25) Describe differences between qualitative and quantitative tests.
A qualitative test is a test executed in order to identify the presence or absence of a particular substance in a sample and a qualitative test is a test given to determine how much of a specific substance is present in a sample.
26) What is a confirming test?
A confirming test is a positive or negative test that confirms the presence or absence of the ion in question. In a this test, one must look for a change in solution color or for the appearance of a precipitate (an insoluble material). If neither appears, indicating a negative test, it means that the ion is either not present, or present in very low quantities.
27) In the water-testing investigation (pages 42-45), what was the purpose of
a. the reference solution
b. the distilled-water bank?
a. The reference solution is a solution where the ion being tested for is present; therefore, it is an example of what the precipitate looks like when the ion is present in the water sample. Usually, however, when the ion is present in the water sample, the precipitate is weaker, for it is usually present in smaller amounts than in the reference solution.
b. Since the distilled-water lacks all ions, it shows that when an ion-stimulating solution is added to it, there is no reaction, but the water remains clear instead.
28) Using the procedure outlined in the water-testing investigation, a student tests a sample of groundwater for iron and observes no color change. Should the student conclude that no iron is present? Explain your answer.
For this class procedure, the student should conclude that no iron is present given no color change. However, if the student was working in a real science laboratory, he or she should conduct further tests, for iron could be present in very small quantities; quantities too small to visibly see through the water-testing investigation lab project.
29) Given an unknown mixture,
a. what steps would you follow to classify it as a solution, a suspension, or a colloid?
b. describe how each step would help you to distinguish among the three types of mixtures.
a. I would stir the mixture and then let it sit for a couple minutes in order to see if any solid particles settle on the bottom of its container. I would also use the Tyndall effect in order to classify the mixture as a solution, a suspension, or a colloid.
b. By stirring and allowing the mixture to sit for a few minutes, I would be able to find out if solid particles large enough to settle to the bottom of the mixture are present in the mixture. These large solid particles would make the mixture an example of suspension. Additionally, a positive Tyndall effect would prove the mixture is a colloid (or a suspension depending on the size of the particles). A negative Tyndall effect would show me that the particles within the water sample are too small, and therefore mixed in and a part of the liquid; a solution.
30) Explain the possible risks in failing to follow the direction "shake before using" on the label of a medicine bottle.
By indicating the necessity to shake the bottle before using, the label shows that the medicine bottle contains a mixture that is an example of suspension. Many of the larger particles of the medicine would settle to the bottom, and therefore require shaking before consuming, in order to mix the particles and liquid together. If one failed to follow the direction "shake before using" on the label of a medicine bottle, they may not get enough, or overdose on components of the medication. The medicine would not work to its potential.
31) Why is it useful for element symbols to have international acceptance?
Since scientists all over the world study the same elements (since they are all present on earth), it is very useful for element symbols to have international acceptance. It is much easier for scientists to deal with the same symbols representing the same things. This contrasts with the US metric system; unlike the SI system that is used internationally, it is only useful in the United States.
32) Draw a model of a solution in which water is the solvent and oxygen gas (O2) is the solute.
See drawing.
33) Is it possible for water to be 100% "chemical free?" Explain.
No. Even with the expensive process of distillation, it is impossible to have 100% "chemical free" water. The atmospheric gases, nitrogen, oxygen, and carbon dioxide all exist in water to some degree; they always dissolve into water.
34) Compare the physical properties of water (H2O) with the physical properties of the elements from which it is composed.
Water, made of 1 hydrogen atom and 2 oxygen atoms has very different physical properties than its components. Although water exists as a liquid at room temperature, oxygen and hydrogen exist as a gas at room temperature. Also, because water is a polar molecule and the attraction of its positive and negative charges create a very strong surface tension, it has a much higher surface tension than the gaseous (and therefore spaced apart) atoms hydrogen and oxygen. Also, the freezing point of water is 0°C, the boiling point is 100°C, and the density is 1g/mL or 1g/cm^3. The freezing, boiling, and densities of hydrogen and oxygen are different.
No comments:
Post a Comment