Essential Knowledge and Skills

Foundations

Chemistry

Learning Objectives Foundations

Essential knowledge and skills:

·  Understand Material Safety Data Sheet (MSDS) warnings, including handling chemicals, lethal dose (LD), hazards, disposal, and chemical spill cleanup.

·  Identify the following basic lab equipment: beaker, Erlenmeyer flask, graduated cylinder, test tube, test tube rack, test tube holder, ring stand, wire gauze, clay triangle, crucible with lid, evaporating dish, watch glass, wash bottle, and dropping pipette.

·  Make the following measurements, using the specified equipment:

volume: graduated cylinder, volumetric flask, buret

mass: triple beam and electronic balances

temperature: thermometer and/or temperature probe

pressure: barometer and/or pressure probe.

·  Identify, locate, and know how to use laboratory safety equipment including aprons, goggles, gloves, fire extinguishers, fire blanket, safety shower, eye wash, broken glass container, and fume hood.

·  design and perform controlled experiments to test predictions, including the following key components: hypotheses, independent and dependent variables, constants, controls, and repeated trials.

·  Identify variables.

·  Predict outcome(s) when a variable is changed.

·  Record data using the significant digits of the measuring equipment.

·  Demonstrate precision (reproducibility) in measurement.

·  Recognize accuracy in terms of closeness to the true value of a measurement.

·  Know most frequently used SI prefixes and their values (milli-, centi-, micro-, kilo-).

·  Demonstrate the use of scientific notation, using the correct number of significant digits with powers of ten notation for the decimal place.

·  Correctly utilize the following when graphing data:

Dependent variable (vertical axis)

Independent variable (horizontal axis)

Scale and units of a graph

Regression line (best fit curve).

·  Use the rules for performing operations with significant digits.

·  Utilise dimensional analysis to convert measurements.

·  Read measurements and record data, reporting the significant digits of the measuring equipment.

·  Use data collected to calculate percent error.

·  Determine the mean of a set of measurements.

·  Discover and eliminate procedural errors.

Essential understandings:

·  The nature of science refers to the foundational concepts that govern the way scientists formulate explanations about the natural world. The nature of science includes the following concepts

a) the natural world is understandable;

b) science is based on evidence - both observational and experimental;

c) science is a blend of logic and innovation;

d) scientific ideas are durable yet subject to change as new data are collected;

e) science is a complex social endeavor; and

f) scientists try to remain objective and engage in peer review to help avoid bias.

·  Techniques for experimentation involve the identification and the proper use of chemicals, the description of equipment, and the recommended statewide framework for high school laboratory safety.

·  Measurements are useful in gathering data about chemicals and how they behave.

·  Repeated trials during experimentation ensure verifiable data.

·  Data tables are used to record and organize measurements.

·  Mathematical procedures are used to validate data, including percent error to evaluate accuracy.

·  Measurements of quantity include length, volume, mass, temperature, time, and pressure to the correct number of significant digits.

·  Measurements must be expressed in International System of Units (SI) units.

·  Scientific notation is used to write very small and very large numbers.

·  Algebraic equations represent relationships between dependent and independent variables.

·  Graphs are used to summarize the relationship between the independent and dependent variable.

·  Graphed data give a picture of a relationship.

·  Ratios and proportions are used in calculations.

·  Significant digits of a measurement are the number of known digits together with one estimated digit.

·  The last digit of any valid measurement must be estimated and is therefore uncertain.

·  Dimensional analysis is a way of translating a measurement from one unit to another unit.

·  Graphing calculators can be used to manage the mathematics of chemistry.

·  Scientific questions drive new technologies that allow discovery of additional data and generate better questions. New tools and instruments provide an increased understanding of matter at the atomic, nano, and molecular scale.

·  Constant reevaluation in the light of new data is essential to keeping scientific knowledge current. In this fashion, all forms of scientific knowledge remain flexible and may be revised as new data and new ways of looking at existing data become available.

Material Safety Data Sheet (MSDS) Activity

Purpose: To become familiar with a MSDS sheet.

