Explain how you feel about adding fluoride (NaF) to drinking water.

/in /by

Paper details:

Respond to the question in at least 2 paragraphs explaining how you feel about adding fluoride (NaF) to drinking water.

The partial pressure at 25 °C of the water vapour above a water-ethanol solution for which x(H2O) = 0.5 is 3.7 kPa. The total vapour pressure is 8.7 kPa. For pure water at 25°C, p*(H2O) = 3.4 kPa; for pure ethanol p*(ethanol) = 4.3 kPa. Calculate the activity and activity coefficient of the water.

/in /by

The pore size of membranes can be measured by using the decrease in vapour pressure of liquid nitrogen condensed in the pores (i.e. cavities) at low temperatures.

Calculate the diameter of the pores in a membrane if at 80.0 K the pressure of N2 gas above the membrane is measured to be 1.310 bar.

At 80.0 K liquid nitrogen has the following properties:
= 8.27 mN m-1
Vm = 3.528 x10-5 m3 mol-1
p*vap = 1.369 bar

(ii) Water droplets adhere weakly to lotus leaves and but strongly to rose petals, but in both cases the contact angle is ~150o. Explain, with the aid of diagrams

Bi) The partial pressure at 25 °C of the water vapour above a water-ethanol solution for which x(H2O) = 0.5 is 3.7 kPa. The total vapour pressure is 8.7 kPa. For pure water at 25°C, p*(H2O) = 3.4 kPa; for pure ethanol p*(ethanol) = 4.3 kPa.

(i) Calculate the activity and activity coefficient of the water.

(ii) Calculate the activity and activity coefficient of the ethanol.

(iii) Calculate the molar excess Gibbs free energy when this water-ethanol mixture is made.

(d) With the aid perhaps of a diagram, briefly describe osmosis and osmotic pressure. Briefly describe the role of osmosis in preservation of foods such as jams or salted meats.

Describe the structure, specificity, reaction mechanism and regulation of one (1) only of the following:

(i) A gastric enzyme that works well at pH 2-3.

(ii) A gastric enzyme that works well at pH 7.6-8.

(iii) A series of enzymes that result in blood clottin

You are adding the non-ionic surfactant Triton X-100 (CMC = 0.25 mM) to an air-water interface and monitoring the surface tension as a function of surfactant concentration. Sketch a graph of surface tension vs surfactant concentration as Triton X-100 is added from 0 mM to 0.5 mM.

(v) Your colleague is using a different Triton X surfactant to do the same experiment. Their surfactant has a longer aliphatic chain. Explain how you think this will affect micelle formation.

Imagine you are investigating the effect of salt on the interparticle forces in an emulsion. The emulsion is made of drops of sunflower oil in water and stabilised by sodium dodecyl sulfate. You observe that adding salt to the emulsion causes the average size of the drops to increase. Adding more salt causes the oil to form a separate layer above the water. Sketch graphs of the potential energy between pairs of oil drops in the emulsions under the conditions of:
(i) no salt
(ii) a low salt concentration and
(iii) a high salt concentration

Did you observe anything during the Jominy Test that confirms the idea that the quenching rate is lower away from the quenched end?

/in /by

Jominy End-Quench Test.
In this lab, we will perform a Jominy Test on a sample of 1018 Steel, which contains 0.18 wt % C.
Our first step is to austenitize our sample, meaning that we heat it up to a temperature where the sample transforms from the BCC α-Fe to the FCC γFe, also called austenite. For our sample, we’ll use a temperature of 1700 °F (about 927 °C), holding it at temperaure for 30 minutes. Notice where the sample would be on the Fe-Fe3C phase diagram, shown below, when it is held at 1700 °F.
Shackelford’s Figure 9.19, page 272. The Fe-Fe3C phase diagram.
The sample is quickly removed from the furnace and placed in the Jominy tester (see Figure 10.21), and the water cooling begins. Notice that only one end of the sample is directly cooled by the water flowing in the Jominy test apparatus. This means the highest quench rate occurs at that end and decreases as we move away from the quenched end. You may be able to demonstrate the validity of this last statement by something you may observe during the test.
When the sample reaches room temperature, we may safely remove it for further testing.
Shackelford’s Figure 10.21, page 325. The Jominy End-Quench test.
Measure the Rockwell hardness at various distances from the quenched end, every 1/16 inch up to one-inch, then every 1/8 inch up to twoinches. Present your data in a graph like Figure 10.24 shown below.
Shackelford’s Figure 10.24, page 326. Hardenability for various grades of steel. These grades all contain 0.40 wt % C.
Some questions you may wish to ponder as you write your report.

