I just bought some (pure) antimony stones from a local store. However, I've heard that some stores deceive their customers by selling lead instead of antimony. I was wondering if there is any simple test that I can perform at home to make sure these stones are antimony and not lead. Since I don't know much about chemistry I thought of asking here...
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$\begingroup$ Lead has much bigger density as melts much easier. $\endgroup$– MithoronCommented May 25, 2015 at 18:15
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$\begingroup$ @Mithoron I actually thought of melting it in the oven but wikipedia says the melting point of lead is 327.4 and antimony is almost double of that. The maximum temperature of my oven is around 250 degrees Celsius. But thanks for the suggestion about density. $\endgroup$– ArtusCommented May 25, 2015 at 18:31
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4$\begingroup$ Yeah, you could do Archimedes' experiment :) $\endgroup$– MithoronCommented May 25, 2015 at 18:35
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$\begingroup$ Definitely agree with @Mithoron. Lead is almost twice as dense as antimony and Archimedes' experiment is easy and safe to do so and should give a clear result. $\endgroup$– bonCommented May 25, 2015 at 19:03
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1$\begingroup$ Eureka! @Mithoron $\endgroup$– MixcelsCommented May 26, 2015 at 6:44
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2 Answers
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As mentioned in the comments, you could perform Archimedes' Experiment.
- Firstly, take the mass ($m$) (in grams) of your sample.
- Then, measure the volume $V$ displaced (according to the first link), in a method summarised in the image below:
You could use any kitchen graduated container. Even though these have graduations for mL (millilitres) and even though the water density changes with temperature (source:USGS), for the temperatures in a home experiment, the following conversion could be used 1 mL = 1 cm3 of water displaced.
- Then determine the density by $\rho = \frac{m}{V}$ and compare it to the known values for lead at 11.3 g.cm-3 and antimony at 6.7 g.cm-3.
Another observed feature is that according to the LennTech site for lead is that as opposed to antimony, lead will tarnish on exposure to air.
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1$\begingroup$ Thanks. The density turned out to be 6.06 (with mL) but I didn't have a graduated container so I used a ruler and a regular container which did not have a 100% flat bottom (and probably it resulted in some error). It looks like the stone is antimony I guess :). $\endgroup$– ArtusCommented May 25, 2015 at 22:22
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Another method that doesn't require calculations, but does involve sacrificing only a very small portion of your sample is to do a flame test. By heating a pure sliver of antimony in a hot flame you should observe a pale green color as opposed to a blue-white color if the sample is lead. If you are a poor judge of color then its helpful to have known pure samples of the elements to compare with your unknown sample.
This method, as well as the gravimetric method suggested by Santiago can fail if your sample is an alloy (mix) of the two elements (and perhaps other ingredients!). But here the flame test can help by using a spectroscope for a more quantitative accounting of the constituents.
answered Jun 21, 2015 at 17:02
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$\begingroup$ Very good point - a spectroscope is not necessarily expensive nor hard to use. $\endgroup$– user15489Commented Jun 22, 2015 at 7:22