2. Watch the video of sodium borohydride reacting with water (Cinked here) Under

Question

2. Watch the video of sodium borohydride reacting with water (Cinked here) Understand that the mixture you see resulted from my adding about 1 gram of solid sodium borohydride to about 250 mL of water and then vigorously stirring, Two reactions are occuring in this video. One occurs in the absence of an ignition source The other reaction occurs after Iignited the gas (off camera) escaping at the solution surface from the first reaction. (a) Write the two balanced reactions including appropriate reactant and product phases (s. I. g aq) (b) If the beaker contained D20, instead of the natural abundant H:0 I used from the tap, would the resulting gas from reaction 1 be mostly D2. HD, or H2? Defend your choice. (c) Which of the two reactions in 2(a) represents a redox change or do both involve redox? 3. Ammonium chloride shows no tendency to form flammable gases when it is exposed to water under the same conditions as sodium borohydride Contrast this behavior of two hydrogen- rich ions: BH,- vs NHs ions.

Explanation / Answer

(a) Balanced equation for the reaction in the absence of ignition source:

NaBH4(s) + 4H2O(l) = NaB(OH)4(aq) + 4H2(g)

Balanced equation for the reaction in the presence of ignition source:

2NaBH4(s) + 4H2O(vap) = 2NaBO2(s) + 8H2(g)

(b) In the mechanism step, BH4- anion attacks on the D-O bond of D2O forming DH as the major gas.

3. BH4- is rich in electrons that is why it attacks on O-H bond of H2O while in NH4+ cation, it is electron deficient and hence can't attack on water to release H2 gas.

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