Definition, Symbol, SI Units, Formula & Measurement of Density

Density is simply mass per unit volume. Density of many samples is measured in labs for example in oil and gas industry. They define density in general way as 'weight per unit volume' although 'weight per unit volume' is not density it is 'Specific Weight' so density is 'mass per unit volume'.

Generally, Hydrometers & Pycnometers are used to measure density of substances.

Example of Density

Don't worry! we will going to learning density in very simple way, with examples.

Do you ever see a dry WOOD piece floating over water in river or pool?

Yes, We all see that, Do you think why it floats. Because density of wood 🪵 is lesser than density of water 💧 so piece of 🪵 wood experience upthrust force and float on water 💧.

Take another example of Iron Metal piece and water. IRON METAL piece has higher density than WATER, so piece of iron metal sink in water.

To understand clearly, we will take another example of 'Sunflower Cooking oil' & 'Water'. When we mix 'Sunflower Cooking oil' & 'Water', after some time oil comes at top and water set below (means separate out). So now question is why this happens? Answer is due to difference in density & nature of water and oil. Oil is nonpolar while water is polar molecule so they don’t interact with each other.

Density of Sunflower Cooking oil is 919 Kg/m3

Density of Water is 1000 kg/m3

What is Density in Chemistry

In science/chemistry, density of a substance is its mass per unit volume. Density is also known as "Volumetric Mass Density".

Generally different materials have different density. Chemical element Osmium (Os having atomic number 76) is naturally occurring densest element. To simplify the comparison of densities of different materials or liquids it is needed to replace density with "relative density" as relative density is dimensionless quantity. Relative Density is also called "Specific Gravity".

Specific gravity or relative density is the ratio of density of sample material to the density of standard material. Generally, water is taken as standard material. If we take water as standard material than if we get relative density of a material is less than '1' means that material floats in water. Water has highest density at 4 °C i.e. 1000Kg/m³.

Density of material depends on the temperature and pressure. Effect of temperature and pressure is very less on solid and liquid but effect of temperature and pressure is very high on gases. If we increase pressure on given material than its volume get decrease that result in increase in density, similarly If we decrease pressure on given material than its volume get increase that result in decrease in density.

And in case of temperature, if we increase temperature on given material than its volume get increase that result in decrease in density, similarly if we decrease temperature on given material than its volume get decrease that result in increase in density.

But there are some exceptions which do not follow these rules, one of them is water means when temperature of water decreases than it makes solid ice which float on liquid water as ice have less density than liquid water i.e. Density of ice is 916.7 Kg/m³ at 0 °C, and water has a density of 999.8 Kg/m³ at 0 °C.

Definition of Density

Density of a material is defined as its mass per unit volume.

Symbol of Density

Symbol of density is 'ρ' or 'D' and pronounces as 'rho'.

Formula of Density

Density = Mass/Volume

or,

ρ = m/V

where,

ρ is density, m is mass and V is volume.

When numerator (mass) is much larger than denominator (volume) in density formula, that shows the given substance has higher density, but when denominator (volume) is much larger than the numerator (mass), that shows the given substance has lower density.

SI Unit of Density

SI Unit of Density is Kg/m³or g/cm³

Density Calculator

Density is calculated by dividing mass by volume. Density is measured as units of mass/volume, often g/cm3, g/Kg3 or g/mL.

Instruments used to measure Density

Weighing balance, Scale, Hydrometer and Thermometer are some instruments used to measure the density of solids & liquids.

Measurement.

Methods of Measuring Density

There are several methods for measuring the density of substances like solids, liquids and gases. We will learn about different methods of measurements of density below.

Methods of measuring density of solids

Measuring the density of solids is essential in various research, scientific, industrial, and engineering applications. There are several methods for determining the density of solids, depending on factors such as the size, shape, and properties of the material.

Here are some common methods for measuring the density of solids:

1. Direct Measurement of Mass and Volume:

1.1 Water Displacement Method: This method is suitable for irregularly shaped solids. Submerge the solid in a container filled with water and measure the volume of water displaced. Then, weigh the solid and use the formula:

Density = Mass / Volume.

