Milk is a nutrient-rich liquid produced by mammals through their mammary glands. Milk is the primary source of nourishment for the infants before they can digest solid foods, and it boosts the immune system and prevents several diseases.
In chemistry, we classify milk as a mixture - a mixture is a combination of two or more substances in an unspecified ratio. This leads to whether milk is a homogeneous mixture or a heterogeneous mixture.
So is milk a homogeneous mixture?Milk is a heterogeneous mixture that appears homogeneous by nature. Viewed under a microscope, milk appears to contain tiny globules of fats and proteins dispersed in a water-based liquid. Although milk appears to be a homogeneous mixture to the naked eye, the fact remains that the fat globules cannot be dissolved in water and remain suspended in the mixture, which is why we say milk is a heterogeneous mixture.
Let's see why we say milk is a heterogeneous mixture and not homogeneous, even though the mixture appears to be evenly distributed throughout.
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Why is milk a heterogeneous mixture?
When we look at milk with the naked eye, we cannot distinguish the components of milk.
Therefore, to an ordinary man, milk could seem like a homogeneous mixture, the components of which are evenly distributed throughout its composition.
But when observed under a microscope we can see insoluble tiny globules of fats and proteins suspended in the liquid, i. H. water.
We know that water and fat are insoluble when mixed together and therefore cannot form a solution, which is why two distinct, immiscible liquid phases occur, and therefore milk is inherently heterogeneous.
We often observe cream settling on top of the milk due to the settling of heavier fat particles, but primarily the insoluble particles do not settle and remain dispersed.
This clearly shows that milk appears to be a homogeneous mixture while it is heterogeneous.
First, let's learn what a mixture is...
What is a mix?
A mixture is a substance consisting of two or more forms of substance in any proportion that can be separated into its component parts by physical means.
When a mixture of two or more substances is made, there is no chemical reaction, so the components of the mixture can be separated again.
A mixture of salt and water, sugar and water, a mixture of gases are some examples of mixtures.
Although the composition of the components of a mixture remains unchanged, the properties of the mixture are found to be different compared to its components.
For example, when water is mixed with alcohol, the properties of the mixture, such as melting and boiling points, do not match any of its components.
Mixtures can be solids, liquids and gases.
Properties of mixtures
1. The components of the mixtures can be easily separated physically.
2. The components are mixed in variable proportions.
3. The properties of the components do not change even when mixed, although the mixture has different properties than its components.
types of mixtures
The mixtures can be divided into two main categories:
●Homogeneous mixtures
● Heterogeneous mixtures
A homogeneous mixture: A mixture in which all components are evenly distributed is called a homogeneous mixture.
Such mixtures are only single-phase and the components of the mixtures cannot be physically separated.
For example, saline solution, sugar solution, air - a mixture of gases, etc.
heterogeneous mixture: Heterogeneous mixtures are those that do not have a uniform composition throughout the mixture.
These mixtures have two or more phases and the components of the mixture are identifiable to the naked eye.
For example soil-sand mixture, sulfur and iron filings, oil and water, etc.
Properties of the homogeneous and heterogeneous mixture
Now that we understand what homogeneous and heterogeneous mixtures are, let's examine the properties of two types of mixtures.
Properties of homogeneous mixtures
1. The particles in the mixture are evenly distributed and therefore the components cannot be seen with the naked eye.
2. The particles in the homogeneous mixtures have the same physical properties in solution.
3. In a homogeneous mixture, the size of the components is usually very small, i.e. at the molecular or atomic level, the particles are usually less than 1 nm in size.
4. Such mixtures can be separated into their respective components by processes based on the difference in physical properties, such as distillation, crystallization, etc.
5. Homogeneous mixtures show no Tyndall effect; The Tyndall effect is the phenomenon of light scattering by the particles of a mixture when a beam of light is shined on them.
Properties of heterogeneous mixtures
1. In heterogeneous mixtures, the components are not evenly distributed, so they can be seen with the naked eye.
2. The constituent particles do not have the same properties in the mixture.
3. The components of heterogeneous mixtures are generally large, which is why they can be separated by simple physical methods such as filtration, sieving, etc.
4. Heterogeneous mixtures show a Tyndall effect, the light beam directed at the mixture is scattered by the particles due to their larger size.
Is milk a colloid or a suspension?
Before knowing whether milk is a colloid or a suspension, let's first understand the further classification of mixtures depending on the size of the components in the mixture.
• Solutions
A solution is a homogeneous mixture in which one substance dissolves (solute) in another (solvent).
The size of particles in a solution is less than 1nm, which are not visible to the naked eye and cannot be easily separated.
The solute is called the dispersed phase and the solvent in which it is dissolved is the dispersion medium.
For example, a salt mixture dissolved in water is a solution because the particles are too small to be visible and easily separable.
• Colloid
Colloids are heterogeneous mixtures in which medium-sized insoluble particles are suspended in another substance.
These insoluble particles do not settle over time. The particle size in colloids is between 1 nm and 0.1 microns.
These appear similar to solutions, but unlike solutions, the particles are suspended rather than fully dissolved.
An example of colloids is colored gelatin, where the particles are suspended in the mixture that gives the gelatin color while the particles are too small to settle.
You may have noticed that it is very difficult to see through the smoke during a fire. The reason for this is the same as that of a colloid composed of suspended particles.
Check out the articleis smoke colloid.
• Lock out
A suspension is a heterogeneous mixture containing large particles that are visible and can settle over time and be filtered.
The particles are not dissolved in the mixture but dispersed. The particle size is between 1 and 50 microns in diameter.
A mixture of sand in water is an example of a suspension, the sand will disperse in the water as it mixes, but will settle if left untouched.
The image below shows the 3 types of blends and their relative sizes:
The figure below shows the Tyndall effect through the three types of mixtures.
Now let's see if milk is a colloid or a suspension...
Milk is a colloidal mixture of tiny butterfat globules (fats and proteins) suspended in a liquid that does not settle on standing due to charged particles. The charged particles repel each other to avoid gathering into large particles that would settle unaffected if they settled.
Milk is an example of an emulsion, i. H. when liquid particles are dispersed in a liquid medium, the colloid is called an emulsion.
What is milk made of?
Now that we know milk is a heterogeneous mixture, let's see what milk is made of?
Milk is an emulsion or colloidal mixture that contains globules of butterfat in a water-based liquid. The fluid is a dissolved mixture of carbohydrates and proteins and contains minerals.
The main components are water, fats, carbohydrates (lactose), proteins and minerals.
In addition, milk contains various other micronutrients such as amino acids, vitamins and trace elements. About 250 compounds are found in a milk sample.
The pH of milk is usually between 6.4 and 6.8.
Diploma
At the end of this article we can conclude that milk is a heterogeneous mixture with the fat globules suspended in the water-based liquid.
Milk may appear homogeneous but is actually a heterogeneous mixture in which the particles are insoluble and not evenly distributed throughout the mixture.
In addition, milk is classified as a colloid in which the insoluble particles in the untouched state do not settle and remain in the mixture for a long period of time. Milk is also a type of emulsion as liquid particles are dispersed in a liquid medium.