Molar Volume Of Hydrogen

CHEMISTRY PRACTICE REPORT Activity III

“Molar Volume of Hydrogen Gas” November, 10, 2008

Name : 1. Ni Made Dewi Pitaloka (X.4/19) 2. Rahadyana Muslichah (X.4/20) 3. Riesfita N. Maharani Firdaus (X.4/21) SMAN 3 Yogyakarta 2008

Activity III

MOLAR VOLUME OF HYDROGEN GAS A. Aim Determine the volume of Hydrogen gas from reaction of magnesium and hydrochloric acid. We measure the volume, temperature, and pressure of hydrogen gas. The data results are used for calculating the volume of 1 mol H

²

at 0°C and 1 atm

pressure.

B. Basic Theory For a specific amount of any ideal gas, the relation between the pressure of the gas, P, its volume, V, its temperature, T, and its number of moles, n, is given by the ideal gas law :

PV = nRT Here R is the proportionality constant, called the gas constant, and it has the same value for all ideal gases under all conditions, namely, 0.08206 L·atm/mol·K. In all calculations in which this constant is employed, pressure must be expressed in atmospheres, volume in liters, and temperature in Kelvins. Standard conditions are defined as exactly 1 atm pressure and 0°C (273 K). The molar volume of a gas is the volume that 1.000 mol of it occupies under these conditions. It is the same for all ideal gases :

V=

nRT

=

22.414 L In this experiment, we will produce hydrogen gas, H , by ² reacting magnesium with hydrochloric acid according to the following equation :

Mg + 2 HCI → MgCl² + H² we will assume the hydrogen is an ideal gas, and we will measure its mass, volume, temperature, and pressure. From these measured values, we will calculate the molar volume of hydrogen and compare the result with the ideal value above.

C. Apparatus 1. Measuring glass (cylinder) 2. Water 3. Thermometer 4. Barometer 5. Magnesium Tape 6. Hydrochloric acid

D. Procedures 1.

Cut the magnesium tape about 7 cm, and weigh its

weight. Twist it with a pencil to make it spiral.

2.

Pour some hydrochloric acid into the measuring glass half

until the half. Fulfill it with some water. Close the glass with a wet paper, and upside down the glass. Do it in a bucket of water. Note : Do first some practice using water. 3.

Add spiral magnesium tape into the measuring glass that

in the upside down position. Notice the hydrogen gas that formed. 4.

After all of the magnesium tape react, let the temperature

down to be room temperature. Note the temperature of water/temperature of the air, the pressure of the air in 1 atm, pressure of steam at the temperature. Arrange the height of cylinder so the surface of liquid in the cylinder as the same as the surface of the water in the bucket. Read and note the volume of the gas in the cylinder (measuring glass).

E. Results 1.

Mass of 7 cm magnesium tape : 0,08 g

2.

Volume of H gas ²

: 75 mL = 0,075 L

3.

Temperature of water/air

: 27°C

4.

Air pressure

: 760 mmHg

5.

Steam pressure

: 26,747 mmHg

6.

H gas pressure ²

: 733, 253 = 0,965 atm

F. Calculating Data 1. Gas in the cylinder consist of H² gas and steam. Look up the pressure of steam in the table.

2. the pressure of H² gas is the total of pressure – pressure of steam = 733,253 mmHg = 0,965 atm

3. Calculate the number of mol of H² gas that formed. 23,96 L 4. The reaction equation :

Mg(s) + 2 HCI(aq) → MgCl²(aq) + H²(g)

G. Tasks 1. Calculate the volume of 1 mol of hydrogen gas that formed at 1 atm pressure.

P1V1 PV = 2 2 TI T2

1atmV 1 0,965 × 0,075 = 289 300 V1 = 0,0718 mol = 0,003

1mol =

0,0718 = 23 ,96 L 0,003

2. Compare the volume of 1 mol of H² (25°C, 1 atm) that formed with the number that grafted in the book. If it’s different, explain it!

3. In the measuring you do, which one is the biggest uncertainty (measuring)? Calculate the percentage of mistake in working!

Mistake =

24 − 23,96 0,04 × 100% = × 100% = 0,17% 24 24

4. What mistake will be happening if the surface of liquid is not being same before measuring the volume? 5.

H. Answer I. Conclusions Hydrogen gas consists of molecules. Hydrogen is gas that has no fixed shape, can easy be compressed and has no fixed volume. It can be able to move anyway in the container.