My chemical is: ______

1.  Are there any common names for your substance?

2.  What does your substance look like? (These are examples of physical properties.)

3.  What may happen if you inhale your substance?

4.  What substances are incompatible with your chemical?

5.  What chemicals should not be stored with your chemical?

6.  How would you clean up a spill of your chemical?

7.  Physical Data:

Melting Point: ______Water Solubility: ______

Boiling Point: ______Appearance & Odour:______

Specific Gravity: ______

8.  Fire and Explosion Hazards:

Flash Point:

9.  Health Hazard Data:

Carcinogenicity:

Acute (Short term) effects:

Chronic (long term) effects:

Routes of Entry into the body:

Scientific Method

Experimental Design worksheet IV, DV, controls, and control groups

DIRECTIONS: Use each description and/or data table to help you identify or describe: 1) any independent variable(s), 2) the best dependent variable, 3) at least 3 variables that should be controlled or held constant, and 4) any control group(s) in the experiment. Make sure your answers are specific. Keep in mind that not all experiments have a control group.

FISH EGGS: A scientist knows that the percent of fish eggs that hatch is affected by the temperature of the water in an aquarium. She is attempting to identify which water temperature will cause the highest percentage of fish eggs to hatch. The scientist sets up 5 aquariums at the following temperatures: 10°C, 20°C, 30°C, 40°C, and 50°C. She adds 50 fish eggs to each aquarium and records the number of eggs that hatch in each aquarium.

independent variable(s):

dependent variable

list 3 variables that should be controlled (held constant):

describe any control group(s) in the experiment (if one doesn’t exist, leave this section blank):

mouthwash
used / time mouthwash
was in mouth / # of bacteria in
mouth (average)
none / 135
A / 60 sec. / 23
B / 60 sec. / 170
C / 60 sec. / 84
D / 60 sec. / 39
E / 60 sec. / 81

MOUTHWASH: The makers of brand A

mouthwash want to prove that their mouthwash kills more bacteria than the

other 4 leading brands of mouthwash.

They organize 60 test subjects into 6

groups of 10 test subjects. The data

for the experiment is shown to the right.

independent variable(s):

dependent variable:

list 3 variables that should be controlled (held constant):

describe any control group(s) in the experiment (if one doesn’t exist, leave this section blank):

GAS MILEAGE: A car magazine is trying to write an article that rates the top 5 most fuel efficient SUVs (the SUVs that can drive the most miles for each gallon of gasoline). They make sure each model of SUV has exactly 10 gallons of gasoline in its fuel tank and reset the odometer (instrument that measures the distance a vehicle has traveled) to zero. The SUVs are then driven until they run out of gasoline. The distance on the odometer is recorded.

independent variable(s):

dependent variable:

list 3 variables that should be controlled (held constant):

describe any control group(s) in the experiment (if one doesn’t exist, leave this section blank):

FIRE EXTINGUISHERS: A firefighter is trying to figure out which type of fire extinguisher (CO2, water, or dry chemical) will put out fires the fastest. Think about the issue being tested and imagine an appropriate experiment to determine which type of fire extinguisher can extinguish fires the fastest. Then, identify the key elements of the experimental design listed below.

independent variable(s):

dependent variable: list 3 variables that should be controlled (held constant):

describe any control group(s) in the experiment (if one doesn’t exist, leave this section blank):

Rules for Graphing:
1.  All graphs should be done by hand in pencil on graph paper.
2.  Unless instructed to do otherwise, draw only one graph per page.
3.  The independent variable should be on the horizontal axis and the dependent variable on the vertical axis, unless otherwise stated. When instructions are given in a lab, such as "graph voltage vs. current", they are always given as vertical axis vs. horizontal axis (so the first variable listed is on the vertical axis).
4.  The graph should use as much of the graph paper as possible. Carefully choosing the best scale is necessary to achieve this. The axes should extend beyond the first and last data points in both directions.
5.  All graphs should have a short, descriptive title at the top of each graph, detailing what is being measured.
6.  Each axis should be clearly labeled with titles and units.
7.  The axes should be linear unless otherwise mentioned. Also, the axes should begin at zero and continue beyond the highest value for that variable, unless otherwise stated.
8.  Never connect the dots on a graph, but rather give a best-fit line or curve.
9.  The best-fit line should be drawn with a ruler or similar straight edge, and should closely approximate the trend of all the data, not any single point or group of points.
10.  A best-fit line should extend beyond the data points.
11.  The slope should be calculated from two points on the best-fit line. The two points should be spaced reasonably far apart. Data points should not be used to calculate the slope.
12.  On a linear graph, draw the rise, ∆y, and run, ∆x, to form a triangle with the best-fit line. Be sure to label these values and include units.
13.  The calculation of the slope, ∆y/∆x, should be clearly shown on the graph itself. Units should be included, and value of the slope should be easily visible.
14.  See the sample graph below which incorporates the above requirements.
See the Example graph below:

Scientific Notation

Sometimes, you may come up with a very long number. It might be a big number, like 4,895,000,000 or it might be a small number, like 0.0000073.

