Standards for Measurement. Preparation for College Chemistry Columbia University Department of Chemistry. The Scientific Method. http://antoine.fsu.umd.edu/chem/senese/101/intro/scimethod-quiz.shtml. Observations. Laws. (analysis). Hypothesis. (explanation). Experiment. (measurement).
Preparation for College Chemistry
Department of Chemistry
Measurement and Interpretations
Diameter = 2.5 cm
Radius = Diameter/2
Area = x r2 = 8.04 cm2
Art of Chemical Measurement:
Resting Potential (Squid Experiment)
Resting Potential = -65 mV
Affected by Uncertainty
This quantity contains 3 significant figures, i.e., three experimentally meaningful digits.
If the same measurement is made with an analytical balance (precision + 0.0001g) , the mass might be 23.5820 g (6 sig. fig.)Significant Figures (Sig. Figs.)
Zero is SIGNIFICANT when:
Is between nonzero digits: 61.09 has four sig Figs.
Appears at the end of a number that includes a decimal point 0.500 has three sig. Figs.; 1000. has four sig. Figs.
Zero is NON SIGNIFICANT when:
Appears before the first nonzero digit. 0.0025 has two sig. Figs. Leading Zeros are non significant
Appears at the end of a number without a decimal point. 1,000 has one sig. Fig.; 590 has two sig. Figs.
Defined numbers, like 12 inches in a foot, 60 minutes in an hour, 1,000mL in one liter.
Numbers that occur in counting operations.
Exact numbers have an infinite number of sig. figs.
Exact numbers do not limit the number of sig. figs. in a calculation.
Number written as a factor between 1 and 10 multiplied by 10 raised to a power.
Useful to unequivocally designate the significant figures.
The answer must contain as many significant figures as in the least precise quantity (measurement with least precision).
What is the density of a piece of metal weighing 36.123 g with a volume of 13.4 mL?
Drop these three digits
Round off to 7
Keep only as many digits after the decimal point as there are in the least precise quantity
Ex. Add 1.223 g of sugar to 154.5 g of coffee:
Total mass = 1.2 g + 154.5 g = 155.7 g
Note that the rule for addition and subtraction does not relate to significant figures.
The number of significant figures often decreases upon subtraction.
Mass beaker + sample = 52.169 g (5 sig. figs.)
- Mass empty beaker = 52.120 g (5 sig. figs.)
Mass sample = 0.049 g (2 sig figs)
Base unit is the meter (m)
1790s: 10-millionth of the distance from the equator to the North Pole along a meridian.
1889: Distance between two engraved lines on a Platinum-Iridium alloy bar maintained at 0°C in Sevres-France.
1960-1983: 1,650,763.73 wavelengths of the orange-red emision of 18Kr at standard conditions
Since 1983: 1/299,792,458 of the distance traveled by light in 1 second through vacuum.
1 km = 103 m 1 in. = 2.54cm
1 cm = 10-2 m 1 mile = 1.61km
1 mm = 10-3 m
1 µm = 10-6 m
1 nm = 10-9 m
1 Å = 10-10 m
A mass of 1 kg has a terrestrial weight of 9.8 newtons (2.2 lbs)
Depending on the precision required and the amount of material, different balances are used:
The Quadruple Beam Balance (+ 10 mg)
The Top Loading Balance (+ 1 mg).
The Analytical Balance (+ 0.1 mg).MassBase unit is the kilogram (kg)
International prototype: a platinum-Iridium cylinder maintained in Sevres-France.
Comparison of Temperature Scales
K = °C + 273.15
°C= (°F - 32) / 1.8
°F= (1.8 x °C) + 32
Boiling point of water
Freezing point of water
Frequency Hertz Hz s-1
Force newton N m.kg.s-2
Pressure, stress pascal Pa N.m-2 = m-1.kg.s-2
Energy work, heat joule J N.m = m2.kg.s-2
Electric charge coulomb C A.s
Electromotive Force volt V J.C-1 = m2.kg.s-3.A-1
Electric Resistance ohm V.A-1 = m2.kg.s-3.A-2Derived Units
Two conversion factors
760 mm Hg
101.3 kPaSimple, One Step Conversions
Conversion factor : 101.3 kPa = 760 mm Hg
pressure (mmHg) = 99.6kPa
Vary with the amount of material
Independent of the amount of material
Density (mass per unit volume)
Temperature (average energy per particle)
Molecules or ions undergo a change in structure or composition
Can be studied without a change in structure or composition
= 0.692g / mL
V = 10.00g x
= 14.5 mLDensity: Conversion factor mass volume
An empty flask weighs 22.138 g. You pipet 5.00 mL of octane into the flask. The total mass is 25.598 g. What is the density?
Octane amount in g:
What is the volume occupied by ten grams of octane?
Expressed as grams of solute per 100 g of solvent in the CRC (Chemical Rubber Company) Chemistry and Physics Handbook.
For lead nitrate in aqueous solution:
Cool the solution to 10°C. How much lead nitrate remains in solution?
= 28g lead nitrate
Mass of lead nitrate = 57g water
28g lead nitrate remain in solution
80g lead nitrate were initially in solution
80g – 28g = 52g lead nitrate crystallizes out of solution
Classification of Matter
More than one phase
Contain two or more elements with fixed mass percents
Glucose: 40.00% C
Sodium chloride: 39.34% Na
Nitrate group: two nitrate groups
Per each calcium atom
Total elements: 1 Ca
Buckyballs (C60 )
Heat: Quantitative Measurement
Types of Energy
Forms of Energy
Kinetic Energy (Motion Energy)
(Capacity to do work)
Potential Energy (Stored Energy)
Law of Conservation of Energy:
In any chemical or physical change, energy can be converted from one form to another, but it is neither created nor destroyed
Units of Energy:
Amount of kinetic energy possessed by a 2kg object moving at a speed of 1m/s. Substituting these values in the equation that defines kinetic energy:
Equivalent to the amount of energy you will
feel if you drop 4.4 lb from about 4 in. onto your foot.
calorie (cal) :
Amount of heat energy needed to raise the temperature of one gram of water by one degree Celsius measured between 14.5 and 15.5°C.
1 cal = 4.3184 J
The joule and calorie are rather small units.
The large calorie (Cal, C) is used to express the energy content of foods.
1kcal = 4.3184kJ
1C = 1kcal = 103 cal
140,000 cal of energy is released when the soft drink is metabolized within the body.
Sprite™ contains 140 C:
1 BTU (British Thermal Unit):
Amount of heat needed to raise the temperature of a lb of water one °F
1BTU =.818 kcal
Joseph Black (~1750):
“Amount of heat needed to raise the temperature of a substance by the same amount depends on the substance”
Amount of heat needed to raise the temperature of a given quantity of substance in a specific physical state.
Amount of heat needed to raise the temperature of 1 g of a substance in a specific physical state by 1°C
The specific heat of a substance changes when the physical state of the substance changes
2 .1 J / g °C
4 . 18 J / g °C
2 . 0 J / g °C
The higher the specific heat of a substance, the less its temperature will change when it absorbs a given amount of heat.
At the beach, sand has a lower specific heat than water, so it heats up while water stays cool.
Heat transferred = mass x Specific heat x ∆T
q = m x Cs x ∆T
Amount of heat energy needed to cause a fixed amount of a substance to undergo a specific temperature change without causing a change of state.
Transfer of heat from one body to another.
Heat always flows from the warmer body to the colder body.
The heat loss by the warmer body is equal to the heat gained by the colder body.
Heat in Chemical Change
Potential Energy Diagrams