Density and graphing today! Woohoo!!! Density is one of the most important properties of matter. POPULATION DENSITY Population density is the number of people in a given area. The equation for population density is:
MASS DENSITY The density of an object is its mass divided by volume.
GRAPHING There are five important things that we must include in a graph; a labelled axis, an appropriate scale, a title, data points, and a line of best fit (do not connect the dots!) are all required. The independent variable goes on the x-axis. The dependent variable goes on the y-axis.
It is important to remember that when plotting graphs, plot the data on 3/4 of the graph. In other words, use your space wisely.
There are three things that we can do with a graph. First, we can read the graph. Second, we can find the slope (rise/run). Third, we can find the area of the graph.
We had only a short block to learn one of the most important things in Chemistry: Unit or Dimensional Analysis. Unit Analysis lets you determine the units of a variable in an equation.
HOW TO CONVERT UNITS In order to convert units, you must first identify what units you want to end up with. Then, find a conversion factor, and place units in the correct place. Finally, cancel units. Below are are few examples of unit analysis:
Don't forget those SI prefixes!
Having trouble? Here's an entertaining step by step tutorial:
Measurements are comparisons between an unknown and a standard result. Accurate measurements are essential in chemistry. Today we drove right into common SI prefixes, and we explored the ideas of accuracy, and error. We were also introduced to some mind-boggling concepts, and had a laugh at a comical snippet of "The Big Bang Theory". The 7 fundamental units are mass (kg), distance (m), time (s), temperature (K), amount of substance (mol), current (A), and luminosity (cd).
SI PREFIXES An SI prefix is a name that precedes a basic unit of measure. It indicates the multiple of the unit. Here are some common SI prefixes (next to each prefix is its multiplier):
Prefixes are all the same for measuring length, (meter), volume (liter), or mass (gram). Metric prefixes both increase and decrease the size of a unit. Here is a chemistry cartoon with SI prefixes that I got from a chemistry book:
Prefixes are used in many areas of our daily lives. Here are a few examples of places that you may see prefixes being used:
ACCURACY VS. PRECISION Accuracy is the degree of closeness of a measured or calculated quantity to its actual (true) value. In other words, it means getting a result that is close to the real answer. Precision is the degree to which further measurements or calculations show the same or similar results. That is, getting a similar result every time you try. A good analogy is that of a dartboard:
EXPRESSING ERROR In chemistry, the definition of an error is a discrepancy between a computed, observed, or measured value or condition and the true, specified, or theoretically correct value or condition. It is a fundamental part of science and we learned that there are usually three reasons for error:
1. Physical errors in the measuring device 2. "Sloppy" measuring 3. Changing ambient conditions
Measurements are uncertain because they are never free of flaws, and estimation is always involved (whether using a digital display or scale). Because the last digit of the measurement is estimated, a plus-or-minus symbol, ±, is used to show the uncertainty of a measurement. To make your measurements as reliable as possible, read the scales and digital displays of your instruments carefully. Also, keep the instruments clean and ensure that they are in tip-top shape. Error is taken to be half the smallest division on your measuring device. There are two possibilities of error; absolute error and percent error.
Examples: *Daniel measures the volume of a chemical to be 40.0mL. The actual value is 41.2mL. Determine the absolute error in this measurement.
absolute error = measured - accepted
absolute error = (40.0) - (41.2)
absolute error = -1.2
(Therefore, Daniel's measurement was off by 1.2mL. Because it is negative, his measurement was below the actual value.)
*Determine the percent error in this measurement.
percent error = [(absolute error) / (accepted value)] X 100
percent error = [(-1.2)/(41.2)] X 100
percent error = [-0.029126213] X 100
percent error = -2.912621359%
percent error = -2.9% (to 2 significant digits)
(Therefore, the percent error of the measurement was -2.9%. Because it is negative, his measurement was below the actual value.)
A meniscus is the curved upper surface of a still liquid in a tube, concave if the liquid wets the walls of the container, convex if it does not, caused by surface tension. With liquids such as water, the bottom of the curved surface of the liquid is the point where the reading is taken.
