Hot Cold BAM!

Heat capacity is the amount of energy needed to raise a substance 1*C. Heat capacities depend on the amount of the liquid and how it is contained.

Specific heat is the amount of heat needed to raise 1 gram of a substance 1*C. Specific heat is measured using a formula with J/gC. (Apparently that now stands for Jancaitis gone crazy instead of Joules per grams Celsius.)

We re-learned endo and exothermic reactions.We discussed them in the reaction unit, but are revisiting the topic because now we are also going to be calculating heat changes and specific heat values.

Endothermic reactions absorb heat and get warmer (End Up).

Exothermic reactions lose or release heat and get colder (Exit down). 

To test this out, students in groups were given a whack-a-pack and asked to make observations. The pack starts off at room temperature and when you hit it, the reaction occurs. This is a chemical reaction for a few reasons - one you can hear it fizzing. Two it blows up so a gas is being formed (1 of the 4 ways you know a chemical reaction has occurred). And Three there is a temperature change (another of the four ways). The pack gets really cold which means it is releasing heat and this is an exothermic reaction.

Watch this little video to see how it works. These are available at Dollar Tree at Valentine's Day if you are interested.

After this lab demo, students answered questions and then worked on math practice for heat changes and specific heat.

Solutions, Suspensions, and Colloids... oh my!

Solutions are homogeneous well-mixed mixtures that cannot be separated easily (a change in phase) - like kool-aid or saltwater. Suspensions will settle and separate over time because of gravity or because of differences in density - like oil and water or orange juice with pulp. Suspensions are heterogeneous. Colloids are weird. Colloids should settle and separate over time but because the particles are super-tiny just running into each other (Brownian motion) keeps them in suspension. Colloids can also represent two different phases so if it seems weird like you cannot classify it as just one phase - like fog, jello, whipped cream - it's a colloid.

We also discussed colligative properties. Adding solutes to a solution changes basic properties like melting points and boiling points, no matter what solute is added. A perfect tie-in for today. Salt is put on our roadways to LOWER the freezing point of water to about -4*C. Because the freezing point is lowered, the ice appears to melt and stay liquid, thus making our roads less icy. They do not salt the roads in places where the normal daily temperature is below 0 because the salt would have little effect.

Because it doesn't matter what the solute is, sugar could be used for the same purpose - it is just a lot more expensive! To read more, click here. 

Electrolytes can conduct electricity because the solute breaks up into ions and the ions can carry the electric current. Pure water does not conduct electricity - but water with solutes in it can. We did an in-class demo similar to this one to test some solutions. Salt water does conduct electricity, but sugar water does not because of the carbon. Gatorade conducts electricity but barely because of the high sugar amount in the drink.

Molarity is moles/Liters and is a quantitative way to measure concentration. Molarity descirbes with numbers if a solution is dilute or concentrated. It is a pretty easy formula so students zoomed through it. Molarity changes with the amount of solute OR the amount of solvent (liquid) so we will be discussing dilutions tomorrow.

Density

 

We have made sure that everyone had a good handle on density in regards to definition, math and formulas, and what it actually means.

Density measures matter in a given volume or the amount of stuff in a space. It can also refer to the amount of space between molecules. We looked at some diagrams and discussed scientifically why a person cannot walk through walls, why moving through air is easy, and why moving through water is slightly more difficult.

Density is how close together the particles are in a substance. If they are close together the substance is more dense. If the particles are far apart, the substance is less dense. I do not float in Lake Anna, but I do float in the ocean - therefore I am more dense than Lake Anna and less dense than the ocean.

Things that are more dense-sink, things that are less dense-rise to the top, things with similar densities-mix. If you were to pour liquids in a random order layers form because of the differences in density. Here is a photo of a demo.

What is a mole?

Moles are used to count atoms. There are 22,000,000,000,000,000,000 quintillion atoms in a grain of sand and even counting grains of sand is a pain. Because atoms are so tiny, we use the mole to estimate.

There are 6.02 x 10 ^23 molecules in one mole. That's a whole lot. This is our new favorite number because it needs to be memorized. We will practice converting from moles to molecules.

Next we discussed molar mass. Molar mass = 1 mole and it also equals atomic mass from the periodic table. To find the molar mass of carbon dioxide you find the mass of carbon and two oxygens and add them together. Finding molar mass is not difficult unless the molecule has tricky subscripts (which we have been practicing).

The third thing about moles is that "one mole of any gas will occupy 22.4 Liters." 22.4 is another favorite number. We can convert from moles to liters and from liters to moles. 

Conversions - Dimensional Analysis

Conversions, or dimensional analysis, are used to change one unit to another. This is really useful when converting to metric units, but is essential to chemistry in terms of mole conversions. Setting up conversions is a skill so we started with learning the format. There are plenty of how to videos out there on the internet for anyone needing a tutorial.

