General Chemistry Fall ‘09

 People often confuse  Controls & Variables in experiments  A control is…  A trial that duplicates all conditions except the variable being investigated  A variable is…  Either dependent (responding)- this is observed during the experiment  Or independent (manipulated)- what you (I) change during an experiment

 People often confuse  Observations & Hypotheses  An observation…  Is information collected with the senses  A hypothesis…  A proposed explanation for an observation. Ivan Pavlov observed dogs salivating and hypothesized that a sound would cause dogs to salivate.

 Identify the following as an observation or a hypothesis  1. Wearing tennis shoes will make one run faster.  2. The tennis shoes are black and red.  3. The Bunsen Burner flame is 1400°C and is blue.  4. People who take good notes will do better on tests. Hypothesis Observation Hypothesis

 Scientists make observations all the time.  There’s two types:  Qualitative  Quantitative  To remember the difference, look at their root

 Qualities of the reaction, object, etc.  Examples  The copper (II) sulfate is blue  The nail is rusty  Gas was given off commons/d/d8/Copper_sulfate.jpg courses/essential/physicalsci/i mages/s4.rusty_nail.jpg

 Quantity= numbers  Mass, a number of paper clips, volume measurements, molar measurements.  Math is usually involved

 Theory  A well-tested explanation for a broad set of observations  Can help predict the behavior of matter and form mental images  Can be modified if new observations are made  Scientific Law  A concise statement that summarizes the results of many observations and experiments.  Do not describe relationships, that requires a theory  Ex) Charles’ Law

 Scientific notation  A number is written as the product of two numbers  A coefficient  10 raised to a power  Example: 602,000,000,000,000,000,000,000  Written as 6.02x10 23  Coefficient is equal to or greater than 1 and smaller than 10

Try these: ,000,000,000 = ___________________ = ____________________ = __________________  If exponent is negative, which way does decimal go?  If exponent is positive, which way does decimal go?

 “Correctness” and “reproducibility”  Accuracy  A measure of how close a measurement comes to the actual or true value of whatever is measured  Precision  A measure of how close a series of measurements are to one another

 Measurements may be accurate or inaccurate  Accepted value- correct value, based on reliable resources  Experimental value- value measured in the lab  The difference between the two is called error

 The absolute value of the error divided by the accepted value, multiplied by 100%  Example: boiling point was measured to be 99.1 o C, but we know it’s 100 o C %error = 99.1 o C – 100 o C x100% 100 o C %error = 0.9%

 Metric system is much easier than the English system…the conversion is always a factor of 10. SI Base Units QuantitySI Base UnitSymbol Lengthmeterm Masskilogramkg TemperaturekelvinK Timeseconds Amountmolemol

 Length is a 1-dimensional measure of distance. Metric system base unit is the meter, abbreviated m Commonly Used Metric Prefixes Prefix MeaningFactor Mega (M)1 million x larger10 6 Kilo (k)1000x larger10 3 Deci (d)10x smaller10 -1 Centi (c)100x smaller10 -2 Milli (m)1000x smaller10 -3 Micro1 million x smaller10 -6 Nano (n)1000 x smaller10 -9 Pico (p)1 trillion x smaller10 -12

 Volume is a measure of the amount of space a substance takes up.  Metric system base unit is the liter, abbreviated L.  Mass is a measure of the amount of matter in a substance.  Metric system base unit is the kilogram, abbreviated kg

Response of mass to the pull of gravity Weight changes when on different planets NOT THE SAME AS MASS!

 A measure of how hot or cold an object is.  Heat moves from hot to cold  Celsius scale  Freezing point =  Boiling point =  Kelvin scale  Freezing point = 273 kelvins (K)  Boiling point = 373 K  Absolute zero = 0K (zero kinetic energy)

 Kilo hecto deka (m, g, L) deci centi milli  k h dk or D d c m  How do you remember the order of the prefixes?

kilo 1000 hecto 100 deka 10 Base Unit deci 1/10 centi 1/100 milli 1/1000 To convert to a larger unit, move the decimal point to the left or divide:  To convert to a smaller unit, move the decimal point to the right or multiply: 

kilo 1000 hecto 100 deka 10 Base Unit deci 1/10 centi 1/100 milli 1/1000 Convert 6 cm = _____ mm We are converting to: a)larger unit b)smaller unit Convert 6 cm = 60 mm

kilo 1000 hecto 100 deka 10 Base Unit deci 1/10 centi 1/100 milli 1/1000 Convert 40 mm = _____ cm We are converting to: a)larger unit b)smaller unit Convert 40 mm = 4 cm

kilo 1000 hecto 100 deka 10 Base Unit deci 1/10 centi 1/100 milli 1/1000 Convert 90 cm = _____ m We are converting to: a)larger unit b)smaller unit Convert 90 cm = 0.9 m

kilo 1000 hecto 100 deka 10 Base Unit deci 1/10 centi 1/100 milli 1/1000 Convert 200 mm = _____ m We are converting to: a)larger unit b)smaller unit Convert 200 mm = 0.2 m

 Make the following metric conversions  cm = _________ m  km = _________ m  3. 90,344 m = _________ km  km = _________cm , / x 1000

 There is always an error in a measurement  The human eye can read one decimal place beyond the accuracy of the instrument  The measurement should be read as 8.0 +/-0.1cm.

Container #1 Container #2Container # mL82 mL62.0 mL Read the volumes of the liquids below