Accel. Chem. Blog 4

                As we come to the end of another chapter in Accelerated Chemistry, I can safely say that this class has probably challenged and pushed me more than my other classes this year.  In our latest unit, we have covered: balancing equations, types of reactions, and reactivity.  These all relate to the overall theme of chemical equations, which builds off of the last chapter, which was about charges in atoms and molecules, where we began to look at how elements are bonded together.

            We started the unit with balancing chemical equations.  The reason we do this is to follow the law of conservation of matter.  It is easy enough to write out a reaction, but you may end up with more of an atom on one side of the reaction, and that defies the law, because you either created to destroyed matter.  First, you make sure that you have written the correct formula, paying attention to charges and diatomic particles.  Then, you need coefficients to ensure that there are equal numbers of the same atoms on both sides.  We also learned some tips to help us in balancing: 1) Adjust the coefficient of a single species (ex. O₂) last.      2) Temporary (key word: TEMPORARY!) use of a fraction or decimal is helpful.  3) If there are polyatomic ions on both sides of the reaction arrow, you should balance them as groups.  To help teach idea of balancing equations, we used models of atoms to put them together and learn about the use of coefficients.

            Next, we learned about the types of chemical reactions.  To learn about this, we performed a series of labs.  There are five types of reactions: Synthesis/Combustion, Decomposition, Single Replacement, Double Replacement, and Combustion.  A synthesis reaction will produce one product. (ex. 2Na + S à Na₂S)  A decomposition reaction will begin with one reactant, but will end with two products, so it’s basically the opposite of a synthesis reaction.  Single replacement begins with an element and a compound, and ends with an element and a compound, but the elements are switched. (ex. 2Li + MgCl₂ à 2LiCl + Mg)  The metal has to react with the compound.  Double replacement basically switches around the elements.  It begins and ends with two compounds.  (ex. 2AgNO₃ + CaCl₂ à 2AgCl + Ca(NO₃)₂)  The last reaction is combustion which is just to burn.  You are always going to end up with Carbon Dioxide and Water, and all you have to do is make sure that the reactant side has O₂ and that the equation is balanced in the end.

            Lastly, we learned about reactivity, because not all elements can react.  There are a few rules when it comes to reactivity.  The main rule is that if an element is above another on the list, it will react with it, but not the other way around.  For example, Barium will react with Tin, but Chromium will not react with Calcium.  (ex. Zn + CuSO₄ à ZnSO₄ +Cu)  Another rule is that all metals about Hydrogen displace Hydrogen from HCl or H₂SO₄.  (ex. Mg + H₂SO₄ à MgSO₄ + H₂)  Another is that metals above Magnesium displace Hydrogen from water.  (ex. Fe + H₂O à no reaction)  Finally, metals above Silver on the list combine directly with Oxygen in a synthesis reaction.  (ex. Pt + O₂ à no reaction)

            A “real life example” of balancing equations is in cooking.  If you have a recipe that calls for two eggs for every three cups of flour, if you put in four eggs, you need to put in six cups of flour.  Another real life application is in a combustion reaction, the fact that you need O₂ in the equation.  I knew that you need oxygen to have a fire, but it is interesting to see that shown in what we are doing with chemical equations. 

            Our work with chemical equations originally proved to be difficult for me, but over the course of the unit I have gained deeper understanding and appreciation for the process.  Balancing equations, knowing the type of reaction, and using the activity series to solve these scientific puzzles is a vital part of chemistry and I am glad for what I have learned in this unit. 

Accel. Chem. Blog 3

             Our most recent chapter in chemistry has been about counting particles.  This has included relative mass, Avogadro’s number, molar mass, mole calculations, and most recently, percentage composition.  A lot of what we covered has had to do with calculations, so a calculator was definitely necessary in this unit! 

            The Periodic Table shows us the masses of all of the elements.  These masses are relative masses, though, based off of Carbon 12.  For example, the relative mass of Lithium is 6.99amu’s, the relative mass of Oxygen is 15.99amu’s, and the relative mass of Sulfur is 31.96amu’s.  We began with a lab activity counting popcorn, rice, and bean particles.  Using a scale, we measured the mass of 1 dozen of each of these objects.  We could then use that number to calculate how much other amounts would weigh.  We could also determine how many dozen of each object would be in say, 400,000 grams by dividing that by the mass of a dozen.  (For the rice, it would have been 400,000 ÷ .22= 1,818,181.818 grains of rice.)

