1. For the following pairs of acids, state which one is the stronger acid, and b
ID: 1033984 • Letter: 1
Question
1. For the following pairs of acids, state which one is the stronger acid, and briefly explain why: a. H2S and H Se b. PHs and SiH 2. Ion-cyclotron resonance experiments allow scientists to observe gas phase reactions of ions. In one study, (Wyatt, R.H.; Holtz, D.; McMahon, T.B.; Beauchamp, J.L. Inorg. Chem., 1974, 13, 1511-1517) it was reported that the following reaction tends to go forward: Based on the direction of this reaction, which is the stronger acid, PH3 or AsH3? Is this in agreement with the general trends for binary acids? What is the usual rationalization for this trend? What other considerations might complicate the picture from this rationalization? 3. The same study reported that the following reaction also tends to go forward: Which is the stronger acid, H2S or AsH3? Is this in agreement with the general trends for binary acids? This is an interesting example in that both the trends across the periodic table and down the periodic table are involved. Which has a greater influence, the trend across the table or the trend down the table? Does this fit with what you know about the relative acidities of binary acids of the second row (CH4, NH3, OH2, etc) and the halogern group (HF, HCI, HBr, etc.)? 4. Estimate the pK, values for HNO, and HNO.
Explanation / Answer
1)
Comparing H2S and H2Se the H–Se bond is longer than the H–S
bond as Se is larger than S. The H–Se bond is therefore weaker than the H–S
bond Hence H2Se is a stronger acid than H2S.
Comparing PH3 and SiH4 as you are going across the period and to determines the acid strength across the period is the electronegativity.Greater is the electronegativity the stronger the acid will be. Electronegativity of Phosphorus is Greater than Silicon Hence PH3 is Stronger acid than SiH4
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