Plz answer the following questions with further explanation instead just gives an answer...thz very much
1. Which of the following cannot be used to prepare calcium sulphate?
A. CaCl2 + H2SO4
B. CaCl2+ Na2SO4
C. Ca(NO3)2 + H2SO4
D. CaCO3 + H2SO4
(I know the answer is given to D since formation of insoluble coating.... why other choices do not form insoluble coating on the surface of CaSO4...does the phenomenon occur between acid base reaction or a reaction between a metal and an scid?)
2. Describe briefly how u can prepare a pure solid sample of zinc sulphate from an aqueous soln of zinc chloride.
(Can I simply add aluminium sulphate or other sulphates only, instead of adding Na2CO3 followed by adding HCl?)
3. Actually I don't know how to distinguish when a reaction of an iron or an iron compund with other compounds... would form what kind of ions (Fe2+/Fe3+)
4. To determine whether the following statements are correct.
(i.) When using a zinc carbon cell in electrolysis, the carbon electrode of the cell is connected to the cathode of the electrolytic cell
(ii.) In a circuit using zinc carbon cell to supply electricity, electrons in the external circuit flow to the carbon electrode of the zinc carbon cell.
Salt and neutralisation
2010-12-24 5:43 am
回答 (1)
2010-12-24 10:37 am
✔ 最佳答案
1. seems that you still don't understand the reason of D.
calcium carbonate is insoluble in water.
when sulphuric acid is added, the SURFACE of carbonate reacts to form insoluble layer of SULPHATE, preventing the CARBONATE inside to further react.
how about ABC? they're soluble, and calcium ions freely exist in water.
you don't worry about prevention of reaction to occur.
2.
notice that zinc sulphate is soluble. even if you add sodium sulphate, the mixture just consists of zinc ion, chloride ion, sulphate ion and sodium ion.
NO solid zinc sulphate could be obtained ---- you can hardly separate and purify the znic sulphate out of solution.
so, FIRST you need to extract the zinc ions by precipitating as carbonate.
filter, wash to get pure zinc carbonate.
add limited amount of sulphuric acid, so carbonate will dissolve and give znic sulphate WITHOUT excess sulphuric acid remained.
filter again to remove excess zinc carbonate. evaporate to get zinc sulphate free of chloride, carbonate or sulphuric acid.
3.
redox?
when oxidizing agent is common like normal, non-oxidizing acids (HCl, dil. H2SO4), iron(II) is formed.
when strong oxidizing agents (dil. or conc. HNO3, conc. H2SO4, dichromate, chlorine...) are used, iron(II) formed will be FURTHER oxidized into iron(III) ion.
only in electrolysis, carbon reduction and metal displacement, iron metal would be produced.
4.
i. false. remember -- RED-CAT. RED-CAT. RED-CAT!
reduction occurs at cathode. oxidation at the other way round.
in the BATTERY, graphite is the anode, as it accepts electorns. but when connected to electrolytic cell, it accepts electrons given by the cathode of electrolytic cell -- electrons are always given by cathode to th external circuit.
ii. false. Zn ------> Zn(2+) + 2e-
zinc reacts to give electrons. where do the electorns go?
electorns are transported away via the external circuit, and return to the cell via carbon electrode.
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