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Solutions and mixtures

Types of Mixtures

Homogeneous mixtures are uniform throughout. The composition is the same in all directions in the substance. The types of particles observed in one direction are the same that are observed in all others. A solution of sugar in water is homogeneous.

Heterogeneous mixtures are not uniform. There are pockets of one substance surrounded by pockets of different substances. A mixture of soil in water to make "mud" is heterogeneous. Likewise a mixture of oil and water in salad dressing is heterogeneous.

Types of Homogeneous Mixtures

Solutions

Particle sizes distinguish one homogeneous mixture from another. Solutions are mixtures with particle sizes at the molecule or ion level. The particles have dimensions between 0.1 to 2 nanometers. Typically solutions are transparent. Light can usually pass through the solution. If the solute is able to absorb visible light then the solution will have a color. A blue liquid transmits blue light and absorbs the other colors of the spectrum.

A mixture of water H2O and ethanol CH3CH2OH is homogeneous. The particles are individual molecules of H2O and CH3CH2OH. The two molecules are spread uniformly throughout the solution.

A mixture of water and sodium chloride is homogeneous by chemistry standards. The particles in the mixture are molecules of H2O and hydrated sodium cations, Na+, and chloride anions, Cl1-.

Solutions are transparent. You can see through them. The mixture remains stable and does not separate after standing for any period of time. The particles are so small they cannot be separated by normal filtration.

A solution may have a "color" but it will still be transparent.

Colloids

Colloids are mixtures with particle sizes that consist of clumps of molecules. The particles have dimensions between 2 to 1000 nanometers.

The colloid looks homogeneous to the naked eye. Fog and milk are examples of colloids.

Colloids frequently appear "murky" or "opaque". The particles are large enough to scatter light. You have experience with the way fog interacts with the light from car headlights. Colloids generally do not separate on standing. They are not separated by filtration.

Suspensions

Suspensions are homogeneous mixtures with particles that have diameters greater than 1000 nm, 0.000001 meter. The size of the particles is great enough so they are visible to the naked eye. Blood and aerosol sprays are examples of suspensions.

Suspensions are "murky" or "opaque". They do not transmit light. Suspensions separate on standing. The mixture of particles can be separated by filtration.

Examples of solutions

Solutions are mechanical combinations of materials. The physical state for the materials in the solutions is surprising varied. The combinations of states of matter that form solutions are listed below.

States of matter in solution

Example

gas in gas

air ( N2, O2 , Ar, CO2 , other gases)

gas in liquid

soda pop (CO2 in water)

liquid in liquid

gasoline (a mixture of hydrocarbon compounds)

solid in liquid

sea water ( NaCl and other salts in water)

gas in solid

H2 in platinum or palladium

liquid in solid

dental amalgams ( mercury in silver)

solid in solid

alloys ( brass, (Cu/Zn), solder (Sn/Pb)

Make an Observation

Scientists are naturally curious about the world. While many people may pass by a curious phenomenon without sparing much thought for it, a scientific mind will take note of it as something worth further thought and investigation.

Form a Question

After making an interesting observation, a scientific mind itches to find out more about it. This is in fact a natural phenomenon. If you have ever wondered why or how something occurs, you have been listening to the scientist in you. In the scientific method, a question converts general wonder and interest to a channelled line of thinking and inquiry.

Form a Hypothesis

A hypothesis is an informed guess as to the possible answer of the question. The hypothesis may be formed as soon as the question is posed, or it may require a great deal of background research and inquiry. The purpose of the hypothesis is not to arrive at the perfect answer to the question but to provide a direction to further scientific investigation.

Conduct an Experiment

Once a hypothesis has been formed, it must be tested. This is done by conducting a carefully designed and controlled experiment. The experiment is one of the most important steps in the scientific method, as it is used to prove a hypothesis right or wrong, and to formulate scientific theories. In order to be accepted as scientific proof for a theory, an experiment must meet certain conditions – it must be controlled, i.e. it must test a single variable by keeping all other variables under control. The experiment must also be reproducible so that it can be tested for errors.

Analyse the Data and Draw a Conclusion

As the experiment is conducted, it is important to note down the results. In any experiment, it is necessary to conduct several trials to ensure that the results are constant. The experimenter then analyses all the data and uses it to draw a conclusion regarding the strength of the hypothesis. If the data proves the hypothesis correct, the original question is answered. On the other hand, if the data disproves the hypothesis, the scientific inquiry continues by doing research to form a new hypothesis and then conducting an experiment to test it. This process goes on until a hypothesis can be proven correct by a scientific experiment.