Water gases collected over

Dalton s law of partial pressures is useful for calculating volumes of gases collected over water. For example, when potassium chlorate (KCIO3) is heated, it decomposes to KCl and O2 ... 

For gases collected over water, the vapor pressure of water is subtracted from the total pressure of the gas mixture to obtain the partial pressure of the dry gas. 

Another type of gas law problem involves stoichiometry. Gas stoichiometry problems are just like all other stoichiometry problems—you must use moles. In addition, one or more gas laws are necessary. Let s look at a gas stoichiometry problem. What volume, in liters of oxygen gas, collected over water, forms when 12.2 g ofKCl03 decompose according to the following equation ... 

Measure the mass, volume, temperature, and pressure of an insoluble gas collected over water. 

When using the ideal gas law for a gas collected over water, you must correct the pressure before you substitute it into the gas law. The following Sample Problem shows you how to do this. 

In this section, you learned how to use Gay-Lussac s law to calculate volumes of gases in a gas reaction. You also learned how to use the ideal gas law to find the volumes of gases used or produced in reactions. Building on Dalton s law of partial pressures, from Chapter 11, you learned how to calculate the molar volume of a gas collected over water. Finally, you learned, first-hand, how to produce hydrogen gas in a laboratory. 

Calculate the volume of oxygen gas, collected over water at 836 torr barometric pressure and 298 K, that can be prepared by the thermal decomposition of 2.40 g of KC103.(Pwater = 24 torr at25°C)... 

At elevated temperatures, sodium chlorate decomposes to produce sodium chloride and oxygen gas. A 0.8765-g sample of impure sodium chlorate was heated until the production of oxygen gas ceased. The oxygen gas collected over water occupied 57.2 mL at a temperature of 22° and a pressure of 734 torr. Calculate the mass percent ... 

A sample of gas collected over water at 25° C was found to have Volume 543.0 ml, the atmospheric pressure being 730 mm of Hg. What is the volume of the dry gas at standard conditions ... 

The only challenge to this variation on Dalton s Law is that it is unlikely that anyone will remind you to use a table such as the one presented in this lesson (Vapor Pressure of Water). Just try to associate questions about water vapor pressure to this type of table. If a question talks about a gas collected over water or if it asks for the pressure of the dry gas, then you probably will need a table of water vapor pressures. 

A gas collected over water at 25 C becomes saturated with water vapor, its partial pressure being 23.8 mm. The measured volume of the moist gas is 5.44 liters, at a total pressure of 752.0 mm. Calculate the volume the dry gas would occupy at a pressure of 760 mm., assuming ideal behavior of the gas and of the water vapor. 

The relevant point here is that a gas collected over water is moist that is, it is saturated with water vapor. Measuring the atmospheric pressure at which the gas is collected, we can write... 

If a gas is collected over a volatile liquid, such as water, a correction is made for the amount of water vapor present with the gas. A gas collected over water is saturated with water vapor, which occupies the total gas volume and exerts a partial pressure. The partial pressure of the water vapor is a constant for each temperature and is independent of the nature or pressure of the confined gas. This definite value of the vapor pressure of water may be found tabulated as a function of temperature in handbooks or in... 

What is the pressure of hydrogen gas collected over water at 15°C The total pressure of the collected mixture, hydrogen gas plus water vapor, is 752 mmHg. 

Example 5.16 shows how to use Dalton s law to calculate the amount of a gas collected over water. 

SAMPLE PROBLEM 5.10 Calculating the Amount of Gas Collected over Water Problem Acetylene (CoHo), an important fuel in welding, is produced in the laboratory when calcium carbide (CaCo) reacts with water ... 

Consider a sample of hydrogen gas collected over water at 25 °C where the vapor pressure of water is 24 torr. The volume occupied hy the gaseous mixture is 0.500 L, and the total pressure is 0.950 atm. Calculate the partial pressure of H2 and the number of moles of H2 present. 

Upon reaction with excess sulfamic acid, HSO3NH2, a 0.111-g sample of a mixture of sodium nitrite, NaN02, and sodium chloride, NaCl, produced 26.3 mL of nitrogen gas collected over water at 22°C and at a barometric pressure of 743 mitiHg. Determine the percent by mass of NaN02 in the original sample. Show clearly your calculations and reasoning. 

In gas mixtures the total pressure is the sum of the partial pressures that each gas would exert if it were present alone under the same conditions (Dalton s law of partial pressures). The partial pressure of a component of a mixture is equal to its mole fraction times the total pressure Ej = XjEf The mole fraction is the ratio of the moles of one component of a mixture to the total moles of all components. In calculating the quantity of a gas collected over water, correction must be made for the partial pressure of water vapor in the gas mixture. 

To determine the amount of O2 or any other gas collected over water, we subtract the pressure of the water vapor (vapor pressure) from the total pressure of the gases ... 

Example 5.10 shows a typical application of Dalton s law in calculating the amount of gas collected over water. 

SAMPLE PROBLEM 5.10 Calculating the Amount of Gas Collected over Water... 

In Lavoisier describes Experiences sur la decomposition du nitre par le charbon said to have been made in 1784. A mixture of oz. of saltpetre with I gros 42 grains of charcoal in a brass tube was kindled by a fuse and the gas collected over water or mercury. The fixed air was absorbed by caustic alkali and the residual mofette (nitrogen) measured. The white fixed alkali (potassium carbonate) left in the tube was decomposed by acid and the fixed air measured. The average result is given as ... 

Calculating the amount of gas collected over water Given the volume, total pressure, and temperature of gas collected over water, calculate the mass of the dry gas. (EXAMPLE 5.11)... 

Practice Problem B Determine the volume of gas collected over water when 0.501 g O2 is produced by the decomposition of KCIO3 at 35.0°C and 1.08 atm. 

SAMPLE PROBLEM 11.15 Moles of Gas Collected Over Water... 

SORT The problem gives the volume of gas collected over water as well as the temperature and the pressure. You are to find the mass in grams of oxygen that forms. 

The zinc within a copper-plated penny will dissolve in hydrochloric acid if the copper coating is filed down in several spots (so that the hydrochloric acid can get to the zinc). The reaction between the acid and the zinc is 2H (a ) -t-Zn(s) —> HiCg) + Zn aq). When the zinc in a certain penny dissolves, the total volume of gas collected over water at 25 °C is 0.951 L at a total pressure of 748 mmHg. What mass of hydrogen gas is collected ... 

Calculate the moles of gas collected over water in a 600 mL container at 756 mmHg pressure at 20°C given that the vapor pressure of water is 2.3388 kPa at 20°C. 

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