Name ____________________________ Block _________ Date __________________

 

 

 

Saccharin or Sahara?

Chem catalyst:

A catalyst is a chemical that allows reactions to move more quickly and with less energy.  Chem catalysts are designed to make the labs easier for you by thinking about what you know before you begin the lab.  Most labs will begin with a chem. catalyst.  Answer these questions immediately after entering the lab.

 

This lab will ask you to separate sugar and sand.  List everything you know about sugar and sand.  Where do you find them? How do they behave in nature? Etc.  Then circle the properties that would allow you to separate them.

                        Sugar                                                              Sand

 

 

 

 

 

 

 

Problem:

A recent investigation found that sugar companies are putting sand into their sugar because it is cheaper to produce (and therefore raises profits).  Pastry chefs everywhere are furious!  We have been asked to look at samples of sugar to measure the amount of sand.  The exact amount of each component in the sample has a bearing on this important court case involving consumer fraud. You will be given a film canister of sugar and will be expected to determine the percentage of sand in the mixture. You must make your determination solely on the basis of the one packet.  Think about variables that could influence your results.    Keep accurate and complete records on this page.  Laboratory notebooks are subpoenable in a court of law, thus you might be called upon to defend the accuracy of your results.  Think about the data you will need in order to realize the purpose of the experiment and how you will go about gathering that data.  Remember, when you are on the witness stand, an attorney is going to ask you how you know that your results are correct? 

 

Good Luck.  Work Safely!

Lab Safety:

            Wear goggles

            Clear your desk and aisles.

            Keep movement to a minimum.

            Keep all talking to a minimum.

            Check all procedures with your teacher before beginning.

Materials:

packet containing a mixture of sugar and sand
common laboratory equipment

 

Question:  What characteristic of sand and sugar will make this separation easy for you?

Hypothesis:  Please give your best educated guess about the above question.

 

Rationale:   Please explain why you think your hypothesis is correct.

 

 

 

Procedure:

Write a procedure that will allow you to separate the sugar and sand as well as measure exactly the amount of each in the sample.  Be very specific!  Your procedure should use the characteristic you identified in your hypothesis.

 

 

 

 

 

 

 

 

 

 

 

Data:

Keep accurate records of all your important data.  Remember, this is the part that is a legal document and must be accurate.

 

 

 

 

 

 

 

 

 

 

 

Summing Up:

Show your calculations for determining the percentage of sand in your mixture.  Be sure to include units on all of your numbers.

 

 

 

 

 

 

Analysis:  Wait until after notes for these questions.

1. Calculate the % error for your group.

 

 

 

 

 

2. Look at your procedure.  Describe at least two sources of experimental error that would shift your results and explain how each error would change your data.

 

 

 

 

 

 

 

 

3. What would you do differently to achieve better results (if I gave you the chance)?

 

 

 

 

 

 

 

 

4. What questions do you have about this lab that could lead to future experiments?

 

 

 

 

5. What experiments would you do to answer those questions?

 

 

 

6. Describe how you used the 5 steps of problem solving to design your procedure (Yes, you probably used them in your head without knowing it).

 

 

 

Problem solving and Evaluating Error Notes

 

PROBLEM SOLVING I will give you two methods for problem solving in chemistry.  They are really identical, but one may be easier for you to work and remember.

 

Method 1: I like this one.

Identify the GIVEN information.

Identify what you are trying to FIND.

Identify the TOOLS you have that may help.

SOLVE the problem.

EVALUATE to see if your answer makes sense.

 

Method 2:  From your book.

ANALYZE – look for given and find.

PLAN – what equations, tools, etc will you need and how will you solve.

SOLVE – do the work.

EVALUATE – Does your answer make sense.

THE MOST IMPORTANT STEPS ARE

IDENTIFYING WHAT YOU ARE ASKED TO DO!

EVALUATING IF YOUR ANSWER MAKES SENSE!

 

 

EVALUATING ERROR

If you are making cookies and you don’t add enough sugar, what will happen?

If you are making a steak and you over cook it, what will happen?

In science, you will observe that the cookie is not sweet enough, and try to figure out why it doesn’t taste right.

            Step 1: Evaluate error.  (What is wrong with the cookie?)

Step 2: Identify everything that could have caused the error you observed. (Did you miss

measure any of the ingredients, cook too long or too short, use wrong ingredient,

wrong temp, etc.)

            Step 3: For each variable in step 2, identify whether the error would cause the final answer

to be too high or too low.  (Adding extra sugar would make your cookie too sweet; addling less sugar would make it not sweet enough)

            Step 4: Identify which of the variables is/are most likely the cause of your error.

 

CALCULATING PERCENT ERROR

If your data is quantitative (has numbers) you should calculate percent error.

Example:  If I told you that bottle A in this lab has 20% sugar, what is your percent error?

            Remember that percent is always:

                          Part        x     100   =   Percent

                        whole

 

With errors, the “part” must be calculated as well.

Observed data – expected data   x   100 = percent error

                        Expected data

 

So:       If you measured 18% sugar, you would…

 

            18% - 20%    x     100 =   -10%  This says that you are 10% too low.

                    20%