Material Safety Data Sheet User's Guide

7. Caractéristiques physiques

This section of the MSDS describes the physicochemical characteristics of a substance based on current scientific knowledge.

	Molecular formula *	Boiling point
	Molecular weight *	Vapour pressure
	Physical state	Concentration at saturation *
	Appearance	Vapour density
	Colour and odour	Evaporation rate
	Odour threshold	Cśfficient of water/oil distribution
	Density	pH
	Freezing point	Solubility in water at saturation *
	Melting point *	Particle size *

*Non-essential information for WHMIS purposes

---

Molecular formula

The molecular formula describes, using their symbols, the elements that make up a substance, and indicates their proportion. Pure substances are the only ones with a definite molecular formula.

Water: H2O Toluene : C7H8

Molecular weight

This is the weight in grams of a fixed quantity of molecules of a chemical product. The molecular weight is defined only for pure chemical substances.

Toluene : 92.15 g

Physical state

This is the form or state in which the product is present: gas, liquid or solid at ambient temperature (20°C) and at normal atmospheric pressure (760 mm Hg (101.32 kPa)).

Solid: lime Liquid: water Gas: oxygen

Appearence

This subsection provides specific information on the product or presents additional information on the product’s physical state or appearance.

If the product is solid, it can be crystalline, granular, powdery, etc. If it is liquid, it can be viscous, gelatinous, oily, etc.

Colour and odour

These are some of the product’s physical characteristics. A product can have a specific colour or be colourless. It may have a characteristic and distinctive odour or be odourless. The odour of some products may be detected, starting at a certain concentration, namely the odour threshold.

Colour: gray: copper sulfate colourless: water	Odour: aromatic: toluene characteristic: chloroform

Odour threshold

This is the minimum concentration of a substance likely to be detected in the air by human smell. It is usually expressed in parts per million (ppm).

Ammonia can be detected at 17 ppm.

Density

Density is a physicochemical property related to the weight of a substance. It represents the weight of a substance per unit volume and is expressed in grams per millilitre (g/ml) at 20°C. Specific gravity is also a physicochemical property that is commonly used instead of density. However, it is a relative value that indicates how many times heavier than water the product is. If the density of a product that is rather insoluble in water is less than 1 g/ml, the product will float. However, if it is greater than 1 g/ml, the product will sink. This information is useful in predicting the behaviour of a product in the event of a leak or accident.

Toluene is not very soluble in water. Its density is 0.8661 g/ml, therefore less than 1, so it floats on water.

Freezing point

This is the temperature at which a substance goes from the liquid state to the solid state at normal atmospheric pressure (760 mm Hg (101.32 kPa)). The freezing point of a pure substance is the same as its melting point.

Water crystallizes at 0°C.

Melting point

This is the temperature at which a substance goes from the solid state to the liquid state at normal atmospheric pressure (760 mm Hg (101.32 kPa)).

Ice melts at 0°C.

Boiling point

This is the temperature at which a substance goes from the liquid state to the gaseous state at normal atmospheric pressure (760 mm Hg (101.32 kPa)).

Water boils at 100°C.

Vapour pressure

When a substance evaporates, its vapours exert pressure in the ambient environment. Vapour pressure is expressed in millimetres of mercury (mm Hg) or in kilopascals (kPa) at 20°C and normal atmospheric pressure of 760 mm Hg (101.32 kPa). A vapour pressure greater than 760 mm Hg (101.32 kPa) indicates that the substance is in the gaseous state. The higher a substance’s vapour pressure, the more it tends to evaporate.

The vapour pressure of water is 17.5 mm Hg (2.33 kPa) and that of diethyl ether, 439.8 mm Hg (58.63 kPa). Therefore, diethyl ether evaporates faster than water.

Concentration at saturation

This is the maximum concentration that a substance can reach in the air at equilibrium, 20°C and normal atmospheric pressure of 760 mm Hg (101.32 kPa).

Toluene has a concentration at saturation of 28,800 ppm.

Vapour density

This information indicates how many times the vapours of a substance are heavier or lighter than air (air = 1). This measurement is taken at the boiling point.

If the vapour density is greater than 1, a substance’s vapours will tend to remain near the ground.

