Why is coffee a mixture and not a pure substance?

Why is coffee a mixture and not a pure substance?

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  1. Coffee is a mixture and not a true solution because it is made by extracting a variety of chemical compounds from coffee beans that have been ground. Unless the filtering of the extracted coffee is perfect, the liquid phase will necessarily contain some of the finer particles (dust) from the grinding operation. These are in soluble in the hot water so what you drink is a mixture of theses ‘fines’ and the solution of extracted compounds.

  2. A pure substance is one in which all of the particles are identical.
    (Actually if you’re being fussy we have to modify that definition a little:
    If a substance is nearly all composed of particle type A but has insignificant amounts of other particles we still call it a pure substance (the threshold for “insignificant” has to be judged on a case-by-case basis).
    Physically speaking salts are composed of at least two types of ions (sodium and chlorine for table salt), however because of the way they’re connected each pair or group of ions is regarded as one particle in many cases, including this definition. So for example table salt is a pure substance with each sodium/chlorine ion pair being loosely regarded as a “molecule” of table salt.
    We also regard the different isotopes (types of a particular element) as being identical for the purposes of this definition since they have the same chemical properties. So for example a gas consisting of 50% helium-3 atoms and 50% helium-4 atoms would still be a pure substance because all the particles are helium atoms.)
    Some examples (including coffee)
    So 100% pure water is a pure substance. It is composed only of water molocules, all of which are identical.
    Real world non-polluted fresh water has some other substances in it, but the vast majority of particles are still water molocules, so for most purposes its fine to regard it as a pure substance.
    Coffee contains a significant number of water molecules, but also has the coffee beans (I think so? I don’t drink the stuff) and whatever else has been added in the way of milk and so forth. So coffee is not a pure substance.
    But how can we use that definition?
    The definition I started with is very good for understanding what a pure substance is, but unless you have magic eyes that can see individual particles connected to a magic brain that can add them up then the definition is difficult to use in a practical sense.
    So in the real world we try and work out if something is a pure substance by seeing if it can be separated. If a substance is not pure it contains more than one type of particle so we should be able to separate the types of particle to make two or more new substances. For example we can separate salt water into salt and water by boiling it.
    Just be careful using that test. An electric current will turn water into hydrogen and oxygen but that doesn’t mean water isn’t a pure substance. That’s because electricity is able to break apart molecules, so the hydrogen and oxygen comes from breaking individual molecules. In other words water molecules consist of hydrogen and oxygen atoms joined together and the molecules are all identical.

  3. You can say coffee is pure because it is a series of compounds solely derived from the coffee bean.
    However chemically coffee is a complex mixture of flavours, hydrocarbons, minerals, moisture, alkaloids and so on.

  4. Q . Why is coffee a mixture and not a pure substance?
    Mixture — a substance made by mixing other substances together.
    A . Coffee is a mixture of two or more coffee types blended together to give the consumer a richer taste experience. The coffee ground from a coffee bean is also a mixture of various chemicals in various proportions (varies between coffee varieties/brands) which contain:
    Quinic Acid.
    3,5 Dicaffeoylquinic Acid.
    Dimethyl Disulfide.
    Here’s everything that’s hiding in your cup of coffee

  5. Good coffee should be made only from coffee beans, although there are blends of different beans to give a variation of taste, but there should be no additives or extennders. In our household, we buy beans and grind them, and there are only beans there.
    However, like teas, the water extracts a heap of different compounds from the beans, and the brewing method and temperature will have an effect on the taste.
    Every plant is complex in the chemicals that give the flavour, and would perhaps be a bit boring if they were uniform in taste.

  6. Coffee contains more than one substance. It contains water, caffeine and many different molecules from the coffee bean that produce the flavor. (Even though it is not a pure substance it is homogeneous because it has the same composition throughout the mixture)

  7. Coffee is a mixture. Pure substances are elements (e.g., 100% gold, silver, oxygen, etc.) and compounds like sodium chloride, sugar, etc. Distilled water is a pure substance (H2O); however tap water is a homogeneous mixture as it contains other minerals in it. In the same way coffee is a mixture of water caffeine and other components of coffee. It could be a homogeneous mixture (everything is completely dissolved in water or a heterogeneous mixture (some of the substances may not be fully dissolved; e.g., milk.) Please remember that milk is a colloid.


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