• Is there a standard size for Jominy samples?

• How does the Jominy apparatus actually work? Note that our apparatus was designed and constructed by one of our students.

• Did you observe anything during the Jominy Test that confirms the idea that the quenching rate is lower away from the quenched end?
• How does your data for 1018 steel compare to the other grades of steel shown in Figure 10.24?

• Can you find for Jominy data for 1018 steel? How does it compare to our data?

• What is ideal hardenability behavior?

• How do the curves we have seen, both in the lab and in our textbook, compare to this ideal?

• What can you conclude about the effect of quenching rate on hardness?
SRT 4/20/2020

In your own words, describe the specifics of what this study involved. What where the samples? How were they grouped? What analysis did they complete? Under what conditions? For how long? What was measured? What was being compared?

/in /by

Critical Reflection of a Journal Article (USE THIS AS A GUIDE –  REFERENCE THE SAME ARTICLE)

Summarizing research articles will help you to develop your critical thinking skills and your ability to express yourself in the written form. A research article is written to get across a lot of information quickly to a reader. Reading such articles can be tedious and sometimes frustrating unless you are familiar with scientific writing and the reasons for this style. Research articles are highly structured to make information easy to find. Unlike literary writing, scientific writing emphasizes quantifiable information; as a result, the writing is very lean and extra words are avoided.

A research article has the following major sections: Title Page, Abstract, Introductions, Method, Results, Discussion, References, Tables and Figures. An article summary highlights the information in the Introduction, Methods, Results, and Discussion. Before you can write such a summary, you need to read and understand the article.

Reading the Article

  • Allow enough time. Plan to spend at least one half of the time you devote to this assignment to reading and understanding the article. Before you can write about research, you have to evaluate it. Before you can evaluate it, you have to understand it. Before you can understand it, you have to digest it. Before you can digest, you have to read it, thoroughly. This takes more time than most students realize.
  • Scan the article first. You will get bogged down in detail if you try to read a new article from start to finish. Initially you should briefly look at each section to identify:
    • general information about the study (stated in the Abstract and Introduction)
    • the hypothesis (-es) or research questions (in the Introduction)
    • the test of the hypothesis, including the sample, variables and operational definitions, and the procedures used (in the Methods)
    • the findings (in the Results, including tables and figures)
    • how the findings were interpreted (in the Discussion).
  • Read for depth. After you have highlighted the question, hypothesis, findings, and interpretations, go back to the article to read about each area in more detail. Now you should expect to read each section more than once. Expect not to fully understand the article the first time. You will have to read it more than twice before you can talk about it in your own words.

Remember that you are digesting information, not swallowing it whole. If an idea is relevant to your topic, you should be able to summarize it in your own words. If you can’t, you probably don’t understand it.

Article Conditions:

  • Must be from a peer reviewed source
    • American Chemical Society and Royal Society of Chemistry are two of the biggest publishers
  • Cannot be more than 50 years old
  • Must be a chemistry research article (not a review article)
  • Must be related to your approved individual proposal topic

Article Critical Reflection Questions

Bibliographic Information:

Article Title: Spectrophotometric Determination of Vitamin C in Pharmaceutical Preparations using Ammonium Metavanadate.

Journal: Asian Journal of Research in Chemistry

Year: 2017   Volume: 10, Issue 3    Page Numbers: 341-344

Other Identifying information if not a journal:

How did you locate this article?

I found this article by logging onto the library database website. I clicked on “New search” and typed “Determination of vitamin C by titration” and I didn’t find anything I was interested in. So, I typed “Determination of vitamin C by spectrophotometry” and refined my search from newest to oldest, peer-reviewed, and articles only. This article was the third up out of 10,333 search results.