Toluene has a vapour density of 3.18. Therefore, at its boiling point, its vapours will tend to remain at the ground. Methyl alcohol has a vapour density of 1.1. Therefore at its boiling point, its vapours will mix easily with air, since its vapour density is close to 1.
Note. The behaviour of vapours is valid only for a rather short period of time and at a temperature close to the boiling point. The vapours given off by a boiling substance disperse into the air over time. The tendency of vapours to remain close to the ground decreases as the difference between the ambient temperature and the boiling point increases.

Evaporation rate

The evaporation rate indicates the relationship between the time that a product takes to evaporate and the time that a reference product takes to evaporate. It indicates, at equal volume, how many times longer a product takes to evaporate than another. The rate varies with the type of product and the temperature. Diethyl ether, for example, is the reference product on which the most data is available.

Toluene’s evaporation rate is 4.5 in relation to that of diethyl ether. Therefore, toluene takes 4.5 times longer than diethyl ether to evaporate.
Note. There are other reference products, such as n-butyl acetate, which are used to establish an evaporation rate. There are also other ways of establishing the evaporation rate. One of the methods used consists of determining, for the same period, the ratio of the volumes of the target product and reference product that evaporated. Another method consists of determining, for the same initial volume of liquid, the ratio of the percentages of the target product and reference product that evaporated. Unfortunately, sometimes a value is given without the method used being indicated.

Cśfficient of water/oil distribution

This is the ratio of the solubility of a product in oil to its solubility in water when they are brought into contact with the product.

A value below 1 indicates a better solubility of the product in oils and greases. The product is therefore likely to be absorbed by the skin. However, a value greater than 1 indicates a better solubility in water. This product could therefore be absorbed by the mucous membranes. This information can be useful in evaluating the first aid to be given and can facilitate the choice of protective equipment.

Toluene has a coefficient of water/oil distribution of 0.0026. Therefore, toluene is more soluble in oil than in water with a value of 0.0026 g in water to 1 g in oil.
Note. On some material safety data sheets, the distribution coefficient is expressed as log Pow, therefore as the logarithm of the n-octanol/water partition coefficient. n-Octanol is in fact the reference substance that is closest to oil. The method for converting log Pow into the coefficient of water/oil distribution is described in the Conversion factors section of this guide.

pH

The pH, expressed as a numerical value, indicates whether a solution is acidic or basic. Water is neutral and has a pH of 7. Acids have a pH below 7, and the lower the value, the stronger the acid. Bases have a pH greater than 7, and the higher the value, the stronger the base.

Vinegar (acid): pH = 2.1 27-30% Ammonium hydroxide (base): pH = 12.3
Note. For regulation purposes, particularly WHMIS, a substance is considered corrosive if its pH is equal to or less than 2 or equal to or greater than 11.5. However, tests carried out on animals that prove that the substance is not corrosive predominate over the pH value.

Solubility in water at saturation

This is the maximum amount of a product that can be dissolved in water. It is expressed in grams per litre at a temperature of 20°C. If the solubility is not precisely known, the product is called, for example, “insoluble”, “slightly soluble” or “very soluble”. A liquid that mixes perfectly with water to form a single phase is called “miscible”.

Particle size

The particle size indicates the size of the particles forming a powder, a dust, a mist, an aerosol or fumes. Particles smaller than 1µm* can penetrate deeply into the respiratory tract and deposit in the alveoli. Slightly larger particles (from 1 to 5 µm) reach the trachea, bronchi and bronchioles. Larger particles (from 5 to 30 µm) reach the nose and pharynx region. Even larger particles (larger than 30 µm) rarely penetrate the upper respiratory tract. Depending on the substance, they may dissolve and be absorbed by the body. Therefore, by knowing the size of the particles of a substance, one can decide on the corrective measures to adopt to reduce or eliminate the hazard at source (for example, by planning for local ventilation). If it is impossible to reduce or eliminate the hazard at source, knowledge of the particle size will make it easier to choose the respiratory protection device. *1 µm (micron) represents 10-6 metres (0.000001 metre) or 10-3 millimetres (0.001 mm). For example, 1 µm is approximately 1,000 times smaller than a grain of sand.