Here is a mind-boggling video of a hypercube - a figure in four or more dimensions with sides that are all of the same length and angles that are all right angles:
In today's class we learned about the classification of chemicals. The homogeneous division of matter consists of only one visible component. The heterogeneous division of matter contains more than one visible component.
HOMOGENEOUS SUBSTANCES
PURE SUBSTANCES Elements are substances that cannot be broken down into simpler substances by chemical reactions. Oxygen (O₂ ), iron, magnesium, and phosphorus (P₄) are all examples of elements. Compounds are substances that are made up of two or more elements (eg. water and sugar) and can be changed into elements (or other compounds) by chemical reactions. It is often very difficult to know if something is an element or a compound, because the differences are only visible on the atomic level. One method is to connect the substance to an electric current. This technique, called electrolysis, can split the compound apart.
Experiment of electrolysis performed in class:
HOMOGENEOUS MIXTURES A solution is a homogeneous mixture of two substances. They usually involve liquids but don't have to (Fog, Steel). The component present in smaller amounts is the solute. In salt water, salt is the solute.
HETEROGENEOUS SUBSTANCES
Many mixtures are easy to identify while many others are easily confused as pure substances. In heterogeneous mixtures the different parts are clearly visible, while in homogeneous mixtures the different parts are not visible. Depending on the different types of mixtures, there are many methods that can be used to separate mixtures. We can do this with our hands (although time-consuming), or by the processes of filtration, distillation, crystallization and chromatography.
WHAT MATTERS? Matter is anything that has mass and takes up space. It undergoes many changes. In chemistry, nearly all changes can be broken down into three categories:
1. Physical changes 2. Chemical changes 3. Nuclear changes
PHYSICAL CHANGES
Physical changes are changes from one state (solid/liquid/gas/aqueous) to another without a change in chemical composition. Other examples of physical changes include crushing, tearing, boiling water, cutting wood, and smashing cars. In any physical change, the basic chemical identity of the substances is unchanged. In other words, no new substances are formed.
Melting: solid → liquid Freezing/Solidification: liquid → solid Condensation: gas → liquid Evaporation: liquid → gas Sublimation/Deposition: gas → solid Sublimation: solid → gas
The following graph demonstrates the process of melting that water follows:
And now here's a song that you can use to help you remember physical changes:
CHEMICAL CHANGES
Chemical changes are changes where bonds are broken and formed between different atoms. New substances are created, and the properties of matter change (conductivity, acidity, color, etc.). Examples of chemical changes include iron rusting, burning wood, and digesting food.
Iron rusting is a chemical change, because oxygen bonds to the iron atoms (which where not chemically bonded to anything before) to create an oxide of iron.
Frying an egg is a chemical change, because the chemical composition of the egg changes. This cannot be reversed easily.
2 NI3 (s) → N2 (g) + 3 I2 (g) + energy
The decomposition of nitrogen triiodide is a chemical reaction. It is an exothermic reaction. We witnessed an astonishing chemical reaction today in chemistry class. Mr. Doktor mixed lead (II) nitrate with potassium iodide. As a result, the two solutions reacted to form lead (II) iodide (precipitate) and potassium nitrate (salt).
Here is a video and a balanced equation of the chemical reaction:
Pb(NO3)2(aq) + 2KI(aq) → PbI2(s) + 2KNO3(aq)
NUCLEAR CHANGES We will not go into great detail for this change just yet, but nuclear changes are changes in which the elemental identity of the atoms are changed.
BALANCING TIPS There are a few things that you can do to make your life much easier when balancing chemical equations. Balance the elements in elemental form last (Fe, O2,S8,P4). If they don't break apart, balance the polyatomic ions (eg. SO42-)as a group. Finally, balance oxygen and hydrogen last.
We were also introduced to the concepts of exothermic and endothermic reactions. An exothermic reaction is a chemical reaction accompanied by the evolution of heat. Check that energy is on the right side of the equation. This indicates that the reaction is exothermic. An endothermic reaction is a chemical reaction accompanied by the absorption of heat. Check that energy is on the left side of the equation. This indicates that the reaction is endothermic.