Summary:

  • In 100 to 150 words summarize the main idea of the paper in laymen terms (non-scientist). Include your word count at the end of the summary.

The aim of this experiment was to test the Spectrophotometric method for measuring the concentration of vitamin C in pharmaceutical products such as Orange peel, Alma squash and Astymin C in order to compare the values obtained to the values on the manufacturer’s label. A Spectrophotometer is an instrument that passes light through a solution and measures how much light it has absorbed (Absorbance, A), but there has to be a color gradient based on the concentration of vitamin C. To accomplish this, ammonium metavanadate was added to the vitamin C, forming a green color which was bolder with increased vitamin C concentration. Using portions of known vitamin C concentration and getting their absorbances, a Beer’s law plot of Absorbance vs Concentration (μg/cm3). Unknown concentrations can be found using the equation of the trendline, of this graph: Absorbance, y = Slope, m (Concentration, x) + y-intercept, C.

(147 words)

Procedures:

  • In your own words, describe the specifics of what this study involved. What where the samples? How were they grouped? What analysis did they complete? Under what conditions? For how long? What was measured? What was being compared?

In this experiment, each of the pharmaceutical products such as Orange peel, Alma squash and Astymin C were prepared differently based on their stock solution, to 1000ppm. For the Orange peel power, they weighed out 10 grams of the powder, diluted to 250 mL of distilled water, boiled for 5 hrs., filtered using Whatman 41 paper, and 5mL was used. For the Amla squash, 10 mL of stock was diluted to 100 mL and 10 mL was used. Lastly for the Astymin C drops, 0.1 mL of stock was diluted to 100 mL and 1 mL was used. Their recommended procedure was to use 1 mL of a solution of 1000 ppm vitamin C with 1 mL of a 0.5 % w/v ammonium metavanadate (prepared by dissolving 0.5g of ammonium metavanadate in 100 mL of distilled water) made to a 25 mL solution using distilled water. This solution was in the 5.0-6.0 pH range.

The maximum wavelength was 395 nm and this was gotten using an absorption spectra of the complex against a blank. It was found that the complex and color was unstable past four hours, however, the color showed instantly. A Beer’s law plot of Absorbance vs Concentration (μg/cm3) was done for known concentrations of vitamin C, and then used to find the concentration of the Unknowns using the equation of the trendline, of this graph: Absorbance, y = Slope, m (Concentration, x) + y-intercept, C. There was no table showing the data values for the known compounds. The results of this method was tested using the pH metric method to validate the results, but this was done only with the Orange squash sample.

For the tools, a. Boush and Lomb spectronic-20 was used with 1cm matched glass cell. Potassium chromate in KOH solution and potassium permanganate in sulphuric acid solution was used to calibrate the spectrophotometer, using an absorption spectra. This was not explained in detail. The pH meter was also calibrated, done pH 4.0, 7.0 and 9.2 buffer solutions.

Findings:

  • In your own words discuss the major findings and results. How useful or significant is this (what did the author(s) say about it?)

For the calibration curve the line was y= 0.009x + 0.014 with an R2 value of 0.9951. Because the R2 value is strong, the correlation is also strong.

For the Orange peel powder, the Spectrophotometric method gave 52.00 ± 4.62 μg/cm3 and the pH metric method 49.00 ± 3.35 μg/cm3 which is very close. There was no data on the manufacturer’s concentration.

For the Amlasquash (Nutri value) the Spectrophotometric method gave 63.33 ±5.76 μg/cm3 with a factory value of 65 μg/cm3, which is also close.

For Astymin C drops the Spectrophotometric value was 66.66 ± 5.77 μg/cm3 and the factory value was 70 μg/cm3 . No data for pH method.

The precision and accuracy of the method was tested by doing 8 replicate sampeles of each solution of 200.0 μg of vitamin C. The average was .94±0.028 at 95% confidence level. The standard deviation was 0.0394 and the variance was 0.0016.

Personal comments:

  • Give your reaction to the study? Such as: What did you learn from the study? How might you apply the results in a future application? Explain how this study might relate to the lab, lab topic, and/or your project. Do you think this is scientifically valid? You must defend your answer.

This was an adaptation of what was learned in class. I believe it was necessary to do both pH metric and spectrophotometric methods to test the result.