1.2 Archimedes' Principle: Submerge the solid in a fluid (usually water) and measure the buoyant force acting on it. Archimedes' principle states that the buoyant force is equal to the weight of the displaced fluid. You can calculate the density of the solid using the formula:

Density = Mass of Solid / (Mass of Solid - Apparent Loss of Weight in Water).

2. Geometric Methods:

2.1 Caliper and Balance Method: For regularly shaped objects with well-defined geometric dimensions, measure the dimensions (length, width, height) using calipers or a ruler and calculate the volume. Then, measure the mass using a balance and use the formula:

Density = Mass / Volume.

2.2 Micrometer or Vernier Caliper Method: For very small objects or objects with intricate shapes, use precise measuring instruments like micrometers or vernier calipers to measure dimensions and calculate volume and density.

3. Gas Pycnometry:

This method involves using a gas pycnometer instrument, which measures the volume of a solid by filling a chamber with a known volume of gas and then placing the solid inside. The change in pressure is used to calculate the volume and subsequently the density.

4. X-ray or Gamma Ray Attenuation:

Density can be measured by passing X-rays or gamma rays through a solid and measuring the attenuation (absorption) of the radiation. This is often used in industrial settings for quality control and non-destructive testing.

5. Archimedes' Water Filling Method:

For objects with irregular shapes or complex geometries, the object is submerged in a container of water, and the change in water level is measured. This method is particularly useful for determining the density of porous materials.

6. Hydrostatic Balance:

This involves suspending the solid from a balance and immersing it in a fluid. The density is calculated by measuring the buoyant force on the solid when it's partially submerged.

7. Ultrasound Velocity Measurement:

Ultrasound can be used to measure the velocity of sound through a solid. The density can then be calculated using the material's known elastic properties.

8. Nuclear Methods:

Techniques like gamma-ray or neutron activation analysis can be used to determine the density of certain materials.

The choice of method depends on the nature of the solid, its size and shape, the required precision, and the available equipment. It's important to select the most appropriate method based on these factors to obtain accurate density measurements.

Methods of measuring density of liquids

Measuring the density of liquids is an important task in various research, scientific, industrial, and laboratory applications. There are several methods for determining the density of liquids, each with its own advantages and suitable scenarios. Here are some common methods for measuring the density of liquids:

1. Hydrometer Method:

Floating Hydrometer: A hydrometer is an instrument that floats in the liquid. The depth to which it sinks is proportional to the liquid's density. Hydrometers are often used to measure the density of liquids like water, alcohol, and various solutions. Different types of hydrometers are available for specific applications.

2. Pycnometer Method:

Glass Pycnometer: A glass pycnometer is a container with a known volume. To measure density, you weigh the empty pycnometer, fill it with the liquid, and weigh it again. The difference in weight, combined with the known volume, allows you to calculate the density of the liquid accurately.

3. Digital Density Meters:

Digital Density Meter (Densitometer): These modern instruments use various principles, such as oscillation, sound velocity, or refractive index, to measure the density of liquids quickly and accurately. They provide highly precise results and are commonly used in laboratories and industrial settings.

4. Buoyancy Method:

Archimedes' Principle: Submerge a solid object of known volume in the liquid and measure the apparent loss of weight. Using Archimedes' principle, you can calculate the density of the liquid by comparing the weight of the displaced liquid with the weight of the solid.

5. Ultrasonic Density Measurement:

Ultrasonic Density Meter: Ultrasonic devices send ultrasonic waves through the liquid and measure the time it takes for the waves to travel through the liquid. The density can be calculated using the speed of sound in the liquid and the time of flight of the ultrasonic waves.

6. Nuclear Magnetic Resonance (NMR):

NMR Spectroscopy: NMR can be used to measure the density of liquids by examining the resonant frequencies of atomic nuclei in the liquid. It is a powerful technique for analysing the chemical composition and density of liquids.

7. X-ray Absorption:

X-ray Absorption Spectroscopy: X-ray absorption spectroscopy can be used to measure the density of liquids by examining the attenuation of X-rays as they pass through the liquid. This method is especially useful for non-destructive testing and studying the composition of liquids.

8. Burette and Pycnometer Method:

Burette and Pycnometer Technique: A precise volume of liquid is dispensed from a burette into a pycnometer, and the change in mass is measured. By dividing the mass by the volume, you can calculate the liquid's density.

