1: Introduction To Chemistry and Scientific Method
- Page ID
- 506109
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The purpose of this experiment is to:
- Introduction to Chemistry
- Demonstrate skill in handling glassware and transferring chemicals.
- Analyze the observations and record the data.
INTRODUCTION
Chemistry is the branch of science that deals with the study of matter, its properties, composition, structure, and the changes it undergoes. It is a fundamental science crucial in understanding the world around us. Chemistry has numerous applications in various fields, including medicine, materials science, agriculture, and environmental science.
The study of science is not just about knowing but also about asking questions, making predictions, testing ideas, and drawing meaningful conclusions. In Chemistry, we do not just mix substances and observe changes. Chemists employ the Scientific method, a structured approach that involves observation, hypothesis, experimentation, and conclusion.
The scientific method is the systematic approach chemists and scientists use to investigate natural and chemical changes, propose explanations based on evidence, and test those explanations through experiments. The scientific method typically involves the following steps:
Observation: Scientists observe and gather information about natural or chemical phenomena or ask questions based on their observations.
Hypothesis: A proposed explanation for an observed phenomenon. It is a testable statement that can be supported or rejected through experimentation and observation.
Experimentation: Scientists design experiments to test the hypothesis. Experiments involve controlled conditions to isolate variables and gather data that support or refute the hypothesis.
Data Collection and Analysis: Data is collected and analyzed during the experiment. Data collection and analysis involve statistical analysis and evaluation to determine if the results support the hypothesis.
Conclusion: Based on the data obtained, scientists conclude whether the hypothesis is supported or rejected. If supported, the hypothesis may become a theory or a scientific law. If not, it may be revised, refined, or discarded.
In this lab experiment, you will practice and explore using the scientific method by performing the experiments.
1) Effect of Heat
When heated, some compounds change, releasing a colorless gas. We will investigate how heat affects the behavior of substances and explore the resulting changes that occur as a result.
Effect of heat on light green ferrous sulfate crystals \(\ce{(FeSO4·7H2O)}\).
Solution
Upon gentle heating, a spatula of light green ferrous sulfate crystals \(\ce{(FeSO4·7H2O)}\) in a test tube, the light green crystals change to white, and a colorless liquid is seen. (If further heated, the solid changes to brown.)
Observation |
Hypothesis |
|---|---|
|
Colorless liquid initially seen upon heating the light green crystals |
Heating Light green crystals produces water |
|
Light Green crystals changed to a colorless solid |
The light green crystals change into a white solid by losing water. |
2) Effect of Water
Some elements are more reactive with water than others. A common characteristic of most Alkali Metals (Group 1) and most of the Alkaline Earth Metals (Group 2) is their ability to displace H2(g) from water. Alkali metals also react violently and explosively with water.
The general reaction of an alkali metal (M) with H2O (l) is given in the following equation:
2M (s) + 2H2O (l) ⟶ 2M+ (aq) + 2OH− (aq) + H2 (g)
Most of the Alkaline Earth Metals (except Beryllium (Be)) also produce hydroxides when reacted with water. The general reaction of calcium, strontium, and barium with water is represented below, where M represents calcium, strontium, or barium:
M (s) + 2H2O (l) ⟶ M(OH)2 (aq) + H2 (g)
Interaction of Magnesium Metal (Mg) with water (H2O)
Solution
A strip of magnesium ribbon, approximately 1 to 2 inches long, is added to a hot water test tube. Magnesium (Mg) reacts with hot water to release clear gas (H2 (g)). (Reaction of Magnesium with steam produces Magnesium oxide and hydrogen gas.)
Observation |
Hypothesis |
|---|---|
| Bubbles are seen adhering to the magnesium ribbon, and these bubbles emerge from the solution as a colorless gas. |
Colorless gas is produced during the reaction. |
|
The solution turns pink when a few drops of Phenolphthalein indicator are added. If litmus paper is used, the solution indicates a basic pH. |
As the reaction proceeds, a base or basic chemical is produced. |
3) Reactivity
Comparing the reactivities of two metals. Some elements are more reactive than others.
A chemical reactivity series helps determine which elements are more reactive or less, which you will learn later in the course when studying chemical reactions.
Identify if the metals (Mg, Al) are reactive or unreactive in 1.0 M HCl.
Solution
To observe which metals are more reactive or unreactive, add 10.0 – 15.0 mL of 1.0 M hydrochloric acid to two test tubes. Cut two inches of Mg ribbon and Al foil and add them to the test tubes.
Observation |
Hypothesis |
|---|---|
|
When a Mg ribbon is added to a test tube containing HCl, it reacts immediately, releasing a clear gas in the form of vigorous bubbles. |
Mg metal is a more reactive metal with acids. |
|
Al metals start reacting with the acid after nearly all the magnesium has reacted. |
Al metal also reacts with acid, but the reaction is slower than that of Mg metal. |
4) Solubility
Some substances are soluble in water, while others are not. Different compounds have different solubilities. Compounds such as Ammonium chloride and silver chloride are dissolved in deionized water, and their solubilities are observed.
Solubilities of ammonium chloride (NH4Cl) and silver chloride (AgCl) in deionized water.
Solution
Add approximately 10.0–15.0 mL of deionized water to each of two test tubes. Using a spatula, add a small amount of ammonium chloride (NH4Cl) and silver chloride (AgCl), respectively, and observe their solubilities.
Observation |
Hypothesis |
|---|---|
|
Add a small amount of ammonium chloride, NH4Cl, to the first test tube and dissolve it in distilled water. |
Ammonium chloride is highly soluble in water. |
|
In the second test tube containing distilled water, when a small amount of silver chloride is added and stirred with a glass rod, a white solid remains in the solution and settles to the bottom of the test tube. |
Silver chloride is not soluble in water. |
5) Temperature
A change in temperature affects the solubility of compounds and the rates of chemical reactions.
Demonstrate the effect of temperature on the solubility of the compound (Lead (II) chloride, PbCl2).
Solution
Take two test tubes and add 10.0-15.0 mL of distilled water to the test tubes. A small amount of Lead (II) chloride, PbCl2, is added to both the test tubes, and their solubilities are observed. Place a 150.0 mL beaker containing approximately 100.0 mL of water on a hot plate to create a hot bath. Turn the hot plate off when the water boils, or use the instructor-provided hot water bath. Take test tube two and place it in the hot water bath, then observe.
Observation |
Hypothesis |
|---|---|
|
In test tube one, 10.0–15.0 mL of distilled water at room temperature is added to a small amount of lead (II) chloride, PbCl2, and the mixture is stirred with a glass rod. Even after stirring it for a few minutes, PbCl2 does not dissolve. |
Lead (II) chloride, PbCl2, is not soluble in distilled water at room temperature. |
|
Test tube two contains 10.0 – 15.0 mL of distilled water at room temperature. A small amount of lead(II) chloride, PbCl2, is added and stirred with a glass rod. After stirring it for a few minutes, PbCl2 does not dissolve. Place test tube two into the hot water bath, and lead chloride, PbCl2, dissolves. |
Lead (II) chloride, PbCl2, is not soluble in room-temperature water but dissolves in hot distilled water. An increase in water temperature helps dissolve PbCl2. |