Lab 6: Mole-Mass Relationships

The purpose of this lab was to practice calculating theoretical yield and percent yield using the experimental data of a reaction of sodium bicarbonate and hydrochloric acid.  We also had to find the limiting reactant using the reaction NaHCO3 + HCl --> NaCl + CO2 + H2O by looking at the relationship of the reactants and products (how much product each reactant yielded).

Questions 1-4:

Our percent yield is lower than 100% most likely because some salt popped out during boiling or we didn't wait long enough for all the water to evaporate before weighing the dish.

The remaining solid in the evaporating dish after boiling.  The salt is a bluish color because the same dish
 was used in the copper sulfate hydrate lab, and the dish was probably not cleaned very well after use. It was
also interesting that the tongs left a yellow-greenish mark on the salt.

Lab 5B: Composition of a Copper Sulfate Hydrate Lab

Hydrate before heating:

Hydrate after heating:

Calculations for Questions 1-4

Question 5: The empirical formula we calculated for the hydrate was 1 CuSO₄ · 4 H₂O.  We predict that the coefficient for H2O will be slightly smaller, if not equal to the actual value since our percent error was so small (8.3%).

Lab 5A: Mole Baggie Lab

The purpose of this lab was to identify a mystery substance in a plastic baggie given only the mass of the empty bag and the number of moles/particles.  We determined the identity of the substance by first weighing the bag on the scale to find the total mass, and then subtracted the mass of the empty bag from that, which gave us the substance mass.  Afterwards, we calculated the molar mass by dividing the substance mass (in grams) by the number of moles in the substance.  For Set B, we were given the number of particles instead of moles, so we just converted it into moles and plugged that into the molar mass equation.  Finally, we matched the calculated answer with one of the given possible compounds using the periodic table.

Bag A4 contained calcium carbonate, and bag B3 contained potassium sulfate.

Lab 4A: Double Replacement Reaction Lab

Well plates after the reactions.  Plates 2-7 show
chemical reactions in which a solid precipitate formed.

Balanced chemical reactions #1-5 with net ionic equations

Balanced chemical reactions #6-10 with net ionic equations

The most surprising part of this lab was how easy writing the net ionic equations turned out to be.  I expected it to be more complicated, but taking the shortcut presented in class instead of writing out the complete ionic equations was a lot quicker and more convenient.  The most challenging part was looking up if certain compounds were aqueous or solid using the solubility rules.

Lab 3: Nomenclature Puzzle

The goal of this activity was to solve a binary and polyatomic ions puzzle by matching the ion formula to their name, using our newly learned knowledge of chemistry nomenclature!  The biggest challenge we encountered was combining the pairs of triangles to form bigger squares and chains.  This puzzle wouldn't have been possible without organization and teamwork, so I think my biggest contributions were helping separate the squares into categories of certain elements, combining single squares at the very beginning, and also looking up certain unknown ions in the lab book.

Our finished puzzle!

Lab 2B: Atomic Mass of Candium

Candium's three isotopes - M&Ms!

The purpose of this lab was to plan and implement a procedure to determine the average atomic mass of the element candium, given a random sample of three different isotopes of the element: regular M&Ms, peanut M&Ms, and pretzel M&Ms.

Average atomic mass: 1.43 g

1.  Ask a group nearby what their average atomic mass was.  Why would your average atomic mass be different than theirs?

Another group's calculated atomic mass was 1.52 g.  Ours is different because each group received different amounts of isotopes (type of M&M) and different total amount and weight.  The sample sizes were also not very big, leading to more variation.

2.  If larger samples of candium were used, would the differences between your average atomic mass and others' average atomic masses be bigger or smaller?

The differences would be smaller, because the larger the sample, the closer the calculated masses will be to the average value as a result of less variation.

3.  If you took any piece of candium from your sample and placed it on the balance, would it have the exact average atomic mass that you calculated?  Why or why not?

No, because the calculated atomic mass is just an average and isn't necessarily the same value, but should be close.  It would be extremely rare for a random candium sample to be exactly the same as the average atomic mass.

4.  Periodic table square for candium!

Lab 2A: Chromatography Lab

Before:

After:

My partner Meghana and I with our two favorite chromatograms!

Questions:

1)  Why is it important that only the wick and not the filter paper circles be in contact with the water in the cup?

It's important that the filter paper isn't entirely saturated at first so the water can seep through the wick and slowly onto the paper, which then gives the ink time to spread out from the center and separate into the different pigments.

2)  What are some of the variables that will affect the pattern of colors produced on the filter paper?

Some variables include the type of pen used (since different inks are composed of different colors), the pattern drawn using the pens, the distance the pattern was drawn from the center, the amount of ink used, and the length of the wick.

3)  Why does each ink separate into different pigment bands?

Each ink has different mixtures and will travel up the paper at different rates depending on their characteristic physical properties.  Some components in the mixture are more strongly adsorbed onto the paper than others, and those will move up the paper more slowly than the solvent.  Components that are not strongly adsorbed onto the paper will move up the paper more slowly than the solvent.  This "partitioning" of the components of the mixture between the paper and the solvent separates the components and creates different pigment bands.

4)  Choose one color that is present in more than one type of ink.  Is the pigment that gives this color always the same?  Do any of the pens appear to contain common pigments?  Explain.

Blue is one color that is present in both chromatograms, and the pigment that gives this color is always the same, since blue is used in the ink of many types of pens and markers.  Many of the pens appear to contain common pigments besides blue, such as yellow, orange, pink, and a bit of violet.  The order that the colors show up from the circle is also similar on both papers -- yellow, orange, and pink (warmer colors) are near the center, and blue, the cooler color, is on the outer side.

5)  Why are only water-soluble markers or pens used in this activity?  How could the experiment be modified to separate the pigments in "permanent" markers or pens?

Only water-soluble pens were used so that water could cause the ink to spread across the filter paper.  The experiment could be modified to separate the pigments in permanent markers by using a solvent, for example, rubbing alcohol, that is able to "remove" or separate permanent markers.