Chemistry and the Scientific Method

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Anonymous
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194492
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Chemistry and the Scientific Method
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2013-01-22 16:57:57
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Lecture Chemistry Scientific Method
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Lecture 1 Chemistry and the Scientific Method
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  1. What are the steps in the Scientific Method?
    • Observation: .
    • Hypothesis: Working model
    • Test: Hypothesis has to be consistent with observations
    • Theory: Based on common principles, reason, logic, math
    • Test/Experimenting: .
    • Laws: Developed from theories. Until someone else makes a different observation
  2. What are the two different types of Observations?
    • Qualitative: What color is it? Smell? Liquid? Etc. No numbers. Usually in chemical reactions.
    • Quantitative: Numerical part/Measurement
  3. What are quantitative observations?
    • Numerical part/Measurement
    • Has Dimensions or Units
    • Can mult/div, CAN'T add/subt quantities with different units
    • Ex: 25.35 g ; 2 ft x3 ft = 6 "squared feet" --> 6 ft^2
  4. What are SI units?
    • Systeme Internationale
    • Based on Metric System
  5. What are the SI units of Length, Mass, Time, Temperature, Energy, Volume?
    • Length: meter (m)
    • Volume: cubed meters (m^3)
    • Mass: kilogram (kg)
    • Time: second (s)
    • Temp: Kelvin (K) = C + 273.15
    • ANY Energy (SI): Joule (J)
    • Heat Energy (Metric): Calorie (cal) = 4.184 J
  6. Define Accuracy.
    • How close to "correct" value.
    • Trying to measure a standard.
    • Calculated by Errors.
  7. Define Error, Difference Error, and Percent Error.
    • Error: Difference between your measurement and real value
    • Ex: My measurement: C = 2.375x10^8 m/s Real: 2.998x10^8 m/s (speed of light)
    • Difference Error: 0.623x10^8 m/s
    • Percent Error: = (|Diff Error|/Correct) x 100
    • Ex % Error: = (0.623x10^8 m/s)/(2.998x10^8 m/s) x 100 = 20.8 %
  8. Define Precision.
    • How repeatable/reproducible a measurement is.
    • Ex: 24.275 g ; 24.286 g ; 24.279 g ; 24.263 g ; 24.273 g
    •        3 digits remain constant, 2 digits vary, first digit to vary is in 2nd dec. place
    • # of CERTAIN digits + 1st UNCERTAIN (estimated) digit = # of significant digits
    •        4 significant digits
  9. How do you find the number of significant digits/figures?
    • 1. Scan #'s from L --> R until you reach 1st NON-ZERO digit
    • 2. Count the digits
    • 3. Watch for TRAILING zeros - Zeros that FOLLOW the non-zero digits
    • Ex: 275.25 = 5 sig figs
    • Ex: 0.00275.25 = 5 sig figs
  10. What are Leading zeros?
    • Come before non-zero digits
    • They NEVER count
    • Ex: 0.00037
  11. What are Trailing zeros?
    • Zeros following the non-zero digits
    • If FOLLOWING the dec. point, ALWAYS significant
    • Ex: 25.0 = 3 sig figs, zero is significant
    • If BEFORE the dec. point, MAY be significant
    • Ex: 250 = 2 sig figs, zero not significant; I know it's 200, not certain if it's 50
    • Ex: 250. = 3 sig figs, zero is significant; I know it's 200, know it's 50, not certain if it's 0
  12. How would you write 25,000 if you're certain of 20000 and 5000 and 1000's but not 10's?
    • 25,000 "4 sig figs"
    • Scientific Notation: 2.500x10^4
  13. Describe Scientific Notation.
    • Convert a number to range between 1 and <10
    • Ex: 250. = 2.50x10^2 ; (2) indicates # of dec. moves to the Left
    • Ex: 0.00025 = 2.5x10^(-4) ; (-4) indicates # of dec. moves to the right; only 2 sig figs
  14. Put these prefixes in order from least to greatest with their powers and symbols: mili, nano, centi, kilo, pico, mega, deci, micro.
    • Pico (p): 10^(-12)
    • Nano (n): 10^(-9)
    • Micro (sexy u, "mu"): 10^(-6)
    • Mili (m): 10^(-3)
    • Centi (c): 10^(-2)
    • Deci (d): 10^(-1)
    • Kilo (k): 10^3
    • Mega (M): 10^6
  15. What are Unit (Conversion) Factors?
    • Start with a known relationship and rearrange to make it a ratio.
    • Ratios could be each other's inverses
    • Ex: 1 ft = 12 in --> (1 ft)/(12 in) = 1 => Converts to ft ; (12 in)/(1 ft) => Coverts to in
    • EX: 240 in => ? ft
    •        (240 in)/1 x (1 ft)/(12 in) = 20 ft
  16. What is Density?
    • Ratio of mass to volume of matter
    • Density = mass(g)/Volume(cm^3 or mL)
    • Ratio of 2 quantities can be used as Unit Factor
  17. What are the 2 types of Temperature scales and what do they include?
    • Degrees Fahrenheit (F) and Degrees Celsius (C)
    • Upper and Lower fixed points
  18. What are Upper and Lower Fixed Points (UFP & LFP)? Of Celsius and Fahrenheit?
    • LFP: Freezing point of water at 1 atmospheric pressure (atm)
    •       C = 0 degrees
    •       F = 32 degrees
    • UFP: Boiling point of water   "   "
    •       C = 100 degrees
    •       F = 212 degrees
  19. What is 1 division (of C/F)?
    • 1 increment (Degree) above the LFP
    • 180 div F = 100 div C
    •       Conversion factor => (9 div F)/(5 div C)
    • Ex: Fries are 425 degrees F
    •      1. Subtract 32 (How far above LFP) = 393 div F
    •      2. Change to # div C by using conversion factor => 218 div C (degrees C)
  20. What are the temperature conversion equations?
    • Temp (C) = (5/9)(Temp (F) - 32) => C = (5/9)(F  - 32)
    • Temp (F) = (9/5)Temp (C) +32 => F = (9/5)C +32

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