Chapter 2 Measuring and Calculating HONORS CHEMISTRY Chapter 2 Measuring and Calculating

General Problem Solving Understand Situation Appreciate importance or unimportance of info. Organize info.

Problem Solving Techniques: 1. Identify known facts. 2. Define answer required. 3. Develop possible solns. 4. Analyze poss. solns. & determine correct one. 5. Develop steps to arrive @ answer. ALGORITHM - pattern for solving a particular type of prob.

Problem Solving Techniques: 6. Solve problem. 7. Evaluate results - number and units

Know 3 things to make a measurement 1. What you’re measuring 2. Standard w/ which to compare measurement 3. method of making comparison

Qualitative Measurement - Described in words No numbers Quantitative Measurement - described by a number of std. units

SI is modern version of metric system 7 Basic units Learn them! Prefixes are used to obtain different units

Mass - a meas. of the quantity of matter Does not vary from place to place Kilogram - SI std. unit for mass Weight - meas. of force of gravity betw. 2 objects Can vary from place to place Newton (N) - Meas. std. for weight or force

Length - Distance covered by line segment connecting 2 pts. Meter - SI std. unit of length defined in terms of wavelength of light Time - interval betw. 2 occurrences Second - SI std. unit of time defined in terms of electron transition

Temperature meas. of average kinetic energy of an object’s particles a meas. of heat intensity Heat flows from high temp. to low temp. until equal. Kelvin (K) - SI std. unit of temp.

Celsius Scale Based on boiling pt. (100oC) and freezing pt. (0oC) of pure water Diff. is divided into 100 = intervals - Degrees 1 Celsius degree = 1 Kelvin

ACCURACY nearness to accepted value refers to quality of instrument

UNCERTAINTY estimate of accuracy + or - 0.2 x smallest unit

PRECISION refers to how close a set of measurements are to one another also refers to: unit used in making estimation number of decimal places reproducibility Be as precise as instrument allow estimate one more place than marked

PARALLAX apparent shift in reading when viewed from side Always take reading straight-on & at eye level

Percent Error = Observed - Accepted X 100% Accepted

Scientific Notation For very large or very small numbers M X 10n 1< M < 10 M has 1 nonzero digit in front of decimal pt. n can be (+) or (-)

Significant Digits Indicates exactness of meas. Depends on instrument Includes all certain digits + 1 estimated digit

Calculations w/ Sig. Digits Add. & Sub. - Answer contains only as many decimal places as the meas. w/ the least # of decimal places Mult. & Div. - Answer contains only as many sig. digits as the meas. w/ the least # of sig. digits.

Derived Units Obtained by combining fundamental SI units 1 dm3 = 1 liter Liter (L) - unit of volume 1 L = 1000 mL = 1000 cm3 = 1 dm3 SI unit of volume is the cubic meter - too large - use dm3 (L)

Density mass per unit volume D = m/v derived unit usually expressed in g/cm3 A change in temp. can change vol. & change density Values usually given @ 25 oC