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Honors Chemistry

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Honors Chemistry

Measurement

- Chemistry is the study of all things and the changes they can undergo.
- Chemistry is called a central science because it overlaps so many sciences.
- Chemical – is any substance with a definite composition.

- Observation
- Question
- Hypothesis
- Experiment
- Conclusion
- All hypotheses must be testable in order to be a valid hypothesis.

- Qualitative: Describes something using the 5 senses
- Quantitative: Uses numbers in the description
- Quantity – something that has magnitude, size, or amount.
- Unit – a quantity adopted as a standard of measurement

- Natural Law – Describes how nature behaves
- Theory – Explains why nature behaves the way it does
- A theory and a hypothesis are both explanations, but a theory is an explanation formed after much experimentation.

- Independent Variable - You control
- Dependent Variable – Variable factor – what is being tested
- Experimental Control – Factor that remains constant for comparison

- Independent:most regular variable – goes on the X-axis
- Dependent:what you are testing – goes on the Y-axis
- Experimental Control:part of the experiment that stays
the same.

Dependent variable

“Y” axis

Independent variable

“X” axis

Measurement is a key ingredient in ALL sciences, especially chemistry.

- Scientific Notation
- Accuracy and Precision
- Significant Figures
- Measurement Devices
- Metric System
- Dimensional Analysis

- Coefficient - a number between 1 and 10 (only 1 digit to the LEFT of the decimal point)
- Base - a power of 10 “power of 10” shows the number of 10’s that are to be multiplied together
- Examples on the number line:
1x1024x1011x100

1x10-101x10-1

Small

Numbers

Negative

Numbers

Large

Numbers

1x10-10

1x10-1

1x102

0

4x101

1x100

- Exponents must be the same
- If number gets bigger, exponent gets smaller
- If number gets smaller, exponent gets larger
(8 x 10-2) + (3 x 10-4) - (2 x 10-3)

(80 x 10-3) + (0.3 x 10-3) – (2 x 10-3) =

78.3 x 10-3 = 7.83 x 10-2

- Multiply number and add exponents (base 10 remains the same)
(6 x 10-6)(8 x 103) =

48 x 10-3 4.8 x 10-2

(6 x 10-3)2 =

36 x 10-6 = 3.6 x 10-5

- Divide number and subtract exponents (base 10 remains the same)
(7.2 x 10-8)÷(8 x 10-5) =

0.9 x 10-3 9 x 10-4

- Make number a whole number, take cube root of number, multiply exponent by 1/3.
(2.7 x 10-8)1/3 =

(27 x 10-9)1/3 =

3 x 10-3

- Make number a whole number, take square root of number, multiply exponent by ½.
(1.44 x 10-6)1/2 =

(144 x 10-8)1/2 =

12 x 10-4 = 1.2 x 10-3

1st Commandment of Chemistry: KNOW THY CALCULATOR!

Find the “EE” key – it may be a 2nd function!

If you have a graphing calculator look for the following keys:

Find the (-) key.

Find the “Exp” or “x10x”

1st Law of Chemistry:

Know Thy Calculator!

Look at the calculator that is similar to yours…

Find the “(-)” or the “+/-” key.

- Measurements are uncertain because:
- 1) Instruments are not free from error.
- 2) Measuring involves some estimation.
- Precision –when the instrument gives you about the same results under similar conditions. The smaller the increments of measurement an instrument has, the more precise it can be.
- Accuracy – when the experimental value is close to the actual value.
- % Error = experimental– acceptedvalue x 100
accepted value

What is the goal for a game of darts?

Hitting the Bulls Eye!

- 1) 200g, 1g, 40g
- Neither
- 2) 78g, 80g, 79g
- Precise
- 3) 16g, 14g, 17g
- Accurate and Precise

Read the

meniscus

36.4 mL

19.0 mL

6.25 mL

3.7

3.6

3.63

21.8

21.68

28.570 g

Ohaus Triple Beam Balance Tutorial

Reading A Triple Beam Balance Tutorial

109.076 g

Ohaus Triple Beam Balance Tutorial

Reading A Triple Beam Balance Tutorial

- A prescribed decimal that determines the amount of rounding off to be done base on the precision of the experiment.
- ALWAYS ESTIMATE 1 DIGIT MORE THAN THE INSTRUMENT MEASURES.
- Significant digits include measured digits and the estimated digit.
- Exact Numbers – Do not involve estimation
- ex. 12 in = 1 ft

- Use Atlantic-Pacific Rule – imagine a US map

decimal

point

decimal

point

Pacific

Atlantic

resent

bsent

2 significant digits

1100

4 significant digits

1100.

8 significant digits

11.010000

2 significant digits

0.025

5 significant digits

0.00035000

1,000,100

5 significant digits

Decimal Absent Start counting with the 1st nonzero digit and count all the rest.

