10 Chem Chapter 1 Measurements In Chemistry

Measurements in Chemistry Units of Measurement: The International System of Units (SI): -Is built upon a set of seven metric unites, called the base units Basic Units for: Length: meter (m) Mass and Weight: -Mass is the amount of material in an object -Kilogram (kg) is the base unit for mass Derived Unit: a combination of base units in SI Area and Volume: Cubic meter -Volume is the amount of space that an object occupies SI Base Units Physical Quantity Mass Length Time count, quantity Temperature electric current luminous intersity Derived Units

Unit Name and Symbol kilogram, kg meter, m second, s mole, mol kelvin, K ampere, A candela, cd

Physical Quantity Unit Name and Symbol area square meter, m2 volume cubic meter, m3 force newton, N pressure pascal, PA energy joule, J power watt, W voltage volt, V frequency hertz, Hz electric charge coulomb, C

Non SI Units: Physical Quantity volume pressure temperature energy

Unit Name and Symbol liter, L atmosphere, atm, millimeters of mercury, mm Hg Celsius degree, Co calorie, cal

Prefix Order: mega, kilo, BASE, deci, centi, milli, micro, nano, pico Uncertainty in Measurement: Why are measurements uncertain? 1. Measuring instruments are never completely free of flaws 2. Measuring always involves some estimation Reliability in Measurement: Precision: When an experiment is repeated and a measurement stays the same (said to have high precision) Accuracy: Testing something against a standard. (Knowing what the correct answer should be). The correct answer is the accepted value. If data is close to its accepted value, it is said to have high accuracy. Significant Digits: What are the significant digits in measurements? The sum of certain digits and the estimated digits Example: If something is measured on a scale with divisions of 100 grams. The measurement comes out to be 1040 grams. You know that the 1,0, and 4 are significant because they were not estimated. The last 0 is a place keeper in place of a decimal point. Scientific Notation 2.25 x 10 ^ -3 = 0.00225

Percents and Percent Error:

Percent Error = measured value – accepted value Accepted value x 100 -Percent error can be positive or negative. If the PE is greater than the accepted value it will be positive and vice versa Ratios: Density is equal to the mass per one unit of volume Density = mass/volume Dimensional Analysis: -Defined as the technique of concerting between units 1. Find unit equality 1 gal = 3.785 L 2. Write conversion factors from unit equality 1 gal = 3.785 L 1 gal = 1 gal 1 gal 3.785 L = 1 3. Use conversion factors The unknown is liters so ….. 4. Cancellation of Units V (volume) = 250 gal X 3.785 L 1 gal V = 950 L Graphing: -

Independent variable versus dependent variable

-

Label all axis

-

Include a title

-

Connect points with a best fit line