Methods
Refer to, Chemistry Lab #1 – What’s the substance?
However, I changed some of procedures during my experiment, here is the changes I made in this experiment:
- I only used the toothpick to place a small amount of each sample on a separate piece of paper, instead of the spatula.
- I placed the 5 small pieces of paper that were with samples on one large piece of paper.
- I fully filled the numbered wells with water, instead of adding 10 drops of water.
- I fully filled the numbered wells with 5% hydrochloric acid, instead of adding 10 drops of 5% hydrochloric acid.
- I tested the electrical conductivity by myself with my partner.
- I added the solid samples in water inside the 5 test tubes when I was doing step 4.
- I shook the test tubes with the solutions, which was covered by stoppers before I dipped the wire ends of the conductivity meter into the solution.
Results
I completed a data table to record my results. Here is the table:
Table 1. Physical and chemical properties of the 5 unknown samples.
Identification of the 5 unknown samples
After I’ve done experiment and compared my data table with the information given by the past student, I found out which sample is which substance. Here are the results:
- Calcium carbonate ( Sample A )
- Sodium chloride ( Sample B )
- Sodium nitrate ( Sample C )
- Sodium thiosulfate ( Sample D )
- Sodium bicarbonate ( Sample E )
Discussion Questions
1
- A property is a characteristic of anything. The word “property” is especially used to describe a substance.
- A chemical property is a characteristic of a substance involves a chemical reaction, people require to change the substance to another substance if they want to determine a chemical property. But a physical property is a characteristic of a substance that is about the appearance of a substance, or anything that can be determined without changing that substance into another substance.
- Color, particle shape, particle size, electrical conductivity and solubility in water are the physical properties I’ve tested.
- Reaction in acid is the chemical property that I’ve tested.
2
The property “particle shape” helped me most to decide on the identity of the unknowns. Because after I found out all the particles shapes of the unknowns, at least I can identify two of the unknown samples. I knew that sodium chloride is sample B and sodium thiosulfate was sample D as I found out that the particle shape of sample B was cubic crystal and the particle shape of sample D was hexagonal crystal. These two samples exactly matched the information about the particle shape section given by the past student.
3
The property “color” helped me least to identify the unknowns. Because the information given by the past student told me that all the unknowns were white. So, it was meaningless to check the color of each substance, because I couldn’t find out which sample was which substance even that student gave the color of each substance.
4
Scientists might have to identify an unknown substance when police send something that helps the investigation of a case. Then, scientists have to find out the chemical and physical properties of that unknown substance and they have to compare the properties of that unknown substance to some known substances, finding out what that unknown substance is.
5
- Qualitative properties are the physical characteristics of a substance or substances that can be described but not measured numerically.
- Quantitative properties are the physical characteristics of a substances or substances that can be measured numerically.
- The examples:
-
The boiling temperature of sodium chloride is 1465 oC.
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The solubility of sodium nitrate in water is 92.1 g/ 100 ml at 20 oC.
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The melting temperature of sodium thiosulfate is 48 oC.
- The pH value of calcium carbonate is 9.8.
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The density of sodium bicarbonate is 2.1 g / cm3.
6
Chemical A: 3 % Hydrochloric acid
One of the physical properties of hydrochloric acid is that the hydrochloric acid has low pH value. If we know that hydrochloric acid has low pH value, then we can know hydrochloric acid is corrosive.
Calcium B: Sodium thiosulfate
One of the chemical properties of sodium thiosulfate is when sodium thiosulfate is decomposed; it can release sulfur dioxide gas and hydrogen sulfide. Sulfur dioxide gas is a toxic and hydrogen sulfide is an irritant.
Conclusion
After the experiment, I knew my hypothesis was correct. I was still able to identify the unknown samples after I compared my data table with the table in the handout even there are some unexpected errors and results in my experiment. I know that sample A is calcium carbonate, sample B is sodium chloride, sample C is sodium nitrate, sample D is sodium thiosulfate and sample E is sodium bicarbonate.
Also, now I am able to find out the chemical and physical properties of an unknown substance in order to identify it.
Sources of Error
As most experiments usually has some errors, here is the list of errors that I have in this experiment:
- The data table in the reference has some mistakes. I can see that one of the samples is yellowish white, not all the samples are pure white.
- I found out that 4 of the samples have high electrical conductivity, but the information given in the reference said that there is only 3 substances have high conductivity. Maybe I did the electrical conductivity wrong as I might use the conductivity meter incorrectly, or the data table in the reference is wrong.
- I found out that three of the samples are crystals. But the data table in the reference told me that only 2 of the samples are crystals. I might be wrong, as I wasn’t sure if one of the samples was crystal or not.
- I have different results about particle sizes after I observed from the samples, because size is a very abstract category and everyone has different point of view for the size of any object.
Ways to Improve Experiment
Firstly, if I want to improve my experiments, I have to learn how to use conductivity meter. Because my partner and I didn’t use the conductivity very correctly, the results about the electrical conductivity for each substance might not be correct.
Secondly, I have to know how to describe the shape of a particle. During the experiment, I had some confusion about the particle shape of a substance. So, I need to learn that.
Application of Knowledge
After this experiment, I am able to find the chemical and physical properties of different substances. If I find any unknown substance in the future, I would be capable to find out the chemical and physical properties of that unknown substance. I might be able to identify that unknown substance.