Download General Chemistry: Chemistry 1000

General Chemistry: CHEM1000
Tutorial #1: Chemical Measurements
Group scribe __________________
Group members_________________
__________________
__________________
Reading assignment: Chapter 1. Homework: Final exercises 11, 17, 24, 36, 76.
Useful web site: http://physics.nist.gov/cuu/Units/index.html
Part I: Tutorial
A. Useful conversions. Fill in the English or Metric equivalents in the table below. Look
in the text or see the web site.
1 meter = _____ inches
1 kilogram = _____ lb
1 inch = _____ cm
1 pound
= _____ g
1 liter = _____qt
1 liter = _____ ml (cm3)
Write formulas for the temperature conversions below:
Celsius from Kelvin ____________________
Fahrenheit from Celsius ____________________
B. Metric Units. Fill in the table below. SI units are the most commonly used units,
however, occasionally the cgs system is still sometimes used when it is more convenient. In the
cgs system the units are centimeter, grams and seconds.
Physical quantity
Unit (SI)
Symbol (SI)
Unit (cgs)
Symbol (cgs)
mass
time
length
C. Derived Units. Units for density, force, and energy are obtained from the basic units for
length, mass and time and are called “derived units”. Determine the units for each of the
following quantities (for the SI units, figure them out and look under SI units in the web
site above to check yourself).
1. Density = mass per volume: d = m/v
SI units: d = ____________
cgs units: d = ____________ (still used for convenience)
Hint: mass is measured in kilograms & volume in m3 in the SI system, and in grams & cm3 in the
cgs system.
2. Force = mass times acceleration: f = m a
SI units:
f = _____________ = newton
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3. Energy. Kinetic energy, work and heat are all different forms of energy.
a. Kinetic energy is the energy of motion. K.E. = ½(mass times velocity squared) = ½(mv2)
SI units:
K.E. = _____________ = joule
NOTE: Energy is sometimes measured in units of calories where 1 cal=4.184 joules.
b. Work is the energy needed to move an object and so is found from the force that must be
applied and the distance the object is moved. W = force times distance = f d
SI units:
W = _________________ = joule
c. Heat is the energy that flows from one object to another if they are at different
temperatures and in contact with each other.
From your own experience, does more or less heat flow when the temperature difference
between two objects is large than when the temperature difference is small?
Your experience is consistent with the experimental fact that heat flow is proportional to the temperature
difference. Write a “proportionality” between heat and the temperature difference (T2-T1):
We can turn the proportionality into an equality by introducing a constant (C): heat = C (T2-T1)
C is called heat capacity. Solve this equation for C and write down the units on C (heat is
energy in joules and T is temperature in Kelvin)
Heat capacity
Formula for heat capacity
SI units for heat capacity
C=
Use the units on C to define it in words. A division sign means “per”.
If a substance has a high heat capacity, it takes a lot of energy to change the temperature of
that substance. Assume that you have equal masses of metal and ceramic (for example an
aluminum coffee cup and a ceramic coffee cup). Which one has the higher heat capacity?
On what experience did you base your decision? Which material would serve as a better
heat insulator?
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Another quantity that is useful is the specific heat (c). The specific heat is the amount of
energy needed to heat a specific amount of material (one gram) a specific number of degrees
in temperature (one degree), specific heat = heat capacity/mass Write the SI units for
specific heat.
c = ________________
D. Temperature scales.
Write the temperature at which water boils and freezes (at sea level) in table below. Indicate
the number of degrees (Celsius, Fahrenheit or Kelvin) between these points.
Celsius
Fahrenheit
Kelvin
Boiling point of water
Difference between the
boiling & freezing point
of water
Freezing point of water
E. Uncertainty in measurements.
1. Define precision.
Define accuracy.
2. Determining the uncertainty or error of a laboratory measurement.
a. The uncertainty of a single measurement is a fraction of the smallest discernable division of
the scale (i.e., how well you can read the value).
Estimate the uncertainty in the measurement made using the following measuring devices:
Graduated cylinder: ____________
Thermometer _______________
50-ml buret _____________
Digital thermometer ____________
F. Significant figures and scientific notation.
1. Counting significant figures. Use the rules in the text to work final exercises 1.29 and 1.30.
Problem 1.29
a. 5 sig fig
b. 2 sig fig
c.
d.
e.
f.
Problem 1.30
a.
b.
c.
d.
e.
f.
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2. Significant figures in calculations. Study examples 1.3, 1.4, 1.5 and 1.6, then work final
exercise 1.33
a.
Problem 1.33
c.
b.
d.
3. Scientific notation. Express the following numbers in scientific notation (keep the number
of significant figures the same).
a. 1,002.0
d. 602,000,000,000,000,000,000,000
b. 200
e. 0.54
c. 0.003650
Part II: Laboratory Measurements and Uncertainties.
The following simple exercises will give you experience in determining uncertainties in
laboratory measurements. SHOW YOUR WORK OR THE METHOD USED.
A. Length and volume determinations
1. The tiles on the floor in the lab are one foot square.
a. Measure the width and length of the lab in feet and report it here with your estimated
uncertainty of the measurement.
Width = __________ +
___________.
Length = __________ +
___________.
b. Calculate the area of the lab in square feet and in square meters.
Area = ______________ft2 = _______________m2
c. Calculate the volume of air contained in the lab in cubic feet and cubic meters (m 3)
assuming that the ceiling is 8ft above the floor. Report your value to the instructor.
Volume = ______________ = ________________.
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d. Calculate the average volume obtained by the class and calculate the standard
deviation of the volume measurements. The standard deviation is reported as the error when
many measurements of the same thing are done.
std. dev. = [1/(N-1){(x1-xa)2 + (x2-xa)2 + (x3-xa)2 +….(xn-xa)2}]1/2
xa is the average, x1, x2, etc. are the individual measurements and N is the number of
measurements..
average vol. = ____________________ std. dev. = ____________________
2.
Obtain a 250 ml Erlenmeyer flask.
a. Determine the volume of the flask. (No, this isn’t a trick question, the volume of an
Erlenmeyer flask is not exactly the volume written on the flask. To determine it’s
volume you can find the volume of water it holds with a graduated cylinder.)
Volume = _______________ + _____________
b. Use the volume and the density of water ( 1.00 g/cm3) to find the mass of water
contained in the Erlenmeyer flask.
Mass = _____________
B. Temperature and energy determinations
Put a known volume of room temperature water in your Erlenmeyer (don’t fill it all the way up).
a. Measure the temperature of the water. T1 = __________ + ___________.
b. Heat the water with a hot plate until the water boils. Measure the temperature of the
boiling water. T2 = ____________ + ________________.
c. Use the specific heat of water to calculate the amount of heat energy added to the water
to bring it to the boiling point in calories and in Joules. The specific heat (c) of water is
1 cal/(goC) or 4.184 joule/(goC).
Heat energy added = _____________ = __________________
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