intro to chemistry and math€¦ · a theory is more like a scientific law than a hypothesis. a...

Intro to Chemistry and Math

Chemistry: study of matter and its composition, structure, properties and changes

Main Branches: analytical, biochemical, inorganic, organic, physical, theoretical

Theory: explanation for an event tested over time, supported by broad body of evidence, explains observations

Example – atomic theory, bonding theory

Law: description of predictable behavior repeatedly observed over time “rule of nature”

Example – law of conservation of mass

A theory is more like a scientific law than a hypothesis.

A theory is an explanation that has been supported by many experiments

Both a scientific theory and a scientific law are accepted by the scientific community.

Models: a visual, verbal, and or mathematical explanation of experimental data

Observation: fact perceived with the senses

Inference: conclusion based on observations

Quantitative: measurements (numbers)examples – temperature, pressure, mass

Qualitative: descriptions (words)examples – blue solution, bubbles formed

Determine what is qualitative and quantitative from the paragraph

Ms. Reed is 5’4” and loves shoes. All of her shoes are a size six. She has brown hair and her favorite color is blue.

Why do scientists worldwide use the SIsystem of measurement?

To improve communicationConvenience Diminish likelihood of errors

What is the purpose of SI prefixes? Easy to convert, represent magnitudes of numbers, based on powers of 10

Quality Unit Name Abbrev Tool to Measure

Length Meter m Ruler/Meter stickMass Kilogram kg BalanceTime Second s Clock/StopwatchTemperature Kelvin K ThermometerAmount of substance Mole mol Not applicable

Derived unit: combination of basic SI units

ex: Density (mass/volume)Volume (l*w*h)Velocity (distance/time)Force (kg*m/s)

The metric system is based on a factor of 10.

This makes conversions easier to use for scientists (and also students! )

You must memorize the prefixes found in your notes!! Please begin memorizing them starting tonight

1 Mega (M) 1x106 base1 kilo (k) 1000 base1 hecto (h) 100 base1 deka (D, dk, da) 10 baseBase Meter, liter,

gram, second10 Deci (d) 1 base100 Centi (c) 1 base1000 Milli (m) 1 base1x106 Micro (µ) 1 base1x109 Nano (n) 1 base1x1012 Pico (p) 1 base

What is a measurement?Something that has magnitude (#) and a

unit (label), and is compared to a standard

Why are measurements always uncertain?Smallest (last) digits always estimated or

error in instrument or human

This is when you read a piece of equipment and round the last digit. We will work out several examples. You need to use estimated digits any time you complete a measurement in a lab.

Tell your neighbor what you think the length of this piece of paper is. It should be measured to the hundredth place (2 decimals)

This ruler allows us to measure up to the tenths place. However you can estimate one digit further.

The true measurement for this piece of paper is 11.6 cm but with an estimated digit you may have said 11.62 or 11.63. There is uncertainty in this number because we each may round the hundredths place differently.

In mL

1) To what place can the graduated cylinder be estimated?

2) What is the measurement with an estimated digit?

In mL

1) To what place can the graduated cylinder be estimated? Hundredths

2) What is the measurement with an estimated digit?

~ 20.39 mL

All pieces of equipment need to include an estimated digit.

Examples: *Triple Beam Balance*Thermometer*Ruler*Graduated Cylinder

Why is scientific notation used?To express very large or very small

numbers easily

What is the correct format for scientific notation?

The number must be between 1 and 9.9 and the exponent can be either positive or negative

A positive exponent represents a number _greater_ than one.

A negative exponent represent a number _less_ than one.

Write the following in scientific notation1) 5, 600, 000 m2) 0.000789 nL3) 3,700 sec

Write the following in standard notation1) 9.12 x 10-3 cg2) 5.6 x 109 m3) 2.2 x 102 sec

You must memorize the prefixes found in your notes!! Please begin memorizing them starting tonight

1 Mega (M) 1x106 base1 kilo (k) 1000 base1 hecto (h) 100 base1 deka (D, dk, da) 10 baseBase Meter, liter,

gram, second10 Deci (d) 1 base100 Centi (c) 1 base1000 Milli (m) 1 base1x106 Micro (µ) 1 base1x109 Nano (n) 1 base1x1012 Pico (p) 1 base

Method for converting units -aka box method

Example:Convert 300,000 meters to kilometers

Convert:1) 571 feet to inches

2) 82,496 kilograms to micrograms

What is the most common type of graph used in chemistry? Line graph

When constructing a graph you should?Title graphLabel axes (x-axis = independent, you

control) (y-axis = dependent variable)Scale axes evenly (spread out as much as

possible)

Direct proportions: both variables change in the same direction

Looks like:

Type of graph: straight line

Example: Temperature vs. Pressure

Inverse proportions: variables change in opposing directions

Looks like:

Type of graph: hyperbola

Example: Pressure vs. Volume

Volume: amount of 3-D space occupied by an object, can be length*width*height or the amount of water displaced

Density: Mass per volume, ratio comparing the mass of an object to its volume Formula: D = m/V

**Helpful way to remember: D = heart divided in two pieces**

D= mass/volume

The Density of water = 1 g/mL

If a sample of aluminum has a volume of 5.0 cm3 and a mass of 13.5 g. Find the density.

A student observes the reading of a graduated cylinder to be 7.3 mL. After dropping an irregularly shaped solid object with a mass of 2.5 grams into the cylinder, the volume rises to 12.9 mL.What is the density of the object?

Accuracy: how close measurements are to a “true” value

Precision: how close measurements are to one another (consistency, reproducibility)

Accurate: WHY?!

Precise: WHY!?

Both accurate and precise: WHY!?

Students Trial 1 Trial 2 Trial 3A 4.75 g 2.25 g 10.5 g

B 4.75g 4.74g 4.75g

C 7.73 g 7.72g 7.73 g3 students completed a lab experiment where they had to find the mass of an unknown object. The students’ data is listed in the table above. Using the information determine if the students are accurate, precise, neither or both.

Memorize this formula!! Percent Error = |measured – actual| x 100

actual

What is Jake’s percent error if he measured 6.8 mL during his experiment and the actual measurement was supposed to be 7.2 mL?