Critical Reflection of a Journal Article (USE THIS AS A GUIDE –  REFERENCE THE SAME ARTICLE)

Summarizing research articles will help you to develop your critical thinking skills and your ability to express yourself in the written form. A research article is written to get across a lot of information quickly to a reader. Reading such articles can be tedious and sometimes frustrating unless you are familiar with scientific writing and the reasons for this style. Research articles are highly structured to make information easy to find. Unlike literary writing, scientific writing emphasizes quantifiable information; as a result, the writing is very lean and extra words are avoided.

A research article has the following major sections: Title Page, Abstract, Introductions, Method, Results, Discussion, References, Tables and Figures. An article summary highlights the information in the Introduction, Methods, Results, and Discussion. Before you can write such a summary, you need to read and understand the article.

Reading the Article

  • Allow enough time. Plan to spend at least one half of the time you devote to this assignment to reading and understanding the article. Before you can write about research, you have to evaluate it. Before you can evaluate it, you have to understand it. Before you can understand it, you have to digest it. Before you can digest, you have to read it, thoroughly. This takes more time than most students realize.
  • Scan the article first. You will get bogged down in detail if you try to read a new article from start to finish. Initially you should briefly look at each section to identify:
    • general information about the study (stated in the Abstract and Introduction)
    • the hypothesis (-es) or research questions (in the Introduction)
    • the test of the hypothesis, including the sample, variables and operational definitions, and the procedures used (in the Methods)
    • the findings (in the Results, including tables and figures)
    • how the findings were interpreted (in the Discussion).
  • Read for depth. After you have highlighted the question, hypothesis, findings, and interpretations, go back to the article to read about each area in more detail. Now you should expect to read each section more than once. Expect not to fully understand the article the first time. You will have to read it more than twice before you can talk about it in your own words.

Remember that you are digesting information, not swallowing it whole. If an idea is relevant to your topic, you should be able to summarize it in your own words. If you can’t, you probably don’t understand it.

Article Conditions:

  • Must be from a peer reviewed source
    • American Chemical Society and Royal Society of Chemistry are two of the biggest publishers
  • Cannot be more than 50 years old
  • Must be a chemistry research article (not a review article)
  • Must be related to your approved individual proposal topic

Article Critical Reflection Questions

Bibliographic Information:

Article Title: Spectrophotometric Determination of Vitamin C in Pharmaceutical Preparations using Ammonium Metavanadate.

Journal: Asian Journal of Research in Chemistry

Year: 2017   Volume: 10, Issue 3    Page Numbers: 341-344

Other Identifying information if not a journal:

How did you locate this article?

I found this article by logging onto the library database website. I clicked on “New search” and typed “Determination of vitamin C by titration” and I didn’t find anything I was interested in. So, I typed “Determination of vitamin C by spectrophotometry” and refined my search from newest to oldest, peer-reviewed, and articles only. This article was the third up out of 10,333 search results.

Summary:

  • In 100 to 150 words summarize the main idea of the paper in laymen terms (non-scientist). Include your word count at the end of the summary.

The aim of this experiment was to test the Spectrophotometric method for measuring the concentration of vitamin C in pharmaceutical products such as Orange peel, Alma squash and Astymin C in order to compare the values obtained to the values on the manufacturer’s label. A Spectrophotometer is an instrument that passes light through a solution and measures how much light it has absorbed (Absorbance, A), but there has to be a color gradient based on the concentration of vitamin C. To accomplish this, ammonium metavanadate was added to the vitamin C, forming a green color which was bolder with increased vitamin C concentration. Using portions of known vitamin C concentration and getting their absorbances, a Beer’s law plot of Absorbance vs Concentration (μg/cm3). Unknown concentrations can be found using the equation of the trendline, of this graph: Absorbance, y = Slope, m (Concentration, x) + y-intercept, C.

(147 words)

Procedures:

  • In your own words, describe the specifics of what this study involved. What where the samples? How were they grouped? What analysis did they complete? Under what conditions? For how long? What was measured? What was being compared?

