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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
Which metal in the first transition series (3d series) exhibits + 1 oxidation state most frequently and why?
Account for the following:
Mn shows the highest oxidation state of +7 with oxygen but with fluorine, it shows oxidation state of +4.
Why do the transition elements have higher enthalpies of atomisation?
Give reasons:
Transition metals show variable oxidation states.
How would you account for the following : Transition metals form coloured compounds
Explain why Cu+ ion is not stable in aqueous solutions?
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
Write the factors which are related to the colour of transition metal ions.
Write the formula of an oxo-anion of Chromium (Cr) in which it shows the oxidation state equal to its group number
The transition metals show _________ character because of the presence of unpaired· electrons and Cu+ is ____________ because of its electronic configuration is [Ar]3d10
Dissociation of H2S is suppressed in acidic medium.
Why do transition metal ions possess a great tendency to form complexes?
Give reasons for the following:
The transition metals generally form coloured compounds.
Metallic radii of some transition elements are given below. Which of these elements will have highest density?
| Element | \[\ce{Fe}\] | \[\ce{Co}\] | \[\ce{Ni}\] | \[\ce{Cu}\] |
| Metallic radii/pm | 126 | 125 | 125 | 128 |
The magnetic nature of elements depends on the presence of unpaired electrons. Identify the configuration of transition element, which shows highest magnetic moment.
When \[\ce{KMnO4}\] solution is added to oxalic acid solution, the decolourisation is slow in the beginning but becomes instantaneous after some time because ______.
When acidified \[\ce{K2Cr2O7}\] solution is added to \[\ce{Sn^{2+}}\] salts then \[\ce{Sn^{2+}}\] changes to ______.
Transition elements form binary compounds with halogens. Which of the following elements will form \[\ce{MF3}\] type compounds?
(i) \[\ce{Cr}\]
(ii) \[\ce{Co}\]
(iii) \[\ce{Cu}\]
(iv) \[\ce{Ni}\]
Transition elements show high melting points. Why?
Although fluorine is more electronegative than oxygen, but the ability of oxygen to stabilise higher oxidation states exceeds that of fluorine. Why?
A solution of \[\ce{KMnO4}\] on reduction yields either a colourless solution or a brown precipitate or a green solution depending on pH of the solution. What different stages of the reduction do these represent and how are they carried out?
Assertion: \[\ce{Cu^2+}\] iodide is not known.
Reason: \[\ce{Cu^2+}\] oxidises \[\ce{I^-}\] to iodine.
Assertion: The highest oxidation state of osmium is +8.
Reason: Osmium is a 5d-block element.
A metallic ion 'M' reacts with chloride ion to form white precipitate which is readily soluble in aqueous ammonia. Identify 'M'?
The element with atomic number 46 belongs to
The product of oxidation of I– with \[\ce{MnO^{-}4}\] in alkaline medium is:-
Why are all copper halides known except that copper iodide?
The number of terminal oxygen atoms present in the product B obtained from the following reactions is:
\[\ce{FeCr2O4 + Na2CO3 + O2 -> A + Fe2O3 + CO2}\]
\[\ce{A + H^+ -> B + H2O + Na^+}\]
Which of the following ions acts as a typical transition metal ion?
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:
Oxidation states
