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Unit 3 Nuclear Chemistry

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HIGHER CHEMISTRY REVISION. Unit 3 :- Nuclear Chemistry 1.Polonium-210 is a radioisotope that decays by alpha-emission. The half life of polonium-210 is 140 days. (a)Write a balanced nuclear equation for the alpha-decay of polonium-210. (b)Calculate the number of atoms in 105 g of polonium-210. 210 208 4 (a) Po Pb + He 84 82 2 (b)In 1 mole, 210g there are 6.02 x 10 23 Po atoms. So in 105 g there are 105 / 210 x 6.02 x 10 23 = 3.01x 10 23 Po atoms.

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2. Carbon-14 dating can be used to estimate the age of charcoal found in archaeological sites. Carbon-14 has a half life of 5740 years. (a) Carbon-14 decays by beta emission. Write a balanced equation for this decay. (b) Why can carbon-14 not be used to estimate the age of fossil fuels? 3. The grid shows the possible effect of temperature change on reaction rate. Identify the graph which shows how the rate of reaction varies with temperature in the radioactive decay of phosphorus-32. A B D EF C 2. (a) 14 14 0 C N + e 6 7 -1 (b) Fossil fuels are millions of years old. Carbon-14s half life is too short for any to remain after millions of years. 3. Graph in box F

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4. Technetium-99, which has a long half-life, is produced as a radioactive waste product in nuclear reactors. One way of reducing the danger of this isotope is to change it into technetium-100 by bombardment with particles, as shown by the nuclear equation. Tc+X Tc (a) Identify particle X. (b) Technetium-100 decays by beta-emission. Write a balanced nuclear equation for this reaction. (c) Technetium-100 has a half-life of 16 s. If a sample of technetium-100 is left for 48 s, what fraction of the sample would remain? 99 43 100 43 (a)X is a neutron = (b) Tc Ru + e (c) 1 / 8. 100 43 100 44 0 1 n 0

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5. (a) Nuclear reactions can be carried out by scientists. For example, lawrencium-257 has been made by bombarding californium-252 with atoms of an isotope of a lighter element. Each successful collision was accompanied by the release of six neutrons. Write a nuclear equation for this reaction. (b) An example of a nuclear equation which happens in nature is: C+HeO Where do reactions of this type take place all the time? 12 6 4242 16 8 (a) Cf + B Lr + 6 n (b) In the upper atmosphere. 257 103 252 98 1 01 0 11 5

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6.Phosphorus-32 is a radioisotope that decays by beta-emission. (a) Write the nuclear equation for the decay of phosphorus-32. (b) (i) An 8g sample of phosphorus-32 was freshly prepared. Calculate the number of phosphorus atoms in the 8g sample. (ii) The half-life of phosphorus-32 is 14.3 days. Calculate the time it would take for the mass of phosphorus-32 in the 8g sample to fall to 1g. (a) (b) (i) 32g contains 6.02 x 10 23 atoms 8 g contains 1.505 x 10 23 atoms (ii) 8g 4g 2g 1g is 3 half lives 3 x 14.3 days = 42.9 days

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