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Practice Exam for Exam 4 1. A wooden object is claimed to have been found in an Egyptian pyramid and is offered for sale to an art museum. Analysis of the object determines that it contains 35.4 mg of Carbon-14. A fresh sample of the same kind of wood contains 62.1 mg of Carbon-14. Is this object likely to have come from a pyramid from 3500 years ago? λ= ln ln2 ln2 ln2 ⇒ k= = = 0.0001291 y −1 λ k 5730 y Nt = −kt No N 35.4 ln t ln No 62.1 = 4354 y = t = −k − 0.0001291 y −1 ( ) Because the measured age is older than 3500 years, the item is likely to be authentic. 2. How much energy in MJ is release when 1.00 mol of Lithium-6 undergoes the following reaction: 6 3Li + 10n 42He + 31H Use the data from your textbook. ∆m = −0.005135 g ( 4.00260 g + 3.01605 g ) − ( 6.01512 g + 1.008665 g ) = = −5.135 × 10 −6 kg ( )( E= ∆mc 2 = −5.135 × 10 −6 kg 2.998 × 10 8 m s−1 ) 2 = −4.615 × 1011 J = −4.615 × 105 MJ 3. Complete or write the following nuclear reactions a. 59 b. 235 92U c. Positron emission of Phosphorus-30 27Co + 10n 5625Mn + 42He + 10n 9940Zr + 13552Te + 2 10n 30 15P 01e + 3014Si 4. Which of the following complexes are tetrahedral and which are square planar based on the data provided? a. Ni(en)22+ (diamagnetic) because it is diamagnetic and Nickel is a d8 ion 2 the hybridization must be dsp and it is square planar (green color) because we see green it must absorb red b. FeCl4therefore is small, therefore the complex is tetrahedral (low spin) With Ag+ it’s always low spin so the only way to c. Ag(CO)4+ tell is by the fact that CO is a strong ligand so must be large so the complex is square planar 5. Name the following transition metal complexes or complex ions a. [CrBr2(NH3)4]+ Tetraamminedibromidochromium(III) ion b. [AlF6]- Hexafluoridoaluminate(V) ion c. [Fe(CN)5(SCN)]4Pentacyanatothiocyanato-S-ferrate(II) ion d. [Ag(S2O3)2]3dithiosulfatoargentate(I) ion e. [Co(NH3)5(SO4)]+ Pentaamminesulfatocobalt(III) ion 6. Write formulas from the following names a. dicyanidoargentate(I) ion [Ag(CN)2]b. pentaaquahydroxidoaluminum(III) chloride [Al(H2O)5(OH)]Cl2 c. (ethylenediamine)dithiocyanato-S-copper(II) [Cu (NH2CH2CH2NH2)(SCN)2] 7. Cr(en)32+ is low spin, what sort of hybridization does it have? Low spin, maximum pairing of electrons d orbital available it is d2sp3. 8. Fe(NO2)2(en)2 is polar, does it have optical isomers? If it’s polar the NO2 ligands are cis and it has optical isomers. 9. MoCl2(H2O)2+ is non-polar, does it have geometric isomers? It’s non polar so it’s square planar, so it does have geometric isomers. 10. A compound with the overall formula CoCl6 3H2O is dissolved in water. Electrical conductivity measurements indicate that there are 3 ions per formula unit. Gentle heating of the compound results in a slight mass loss. X-ray crystallography measurements indicate that the cobalt has octahedral geometry. Write a formula for this compound indicating what the ligands are, what the anions are and if how many waters of hydration there are. (i.e. [ML1nL2m]Ay xH2O) 3 ions per formula unit indicates that 2 of the chlorides are anions to the complex ion. Gentle heating resulting in a slight mass loss indicates that at least one of the water molecules is a hydrate water. Because the complex ion is octahedral we have to have six ligands. 2 of the chlorides are anions so the other 4 are ligands which means that 2 of the waters also have to be ligands. The remaining water is the water of hydration. The formula of the compound is: [CoCl4(H2O)2]Cl2 H2O 11. Predict the type of decay for the following isotopes and write the nuclear equation. a. 29 14Si N/Z = 15/14 > 1.0 so the likely decay type is beta decay: 29 14Si 0-1e + 2915P b. N/Z = 67/51<1.5 (because Z >20) so the likely decay type is positron emission or electron capture 118 0 118 51Sb +1e + 50Sn c. 232 90Th d. 11 118 51Sb 5B Z>61 so the likely decay type is alpha decay 232 4 228 90Th 2He + 88Ra N/Z = 6/5 > 1 so the likely decay type is beta decay: 11 0 11 5B -1e + 6C