Scientific Notation is a used to make these numbers easier to work with. Scientific Notation for a number is expressed as M x 10n.

In this expression “n” is an integer, and “M” is a number greater than or equal to 1 and less than 10. M is expressed in decimal notation.

Example 1: Convert 4,895,000,000 to Scientific Notation.

Steps to conversion

·  Remember that any whole number can be written with a decimal point. For example: 4,895,000,000 = 4,895,000,000.0

·  The decimal place is moved to the left until you have a number between 1 and 10.

·  In this example the decimal point was moved nine places to the left to achieve 4.895.

·  The fact that the decimal was moved 9 places to the left is balanced by applying a multiple of 109.

4.895 x 109 = 4.895 x 10 x 10 x 10 x 10 x 10 x 10 x 10 x 10 x 10 = 4,895,000,000

Scientific Notation can also be used to turn 0.0000073 into 7.3 x 10-6.

Example 2: Convert 0.0000073 to Scientific notation.

Steps to conversion

·  First, move the decimal place until you have a number between 1 and 10. If you keep moving the decimal point to the right in 0.0000073 you will get 7.3.

·  Next, count how many places you moved the decimal point. You had to move it 6 places to the right to change 0.0000073 to 7.3. You can show that you moved it 6 places to the right by noting that the number should be multiplied by 10-6.

7.3 x 10-6 = 0.0000073

Remember:

In a power of ten, the exponent — the small number above and to the right of the 10 tells which way you moved the decimal point.

·  A power of ten with a positive exponent, such as 105, means the decimal was moved to the left.

·  A power of ten with a negative exponent, such as 10-5, means the decimal was moved to the right.

Practice Problems

Express the following in scientific notation:

1) 0.00012

2) 1000

3) 0.01

4) 12

5) 0.987

Express the following as whole numbers or as decimals.

1) 4.9 x 102

2) 3.75 x 10-2

3) 5.95 x 10-4

4) 9.46 x 103

5) 3.87 x 101

Using Scientific Notation in Multiplication, Division, Addition and Subtraction

MULTIPLYING in scientific notation

Multiply the mantissas and ADD the exponents

.00000055 x 24,000

= (5.5 x 10-7) x (2.4 x 104)

= (5.5 x 2.4) x 10-7+4

= 13 x 10-3

= 1.3 x 10-2

DIVIDING in scientific notation

Divide the mantissas and SUBTRACT the exponents

•  (7.5 x 10-3) / (2.5 x 10-4)

= 7.5/2.5 x 10-3-(-4)

= 3 x 101

= 30.

ADDING or SUBTRACTING in scientific notation

1. First make sure that the numbers are written in the same form (have the same exponent)

3.2 x 103 + 40. x 102 (change to 4.0 x 103)

2.  Add (or subtract) first part of exponent (mantissas)

3.2 + 4.0 = 7.2

3.  The rest of the exponent remains the same

Answer: 7.2 x 103

How do you make the exponents the same?

Let’s say you are adding 2.3 x 103 and 2.1 x 105. You can either make the 103 into the 105 or vise versa. If you make the 103 into 105, you are moving up the exponent two places. You will need to move your decimal place in the mantissa down two places to the left.

2.3 x 103 = .023 x 105

•  Take 2.3 and move the decimal three places to the right. It equals 2300.

•  Take .023 and move it five places to the right…it is still 2300

•  Now add the two mantissas (2.1 + .023) = 2.123

•  Add the exponent ending: 2.123 x 105

In conclusion

*if you increase (↑) the exponent, you must move the decimal in the mantissa to the left (←) the same number of places.

*If you decrease (↓) the exponent, you must move your decimal point to the right (→) in the mantissa that number of places.