9. Pressure-Volume-Temperature (PVT) Analysis:

PVT Analysis: In this method, the density is calculated based on the measurement of pressure, volume, and temperature changes of the liquid.

The choice of method depends on factors such as the precision required, the nature of the liquid (e.g., corrosive, viscous, opaque), and the equipment available. Each method has its advantages and limitations, so it's important to select the most appropriate one for your specific needs.

Methods of measuring density of gases

Measuring the density of gases is essential in various scientific, industrial, and engineering applications. There are several methods for determining the density of gases, each suited to different scenarios and levels of precision. Here are some common methods for measuring the density of gases:

1. Manometer Method:

U-Tube Manometer: A U-tube manometer measures the pressure difference between the gas and a reference column of liquid (usually mercury or a water-glycerol mixture). By knowing the pressure difference and the properties of the liquid, you can calculate the gas density using the ideal gas law.

2. Gas Pycnometer:

Gas Pycnometer or Helium Pycnometer: This method measures the volume of a known mass of the gas (usually helium) at a known pressure and temperature. By using the ideal gas law, you can calculate the gas density. This method is particularly useful for measuring the density of gases at high pressures.

3. Gravimetric Method:

Gravimetric Method: In this method, a known volume of gas is collected and weighed. By dividing the weight by the volume and considering the temperature and pressure, you can determine the gas density.

4. Vibrating Tube Method:

Vibrating Tube Densitometer: A vibrating tube densitometer measures the natural frequency of a vibrating tube when empty and when filled with the gas of interest. The change in frequency is used to calculate the gas density.

5. Buoyancy Method:

Buoyancy Method: This method involves immersing a solid object in the gas whose density you want to measure. The buoyant force acting on the object can be used to calculate the gas density using Archimedes' principle.

6. Capillary Tube Method:

Capillary Tube Method: In this method, gas flows through a capillary tube, and the rate of flow is measured. By knowing the pressure, temperature, and the properties of the gas, you can calculate the gas density.

7. Sonic Velocity Method:

Sonic Velocity Method: The speed of sound in a gas is related to its density. By measuring the speed of sound in the gas and knowing other parameters such as temperature and pressure, you can determine the gas density.

8. Interferometry:

Interferometry: Interferometers can be used to measure changes in the refractive index of a gas, which is related to its density. This method is highly sensitive and can be used for precise density measurements.

9. Radiation Attenuation:

Radiation Attenuation: Similar to X-ray or gamma-ray attenuation for solids and liquids, this method involves passing radiation (e.g., X-rays or gamma rays) through the gas and measuring the attenuation to determine the gas density.

The choice of method depends on factors such as the type of gas, the range of pressures and temperatures involved, the required precision, and the available equipment. It's essential to select the most appropriate method based on these factors to obtain accurate gas density measurements.

Now we will learn about some basic questions aksed about densiy:

What is Density of water

The density of water at standard atmospheric conditions (1 atmosphere of pressure and 0 degrees Celsius or 32 degrees Fahrenheit) is approximately 0.998 grams per cubic centimeter (g/cm³) or 998 kilograms per cubic meter (kg/m³).

However, the density of water can vary with changes in temperature and pressure. Water is most dense at around 4 degrees Celsius (39.2 degrees Fahrenheit), where its density is approximately 1.000 g/cm³ or 1000 kg/m³. As water is cooled from higher temperatures, it becomes denser until it reaches this point. When water is cooled below 4 degrees Celsius or heated beyond this point, it becomes less dense.

It's important to note that the density of water can also be affected by impurities or the presence of dissolved substances, which can alter its density slightly from the values mentioned above.

What is hydrometer and what is its use and how it works?

A hydrometer is an instrument used to measure the relative density or specific gravity of liquids, primarily in comparison to the density of water. It's a commonly used device in various industries, including chemistry, brewing, winemaking, and petrochemicals.

Hydrometers are especially valuable for assessing the concentration of solutes in solutions and for determining the proof or alcohol content of alcoholic beverages.

Structure of a Hydrometer:

A typical hydrometer consists of a thin, cylindrical glass tube with a weighted bulb at one end. The tube is sealed and graduated with a scale, often calibrated in specific gravity units or potential alcohol content (for alcoholic beverages).