Decimal Present Start counting with the 1st nonzero digit and count all the rest.

- Add or subtract numbers
- Answer can only be as exact as the least exact number. (Look at the decimal place)
- Ex. 4.1 cm + 0.07cm
- 4.17 cm
- 4.2 cm

- Multiply and Divide the numbers.
- Round answer to the same number of significant digits as the number with the fewest significant digits.
- Ex. 7.079 cm / 0.535 cm
- 13.2317757
- 13.2

Atmospheric pressure is measured with a barometer. This is a glass tube sealed at one end and filled with Hg.

- Reading a Manometer
- Barometer containing Hg

- K = °C + 273
- °C = K - 273
- Zero Point on Kelvin Scale – Absolute Zero
- 0 K and -273 °C

- Kinetic energy is energy of motion. Temperature is a measure of kinetic energy. Since the temperature at absolute zero is a true zero, there is no particle motion Therefore, nothing can exist at absolute zero.

TEMPERATURE SCALES

- English – still used in US
- Metric – devised in the late 1700’s in France
- SI – Le SystèmeInternationaled’Unités
- Modern metric system (1960)
- Based on 7 base units
- Base units are modified by prefixes

meter (m)

- Length
- Mass (SI standard unit)
- Time
- Temperature
- Amount of a substance mole (mol)
- Electric current ampere (A)
- Luminous intensitycandela (cd)

kilogram (kg)

second (s)

Kelvin (K)

- The original standard for the meter was kept in a safe in France.
- The meter stick is a replica of that standard.
- A meter is made up of 100 centimeters and 1000 millimeters.
- Lasers are now used to determine the standard for a meter.

Mass is the amount of matter in an object.

1 cm3 of water = 1 gram.

The standard kilogram is kept under lock and key in Washington, DC and other cities around the world.

- Area: 2-D
- L x W (m2)

- Volume: 3-D
- Solid - L x W x H (m3)
- Liquid or irregular shaped object - graduated cylinder (L or cm3)

- Density
- mass/volume(kg/m3)

- The liter is 1000 mL
- 10cm x 10cm x 10cm
- 1 liter= 1000 cm3 = 1 dm3
- 1 milliliter = 1 cm3 = 1 cc = 20 drops

=

- Factor-label method or dimensional analysis – based on using unit equalities
60 s = 1 min

60 s OR 1 min

1 min 60 s

3.6 x 104 s

1 hr

60 min

1 day

24 hr

1 min

60 s

=

0.42 days = 4.2 x 10-1 days

1 min

__________________

60 s

1 hr

__________________

60 min

1 day

__________________

24 hr

3.6 x 104 s

x

x

x

=

36 mm3

1 cm3

= 0.036 cm3

mm3

1000 mm3

1 cm

1 cm

36 mm3

1 cm

10 mm

10 mm

10 mm

180 ft2

1 yd2

= 20 yd2

9 ft2

- Physical = A characteristic of a substance that does not involve a chemical change
- Examples: texture, state of matter, density, hardness, boiling point
- Density = The ratio of the mass of a substance to the volume of the substance.
- D = mass / volume

1- Find the mass of the object

2- Find the volume if the

object by water displacement!

- The characteristic plot for a Direct Relationship is a straight line graph.
- Indirect Relationship
- The characteristic plot for an Inverse Relationship is a curve of the type illustrated here. As one of the variables increases, the other decreases. Note: It is not a straight line sloping downward.

- Determine the density of aluminum from the analysis of data from 5 samples.
- 54.0-g sample has a volume of 20.0 mL
- 14.0-g sample has a volume of 5.0 mL
- 41.0-g sample has a volume of 15.0 mL
- 27.0-g sample has a volume of 10.0 mL
- 19.0-g sample has a volume of 7.0 mL
HINT: Graph the data with volume as the independent variable.

Find the slope of the line!

- Convert the density of benzene, 0.8787 g/cm3, to kg/m3.
878.7 kg/m3

- Calculate the density of mercury if 1.00 x 102 g occupies a volume of 7.36 cm3.
13.6 g/cm3

BACK

- Heat-energy that is transferred from one object to another due to a difference in temperature. (symbol for heat = q)
- Temperature = a measure of the average kinetic energy of the particles in a substance. Temperature is an intensive property, and heat is an extensive property.
- Thermochemistry – the study of heat changes in a chemical reaction.
- Heat vs. Temperature

- Calorimetry is the study of heat flow and measurement.
- Calorimetry experiments determine the heats of reactions by making accurate measurements of temperature changes produced by a calorimeter.

- Heat Capacity – amount of heat needed to raise the temperature of an object 1°C.
- Specific Heat – amount of heat needed to raise 1g of a substance 1°C.
-Symbol for specific heat is C.

- Formula for heat absorbed for released:
q = C x m x ∆T

- Remember: Specific Heat of Water =
4.184 J/g· °C