Chemistry homework help

FST101A: Lab 9 Water Activity
Student Lab Report Guidelines
Fall 2020
Pay careful attention to the instructions. If you are unsure about what to do, contact any of the
TA’s for the course.
INTRODUCTION:
An introduction is the place in a manuscript where the reasoning behind an experiment is
introduced. It often contains a brief synopsis of what is currently known about the subject, which
segues into the purpose of the experiment and the hypothesis you had before performing the
experiment. Your hypothesis does not need to be correct – it just needs to be testable. You describe
whether your hypothesis was correct or not in the Discussion.
For this week, you will need to write a formal introduction in paragraph format. For the
introduction to this week’s laboratory report, answer each question full sentences, and then
organize into paragraphs that will constitute your introduction.
1. What is adsorption and de-absorption relative to moisture content?
2. What is the difference between water activity and moisture content?
3.
If you are a pathogen, is water content or water activity more important for your
survival?
4. Describe how to use water activity in the formulation of a product.
5. Describe some water activity regulations.
PURPOSE AND HYPOTHESIS
Based on your introduction, write the purpose of this lab. You can start the sentence with the
following: The purpose of this experiment is to ….. Remember that your introduction segues into
the purpose of the experiment.
Based on what is being tested in this lab, write a sentence describing what you think the outcome
will be. You can start the sentence with the following: I hypothesize that …..
METHODS:
Re-read the laboratory manual for the experiment this week. The manual provides you with a set
of instructions. A methods section is a description in sentences of what was actually done during
the experiment, such that someone could read it and be able to repeat what you did on their own.
The methods section contains the essential information for reproducing the results, but is not meant
to be an instruction manual. It is often helpful to break it up into sections.
In your statistical section of the methods, be sure to include one sample calculation for each of the
following:
• Initial sample weight
• Final sample weight
• Percent moisture final on a dry weight basis
• Percent moisture change on a dry weight basis
RESULTS:
Once you have made all of your Tables and Figures, remember to refer to them and describe them
to the reader in this section.
For this week, you need to create the following tables and figures for your report:
Tables:
1. Dish weight, initial + dish weight, and final + dish weight for potatoes for each salt used.
Please include the name and aw (water activity) for each salt. Also include the percent initial
moisture content for potatoes.
2. Dish weight, initial + dish weight, and final + dish weight for dog food for each salt used.
Please include the name and aw for each salt. Also include the percent initial moisture
content for dog food.
3. Calculated data for potato flakes: initial (wti), dry (wtd), final sample weights (wtf), and
percent moisture final (dry weight basis), and percent moisture change (dry weight basis).
Weights are the weight of the food- no dish!
4. Calculated data for dog food: initial (wti), dry (wtd), final sample weights (wtf), percent
moisture final (dry weight basis), and percent moisture change (dry weight basis). Weights
are the weight of the food- no dish!
Figures:
1. Percent moisture change vs aw for potato flakes. Make sure you take into account the
direction of change (i.e. + or -).
2. Percent moisture change vs. aw for dog food. Make sure you take into account the direction
of change (i.e. + or -).
When writing your results, be sure introduce and discuss each of the tables and figures and what
they are telling the reader (remember that the reader will not have observed the lab).
As you are making tables and writing about your results, remember to think about the number of
significant figures. Only use the number of significant figures appropriate for the measurement,
and make sure that you are consistent.
Also be sure to mention the reproducibility of the experiment.
DISCUSSION:
The discussion section is the section where you will interpret your results. For the Discussion for
this week’s laboratory report, use the questions below as a guide. The Discussion should be written
as paragraphs, and describe the results. The questions below are provided to guide you to thinking
about the data that was collected and its meaning. It might be helpful to answer each question first,
and then formulate your Discussion into meaningful paragraphs.
1. Why is the aw (water activity) of food important?
2. What is the difference between water content and water activity? Identify one limitation of
both measurements.
3. How is moisture content and water activity related?
4. What methods can be used to adjust the aw of a food?
5. How were the relative humidity of the salt chambers established? Discuss this in relation
to the water activities of each salt.
6. Discuss your results by comparing the dog food versus the potato flake samples. How were
they different? Specifically, explain reasons for your results based on the classification of
foods (i.e., dehydrated and intermediate moisture foods).
7. Discuss which salts gave moisture to each food and which removed moisture from the
foods, and explain whether the data yielded from the potato flakes and dog food could
correspond to an adsorption or desorption isotherm.
8. For dog food, estimate the initial aw from the graph of % moisture change vs aw (Figure 2).
(Hint: The estimated aw at which the % moisture change would be zero is an indication of
the initial aw of the food). Based on this value, discuss whether you would expect this
product to be stable against microbial growth.
9. Discuss advantages and disadvantages of this method for measuring moisture in foods. Is
this the industry standard?
10. What is the function of a humectant?
11. Explain and expand on water activity and pathogenic relationships. Include anecdotal
evidence.
12. Design an experiment to measure the impact of humectants on a product. (+/- controls)
13. You made relative humidity chambers for your food and added different salts and water to
them. Why did you add the salts first and the water last?
14. Replicates – discuss how reproducible this way of determining water activity is. Is there
another way to determine water activity?
15. Discuss the relationship of the environment in relation to the spoilage of food.