We practiced conversions with some of the crazy things people do to get in the Guinness Book of World Records - like longest ear hair, skinniest waist, tallest man, etc. I think the one the kids thought was the weirdest was the lady who can pop her eyes out 12mm.

Check out more crazy records here!

Next week we will be learning how to do conversions with moles!

Percent Composition

Percent composition is just like determining your grade - the amount you got divided by the the whole amount. 


With compounds, you find the mass of a particular element and divide it by the mass of the whole compound. So if you wanted to know the percent composition of oxygen in water, you would take the mass of oxygen and divide it by the mass of water. 

We practiced some basics and the students measured the amount of sugar found in DubbleBubble bubble gum. 

Soon, students will begin a paper forensics investigation that is using percent composition to determine which passengers in a plane crash are which, which passenger is responsible for the plane crash, and more. 

Significant Digits & Scientific Notation

Significant digits are used so that our calculations are not more precise than our measurements. All digits other than zero are significant.

Its the zeros that are the tricky ones. We went over the rules and then did some practice situations. We will continue to practice this and all calculations made for the rest of the year must be rounded to the correct number of significant digits. 

Scientific Notation is used for very large and very small numbers that usually have a lot of zeros to make the numbers for manageable. Most students are familiar with scientific notation and just need a bit of practice. 

Chromatography

Chromatography is the separation of liquids based on particle or molecule size. Chromatography is used to separate inks into the colors that make them up. Most inks are mixtures of colors and the ink will separate into bands of colors based on the size of the differnt ink molecules.The small particles move faster and will move further up the paper strip. Some black inks are actually made up of blue red, pink, and yellow.

Pairs or groups of students received a strip of filter paper and made a pencil line about 3 cm from the end. They then traced over the pencil line with a marker, dipped the paper into water and waited.

Chromatography can be used to separate any mixtures with different size particles and actually  gel  electrophoresis used for DNA analysis works on a similar principle.

NFPA Hazard Diamonds

Most of us have seen these diamonds on trucks as we pass them on the highway. These diamonds are useful for safety and response teams to identify what is in the truck so the correct precautionary and clean up measures can be made. 

The NFPA 704 fire diamond (or hazmat diamond) is described in NFPA Standard 704, maintained by the National Fire Protection Association. The system identifies four key hazards (health (blue), flammability (red), instability (yellow), and special (white)) and their degree of severity. Hazard severity is rated numerically, ranging from 0 (minimal) to 4 (severe).

The hazard diamond is useful because it allows emergency personnel to quickly and easily identify the risks posed by hazardous materials and is  useful to determine what, if any, special equipment should be used, procedures followed, or precautions taken during an emergency response. (Summarized & more information here.)

Want to make your own customizable hazard diamond? Click here. Why does this feature exist? So people can make easily identifiable hazard diamonds for any chemical they have on hand. 

Lab Equipment

Students need to be familiar with certain lab equipment and its purpose, even if we won't use it in labs for high school chemistry. Students identified equipment using examples of the real thing (we made this into a contest) and also by cutting a pasting black and white drawings.

Finally students had to sort equipment based on what its main purpose is. Some equipment is used for liquids, some for solids, and some for heating. Some is used for all of those things. 

The three pieces of equipment most likely to come up, and the most confusing when in black and white photos are the watch glass, evaporating dish, and the crucible (which has a lid). All three of these can be used for heating substances to remove water among other things. In real life they look different - but in drawings they look similar. How to tell them apart? The watch glass resembles a contact lense; the evaporating dish has a pour spout; and the crucible is more cup shaped and often is pictured with a lid. 



Here is an online quiz on lab equipment with photos! Try it!

Spring 2012 - Welcome Back!

Greetings students, parents, and guardians.

Welcome to a new school year with Ms Jancaitis! This blog has been set up to connect students, parents, and guardians with the chemistry class.

At Open House or in class, each student will receive a course syllabus. The course syllabus outlines what the course will be like, what topics will be covered, and course expectations. It also contains contact information. There will be a quiz on this syllabus on Thursday.

Our first unit will cover lab safety and equipment. Each note packet comes with the safety rules and contract. The safety rules and contract need to be read and signed by both the student and parent guardian. The safety rules are rules designed to keep the classroom safe and orderly to maximize learning and prevent accidents and injuries. These rules need to be studied because there will be a safety test on Monday or Tuesday and infractions of these rules can lead to disciplinary action as well as low assignment grades. A contract holds students accountable for the items that are broken if the student is acting a manner that is unsafe for themselves or those around them.


Please have these papers signed and returned by Monday the 14th. Students not returning signed safety rules and safety contracts will not be able to participate in labs and activities until the contracts are signed and returned.