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Tutor profile: Cheryl B.

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Cheryl B.
Need to find information for a science paper? Ask this librarian!
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Subject: Library and Information Science

TutorMe
Question:

Your professor wants you to find "reputable sources" for your research paper. What does this mean?

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Cheryl B.
Answer:

Basically, your prof wants to know if the sources you quote are, well, CRAAP. When you have found a source of information (a book, journal article, website, etc.) you should evaluate it before using it. I use the CRAAP (Currency, Relevance, Authority, Accuracy, and Purpose) analysis to figure this out. Currency: how timely is the information? For most science papers this means how recently was the information published. It is also affected by how cutting edge the topic you are looking into is. If you are looking up how to properly mix up a solution of potassium iodide, realistically any basic chemistry text or lab book published in the last 30 years would be a completely reasonable source. However, want to discuss recent developments in the synthesis of a class of compounds, your sources will need to be much more recent - probably published in the last few years. How timely an information source is changes depending on what you are trying to learn! Relevance: Does the information source relate to your topic? As much fun as it would be to cite a cute cat YouTube video in your paper on global warming, the video probably doesn't cover your topic. Authority: Does the creator know what they are talking about? Can you trust them to give you accurate information? If you break your arm and ask for a doctor which would be the best source of a treatment plan: a medical degree or a history degree? Remember how authoritative an information source depends on what the question is! If you are trying to evaluate if you should use a source of information find out a bit about the author/creator. Many books and internet sources have "about us" or biography sections. This is the area that takes the most time to be able to assess accurately. As you become more knowledgeable in your field, you will start to know which universities, publishers, etc tend to publish quality information. When in doubt ask a librarian or instructor for help evaluating if the source is a good one. Accuracy: how correct is the information? A source can demonstrate how correct they are by providing evidence. Sometimes this will be providing their experimental results. Sometimes this will be done by citing other (non-CRAAP) sources. One thing I tend to look at is the basic facts that the source did not feel the need to cite. If they stated that water boiled at 10^{o}C, I would have questions - are they wrong, or simply careless? Either is a concern. Purpose: why was the information made available? If the source was aimed at children it probably doesn't have the depth of information you'd need for a term paper on the eating habits of tyrannosaurs. (However, it would be great for teaching your curious niece about the same topic. Matching purpose depends on who needs the answer!) Additionally, you need to be careful when using something that has a potential political bias or is intended as advertising. Usually, the way we evaluate the purpose for which an information source exists is by looking at the tone and vocabulary used to communicate.

Subject: Chemistry

TutorMe
Question:

How many grams potassium iodide to we need to create 100.0 mL of 1.0 M aqueous solution?

Inactive
Cheryl B.
Answer:

The first thing I usually do is make certain that all of my units will play nicely together. So: 1.0M = 1.0 mol/L this is the desired concentration, c 100.0 mL = 0.1000 L this is the desired volume, v We could look up the formula to convert between these, but I usually look at the units to determine what additional information I can learn from what I have. If we multiply mol/L by L, then we have how many moles of potassium iodide we need since 1/L and L will cancel out when multiplied. 1.0\frac{mol}{L} \times 0.1000L=0.10mol=n However, we want to know the mass (m) of potassium iodide (KI). To do that we need the molar mass of KI. A periodic table gives the atomic mass of K (39.098 g/mol) and I (126.904 g/mol). There is only one of each atom in KI, so we add them to get 166.002 g/mol. I again look at the units. Multiplying the number of moles n by the molar mass will cancel out moles. 0.10mol \times 166.002\frac{g}{mol} = 16.6002g To the correct number of significant figures, this would be 17g

Subject: Basic Chemistry

TutorMe
Question:

What is the balanced reaction between potassium iodide and lead(II) nitrate?

Inactive
Cheryl B.
Answer:

The first thing we need to do is figure out what the reaction is. Potassium (K) normally has a +1 charge when it is part of a salt, and iodide (I) has a -1 charge, so each ion brings enough charge to balance the other. The formula for potassium iodide is therefore KI. Lead (Pb) can have a couple different charges, but the (II) in the compound name tells us, in this case, it will be +2, and nitrate (NO$_{3}$) is -1. To balance the charge of one lead ion we need two nitrates. Therefore, the compound will be Pb(NO$_{3})$_{2} So, we know the reactants. KI + Pb(NO$_{3})$_{2}. What are the products? Since we have two ionic compounds, the most likely reaction type is a "double replacement reaction." The potassium and lead positively charged cations will replace the other, so both negatively charged anions (iodide and nitrate) will have new partners. We determine the chemical formula of newly created potassium nitrate and lead (II) iodide as we did above. Therefore, the unbalanced reaction is: KI + Pb(NO{_3}){_2}\rightarrow KNO{_3} + PbI{_2} A balanced reaction means we have the same number atoms/ions on both the product and reactant side of the reaction arrow. As currently written we have the same number of cations, the anions are unbalanced. We start with one iodide and end up with two. So, there must be two potassium iodides to act as the source for the iodides in the products: 2KI + Pb(NO{_3}){_2}\rightarrow KNO{_3} + PbI{_2} Now the potassium is unbalanced. There must be two potassium nitrates on the product side: 2KI + Pb(NO{_3}){_2}\rightarrow 2KNO{_3} + PbI{_2} After double checking the number of nitrates and lead (II) ions, we can confirm the reaction is balanced. Note: you could have started by balancing the nitrates and gotten to the same place.

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