Dehydration of Hydrated Salts
SAFETY FIRST: You will wear goggles at all times! If you are caught without them on, you will not be able to participate in the lab. You must also be quiet during the lab so we can all hear what is happening around us. Talk in a whisper to your partner.
BACKGROUND: Crystals of many compounds naturally contain some molecules of water. For this reason, they are referred to as hydrates, and their formulas are written to indicate the ratio of water molecules to the main compound. For example, one common form of sodium sulfate is called sodium sulfate decahydrate and its formula is written
Na2SO4 • 10H2O
This formula indicates that there are ten moles of water (“10 waters of hydration”) and one mole of Na2SO4 in every mole of this hydrate. Obviously, a mole of the hydrate weighs more than a mole of Na2SO4; the difference is due to the water. Moderate heating of most hydrates will drive off the water, leaving behind the anhydrous ("without water") compound. This will be the basis of your experiment.
PRE LAB QUESTIONS Answer in your final lab write up on a separate piece of paper. You must SHOW WORK to receive ANY credit for these prelab questions.
1. Calculate the percent composition of magnesium sulfate in magnesium sulfate heptahydrate.
2. Calculate the percent composition of water in magnesium sulfate heptahydrate.
3. After driving off the water from an 0.80 g sample of sodium sulfate decahydrate, what is the mass of the solid that remains?
4. A different hydrate of sodium sulfate weighed 1.20 g before dehydration and 0.64g after dehydration.
a. how many moles of Na2SO4 are in .64 g?
b. how many moles of water were driven off in the experiment?
c. how many waters of hydration did this hydrate have?
5. In general, how can you tell when you have successfully driven off all the water of hydration in a dehydration experiment?
OBJECTIVE: Your class challenge is to experimentally determine the number of waters of hydration in five different hydrates. You can use the equipment that has been put out for you (scales, spatulas, samples of each hydrate, crucibles, crucible tongs, bunsen burners, lighters). If you need something else, you may ask for it. I recommend you work with samples that weigh approximately a 2-3 grams.
POST LAB QUESTIONS:
1. Calculate the percent error for your each hydrated salt. Look up the formula for each salt you used. Be sure to put this “source” in your cited sources section of your lab report.
2. Why was there error present in your experiment? Think critically and DO NOT SAY:
a. I calculated my math wrong
b. I measured wrong
NOTE: You may repeat any part of this experiment with another sample if time allows. This will help you to reduce the amount of error when you average your results. Remember: in the scientific method, your results should be reproducible!
LAB WRITE UP
You must turn in a typed lab write up for this experiment. A proper lab write-up format is given below. Another copy is also available on the class website.
Dehydrating Epsom Salts Lab grade sheet
Included / Points possible / Points earnedPrelab / Prelab questions with work shown. / 7
Theory / Explains what hydrated salts are, the purpose of the lab, and explains how to find the mass of dehydrated salt, and % error at end of lab. Careful: don’t report or show any of your actual data…just explain how to calculate these things (look at prelab). / 10
Data / NEAT, complete, well organized, units shown, all data has proper units shown. / 10
Results / Mole ratios of each hydrated salt shown and well organized. / 15
Post Lab Questions / Error calculations with work shown for each salt. An explanation for error for EACH salt provided. / 5
Conclusion / Go back to your goal for the lab. Restate the formula you obtained for each salt and the error you obtained with an explanation of that error / 3
Safety/community/ accuracy / You need to have a valid interpretation of your data, work well with others, and perform this lab safely and accurately / 5
TOTAL POINTS / 55
name: ______per: ______
due date: ______
How to Write a Lab Report
· In this class, lab reports must always be word processed. Your lab reports are the most accurate and helpful record of what goes on in science class this year.
· A good scientist must keep accurate records. When you do a lab in this class, you must also keep good records. Any data collected in the lab must be kept in your lab report.
· Lab reports are to be submitted as professional documents. For this reason, points will be taken off for spelling and grammatical errors.
· You may e-mail your lab reports to me: () the morning they are due instead of bringing them into class.
· Your lab MUST be double spaced and 12 size font and 1 inch margins. I typically write all over labs and give you lots of feedback. GIVE ME SPACE! Don't get all fancy, please!
· Attach any original data you may have to your “final draft.”
· Peer reviews are strongly encouraged!
· Be mindful of copying! This should be YOUR lab. Labs should never by copied by partners. It is reasonable to expect 2 partners to have the same data, but data analysis and interpretation is up to the individual.
You are expected to write up your labs in the following manner………
Title each section in exactly this order.
I. TITLE:
This should be short and to the point, yet tell briefly what is happening in your investigation. Often times the title will already be given to you, in which case use that.