The distinction between the two types of reactions:
In today's class we learned how to balance and name chemical equations. Yay!!!
PHASE SYMBOLS Phase symbols are subscripts that indicate the phase of the chemical:
-solid (s) -liquid (l) -gas (g) -aqueous (aq)
It is important to indicate the phases of each element and compound when specified in the word equation, as well as balance the equation.
SOLUTIONS A solution is a substance consisting of two or more substances mixed together and uniformly dispersed, most commonly the result of dissolving a solid, fluid, or gas in a liquid. More simply put, it is something that is dissolved in water. The phase is, therefore, aqueous (dissolved in water). The solvent is the substance that dissolves things. The solute is the dissolved substance.
WRITING FORMULAS We write the formulas for compounds by using the cross-over method:
When balancing, we use coefficients in front of certain formulas, so that there will be an even number of each chemical's atoms when we are finished. We are told that trial and error is much simpler than the "laundry list method" (where you write a list of all of the elements present in the equation).
Certain elements are diatomic (molecules composed of two atoms), while certain elements are polyatomic (molecules composed of several atoms). You can remember the diatomic elements by remembering Dr. HOFBrINCl (hydrogen, oxygen, fluorine, bromine, iodine, nitrogen, and chlorine). They also form a 7 (in addition to hydrogen) in the periodic table. The diatomic elements have a subscript of 2 when the elements are by themselves in a chemical equation. Other polyatomic elements are phosphorus and sulfur. Ozone is another polyatomic element. It is formed by electrical discharge in oxygen. Phosphorus has a subscript of 4, sulfur has a subscript of 8, and ozone has a subscript of 3.
-hydrogen, H2
-nitrogen, N2
-oxygen, O2
-fluorine, F2
-chlorine, Cl2
-bromine, Br2
-iodine, I2
-ozone, O3
-phosphorus, P4
-sulfur, S8
Here is an instructional video on balancing chemical equations:
We also began using coloured cards to indicate to Mr.Doktor whether we "understand the material," "kind of understand the material" or if we are "totally lost."
-Green("totally understand it") -Yellow("kind of understand it") -Red("totally lost")
Safety is crucial in the chemistry lab. We must always put our safety first! There are so many hazards that we must work to avoid. Here's the list of rules that our class came up with: 1. No eating in the lab 2. No horseplay 3. Follow instructions 4. Do not mix chemicals 5. Wash your hands before and after conducting an experiment 6. Wear appropriate lab safety equipment 7. Waft chemicals when smelling 8. Tell Mr. Doktor if you spill something or if you are hurt 9. Tie long hair back 10. No loose clothing 11. Be aware of your surroundings
WHMIS divides hazardous materials into six main classes based on their specific hazards:
Compressed Gas: Products held under pressure Flammable and Combustible Material: Products that will burn or catch on fire easily Oxidizing Material: Products that can cause or promote combustion of another material (whether or not they are themselves combustible) or products that are organic peroxides Materials Causing Immediate and Serious Toxic Effects: Products that can cause or promote combustion of another material (whether or not they are themselves combustible) or products that are organic peroxides Materials Causing Other Toxic Effects: Products whose health effects generally appear over time following one or several exposures Biohazardous Infectious Materials: Living organisms or their toxins that can cause disease in people or animals Corrosive Materials: Products that can corrode metal surfaces or cause burns to skin Dangerously Reactive Material: Products that can be health or safety hazards under certain conditons (pressure, temperature, impact, violent reaction with water or air)
Here is a very funny, yet very serious instructional video on lab safety:
We then familiarized ourselves with the lab equipment that we were given. This year, as chemistry students, we will be working with the following equipment:
(Note that we will even be working with bunsen burners. Clearly, safety is a must in the chemistry lab.)
To top the lesson off, Mr. Doktor made styrofoam cups vanish! The cups "disappear" because acetone breaks down carbon bonds:
Next class, balancing and naming chemical equations!
Here is a cool experiment that Mr. Doktor similarly conducted with ethanol on the first day of class. Did you know that you can burn money, without actually burning money?
