A mixture of MgSO4.7H2O and CuSO4.5H2O is heated until a mixture of the anhydrous salts are obtained. If 5.0 g of the hydrated mixture when heated gives 3.0 g of the anhydrous salts, calculate the % by mass of CuSO4.5H2O in the initial hydrated mixture.
Q30 (02 Nov 07)
Dietary supplement pills for helping anemiac medical conditions contain iron(II) salts, the amount of which can be determined by titration with KMnO4(aq). One such supplement pill (dissolved in 10cm3 of dilute sulphuric acid) was titrated with 0.02 mol/dm3 KMnO4. The results obtained are shown in the graph above.
a) Use the Data Booklet to suggest approximate standard reduction potential (E standard) values in volts, for points X and Y.
b) Using information from the graph, calculate the number of moles of Fe2+ contained in the pill.
Q31 (02 Nov 07)
A bubble of gas (initial diameter 1.585 cm; mass 2.0973 x 10-2 g) that contains twice as much oxygen as it does carbon dioxide, emerges from a photosynthesizing aquatic plant (there’s a plesiosaur reptile aka “Loch Ness monster” right next to the plant, btw) at the bottom of a lake, where the temperature is really cold and the pressure is 6.4 times greater than at the lake’s surface; and the bubble rises until it reaches the surface of the lake (which happens to be at sea level, and at that moment is equivalent to room temperature), and bursts “pop!”.
i) Calculate the diameter (in cm) of the bubble just before it bursts.
ii) Calculate the body temperature (in °C) of the plesiosaur at the time the bubble emerges.
iii) Calculate the diameter (in cm) of this gas bubble if it were instantaneously teleported to the core of the sun (600 thousand times hotter than room temperature and 340,000 million times more crushing than Earth’s sea level atmospheric pressure), and assuming it somehow remains miraculously intact.
Q32 (02 Nov 07)
Vladimir Vasilyevich Markovnikov (1808–1904), a Russian chemist, is best known for Markovnikov's rule, which he developed in 1869. The rule is useful for predicting the molecular structures of products of addition reactions. Alexander Mikhailovich Zaitsev, also spelled Saytzeff, or Saytzev (1841–1910), was a Russian chemist at the University of Kazan (Russia) in the late 1800s. In 1875 he put forth a generalization about the regioselectivity of â elimination reactions from alcohols. Zaitsev said,"The alkene formed in greatest amount is the one that corresponds to removal of the hydrogen from the â-carbon having the fewest hydrogen substituents.". This rule is correct only when there are no other substituents beside carbon and hydrogen. Once other atoms or groups are added, electronegativity, resonance, steric hindrance and other factors make the rule no longer necessary valid. For instance, during the elimination reaction, the base that causes the double bond to form has to be sterically unhindered for the reaction to follow Zaitsev. If the base, for example, is (CH3)3CO-Na+, the bulkiness prohibits the base from pulling the leaving group off of the most substituted carbon. Another carbon atom is chosen and the Hofmann Product forms.