Question

 

a). Polonium is a rare element with 33 radioisotopes. The most common one, 210Po, has 82 protons and 128 neutrons. When 210Po decays, it emits an alpha particle, which is a helium nucleus (2 protons and 2 neutrons). 210Po decay is tricky to detect because alpha particles do not carry very much energy compared to other forms of radiation. They can be stopped by, for example, a sheet of paper or a few inches of air. That is one reason that authorities failed to discover toxic amounts of 210Po in the body of former KGB agent Alexander Litvinenko until after he died suddenly and mysteriously in 2006. What element does an atom of 210Po change into after it emits an alpha particle?

b). Some undiluted acids aremore corrosive when they are diluted with water. That is why laboratory workers are told to wipe acid splashes with a towel before washing with a copious amounts of water. Explain.

Answer 1

a) The supplied information is wrong. Po has atomic number 84 (82 protons) while lead has atomic number 82 (82 protons). Since you have said Po, I will use the atomic number 84.

Po-210 has 128 neutrons and 84 protons. An alpha particle is ⁴He₂. The loss of an alpha particle reduces the mass number by 4 units and the atomic number by 2 units. Therefore, the new element that is formed from Po-210 will have mass number (210 – 4) = 206 and atomic number (84 – 2) = 82. A look at the periodic table tells us that the element having atomic number 82 is lead (Pb). Hence, the loss of an alpha particle converts Po-210 to Pb-206. The equation is as below.

²¹⁰Po₈₄ -------> ²⁰⁶Pb₈₂ + α (⁴He₂)

b) Dilute sulfuric acid (H₂SO₄) is found to be more corrosive than concentrated sulfuric acid. This is due to the fact that dilute sulfuric acid produces a higher concentration of protons. An acid can only protonate in solution; therefore, concentrated sulfuric acid is largely undissociated (since it doesn’t have enough water to protonate) while dilute sulfuric acid is almost completely protonated (since a dilute acid has more water available). A “free” proton cannot exist in solution; hence the proton combines with water to form hydronium ion. It is this hydronium ion that oxidizes metals to the respective cations and itself gets reduced to hydrogen gas. It is due to this oxidizing property of proton that dilute sulfuric acid is more corrosive than concentrated acid.