Classify each of these statements as always true, sometimes true, or never true.
7____AT____It is necessary to know the formula of a compound in order to calculate its percent composition.
8___ST_____If the percent by mass of carbon in methane, CH4, is 75%, then 100 grams of methane contain 25.0 grams of hydrogen.
9____AT____The formula for methane, CH4, is both a molecular and an empirical formula.
10____NT___The empirical formula for glucose, C6H23O6, is C2H4O2.
7. I may not understand this question very well but I can calculate the percent composition if I know the grams of A that combine with the grams of B as well as if I know the formula.
8. You need to rethink this. If CH4 is 75% C it must be 25% H and 100 g CH4 will contain 25g H. If it is sometimes true, when is it not true?
9. I go along.
10. Glucose is C6H12O6; therefore, the empirical formula is CH2O. Since the incorrect formula is given for glucose I don't know how to answer this.
Help on Completion.
The Percent by mass of an element in a compound is the number of grams of the element per _____g of the compound, multiplied by 100%.
The "Help on Completion." question is the same one I am struggling with! ahhh!
7. The statement is sometimes true. In order to calculate the percent composition of a compound, it is necessary to know the formula of the compound. The formula provides information about the elements present in the compound and their ratios. Without knowing the formula, it is not possible to determine the percent composition accurately.
8. The statement is sometimes true. If the percent by mass of carbon in methane is 75%, then it means that 100 grams of methane contain 75 grams of carbon. However, the statement incorrectly states that 100 grams of methane contain 25.0 grams of hydrogen. This is incorrect because the remaining mass in methane is attributed to hydrogen, so it would be 100 grams minus 75 grams (mass of carbon) equals 25 grams of hydrogen.
9. The statement is always true. The formula for methane, CH4, is both a molecular and an empirical formula. The molecular formula represents the actual number of atoms of each element in a molecule, in this case, one carbon and four hydrogen atoms. The empirical formula represents the simplest whole-number ratio of atoms in a compound, which is also CH4 for methane.
10. The statement is never true. The empirical formula for glucose is not C2H4O2, but rather CH2O. The empirical formula represents the simplest whole-number ratio of atoms in a compound, and glucose has a molecular formula of C6H12O6. By dividing each subscript by the greatest common divisor, we obtain the empirical formula CH2O.
Help on Completion: The percent by mass of an element in a compound is the number of grams of the element per 100 grams of the compound, multiplied by 100%.