Percent composition by mass

A 0.500-g sample of zinc-copper alloy was treated with dilute hydrochloric acid. The hydrogen gas evolved was collected by water displacement at 27°C and a total pressure of 755 mm Hg. The volume of the water displaced by the gas is 105.7 mL. What is the percent composition, by mass, erf the alloy (Vapor pressure of H20 at 27°C is 26.74 mm Hg.) Assume only the zinc reacts. 

Which one of the following could possibly be defined as the ratio of moles of each of the given elements to moles of each of the others (a) Empirical formula, (b) molecular formula, or (c) percent composition by mass. 

Urea, a substance commonly used as a fertilizer, has the formula CH4N20. What is its percent composition by mass ... 

Which statement is true about the percent composition by mass in C6H1206 ... 

The number of atoms or the mass percent of its elements can describe a compound s composition. The percent composition by mass can be calculated by comparing the mass of one mole of each element to the molar mass. 

To calculate a formula mass To calculate the percent composition by mass from the formula of a compound... 

List as many similarities and differences as possible between mole fraction and percent composition by mass. 

In 1987 the first substance to act as a superconductor at a temperature above that of liquid nitrogen (77 K) was discovered. The approximate formula of this substance is YBa2Cu307. Calculate the percent composition by mass of this material. 

A 1.500-g sample of a mixture containing only Cu20 and CuO was treated with hydrogen to produce 1.297 g of pure copper metal. Calculate the percent composition (by mass) of the mixture. 

From the empirical formula and the atomic weight of each atom, we can find the percent composition of a compound by mass. To do this, multiply an atom s atomic weight by the number of atoms it contributes to the empirical formula. Divide your result by tire weight of all the atoms in tire empirical formula. This gives you the mass fraction of the compound represented by the atom. Now multiply this fraction by 100, and you have the percent composition by mass. 

For Questions 1 through 5, determine the percent composition by mass of each compound. 

The percent composition by mass is the percent by mass of each element in a compound. Percent composition is obtained by dividing the mass of each element in 1 mole of the compound by the molar mass of the compound and multiplying by 100 percent. Mathematically, the percent composition of an element in a compound is expressed as... 

Since both the molecular formula and the empirical formula tell us the composition of the compound, it is not surprising that they give us the same percent composition by mass. 

Phosphoric acid (H3PO4) is a colorless, syrupy liquid used in detergents, fertilizers, and toothpastes, and in carbonated beverages for a tangy flavor. Calculate the percent composition by mass of H, P, and O in this compound. 

The procedure used in the example can be reversed if necessary. Given the percent composition by mass of a compound, we can determine the empirical formula of the compound. Since we are dealing with percentages and the sum of aU the percentages is 100 percent, it is convenient to assume that we started with 100 g of a compound, as Example 3.9 shows. 

Chemists often want to know the actual mass of an element in a certain mass of a compound. Since the percent composition by mass of the element in the substance can be readily calculated, such a problem can be solved in a rather direct way. 

The formula calculated from percent composition by mass is always the empirical formula because the coefficients in the formula are always reduced to the smallest whole numbers. To calculate the actual, molecular formula we must know the approximate molar mass of the compound in addition to its empirical formula. Knowing that the molar mass of a compound must be an integral multiple of the molar mass of its empirical formula, we can use the molar mass to find the molecular formula, as Example 3.11 demonstrates. 

Percent Composition by Mass of Nitrogen in Five Common Fertilizers... 

Mole method, p. 89 Molecular mass, p. 74 Percent composition by mass, p. 77... 

For many years chloroform (CHCI3) was used as an inhalation anesthetic in spite of the fact that it is also a toxic substance that may cause severe liver, kidney, and heart damage. Calculate the percent composition by mass of this compound. 

Cinnamic alcohol is used mainly in perfumery, particularly in soaps and cosmetics. Its molecular formula is C9H10O. (a) Calculate the percent composition by mass of C, H, and O in cinnamic alcohol, (b) How many molecules of cinnamic alcohol are contained in a sample of mass 0.469 g ... 

Allicin is the compound responsible for the characteristic smell of garlic. An analysis of the compound gives the following percent composition by mass C 44.4% H 6.21% S 39.5% O 9.86%. Calculate its empirical formula. What is its molecular formula given that its molar mass is about 162 g ... 

Peroxyacylnitrate (PAN) is one of the components of smog. It is a compound of C, H, N, and O. Determine the percent composition of oxygen and the empirical formula from the following percent composition by mass 19.8 percent C, 2.50 percent H, 11.6 percent... 

Mustard gas (C4HgCl2S) is a poisonous gas that was used in World War I and banned afterward. It causes general destruction of body tissues, resulting in the formation of large water blisters. There is no effective antidote. Calculate the percent composition by mass of the elements in mustard gas. 

A mixture of Na2C03 and MgC03 of mass 7.63 g is reacted with an excess of hydrochloric acid. The CO2 gas generated occupies a volume of 1.67 L at 1.24 atm and 26°C. From these data, calculate the percent composition by mass of Na2C03 in the mixture. 

Acidic oxides such as carbon dioxide react with basic oxides like calcium oxide (CaO) and barium oxide (BaO) to form salts (metal carbonates), (a) Write equations representing these two reactions, (b) A student placed a mixture of BaO and CaO of combined mass 4.88 g in a 1.46-L flask containing carbon dioxide gas at 35°C and 746 mmHg. After the reactions were complete, she found that the CO2 pressure had dropped to 252 mmHg. Calculate the percent composition by mass of the mixture. 

Proteins have high molar masses, ranging from about 5000 g to 1 X 10 g, and yet the percent composition by mass of the elements in proteins is remarkably constant carbon, 50 to 55 percent hydrogen, 7 percent oxygen, 23 percent nitrogen, 16 percent and sulfur, 1 percent. 

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