16NaOH + 7O2 → 8NaCrO4 + 2Fe2O3 + 8H2O
Step (2): Conversion of sodium chromate into sodium dichromate
2Na2CrO4 + conc.H2SO4 → Na2Cr2O7 + Na2SO4 + H2O
Step(3): Conversion of sodium dichromate to potassium dichromate
Na2Cr2O7 + 2KCl → K2Cr2O7 + 2NaCl
Potassium dichromate being less soluble than sodium chloride is obtained in the form of orange coloured crystals and can be removed by filtration.
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संबंधित प्रश्न
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ln which pair highest oxidation states of transition metals are found:
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Cr2+ is a strong reducing agent.
Account for the following:
Cu+2 salts are coloured, while Zn2+ salts are white.
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Answer the following: Which element shows only +3 oxidation state?
The elements of 3d transition series are given as: Sc Ti V Cr Mn Fe Co
Answer the following: Which element is a strong oxidising agent in +3 oxidation state and why?
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Compare the general characteristics of the first series of the transition metals with those of the second and third series metals in the respective vertical columns. Give special emphasis on the following point:
Electronic configurations
How would you account for the following?
Transition metals and their compounds act as catalysts.
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Explain why Zn2+ salts are white whereas Cu2+ salts are coloured.
Explain why transition metals and their compounds act as a catalyst.
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Which of the following statements is not correct?
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(i) \[\ce{Co^{2+}}\]
(ii) \[\ce{Cr^{2+}}\]
(iii) \[\ce{Mn^{2+}}\]
(iv) \[\ce{Cr^{3+}}\]
Which of the following ions show higher spin only magnetic moment value?
(i) \[\ce{Ti^3+}\]
(ii) \[\ce{Mn2+}\]
(iii) \[\ce{Fe2+}\]
(iv) \[\ce{Co3+}\]
Why EΘ values for Mn, Ni and Zn are more negative than expected?
Transition elements show high melting points. Why?
Identify A to E and also explain the reactions involved.
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Only those transition metal ions will be coloured which have ______ filled d-orbitals facilitating ______.
Account for the following:
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Read the passage given below and answer the following question.
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Are there nuclear reactions going on in our bodies? There are nuclear reactions constantly occurring in our bodies, but there are very few of them compared to the chemical reactions, and they do not affect our bodies much. All of the physical processes that take place to keep a human body running are chemical processes. Nuclear reactions can lead to chemical damage, which the body may notice and try to fix. The nuclear reaction occurring in our bodies is radioactive decay. This is the change of a less stable nucleus to a more stable nucleus. Every atom has either a stable nucleus or an unstable nucleus, depending on how big it is and on the ratio of protons to neutrons. The ratio of neutrons to protons in a stable nucleus is thus around 1 : 1 for small nuclei (Z < 20). Nuclei with too many neutrons, too few neutrons, or that are simply too big are unstable. They eventually transform to a stable form through radioactive decay. Wherever there are atoms with unstable nuclei (radioactive atoms), there are nuclear reactions occurring naturally. The interesting thing is that there are small amounts of radioactive atoms everywhere: in your chair, in the ground, in the food you eat, and yes, in your body. The most common natural radioactive isotopes in humans are carbon-14 and potassium-40. Chemically, these isotopes behave exactly like stable carbon and potassium. For this reason, the body uses carbon-14 and potassium-40 just like it does normal carbon and potassium; building them into the different parts of the cells, without knowing that they are radioactive. In time, carbon-14 atoms decay to stable nitrogen atoms and potassium-40 atoms decay to stable calcium atoms. Chemicals in the body that relied on having a carbon-14 atom or potassium-40 atom in a certain spot will suddenly have a nitrogen or calcium atom. Such a change damages the chemical. Normally, such changes are so rare, that the body can repair the damage or filter away the damaged chemicals. The natural occurrence of carbon-14 decay in the body is the core principle behind carbon dating. As long as a person is alive and still eating, every carbon-14 atom that decays into a nitrogen atom is replaced on average with a new carbon-14 atom. But once a person dies, he stops replacing the decaying carbon-14 atoms. Slowly the carbon-14 atoms decay to nitrogen without being replaced, so that there is less and less carbon-14 in a dead body. The rate at which carbon-14 decays is constant and follows first order kinetics. It has a half-life of nearly 6000 years, so by measuring the relative amount of carbon-14 in a bone, archeologists can calculate when the person died. All living organisms consume carbon, so carbon dating can be used to date any living organism, and any object made from a living organism. Bones, wood, leather, and even paper can be accurately dated, as long as they first existed within the last 60,000 years. This is all because of the fact that nuclear reactions naturally occur in living organisms. |
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Sodium this sulphate is used in photography because of its:-
Account for the following:
Sc3+ is colourless whereas Ti3+ is coloured in an aqueous solution.
Account for the following:
Ce4+ is a strong oxidising agent.
Which of the following ions has the electronic configuration 3d6?
(Atomic number: Mn = 25, Co = 27, Ni = 28)
Account for the following:
Copper has an exceptionally positive `"E"_("M"^(2+)//"M")^0` value.
Explain the magnetic properties of d-block (or transition) elements.
