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Offline Twoacross

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Gravi. Analysis - assistance needed
« on: October 10, 2011, 06:17:58 pm » I am truly sorry for the double post, i should have known "help" is not good in the title:So i just did a gravimetric experiment where we took an unknown mass of a compound containing nickel and with the data gathered and some formulas to work with, Ni^2+ (aq) + 2 C4H7O2N2H (alc) =====> Ni (C4H7O2N2)2 (s) + 2H^+ (aq)Let me list my data first:Mass of original sample: 1.0601 gMass of precipitate9A: 0.2857 g9B: 0.2815 gAnd im asked to find the percentage of nickel in the unknown sample, which would be the 1.0601 gSo what i did first was took the mass of 9A's precipitate and converted it to moles, 0.2857 g / 288.9158 g /mol = 9.8887 x 10^-4 mol Ni(C4H7O2N2)2From here, i converted that value into moles of nickel which would be the same since: 9.8887 x 10^-4 mol Ni(C4..)2 x 1 mol Ni divided by 1 mol of Ni(C4..)2 = 9.8887 x 10^-4 mol NiFrom here i can calculate the mass by taking the mass of the nickel and multiplying it by the molar mass of nickel: 9.8887 x 10^-4 mol Ni * 58.693 g / mol = 0.058039 g NiAnd then i divided it by the unknown sample's mass to obtain: 0.05803 g / 1.0601 g *100% = ~5.50%2. Then the second part asks which of these choices my sample could be: NiCl2*6H2O, NiSO4*6H2O, NiSO4*7H20, NiBr2*6H2ONow what i decided to do was compare the percentages of nickel within each compound, I thought of a couple ways of doing this:1. Take the molar mass of nickel and divide it by the total molar mass of the given compounds2. Find equations like taking NiCl2*6H2O and then adding the alc shown above and then from there balance it and then here i thought which mass i would use, the unknown or the precipitate?I gave it some thought and im still kinda stump on which approach would be appropriateAll feedback and help is greatly appreciated!Thank you! Logged

Offline fledarmus

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Re: Gravi. Analysis - assistance needed
« Reply #1 on: October 10, 2011, 09:24:46 pm » Compare:Quote
And then i divided it [the mass of Ni] by the unknown sample's mass [the total mass of the compound] to obtain: 0.05803 g / 1.0601 g *100% = ~5.50%
toQuote
1. Take the molar mass of nickel and divide it by the total molar mass of the given compounds
Does this help answer your question? Logged

Offline Twoacross

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Re: Gravi. Analysis - assistance needed
« Reply #2 on: October 10, 2011, 11:20:14 pm » Hmm, I tried doing that but none of the compounds to choose from are not close to 5%, do I go with the one with the nearest percent?Thanks Logged

Offline Borek

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Re: Gravi. Analysis - assistance needed
« Reply #3 on: October 11, 2011, 03:07:58 am » You have two results - does it mean you did two identical experiments, starting with two identical 1.0601g samples? Logged Chembuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Offline Twoacross

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Re: Gravi. Analysis - assistance needed
« Reply #4 on: October 11, 2011, 02:52:44 pm » Okay, its clear now, Thanks everyone, I guess I overcomplicate things whereas I should be thinking more theoretically.Thanks Borek and fledarmus =D Logged
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