In this experiment, each of the pharmaceutical products such as Orange peel, Alma squash and Astymin C were prepared differently based on their stock solution, to 1000ppm. For the Orange peel power, they weighed out 10 grams of the powder, diluted to 250 mL of distilled water, boiled for 5 hrs., filtered using Whatman 41 paper, and 5mL was used. For the Amla squash, 10 mL of stock was diluted to 100 mL and 10 mL was used. Lastly for the Astymin C drops, 0.1 mL of stock was diluted to 100 mL and 1 mL was used. Their recommended procedure was to use 1 mL of a solution of 1000 ppm vitamin C with 1 mL of a 0.5 % w/v ammonium metavanadate (prepared by dissolving 0.5g of ammonium metavanadate in 100 mL of distilled water) made to a 25 mL solution using distilled water. This solution was in the 5.0-6.0 pH range.

The maximum wavelength was 395 nm and this was gotten using an absorption spectra of the complex against a blank. It was found that the complex and color was unstable past four hours, however, the color showed instantly. A Beer’s law plot of Absorbance vs Concentration (μg/cm3) was done for known concentrations of vitamin C, and then used to find the concentration of the Unknowns using the equation of the trendline, of this graph: Absorbance, y = Slope, m (Concentration, x) + y-intercept, C. There was no table showing the data values for the known compounds. The results of this method was tested using the pH metric method to validate the results, but this was done only with the Orange squash sample.

For the tools, a. Boush and Lomb spectronic-20 was used with 1cm matched glass cell. Potassium chromate in KOH solution and potassium permanganate in sulphuric acid solution was used to calibrate the spectrophotometer, using an absorption spectra. This was not explained in detail. The pH meter was also calibrated, done pH 4.0, 7.0 and 9.2 buffer solutions.

Findings:

  • In your own words discuss the major findings and results. How useful or significant is this (what did the author(s) say about it?)

For the calibration curve the line was y= 0.009x + 0.014 with an R2 value of 0.9951. Because the R2 value is strong, the correlation is also strong.

For the Orange peel powder, the Spectrophotometric method gave 52.00 ± 4.62 μg/cm3 and the pH metric method 49.00 ± 3.35 μg/cm3 which is very close. There was no data on the manufacturer’s concentration.

For the Amlasquash (Nutri value) the Spectrophotometric method gave 63.33 ±5.76 μg/cm3 with a factory value of 65 μg/cm3, which is also close.

For Astymin C drops the Spectrophotometric value was 66.66 ± 5.77 μg/cm3 and the factory value was 70 μg/cm3 . No data for pH method.

The precision and accuracy of the method was tested by doing 8 replicate sampeles of each solution of 200.0 μg of vitamin C. The average was .94±0.028 at 95% confidence level. The standard deviation was 0.0394 and the variance was 0.0016.

Personal comments:

  • Give your reaction to the study? Such as: What did you learn from the study? How might you apply the results in a future application? Explain how this study might relate to the lab, lab topic, and/or your project. Do you think this is scientifically valid? You must defend your answer.

This was an adaptation of what was learned in class. I believe it was necessary to do both pH metric and spectrophotometric methods to test the result.

What did you learn from the study? How might you apply the results in a future application? Explain how this study might relate to the lab, lab topic, and/or your project.

/in /by

Critical Reflection of a Journal Article (USE THIS AS A GUIDE –  REFERENCE THE SAME ARTICLE)

Summarizing research articles will help you to develop your critical thinking skills and your ability to express yourself in the written form. A research article is written to get across a lot of information quickly to a reader. Reading such articles can be tedious and sometimes frustrating unless you are familiar with scientific writing and the reasons for this style. Research articles are highly structured to make information easy to find. Unlike literary writing, scientific writing emphasizes quantifiable information; as a result, the writing is very lean and extra words are avoided.

A research article has the following major sections: Title Page, Abstract, Introductions, Method, Results, Discussion, References, Tables and Figures. An article summary highlights the information in the Introduction, Methods, Results, and Discussion. Before you can write such a summary, you need to read and understand the article.

