2 Types of observations Qualitative Properties that can be observed and described that do not involve measurement. If they do refer to quantities, they are vague (ie fast, hot, large etc…)QuantitativeProperties that can be observed and described numerically and which result from measurement.
3 Commonly measured values in chemistry Mass (grams)Volume (liters)Length (meters)Temperature (degrees Celsius or degrees Kelvin)Time (seconds)Pressure (atmospheres)Concentration (percent, molar)
4 Length, Mass and Volume Length - distance between two points Mass - amount of matter in an object(weight is dependent upon the force ofgravity on the object)Volume - the amount of space an objectoccupies
9 Common metric prefixes 1000 base / 1 kilo g / 1 kilogram x 103100 centi / 1 base 100 centimeters/ 1 meter 1 x 1021000 milli / 1 base millimeters/ 1 meter 1 x 1031,000,000 micro / 1 base 1,000,000 micrometers/1 meter 1 x 106
10 Converting between units (Dimensional analysis – factor label method) Given unit x (Desired unit) = Desired unit(Given unit)12.4 kg x (1000 g) = 12,400 g(1kg)1265 mm x (1 m) = m(1 x 103 mm)
11 Exact and inexact numbers Exact numbers No uncertainty to their valueValue is known exactlyDefinedConversions within a systemsInexact numbers Uncertainty of their true valueMeasuredConversions between differentsystems
12 Expressing numbers in scientific notation Why do it?How to enter them into your calculator1.5 x 1023EXP (or EE)2.67 x 10-16EXP (or EE) /
13 Making measurementsAccuracy: How close a measured value is to the true valuePrecision: How close multiple measured values are to each other
14 There is estimation (and therefore uncertainty) in all measurements
15 Significant figuresThe digits in a measurement that are known with certainty, plus the single estimated digitOnly applies to measured (inexact) valuesDoes not apply to defined (exact) values
16 Measured Values What figures (digits) are significant? (not applied to defined or exact values such as conversions within the same system)Non zeros are significantZeros between non zeros are significantZeros at the beginning are not significantZeros at end after decimal are significantZeros at end before the decimal dependThree ways to represent these zeros
17 How many significant figures are in these measured values? cmLmm100 kgx mg
18 Rules for working with measured values Since there is uncertainty in measurement, we risk “amplifying” the uncertainty when we add, subtract, multiply and divide measured valuesSo…. There are rules for working with measured values
19 Calculations involving measured values Multiplying and dividing:Answer can have no more total sig. figs. than the starting value with the fewest total sig. figs.Adding and Subtracting:Answer can have no more sig. figs. after the decimal than any original number
20 Dimensional analysis helps solve conversion problems What are you starting with?What do you need to convert it into?What conversion factor(s) do you need?Must know conversions within the metric system.Must know other conversions we will identify.Do not have to memorize conversions between systems.
24 Calories and specific heat calorie: amount of heat1 cal raises 1 g of water 1° C60 Calories = 60 kcal = 60,000 caloriesSpecific heat of any substanceAmount of heat (in calories) required to raise 1 gram of the substance 1° C