READ: Solutions
READ: Solutions
Solutions
If you go to the store to buy apple juice you have many different options. If you buy juice concentrate some of the water has been removed and the directions on the back of the can tell you how much water to add to turn the concentrate into juice. Other bottles of apple juice may be ready to drink straight from the container.
Most juices are solutions (homogeneous mixtures of substances) they are made of multiple compounds that are thoroughly mixed. Salt water is another example of a common household solution. The salt and the water are uniformly mixed at a particle level. Most of the time the different parts of the solution are not visible.
The water on the left looks like a pure substance, but actually it is actually a salt water solution. If you were to look at it on a molecular level (like the illustration on the right) you would see that the NaCl is evenly distributed.
The solvent and solute are the two basic parts of a solution. In the drawing above, H2O is the solvent (the substance present in the greatest amount). The solute, (the substance present in the least amount) is the NaCl. When you are making a cup of hot chocolate, you take a teaspoon of cocoa powder and dissolve it in a cup of hot water. Since much less cocoa powder is used than water, the cocoa powder is thesolute and the water is the solvent.
If you were to add a half teaspoon of salt to a cup of water, you would still make a solution, but the composition of this solution would be different from the last one. What would happen if you tried to dissolve one-half cup of salt in the same cup of water? At this point, the solution has passed the limit of the amount of salt that can be dissolved in it, so it would no longer be a solution—salt would sink to the bottom of the container and never dissolve. As a result, solutions have a constant composition that can be varied up to a point. There are, however, limits to the amount of substance that can be dissolved into another substance and still remain evenly mixed.
Summary
- In a solution, a solute is present in the least amount whereas the solvent is present in the greater amount.
- A solution is a mixture that has the same properties throughout.
Measurement
We already know that observations are an important part of the scientific method. Hypotheses are accepted or rejected based on how well they explain observations. Some observations, such as "the plant turned brown" are qualitative; these observations have no associated numbers. A quantitative observation includes numbers, and is also called a measurement. A measurement is obtained by comparing an object to some standard. Any observation is useful to a scientist, but quantitative observations are commonly considered more useful. Even if the measurement is an estimate, scientists usually make quantitative measurements in every experiment.
CC-BY-NC http://www.ck12.org/user%3Adxrhac1vzxitzg9llnbhcnruzxjay2sxmi5vcmc./book/Chemistry/section/7.1/
CC-BY-NC http://www.ck12.org/physics/Scientific-Measurement/lesson/Measurement-PHYS/
After you have completed this part of the lesson, you can check the associated box on the main course page to mark it as complete 