Repeated experiments involving the combination of copper and oxygen produces a p
ID: 532332 • Letter: R
Question
Repeated experiments involving the combination of copper and oxygen produces a product containing large variations in percentages of copper and oxygen by weight. Is this an exception to the law of definite proportions? If not, can you propose a possible explanation for this apparent anomaly? A sample of a salt was found to contain 2.83 g of calcium and 2.68 g of fluorine. a) Calculate the percent composition of calcium and fluorine in this compound. b) Using the accepted atomic weights, find the empirical formula of this compound. One pound of sulfur combines with one pound of oxygen to produce a gas. What is the percent by weight composition of this gas?Explanation / Answer
Posted first two answers, post multiple question to get the remaining answer
Q1) In the case of Cu2O (cuprous oxide) where copper is present in the oxidation state, the reaction happening is
2Cu + 0.5O2 --------- Cu2O
mass percent of Cu in the compopund = 126/142 * 100 = 88.73%
mass percent of oxygen in the compound = 11.27%
In this compound, law of definite proportions is valid since 2 atoms of Cu will connect with one atom of oxygen but the differnce in atomic weigjt of copper and oxygen is two high leading to the too much variation in the weight percentage
Q2)
a) percentage composition of calcium = 2.83/(2.83+2.68) = 51.36%
percentage compositon of flourine = 100% - 51.36% = 48.64%
b) Let us assume molar mas of compound is 100g
Number of moles of calcium = 51.36/40 = 1.284 moles
Number of moles of flourine = 48.64/19 = 2.56 moles
hence the ration of Ca to F is 1:2, therefore the empirical formula of the compound is CaF2