Reading the Article

  • Allow enough time. Plan to spend at least one half of the time you devote to this assignment to reading and understanding the article. Before you can write about research, you have to evaluate it. Before you can evaluate it, you have to understand it. Before you can understand it, you have to digest it. Before you can digest, you have to read it, thoroughly. This takes more time than most students realize.
  • Scan the article first. You will get bogged down in detail if you try to read a new article from start to finish. Initially you should briefly look at each section to identify:
    • general information about the study (stated in the Abstract and Introduction)
    • the hypothesis (-es) or research questions (in the Introduction)
    • the test of the hypothesis, including the sample, variables and operational definitions, and the procedures used (in the Methods)
    • the findings (in the Results, including tables and figures)
    • how the findings were interpreted (in the Discussion).
  • Read for depth. After you have highlighted the question, hypothesis, findings, and interpretations, go back to the article to read about each area in more detail. Now you should expect to read each section more than once. Expect not to fully understand the article the first time. You will have to read it more than twice before you can talk about it in your own words.

Remember that you are digesting information, not swallowing it whole. If an idea is relevant to your topic, you should be able to summarize it in your own words. If you can’t, you probably don’t understand it.

Article Conditions:

  • Must be from a peer reviewed source
    • American Chemical Society and Royal Society of Chemistry are two of the biggest publishers
  • Cannot be more than 50 years old
  • Must be a chemistry research article (not a review article)
  • Must be related to your approved individual proposal topic

Article Critical Reflection Questions

Bibliographic Information:

Article Title: Spectrophotometric Determination of Vitamin C in Pharmaceutical Preparations using Ammonium Metavanadate.

Journal: Asian Journal of Research in Chemistry

Year: 2017   Volume: 10, Issue 3    Page Numbers: 341-344

Other Identifying information if not a journal:

How did you locate this article?

I found this article by logging onto the library database website. I clicked on “New search” and typed “Determination of vitamin C by titration” and I didn’t find anything I was interested in. So, I typed “Determination of vitamin C by spectrophotometry” and refined my search from newest to oldest, peer-reviewed, and articles only. This article was the third up out of 10,333 search results.

Summary:

  • In 100 to 150 words summarize the main idea of the paper in laymen terms (non-scientist). Include your word count at the end of the summary.

The aim of this experiment was to test the Spectrophotometric method for measuring the concentration of vitamin C in pharmaceutical products such as Orange peel, Alma squash and Astymin C in order to compare the values obtained to the values on the manufacturer’s label. A Spectrophotometer is an instrument that passes light through a solution and measures how much light it has absorbed (Absorbance, A), but there has to be a color gradient based on the concentration of vitamin C. To accomplish this, ammonium metavanadate was added to the vitamin C, forming a green color which was bolder with increased vitamin C concentration. Using portions of known vitamin C concentration and getting their absorbances, a Beer’s law plot of Absorbance vs Concentration (μg/cm3). Unknown concentrations can be found using the equation of the trendline, of this graph: Absorbance, y = Slope, m (Concentration, x) + y-intercept, C.

(147 words)

Procedures:

  • In your own words, describe the specifics of what this study involved. What where the samples? How were they grouped? What analysis did they complete? Under what conditions? For how long? What was measured? What was being compared?

In this experiment, each of the pharmaceutical products such as Orange peel, Alma squash and Astymin C were prepared differently based on their stock solution, to 1000ppm. For the Orange peel power, they weighed out 10 grams of the powder, diluted to 250 mL of distilled water, boiled for 5 hrs., filtered using Whatman 41 paper, and 5mL was used. For the Amla squash, 10 mL of stock was diluted to 100 mL and 10 mL was used. Lastly for the Astymin C drops, 0.1 mL of stock was diluted to 100 mL and 1 mL was used. Their recommended procedure was to use 1 mL of a solution of 1000 ppm vitamin C with 1 mL of a 0.5 % w/v ammonium metavanadate (prepared by dissolving 0.5g of ammonium metavanadate in 100 mL of distilled water) made to a 25 mL solution using distilled water. This solution was in the 5.0-6.0 pH range.

The maximum wavelength was 395 nm and this was gotten using an absorption spectra of the complex against a blank. It was found that the complex and color was unstable past four hours, however, the color showed instantly. A Beer’s law plot of Absorbance vs Concentration (μg/cm3) was done for known concentrations of vitamin C, and then used to find the concentration of the Unknowns using the equation of the trendline, of this graph: Absorbance, y = Slope, m (Concentration, x) + y-intercept, C. There was no table showing the data values for the known compounds. The results of this method was tested using the pH metric method to validate the results, but this was done only with the Orange squash sample.

