Math is the language of science Data Analysis Ch. 2.1, 2.2, 2.3.

Math is the language of science

Data AnalysisCh. 2.1, 2.2, 2.3

Problem solving in chemistry

Step 2 – ANALYZE THE PROBLEM Re-read problem. What do you know? What is

unknown? Make a list. Consider units, gather info from graphs, tables,

figures Plan steps to take in problem solving

Step 1 – THE PROBLEM Read problem. Be sure you understand what is being asked

Problem Solving in Chemistry Step 3 – SOLVE FOR THE UNKNOWNS

Determine equation needed Plug in the knowns to solve for the unknowns Solve the problem Don’t forget your conversions

Step 4 – EVALUATE Think about your answer – does it make sense? Consider units – do they make sense? Check your work!

Measurements Measurement – a quantity that has a number

and a unit

Qualitative vs. Quantitative measurements

What’s the difference?

EXAMPLES:

Hot and cold – qualitative or quantitative?

Temperature scale (degrees Celsius or Kelvin) – qualitative or quantitative?

Units of Measurement

Base Unit – defined unit in a system of measurement that is based on an object or an event in the physical world

SI Base UnitsTable 2-1, p. 26

Units of Measurement

Metric use of prefixes to alter base units:

Kilo (k) – 1000 1000 m = 1 km

Deci (d) – 1/10 1 m = 10 dm

Centi (c) – 1/100 1 m = 100 cm

Milli (m) – 1/1,000 1 m = 1000 mm

Micro (μ) – 1/1,000,000 1 m = 1,000,000 μm

Units of Measurement Derived Units – a unit that is defined by a

combination of base units

Volume – the space occupied by an object (cm3 or L) Volume of an irregular object – water

displacement

Density – a ratio that compares the mass of an object to its volume (g/cm3)

Density = mass volume

Practice Problems, p. 29 1, 2

How Reliable are Measurements?

Accuracy – how close a measured value is to an accepted value

Precision – how close a series of measurements are to one another

Error Error = Accepted value – Experimental

value Ignore + or – signs

Percent Error = l error l x 100

accepted value

We use absolute value because we want the % error to be a positive value.

Example p. 37: Calculate Student A’s percent errorPractice: Calculate Student B’s percent error

Scientific Notation

Exponential notation is used as shorthand for writing very large or very small numbers

3.6 x 104 3.6 is the coefficient and 4 is the exponent (power of ten)

What is the difference between 3.6 x 104 and 3.6 x 10-4?

Refer to notes in packet!

Dimensional Analysis

A CONVERSION FACTOR is a ratio of equivalent values used to express the same quantity in different units.

Ex. 3 teaspoons = 1 tablespoon

Conversion Factors:

3 teaspoons 1 tablespoon

1 tablespoon 3 teaspoons= = 1

Let’s do the examples on the notes pages!

Significant Figures

Scientists indicate the precision of measurement by the number of digits they report

Sig Fig Rules (VERY IMPORTANT!!!):

1. If the number has a DECIMAL: Start counting with the first non-zero (1-9) and count ALL THE WAY TO THE END.

2. If the number has NO DECIMAL: Start counting with the FIRST non-zero (1-9) and count to the LAST non-zero

Let’s practice on notes pages!

Rules for conversions 1. To convert from one unit to another, use the

equivalence statement that relates the two units - a ratio of the two parts of the equivalence statement.

2. Choose the appropriate conversion factor by looking at the direction of the required change (Remember algebra class and make sure unwanted units cancel)

3. Multiply the quantity to be converted by the conversion factor to give the quantity with the desired units.

4. Check that you have the correct number of significant figures.

5. Check your work. Does your answer make sense?