the weight of 2L of nitrogen at NTP is? And how to find the strongest reducing agent in chemistry?

Question

please explain the questions above. And one last question what is the oxidation number of sulphur in Na2HNS4O6.please give details and help me.

Answer 1

Megha(?) or Meghan,

NTP stands for Normal Temperature and Pressure. It's now defined as 101.325 kPa pressure, and 20C temperature.

This compares with STP == Standard Temperature and Pressure, defined as 100 kPa and 0C temperature. To convert your 2L of nitrogen gas, you need to calculate the # moles it has, first. That's 1 mole per 22.4 L at 1 atm and 0C. So, you have to ratio the volume and temperature appropriately: = 1 mole x 2L/22.4L x (273.15K)/(293.15K) x molecular weight of N₂ (which you can figure). The pressure is already appropriate (1 atm = 760 mm Hg = 101.325 kPa).

The strongest reducing agent in chemistry is the pure electron. It's very rare however to find naked electrons just drifting about; you can generate them at an anode in an electrochemical cell however (from a battery). But barring that, the H^-1 or hydride ion is pretty strong.

Maybe it would be a good idea to put your question in a little context, though: in chemistry, you frequently don't want to use the "strongest" reagent available. It's non-selective (it causes other reactions than the one you want to occur), hazardous, and possibly expensive as well. Rather, you try to use a reagent just strong enough, but selective enough, to do what you want it to.

For your other molecule, you could try to draw some Lewis structures, to make sure you don't possibly have a ring -- but if not, you assign standard oxidation numbers to each of the other atoms, and the 4 sulfur atoms then share the positive formal charge required to balance the molecule to neutral. Na = H = +1, N = -3, each O = -2.

*** Response to your comments: Looks like your question (originally) wanted the strongest neutrally charged reducing agent, which they took from an old electrochemical series table. BUT -- lithium is even stronger, in that case! (look up some images for electrochemical series on Google). However, since the question didn't limit the agents, I supplied the strongest one generally used in my experience. In general, if you take an atom and load extra electrons onto it (make it a negative ion), it then wants to (to some degree) get rid of the excess electrons and become neutral again -- that is, to act as a reducing agent (donator of electrons). So, K+ ion would be a very weak reducing agent, K (neutral atom) would be a stronger reducing agent (very strong, in fact), and K- ion would be so strong a reducing agent that you couldn't keep it contained in a container, it would react with the material of the container!

*** response to 1.25g: no way, nitrogen in standard state is a gas, formula N₂. That's molecular weight about 28 daltons/molecule, or grams/mole. Taking about 2L is close to 1/10 of 22.4L, so you have about 1/10 of a mole, and that's about 2.5 g, not 1.25 g. You can't TAKE 2L of nitrogen atoms, they immediately assemble to form diatomic molecules.

*** response to "how to find standard oxidation numbers?" -- easiest way is to memorize a few, and figure the rest from the Periodic Table. For Hydrogen and other elements towards the left edge, you REMOVE as many electrons as needed to empty the valence shell completely. So H becomes H+ (that's a +1), Na becomes Na+ (that's a +1), and so on. Elements in the second column become +2 ions (that's a +2 formal charge), and so on.

On the right edge of the Periodic Table, you instead ADD electrons to fill up the valence shell completely. So F adds 1 electron to become F- (that's a -1 charge), and so on. Oxygen, sulfur, etc. add two electrons, so you count them as -2 charge, and so on.

To assess the charge on elements which may be at the center of a polyatomic ion or in another covalent structure (such as your sulfur, in the molecule in question), you figure the total charge (as above) on everything else BUT that atom or atoms. The atom or atoms in question then must have the opposite total charge to the sum of everything else, because when *all* the atoms in the molecule or compound are added up, it must sum to zero charge (if it is a neutral molecule!)