            This then ties into Avogadro’s number, which is the number of atoms in 12.00 grams of C-12.  This number is 6.02x10²³, which is also known as the mole.  Mole (mol.) is the word for 6.02x10²³ of anything, so you could have a mole of grass seeds, a mole of M&M’s, or a mole of seconds.  Molar mass is then the mass of 1 mole of atoms/molecules, but expressed in grams.  For example, a mole of Sulfur weighs 32.1 grams.  To help us understand the enormity of the mole, we ran calculations and we will be creating an electronic poster comparing a mole of something to something large like a planet.

            Mole calculations revolve around a “for every…” statement.  6.02x10²³ stands for the number of atoms/molecules and its statement could read like this: For every one mole of Copper, there are 6.02x10²³ atoms of Copper.  Molar mass is really just equal to grams.  Its statement could read: For every one mole of Copper, there are 63.6 grams of Copper.  This knowledge helped us in a lab in which we found the number of water molecules and where we found how many pieces of chalk it would take to contain 5.62x10²³ molecules of chalk.  Using my mouth, we discovered that I could hold 1.91x10²⁴ molecules of water.  We also discovered that it would take 93.45 pieces of chalk to hold the given amount of molecules.  We needed information like the mass and the number of molecules to solve these problems.

 

   

            Lastly, we covered percentage composition.  This can be used to find the amount of a certain element.  There are two approaches.  One is through relative mass data.  To find the percent of Oxygen in 15 grams of Potassium, Chlorine, and Oxygen, you take the total number of grams (15) and subtract the number of grams in K and Cl (9.1) from that.  That leaves 5.9 grams of Oxygen.  Then, to find the percentage, you calculate 5.9g of O divided by 15.0g total, and multiply your answer by 100.  This shows that it’s 39% Oxygen.  The second method is from the formula.  If we have KClO₃, we find the mass on the periodic table of each of them and add those together (122.6g).  To find the percent of Oxygen again, you would find the mass of 3 Oxygens (48.0) and divide that by the total.  Multiply that by 100, and you have your percentage total of 39%.  In the case of a hydrated compound, you do the same thing, but instead of separately adding 2 Hydrogens and an Oxygen for water, you just add the water, which is 18 grams.

            While explaining this all is rather complicated and probably a pain to read, I can truly say that I feel that I’ve improved my skills in this chapter.  The idea of moles is really mindboggling.  Even when you think about the size of a stick of gum and the size of the moon, it’s still a little hard to grasp, because there’s nothing that we are familiar with that comes close.  That’s probably what will stick most in my mind leaving this unit, and I doubt (especially after being inducted into the Mole Patrol) that I will ever forget Avogadro’s number.


 

Accel. Chem. Blog 2

            Recently in chemistry, we have been learning about particles and particle movement and how that relates to the states of matter.  We completed several activities to illustrate this concept and I believe that they did a good job of teaching us about particle motion.  The way that we showed movement was through “wooshies” which were like little tails on the particles to show speed and direction of particle movement.

			For some reason, I cannot delete the table. Sorry!

            One key term was diffusion.  Diffusion is the effect of particles moving in all directions due to collisions to completely fill a container.  This container could be as small as a beaker or as big as a room.  Particles are in constant, random motion.  They change direction when they collide with each other or the container.  To illustrate diffusion, we did a spray activity.  A spray bottle filled with a scent was sprayed at the front of the room and as we began to smell it, we had to raise our hand.  This way, we could actually see how the particles moved through the room because it took longer for the people at the back of the room to smell the spray because the particles needed time to get around.

            Another illustration of diffusion is to have two beakers: one with hot water, one with cold water.  Put food coloring in both of them and observe how they spread out.

The red water is hot, the blue is cold.  The hot water spreads the dye out faster, because the particles are moving faster, colliding with the dye particles and moving them all around in the beaker.  The cold water particles are moving slower so they take longer to spread out because they collide with the dye particles less often.  We did a computer simulation to show this.  It showed how the particles moved and collided.  It also showed another important concept.  Energy is a quantity that has the capacity to cause change and is conserved.  Conserved is the key word.  Energy is transferred between particles when particles collide, but the total energy does not change.  The speed of the particles tells us temperature or thermal energy.  We learned about this through the Eureka videos.

            So basically, there are three states of matter.  Solids have a definite volume a definite shape, are not compressible, and their particles are in a vibrating, regular lattice.  Liquids have a definite volume, take the shape of their container, are slightly compressible, and their particles are free to move past and along each other.  Gasses have no definite volume, take the shape of their container, are compressible, and their particles move randomly in all directions. 

