The most important thing to understand why this happens is to be clear about what a resolution is. A solution is any homogeneous mixture of at least two components. The homogeneity is important, it’s like if we put sugar in water, if particles are in suspension it wouldn’t be a solution. And in a solution, we always have the solvent, which is the medium in which the dispersion or solubilization is done, and the solute that we want to dissolve. In the case of your question, the solvent would be milk and the solute would be instant coffee.
The ability of a solvent to absorb dissolved substances is what we call the solubility of a compound. There are several parameters that affect solubility, that is, the amount of solute that can be dissolved in the solvent. The first is the type of solute, for example dissolving instant coffee is not the same as dissolving pure cocoa. The properties of the compound that acts as a solute affect its solubility. But there are other parameters that affect it, such as temperature or pressure.
From experience we know that it is much easier to dissolve coffee in hot milk than in cold milk. In fact, in order to disperse or solubilize, we must favor the breaking of the bonds (the bonds between the molecules) of the milk, so that its interaction with the coffee molecules is easier. The higher the temperature, the easier this is to achieve.
We can also facilitate dissolution by giving the solvent the necessary energy to break and make new bonds, as is the case at high temperatures. And we do that through the movement of the spoon. When we move the solvent, we give it an energy contribution that favors the dispersion of the solute in the solvent.
Your perception that instant coffee dissolves better in less milk is correct. And that’s precisely because milk has a great capacity to absorb solutes. That is, coffee has a very high solubility in milk. When we have a small amount of milk and add the coffee, the movement that we make with the spoon is important. With a small amount of milk we can perform this movement more easily than with a full glass, making the molecules move faster and more homogeneously. And in this case it is not a limitation that the amount of milk is small because we would still be below the solubility of the solute, the coffee.
Pressure doesn’t affect the example you give us in your question since we’re talking about dissolving instant coffee in milk at home, i.e. at atmospheric pressure. In order for it to have an appreciable effect on solubility, higher pressures must be applied. But the effect of pressure on solubility can be seen at home in a bottle of carbonated soda. A large part of the gas is dissolved because it has pressure, if we remove that pressure by opening the bottle, the gas escapes. When we leave a bottle open we say it has lost the gas and that is because it has lost the pressure it needs for the gas to continue dissolving in the liquid.
Noelia Caballero Homemade She is a PhD chemist and researcher in the Department of Analytical Chemistry at the University of Cordoba.
Question sent by María Vei Pe.
Coordination and writing: Victoria Bull.
we answer is a weekly scientific advisory session hosted by the Dr. Antoni Esteve Foundation and the L’Oréal-Unesco program “For Women in Science” and answers readers’ questions about science and technology. They are scientists and technologists, members of AMIT (Association of Women Researchers and Technologists) who answer these questions. Send your questions to [email protected] or on Twitter #weanswer.
you can followTHE COUNTRY Health and well-beingon Facebook, Twitter and Instagram.