How to Measure the Density of Gasoline

Measuring the density of gasoline can give you a better understanding of the uses of gasoline for various purposes in different types of engines.

Density of Gasoline

The density of a liquid is the ratio of its mass to volume. Divide the the mass by its volume to calculate it. For example, if you had 1 gram of gasoline that measures 1.33 cm³ in volume, the density would be:\frac{1}{1.33}=0.75\text{ g/cm}^31.331​=0.75 g/cm3

The density of diesel fuel in the United States depends on its class 1D, 2D or 4D. 1D fuel is better for cold weather because it has a lower resistance to flow. 2D fuels are better for warmer outside temperatures. 4D is better for low-speed engines. Their densities, respectively, are 875 kg/m³, 849 kg/m³ and 959 kg/m³. The European density of diesel in kg/m^{3 .}ranges from 820 to 845.

Specific Gravity of Gasoline

Density of gasoline can also be defined using the specific gravity of gasoline. Specific gravity is an object's density compared to the maximum density of water. The maximum density of of water is 1 g/ml at around 4°C. This means, if you know the density in g/ml, that value should be the specific gravity of gasoline.

A third way of calculating density of a gas uses the ideal gas law:PV=nRTPV=nRT

in which ​P​ is pressure, ​V​ is volume, n is the number of moles, ​R​ is the ideal gas constant and ​T​ is temperature of the gas. Rearranging this equation gives you ​nV = P/RT​, in which the left-hand side is a ratio between ​n​ and ​V​.

Using this equation, you can calculate ratio between the number of moles of gas that are available in a quantity of gas and the volume. The number of moles can then be converted to mass using the atomic or molecular weight of the gas particles. Because this method is meant for gases, gasoline in liquid form will deviate much from the results of this equation.

Experimental Density of Gasoline

Weigh a graduated cylinder using a metric scale. Record this amount in grams. Fill the cylinder with 100 ml of gasoline and weigh it in grams with the scale. Subtract the mass of the cylinder from the mass of the cylinder when it contains gasoline. This is the mass of the gasoline. Divide this figure by the volume, 100 ml, to get the density.

Knowing equations for density, specific gravity and the ideal gas law, you can determine how density varies as function of other variables such as temperature, pressure and volume. Making a series of measurements of these quantities lets you find the way density varies as a result of them or how density varies as result of one or two of these three quantities while the other quantity or quantities are held constant. This is often handy for practical applications in which you don't know all the information about every single gas quantity.

Gases in Practice

Keep in mind that equations such as the ideal gas law may work in theory, but, in practice, they don't account for the proper of gases in practice. The ideal gas law doesn't take into account the molecular size and intermolecular attractions of the gas particles.

Because the ideal gas law doesn't account for the sizes of the gas particles, it is less accurate at lower densities of gas. At lower densities, there is greater volume and pressure such that the distances between gas particles becomes much larger than particle size. This makes the particle size less of a deviation from the theoretical calculations.

Intermolecular forces between the gas particles describe the forces caused by differences in charge and structure between the forces. These forces include dispersion forces, forces between the dipoles, or charges, of atoms among the gas particles. These are caused by the electron charges of the atoms depending on how the particles interact with their environment among non-charged particles such as noble gases.

Dipole-dipole forces, on the other hand, are the permanent charges on the atoms and molecules that are used among polar molecules such as formaldehyde. Finally, hydrogen bonds describe a very specific case of dipole-dipole forces in which molecules have hydrogen bonded to oxygen, nitrogen, or fluorine that, due to the difference in polarity between the atoms, are the strongest of these forces and give rise to qualities of water.

Density of Gasoline by Hydrometer

Use a hydrometer as a method of experimentally measuring density. A hydrometer is a device that uses the principle of Archimedes to measure specific gravity. This principle holds that an object floating in a liquid will displace a quantity of water that's equal to the weight of the object. A measured scale on the side of the hydrometer will provide the specific gravity of the liquid.

Fill a clear container with gasoline and carefully place the hydrometer on the surface of the gasoline. Spin the hydrometer to dislodge all of the air bubbles and allow the hydrometer's position on the surface of the gasoline to stabilize. It's essential that the air bubbles be removed because they will increase the buoyancy of the hydrometer.

View the hydrometer so that the surface of the gasoline is at eye level. Record the value associated with the marking at the surface level of the gasoline. You'll need to record the temperature of the gasoline since the specific gravity of a liquid varies with the temperature. Analyze the specific gravity reading.

Gasoline has a specific gravity between 0.71 and 0.77, depending on its precise composition. Aromatic compounds are less dense than aliphatic compounds, so the specific gravity of gasoline can indicate the relative proportion of these compounds in the gasoline.