Posted by **laura** on Monday, December 5, 2011 at 9:31pm.

Two gas tanks containing compounds A and B are connected by separate valves to two ends of a 10 meter glass tube as shown below. When both valves are thrown open at the same time A and B travel down the tubes towards each other. A white line appears when they meet and b has only gone 3.534 meters

Given that A and B are one of the compounds below determine what A and B’s identities are.

Possible compounds that can be A and B: HF, HCl, HBr, HI (acids) NH3, NCl3, NF3, PH¬3, PCl3 (bases)

- chem -
**DrBob222**, Monday, December 5, 2011 at 10:49pm
A------------------------B

|....6.466.....|..3.534..|

rate A travels = 6.466 m/s

rate B travels = 3.534 m/s (You can use any time period; I chose 1 s for convenience).

(6.466/1/3.534/1) = sqrt(MB/MA) where MA = molar mass A and MB = molar mass B.

Solve for ratio of B/A. I get something like 3.0 but you need to do it more accurately.

Then look up the molar mass of the acid and bases and put them in a table or whatever you find easy to do.

HF =abou5 20......NH3 = ?

HCl = ?...........NCl3. ?

HBr = ?...........NF3 = ? etc.

HI = ?

Then look at ratios. Some will obviously not fit but some will be close enough to do on a calculator. I

think NCl3 and HCl are close for A and B BUT I don't know if they will react to form a white ring or not. In addition, NCl3 can be explosive. Check my thinking.

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