II. PRELAB ASSIGNMENT:
Often, a prelab assignment is given to students before they begin the lab. All work must be shown.
III. PURPOSE/BACKGROUND INFORMATION:
What are you trying to find out or do in this experiment? What are you investigating? This should be at least a paragraph, as specific as possible.
Many times, it is also necessary to provide scientific background information so that people who read the lab can follow all necessary calculations that you plan to do in the lab. What kind of background knowledge and/or research did you do before you started the lab? Sometimes it is helpful to look at the prelab assignment and/or your notes. Often times the prelab will have you do calculations and/or answer questions before you begin. Be detailed, but never (EVER) use actual data collected. This should just logically explain and SHOW how to do all necessary calculations that you plan on using in the lab itself. Again, look at your notes/worksheets/prelab for sample problems to use.
IV. HYPOTHESIS/PREDICTION:
Make an educated guess: What do you expect the outcome will be of this experiment? This statement should be based off of you previous knowledge (see background info) that you have walking into the lab. This is not the place to discuss any results. (Do NOT offer any explanation yet. Do not discuss actual data. This happens in the conclusion!) Not all labs have a typical hypothesis, but may have you testing a concept or chemical process. Explain that here. Be sure to mention your independent variable, dependent variable, and constants (when applicable).
V. MATERIALS/PROCEDURE
A generalized statement of the equipment used and procedure used in lab it typically acceptable at the honor’s level, as long as you don’t UNDER emphasize the process. Take care to discuss the main procedure steps and chemical processes involved. For certain complex labs, it may be necessary to give EXACT measurement directions.
VI.DATA (observations, data, charts, and graphs):
Record all raw data that you obtain during the lab in this section. This can be in the form of written observations, measurements in a data table or both. NO MATH should be done in this section. The measurements may be things like masses, lengths, times, etc., or observations like color, texture, what something looks like, etc. Drawings, charts, and graphs should be included in this section. DO NOT draw conclusions in this section. Just report the facts in this section! DO NOT show do any math calculations in this section. All math work should be done in the discussion and/or conclusion section (depends on the lab hand-out and the format of the lab given).
If possible, use your data to create a graph. Graphs and figures must both be labeled with a descriptive title. Both axes on a graph must be labeled with specific units of measure. The independent variable should always be recorded on the X-axis. The dependent variable is recorded on the Y-axis.
VII. DISCUSSION/ANALYSIS
In this section you are to answer discussion or analysis questions from the text or lab handout, which will help you make sense of your data. Depending on the lab questions given, this may also be where you do calculations with your data. Be sure to show ALL work.
VIII. CONCLUSION:
The purpose of your lab exercise is not to get the "right" answer, but to ask the "right" questions and learn from your failings. Therefore, in this section prove to me that you understand the nature of the experiment and the scientific process involved.
1. Start by talking about your data. Discuss and give a narrative of your data. Can you make any REASONABLE conclusions?
2. Next, discuss your hypothesis: was it supported? If not, do you have an alternate hypothesis? What was the MAIN purpose of the lab? Does your DATA support your reasoning/conclusion? Does further experimentation need to be done in order to confirm the hypothesis/purpose? What would that look like? Are there any REAL WORLD connections? How would this lab connect to the real world?
Please keep the following in mind:
a) I don't care what you “think.” Let the data speak for itself. You MUST refer back to your data in this section. If you don't talk about your data here...you're doing something wrong!
b) When offering your explanation, give data as evidence. Again…I don’t CARE what you think! Example “The front door handle of the school did in fact contain the most bacteria because a swabbing created 14 colonies, whereas the other two areas had only 5 colonies and 2 colonies. This proves that the front door has more germs than the other two locations.” Never leave any open ended statements. For example: “The front door has more germs.” Or “I think I learned a lot in this lab.” Or this: “My % yield was perfect, so I did a great job on this lab. It was fun.” Never leave anything up to the reader to interpret. In other words, “BACK IT UP!”
c) If you had to do ANY calculations using your data, you MUST show it in this section (or in the discussion section as mentioned above). DO NOT do any math calculations in your data section.
IX. CRITIQUE/EXPERIMENTAL ERROR:
In a paragraph, evaluate the lab using the questions below as guidance:
a) Could anything about the procedure been changed to improve the outcome of the lab? If so, HOW exactly would it improve about your data?
b) Did anything go wrong? If so, what? What effect did this have on your data?
c) If necessary, list the % error or % yeild. Show all work.
X. REFERENCES
Did you look up any information to help you draw any conclusions in this lab or help you interpret your data? If so, list them here using APA format, alphabetical.