            When particles are heated up, they expand in any way they can.  This was shown through an activity where we had a tube of colored liquid that was placed in a beaker of heating water.  A rubber stopper held a long, clear tube.  As the liquid heated, the particles wanted to expand, so they traveled up the tube.  Another activity that showed this concept was where we had a large, sealed garbage bag with straws at every corner to blow into.  Four people blew into the bag while one person sat on the bag.  The hot air particles from our breath bounced all around and hit the inside of the bag to the point where the bag expanded enough to hold the person off of the ground.

            Most recently, we have learned about gas pressure.  The air that is all around us was once thought to be weightless, but we know that there is indeed weight to the air, and we call this air pressure.  Air pressure changes with altitude and with the weather.  The higher up you go, for example, Mount Everest, the less air pressure there is, because there is just that much less than if you were at sea level.  Air pressure is measured in mmHg, atm, and kPa.  We did an activity to illustrate air pressure with Kool-Aid pouches.  Almost everyone thinks that when you use a straw, you simply suck the straw, and that is how the juice gets to your mouth.  But the scientific answer is that you suck the air out of the straw on top, and then the air pressure around the juice pushes down and forces the juice up the straw. 

This leads me to wondering if it would be harder to suck through a straw if you were at a higher elevation, like Mount Everest.  If I were to climb it, I would be sure to test this.  We also learned with this that a barometer works better with Mercury than with water, because if you used water in a barometer, it would need to be an extremely long tube because of the amount of air pressure.

            Most people would wonder what any of this has to do with “real life”.  But I have been thinking about this all a lot, recently.  In indoor emergency sprinkler systems, knowledge of particle movement is used because of the heat that a fire generates.  Understanding particle movement is important because everything is made up of particles.  We are in constant contact with particles.  And knowledge of particles may lead to great inventions and ideas.  It might be a little hard to grasp at times because they are so small, but with enough effort, you can understand particles well.

Chemistry Reflection One

With two weeks of school completed, I have started to have a feel for all of my classes.  I have been very nervous about this year because I have quite a lot on my plate, but so far, while I know that the first two weeks are slightly different from the rest of the year, it looks like things will be working out fine.

These past two weeks, we have focused on the ideas of the mass of an object, physical and chemical changes, and on volume.  The mass of an object is the amount of matter in an object and volume is how much space that an object takes up.  These measurements can be altered when an object undergoes a change.

          To learn about mass, we did a lab that consisted of eight experiments.  In each lab, we weighed the object before and after to demonstrate how the object’s mass changed, if at all.  The experiment that I found most interesting in this lab was when we put Alka-Seltzer into a bottle of water.  Below are the details for this experiment. 

When our group performed this experiment, we found that the mass decreased by .07mg because gas was released from the top of the bottle.  Another experiment that we did was to take a piece of steel wool and hold it over a Bunsen burner.  The mass of the steel wool increased by .18mg because it took in oxygen.

          We also did a lab to demonstrate whether or not a change was a physical or chemical change.  In one experiment, we combined iron chloride and thiocyanate.  The iron chloride was a yellow color, and the thiocyanate was clear.  When we combined them in a beaker, the result looked like this:

The new substance was thick and a dark red, resembling blood.  This was an example of a chemical change.  We knew this because the color change was unexpected.  In another experiment, we dropped a piece of Zinc into a beaker of dilute sulfuric acid and the Zinc began to bubble and fizz.  The Zinc was reacting with the dilute sulfuric acid.

          Finally, we began to learn about volume and how to measure volume.  We practiced this by measuring volume in both milliliters and centimeters³.  Each group was given a container.  It was either a box or a cylindrical bottle.  My group got the bottle.  We then marked the bottle at different heights and found the volume at those different heights in cm³.  Then, we filled the bottle with water up to the lines that we had marked, and poured all of that water into a graduated cylinder to measure it in mL.  Lastly, we put our data into Microsoft Excel and made a graph, which we copied on to a whiteboard to share with the class.  When we discussed our answers as a class, we decided that measurements in cm³ are far more precise than measurements in mL.  Here are some pictures from this lab:

It’s pretty clear that we covered a fair amount of information.  Along with that, we have been able to get to know each other as a class, which is a good thing since we will have to work together in the months ahead.  I feel that I have been a team player and have worked with my lab partners well and that I accomplished a lot.  I may have been afraid to be in Accelerated Chemistry at the beginning of the year, but I know now that this will be a very fun, very engaging class and I look forward to the rest of the year.