For the tools, a. Boush and Lomb spectronic-20 was used with 1cm matched glass cell. Potassium chromate in KOH solution and potassium permanganate in sulphuric acid solution was used to calibrate the spectrophotometer, using an absorption spectra. This was not explained in detail. The pH meter was also calibrated, done pH 4.0, 7.0 and 9.2 buffer solutions.

Findings:

  • In your own words discuss the major findings and results. How useful or significant is this (what did the author(s) say about it?)

For the calibration curve the line was y= 0.009x + 0.014 with an R2 value of 0.9951. Because the R2 value is strong, the correlation is also strong.

For the Orange peel powder, the Spectrophotometric method gave 52.00 ± 4.62 μg/cm3 and the pH metric method 49.00 ± 3.35 μg/cm3 which is very close. There was no data on the manufacturer’s concentration.

For the Amlasquash (Nutri value) the Spectrophotometric method gave 63.33 ±5.76 μg/cm3 with a factory value of 65 μg/cm3, which is also close.

For Astymin C drops the Spectrophotometric value was 66.66 ± 5.77 μg/cm3 and the factory value was 70 μg/cm3 . No data for pH method.

The precision and accuracy of the method was tested by doing 8 replicate sampeles of each solution of 200.0 μg of vitamin C. The average was .94±0.028 at 95% confidence level. The standard deviation was 0.0394 and the variance was 0.0016.

Personal comments:

  • Give your reaction to the study? Such as: What did you learn from the study? How might you apply the results in a future application? Explain how this study might relate to the lab, lab topic, and/or your project. Do you think this is scientifically valid? You must defend your answer.

This was an adaptation of what was learned in class. I believe it was necessary to do both pH metric and spectrophotometric methods to test the result.

Write the expression of Kc1 as a function of the equilibrium concentrations of the reactants and products of reaction (I)

/in /by

Chemistry Module 3 Assignment 1
Redox and Chemical Equilibria
Answer all the following questions ON PAPER and submit to your lecturer with a signed cover sheet. Presentation and the accuracy of your written English will be taken into account in marking. Set all calculations out in full. Numerical answers should be given to the appropriate number of significant figures.

Due: Week 3 beginning 23rd March 2020

1. At 250oC, the value of the equilibrium constant Kc1, for the reaction equation labelled (1) below, is 0.0835

(1) C2H4(g) + H2O(g) ⇌ C2H5OH(g) ΔHoR1 = – 45.0 KJ mol-1

(a) (i) Write the expression of Kc1 as a function of the equilibrium concentrations of the reactants and products of reaction (I) (1 mark)

(ii) give the unit of Kc1. (1 mark)

(b) Kc2 and Kc3 are the equilibrium constants for respectively reaction (2) and reaction (3). (2) C2H5OH(g) ⇌ C2H4(g) + H2O(g) (3) 3 C2H4(g) + 3 H2O(g) ⇌ 3 C2H5OH(g)

ΔHoR2 and ΔHoR3 are the standard enthalpy changes for respectively reaction (2) and reaction (3):

(i) Write the expression of Kc2 as a function of the equilibrium concentrations of the reactants and products of reaction (II)

-Compare the expressions of Kc2 and Kc1 and write Kc2 as a function of Kc1 – Calculate the value of Kc2
– Give the unit of Kc2 – Give the value of ΔHoR2 (5 marks) (ii) Write the expression of Kc3 as a function of the equilibrium concentrations of the reactants and products of reaction (3)

– Compare the expressions of Kc3 and Kc1 and write Kc3 as a function of Kc1 – calculate the value of Kc3 – give the unit of Kc3 – give the value of ΔHoR3 (5 marks)

Chemistry Module 3 Assignment 1
Redox and Chemical Equilibria
(c) When reaction (1) is conducted at a higher temperature than 250oC, the value of Kc1 decreases. Using Le Châtelier’s principle give a clear explanation (in complete sentences) as to why the value of Kc1 decreases. (4 marks)

(d) A student wrote about reaction (1): “When pressure is increased, more products are formed, so the value of Kc1 goes up”

Comment the statement made by the student by stating clearly why you believe that the student is right, or wrong, or partially wrong.
(5 marks)

2. Dinitrogen tetroxide (N2O4) is a colourless gaseous oxidising agent that can be used in conjunction with some reducing agents to form rocket propellants. In a closed system, dinitrogen tetroxide is formed from nitrogen dioxide (NO2), a brown toxic gas, by a reversible reaction. A chemical equilibrium is eventually achieved.

