[jsc]

Please help me answering the following gravimetric analyses problems:

1. At elevated temperatures, NaHCO3 is converted quantitatively to Na2CO3: 
                    2NaHCO3 = Na2CO3 + CO2 + H2O

Ignition of 0.3592 g sample containing NaHCO3 and non-volatile impurities yielded a residue weighing 0.2362 g. Calculate the percent purity of the sample.


2. A sample containing only CaCO3 and MgCO3 is ignited to CaO and MgO. The mixture of oxides weighs exactly half as much as the original sample. Calculate the percentages of CaCO3 and MgCO3 in the sample.


3. A 0.5000 g sample that contains KCl and KI gives a precipitate of AgCl and AgI that weighs 0.2818 g. A 0.8000 g sample is titrated with 0.1053 M AgNO3, requiring 26.74 mL. Calculate the percentages of KCl and KI in the sample.


4. A 0.8000g sample of iron ore containing 21.00% Fe is analyzed gravimetrically. If the final precipitate (assumed to be Fe2O3) contains 20.0 mg Al2O3 by mistake, what percentage of Fe does the analyst find?


5. 1.000 g of soil, as received, gave a moisture of 14.00%. The oven dried sample, completely moisture-free, showed 18.00% K. Find the percentage of K in the sample as received.


6. A mixture of KI and NaCl was converted to K and Na sulphates. The combined sulphate precipitate was found to weigh the same as the original mixture. Calculate the % KI in the original mixture.


7. A 0.2000g sample of an alloy containing only Ag and Pb was dissolved in HNO3. Treatment of the resulting solution with cold HCl gave a mixed precipitate (AgCl and PbCl2) weighing 0.2466 g. When this mixed chloride precipitate was treated with hot water to dissolved all the PbCl2, 0.2067 g of AgCl remained. Calculate the percentage of Ag in the alloy. Calculate what weight of PbCl2 was not precipitated by the addition of cold HCl.


8. A fish meal sample has the following composition: protein 20%, moisture 12%, additive 66%. The sample is placed in drying oven and subsequent analysis gave a value of 22% protein. Calculate the % moisture content of the dried sample.

     ----Thanks in advance. I will be posting several problems not only in analytical chemistry but as well as in inorganic, organic, biochemistry and physical chemistry in my future post. Hope to help me on these. 

[Borek]

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[jsc]

I will be posting my attempted solutions on the problems that I've posted a while ago. My solutions may be right(on my own perspective) or wrong ( for the others perspective). I hope many would join to find the right and most practical answers. Thank you very much and my apology also for this action.