Some hydrometers may also have additional scales to measure properties like Brix (for sugar concentration in solutions).

How a Hydrometer Works:

The operation of a hydrometer is based on Archimedes' principle, which states that an object submerged in a fluid experience an upward buoyant force equal to the weight of the fluid it displaces.

Here's how a hydrometer works:

1. Preparation: To use a hydrometer, you first need to fill a container (usually a graduated cylinder or a sample jar) with the liquid whose density you want to measure. Ensure that the hydrometer and the liquid are at the same temperature to avoid temperature-related errors.

2. Submersion: Gently place the hydrometer into the liquid, making sure it floats freely without touching the sides of the container. Allow it to come to rest.

3. Reading the Scale: Read the value on the hydrometer scale at the liquid's surface level. This reading corresponds to the relative density or specific gravity of the liquid.

If using a specific gravity scale, water has a specific gravity of 1.000 at standard conditions (e.g., 20°C or 68°F), so any reading above 1.000 indicates a denser liquid than water, while a reading below 1.000 indicates a less dense liquid.

If using a potential alcohol scale, it provides information about the alcohol content in the liquid, typically in percentage by volume.

Applications of Hydrometers:

Hydrometers have various applications, including:

1. Determination of Alcohol Content: In the production of alcoholic beverages, hydrometers are used to measure the sugar content of the initial solution (e.g., grape juice) and the alcohol content of the final product.

2. Quality Control in Industrial Processes: Industries such as petrochemicals, food and beverage, and pharmaceuticals use hydrometers to monitor the concentration of substances in their processes.

3. Chemical Analysis: In chemistry laboratories, hydrometers help analyze the density of chemical solutions, which can be crucial for precise reactions and experiments.

4. Battery Testing: In the automotive industry, hydrometers are used to check the specific gravity of battery electrolytes, helping assess battery health.

5. Oil and Petroleum Industry: Hydrometers are employed to determine the density of crude oil, helping classify and measure the petroleum product.

6. Brewing and Winemaking: Brewers and winemakers use hydrometers to monitor the fermentation process and to calculate alcohol content.

Hydrometers are valuable tools for quick and simple density measurements, and they come in various types and designs to suit different applications and liquid types.

What is pycnometer and what is its use and how it works?

A pycnometer is a specialized laboratory instrument used for accurately measuring the density of a substance, whether it's a liquid or a solid. It is particularly useful for measuring the density of liquids and small solid samples with irregular shapes or those that cannot be measured easily by other methods. The name "pycnometer" comes from the Greek words "pykno" (meaning dense) and "meter" (meaning measure).

Structure and Design of pycnometer:

A typical pycnometer consists of a small glass container with a known and precisely calibrated volume. The container often has a narrow neck and a ground glass stopper to ensure an airtight seal. The pycnometer is usually made of high-quality borosilicate glass to minimize interactions between the glass and the substance being measured.

How a Pycnometer Works:

The principle behind the operation of a pycnometer is straightforward:

1. Sample Weighing: To begin, you first weigh the empty pycnometer using a precise balance.

2. Filling with Liquid or Solid: Next, you fill the pycnometer with the substance whose density you want to measure. Depending on whether you're measuring a liquid or a solid, you can either fill it with the liquid directly or immerse the solid into a suitable liquid (often water or a reference liquid) to displace it.

3. Re-Weighing: After filling the pycnometer with the sample, you re-weigh it. This provides the combined mass of the pycnometer and the sample.

4. Calculating Density: With the volume of the pycnometer (known from its calibration) and the combined mass of the pycnometer and the sample, you can calculate the density of the substance using the formula:

Density = (Mass of Sample + Mass of Pycnometer with Sample - Mass of Empty Pycnometer) / Volume of Pycnometer

The density is typically expressed in units like grams per cubic centimeter (g/cm³) or kilograms per cubic meter (kg/m³), depending on the units of mass and volume used.

Applications of Pycnometers:

Pycnometers have various applications in scientific research, quality control, and material testing, including:

1. Determination of Liquid Densities: Pycnometers are commonly used to measure the densities of liquids accurately. This is important in fields such as chemistry, petrochemistry, and material science.