2NO2 (g) N2O4 (g) ΔHo = -57 KJ mol-1 brown colourless

0.100 mol of NO2(g) is placed in a 2.00 dm3 closed flask at 25oC. As time passes, the brown colour of the gas mixture gets lighter. Equilibrium is reached when the shade of brown stops changing. At equilibrium, 40% of the NO2(g) has reacted to form N2O4(g).

(a) (i) Explain why the colour of the gas mixture remains constant at equilibrium (2 marks)

(ii) Is it correct to state “The reaction stops once the state of equilibrium is reached”? Justify your answer. (2 marks) (b)

(i) Write an expression for the constant of equilibrium Kc of the reaction as a function of the equilibrium concentrations of the reactant and product.

(ii) Give the units of Kc
(2 marks)

(c) Reproduce the table below, and complete it: (3 marks)

NO2 N2O4 initial amount (mol) 0.100 mol 0.00 mol change of amount amount at equilibrium (mol) concentration at equilibrium

(d) Hence calculate the value of Kc at 25oC. (2 marks)
Chemistry Module 3 Assignment 1
Redox and Chemical Equilibria

(e) (i) What change of colour would you observe if the flask containing the gas mixture at equilibrium were placed in an ice bath? (1 mark)

(ii) Comment on the speed at which that change of colour would occur compared to the initial change of colour to reach equilibrium. (1 mark)

(iii) Give full explanations to your previous two answers to questions (e).(i) and (e).(ii). (4 marks)

3. A rocket propulsion system uses the very exothermic reaction between the gases dinitrogen tetroxide (N2O4(g)) and hydrazine (N2H4(g)). The reaction forms the gas nitrogen and water vapour. The following equation is not balanced:
N2O4(g) + N2H4(g) → N2(g) + H2O(g)

(a) Assign the oxidation states of each element in the reactants and products
of the equation above. (3 marks)

(b) (i) Which reactant is oxidised? (0.5 mark)

(ii) Identify the element that undergoes oxidation and state how many electrons are lost through oxidation by an atom of that element. (1 mark)
(iii) Which reactant is reduced? (0.5 mark)

(iv) Identify the element that undergoes reduction and state how many electrons are gained through reduction by an atom of that element. (1 mark)

(c) Therefore, in what ratio should N2O4 and N2H4 react with each other? Justify your answer. (2 marks)

(d) Balance the reaction equation above. (1 mark)

(e) (i) Which reagent is the oxidising agent? Justify your answer (2 marks)

(ii) Which reagent is the reducing agent? Justify your answer (2 marks)

4. MnO4-, manganate(VII) ions (or permanganate ions) react under alkaline aqueous conditions with C2O42-, ethanedioate ions (or oxalate ions) to form MnO2, manganese(IV) oxide and CO2(g), carbon dioxide.

(a) Balance step by step the following half-reaction equation (A) under alkaline aqueous conditions: (you must show and explain all the steps followed to balance the half-reaction equation in order to get the marks)
Chemistry Module 3 Assignment 1
Redox and Chemical Equilibria

(A) MnO4- (aq) → MnO2(s) (3 marks)

(b) Balance step by step the following half-reaction equation under alkaline aqueous conditions: (you must show and explain all the steps followed to balance the half-reaction equation in order to get the marks)

(B) C2O42- (aq) → CO2 (g) (1 mark)

(c) (i) state whether half-reaction (A) is a reduction or oxidation step, and justify your answer. (1 mark)

(ii) state whether half-reaction (B) is a reduction or oxidation step, and justify your answer. (1 mark)

(iii) combine the two half-reactions to form a balanced redox reaction, include state symbols. (3 marks)