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Ka law of definite proportions the relative amount of

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Unformatted text preview: distillation ﬂask. Heterogeneous: Not uniform from point to point. Condenser Water out Cool water in Receiving flask Distillate Law of constant composition (a.k.a. Law of definite proportions): The relative amount of each element in a compound is always the same, independent of source or how it was made. Example:! A!2.485!gram!sample!of!of!a!compound!of!sodium!and!chlorine!contains!0.978!grams! of!sodium!and!1.507!grams!of!chlorine.!Calculate!the!mass!%!of!sodium!and!chlorine! in!the!compound.! 1.  The mass % of Na in the compound is given by: mass of Na mass % of Na = × 100 mass of compound = 0.978 g × 100 = 39.36% 2.485 g 2. € The mass % of chlorine in the compound is given by: mass of Cl mass % € f Cl = o × 100 mass of compound = € 1.507 g × 100 = 60.64% 2.485 g Reaction of metallic sodium with water: 2Na!+!2H2O!#!H2!+!2Na+!+!2OHJ! John Dalton Law of Multiple Proportions When a given element (X) combines with another (Y) to form two different compounds, then for a fixed mass of X, the ratio of the masses of y in the two compounds consists of small integer, or ratio of small integers. Compounds are made of units which he called atoms. These atoms behave according to a fixed set of rules. John Dalton Father of the Atomic Theory Example: The law of Multiple Proportions Carbon forms two stable compounds with oxygen; CO (carbon monoxide) and CO2 (carbon dioxide). Chemical analysis shows that: For CO , € mass of C 12 g = mass of O 16 g For CO2 , mass of C 12 g = mass of O 32 g The ratio of masses of O€ that combine with 12 g of C in these two compounds is given by: mass of O in CO 16 g 1 = = mass of O in CO2 32 g 2 The ratio of 1:2 supports the law of multiple proportions. € Example #2: The law of Multiple Proportions Two combinations of phosphorous (P) and chlorine (Cl) are observed. In compound A, 22.54% of the mass is from P; in compound B, 14.88%. In!A,!the!Cl!is!(100J22.54)%=77.46!%! In!B,!the!Cl!is!(100J14.88)%=85.12!%! Assume a fixed mass of P; call it 1 gram in either case. In compound A, we would expect 1 gram (7...
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