2. Solid Density Measurements: Pycnometers can also be used to measure the density of solid samples, especially when their shapes are irregular or when they are porous.

3. Quality Control: Industries such as pharmaceuticals, food, and cosmetics use pycnometers for quality control and compliance with standards.

4. Material Characterization: Researchers use pycnometers to study the properties of materials, including polymers, ceramics, and composites.

5. Archaeological and Geological Studies: Pycnometers are employed in the determination of the density of archaeological artifacts, geological samples, and rocks.

Overall, pycnometers are valuable tools for precise density measurements, particularly when the substance being measured may not conform easily to other measurement methods or when high accuracy is required.

Sinker method of density measurements

The sinker method is a laboratory technique used to measure the density of liquids. This method is particularly suitable for opaque, viscous, or corrosive liquids that may not be easily measured using other techniques like hydrometers or pycnometers.

It involves immersing a solid object, known as the sinker, into the liquid of interest and measuring the buoyant force experienced by the sinker. The density of the liquid can then be calculated based on Archimedes' principle.

Here's how the sinker method works:

1. Selection of Sinker:

Choose a solid object, known as the sinker, with a well-defined and known volume. The sinker should be made of a material that is not affected by the liquid and should be denser than the liquid to ensure it sinks.

2. Weighing the Sinker:

Weigh the sinker accurately using a precise balance.

3. Immersion in the Liquid:

Submerge the sinker into the liquid whose density you want to measure. Ensure that the sinker is fully immersed and free from any air bubbles.

4. Measuring the Apparent Loss of Weight:

When the sinker is immersed in the liquid, it experiences an upward buoyant force that partially counteracts its weight. This results in an apparent loss of weight compared to when the sinker is in air. Measure this apparent loss of weight using the balance.

5. Calculating the Liquid Density:

Using Archimedes' principle, you can calculate the density of the liquid with the following formula:

Density of Liquid = Density of Sinker × [(Weight in Air - Apparent Loss of Weight) / Weight in Air]

Here, the density of the sinker is known, and the weight in air is the initial weight of the sinker before immersion.

6. Correcting for Temperature and Pressure (if necessary):

Depending on the experiment's conditions, you may need to correct the density calculation for temperature and pressure variations. The ideal gas law or other relevant equations may be used for this purpose.

The sinker method is versatile and can be applied to a wide range of liquids and sinker shapes, making it a valuable technique in various scientific and industrial applications, including the study of liquids' properties, quality control, and materials testing.

It is especially useful when you need to measure the density of liquids that are not suitable for other common methods like hydrometry or pycnometry.

Hydrometer

Hydrometer dip in mineral oil and engine oil to measure the Density of these samples

Density Chart
Material	Density (Kg/m³)	Remark
Air	1.2	At sea level
Milk	1027 to 1033	At 20 ^oC
Honey	1420	At 20 ^oC
Coconut Oil	925	At 15 ^oC
Cotton Seed Oil	926	At 16 ^oC
Olive Oil	918	At 15 ^oC
Sunflower Oil	919	At 20 ^oC
Rice Bran Oil	918	At 20 ^oC
Groundnut Oil	913	At 20 ^oC
Liquid Hydrogen	70	At about -255 ^oC
Ice	916.7	At 0^oC
Fresh Water	1000	At 4^oC
Plastics	1175	Approx for PVC
Glycerol	1261	Also called Glycerine or Glycerin
Aluminium	2700	Chief ore of Aluminium is Bauxite
Diamond	3500	Precious stone
Zinc	7000	Zinc is found in cells throughout the body.
Iron	7870	Used since ancient times
Cobalt	8900	Found in the Earth's crust only in chemically combined form
Nickel	8900	Silvery-white lustrous metal
copper	8940	Very high thermal and electrical conductivity
Silver	10500	Highest electrical conductivity, thermal conductivity
Lead	11340	Soft, malleable, and heavy metal
Mercury	13546	Only metallic element that is liquid at room temperature
Uranium	18800	weakly radioactive because all its isotopes are unstable
Iridium	22420	Densest naturally occurring element
Osmium	22570	Densest naturally occurring element

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What is Density in Chemistry - Definition, Symbol, SI Units, Formula & Measurement of Density