5

Liquid phosphorus is white phosphorus. It melts at 44.1 °C. Red phosphorus does not melt. It burns at 200 °C and sublimes in an argon atmosphere at 280 °C, without melting.


3

The query you have is a common mistake, and this is aksed as a very common question in examinations, well, I wouldn't blame you as the reason is simple but not easy to think of. What you said about E.N. of phosphorous being more than arsenic and antimony is absolutely correct. But what you missed, is that lower down the group the direction of dipole itself ...


3

Oil production areas use a personal badge; lead acetate , it darkens if H2S is present ( Draeger was a brand for detection equipment).


3

On the premises of an oil refinery, if you are not staying completely indoors, everybody gets one of these: They give you an alarm if the H2S concentration goes above a few ppms, and the sensor inside typically can (quantitatively) measure up to one or two hundred ppm before it goes into saturation.


3

There are simple test tubes available for the measurement of $\ce{H2S}$ and similar compounds in air. For example this one by Dräger (no affiliation), which uses oxidation by iodine. $$\ce{H2S + I2 -> 2 HI + S2}$$ The (discoloration of the) brown color of the absorbed iodine serves as indicator. In order to get a quantitative result for the concentration ...


3

This seems to be the case of "show, don't tell". IUPAC's definition of coordination number (C.N.) which applies to inorganic complexes: In an inorganic coordination entity, the number of σ-bonds between ligands and the central atom. π-bonds are not considered in determining the coordination number. Let's have a look at the one of the first determined ...


2

As Ivan Neretin told it, each group oxalate has two groups $\ce{-COO^-}$. So it may be bound to a central metal by two oxygen atoms, one per group $\ce{-COO^-}$.


1

Consider three compositions: A. 2NaF + CaCO3 B. CaF2 + Na2CO3, and C. NaF + 0.5 CaCO3 + 0.5 CaF2 + 0.5 Na2CO3. Using data from the CRC Handbook (62nd ed), the heats of formation of A and B are respectively 560.47 and 560.6 kcal, so there is little driving force to make a reaction go to completion. Note that A should be near neutral pH, but B ...


1

The mechanics of the reaction on Pb with concentrated HNO3 likely commences as follows: $\ce{Pb -> Pb(II) + 2 e-}$ $\ce{HNO3 = H+ + NO3-}$ $\ce{Pb(II) + 2 NO3- = Pb(NO3)2}$ $\ce{H+ + e- = .H}$ $\ce{.H + NO3- = OH- + .NO2}$ (1997 Source) The literature also contains citations (see, for example, Page 37) of an associated mechanism involving ...


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