CH102: Textbook Review Questions
| CHAPTER 1: Chemical Foundations
Important Formulas:
TC = (TF - 32ºF) x 5ºC/9ºF. TF = TC * (9ºF/5ºC) + 32ºF K = TC + 273.15
The difference between a law and a theory is the difference between what and why. Explain. A law is a statement that describes how nature behaves, while a theory is an explanation for why nature behaves in a particular way that can revised or debunked over time.
Why is the separation of mixtures into pure or relatively pure substances so important when performing a chemical analysis? The purity of the substance when separated or extracted is important to ensure the method of separation was effective and the sample was actually separated properly, without other components still mixed in.
Is the doubling of the temperature on the Celsius scale equivalent to the doubling of the temperature on the Kelvin scale? If not, which doubling of temperature is the larger temperature increase? Explain. Yes, there is an equal gap between the high and low extremes of the Kelvin and Celsius scale of 100 degrees. As the celsius temperature doubles, it will reflect the same on the Kelvin scale. For example, if the original celsius temperature is 20ºC and doubles to 40ºC, the Kelvin temperature would increase by another 20 degrees (293.15 + 40 = 313.15)
Is the density of a gaseous substance larger or smaller than the density of a liquid or a solid at the same temperature? Why?
Challenge Problems (33G):
A rule of thumb in designing experiments is to avoid using a result that is the small difference between two large measured quantities. In terms of uncertainties in measurement, why is this good advice? All measured quantities, especially large ones, have their own uncertainties. There is little guarantee that these measured quantites are completely true. If asked for the difference between these two, that result may not be accurate. The result could be larger than what it actually is. For example, if one quantity is 1000 \pm 5 g and the other 990\pm5 g, the “result” could be 10 g, but there is an uncertainty of 5 (more or less) for each measurement. The 10 g result could be larger or smaller than anticipated.
Draw a picture showing the markings (graduations) on glassware that would allow you to make each of the following volume measurements of water, and explain your answers (the numbers given are as precise as possible).
128.7 mL
18 mL
23.45 mL
Many times errors are expressed in terms of percentage. The percent error is the absolute value of the difference of the true value and the experimental value, divided by the true value, and multiplied by 100.
percent.err=\frac{\vert true.val-\exp.val\vert}{true.val}\cdot100
Calculate the percent error for the following measurements:
The density of an aluminum block determined in an experiment was 2.64 g/cm3. (True value 2.70 g/cm3.) = 2%
The experimental determination of iron in iron ore was 16.48%. (True value 16.12%.) = 2.2%
A balance measured the mass of a 1.000-g standard as 0.9981 g. = 0.2%
A person weighed 15 pennies on a balance and recorded the following masses:
Yes, the Bureau of Mint may have changed to way they made their pennies. The older pennies (1970-1982) are almost 1 g heavier than after 1982. However, the transition must have taken place in 1982, for there to be some heavier or lighter pennies from the same year.
The masses of the pennies all have 4 significant figures, but the average mass has 5 and the uncertainty has an extra decimal place. It should be 3.083 g ± 0.048 g.
On October 21, 1982, the Bureau of the Mint changed the composition of pennies (see Exercise 132). Instead of an alloy of 95% Cu and 5% Zn by mass, a core of 99.2% Zn and 0.8% Cu with a thin shell of copper was adopted. The overall composition of the new penny was 97.6% Zn and 2.4% Cu by mass. Does this account for the difference in mass among the pennies in Exercise 132? Assume the volume of the individual metals that make up each penny can be added together to give the overall volume of the penny, and assume each penny is the same size. (Density of Cu 5 8.96 g/cm3; density of Zn 5 7.14 g/cm3.) Yes, the new composition of the pennies directly impacts the difference in mass. Copper has a slightly greater density than zinc, and now that the new penny consists of much less copper than zinc, the penny becomes lighter. Despite the size or the overall volume of the penny being the same.
As part of a science project, you study traffic patterns in your
city at an intersection in the middle of downtown. You set up a
device that counts the cars passing through this intersection
for a 24-hour period during a weekday. The graph of hourly
traffic looks like this:
From 8 AM to noon and towards 5 PM
Before 6 AM and after 6 PM
The number of cars passing at the intersection are highest from 8 AM to noon, and then approaching 5 PM. They are lowest before 6 AM and after 6 PM
The number of cars passing through the designated intersection depends on the time of day, because more people are likely to drive to their day-to-day activities in the early morning and head home in the late afternoon.
Create a poll or short interview targeting vehicle-owners, asking them what time they would most likely leave their residence for their daily activities (work, school, errands, etc.) and when they would decide to drive back to their residence.
Sterling silver is a solid solution of silver and copper. If a piece of a sterling silver necklace has a mass of 105.0 g and a volume of 10.12 mL, calculate the mass percent of copper in the piece of necklace. Assume that the volume of silver present plus the volume of copper present equals the total volume. = 86.4%
The temperature in ºF (TF) is plotted versus the temperature in
ºC (TC). The result is a straight line. A straight-line plot also
results when TC is plotted versus TK (the temperature in K).
Reference Appendix A1.3 to determine the slope and y intercept
of each plot.
Fahrenheit v. Celsius =
Confronted with the box shown in the diagram, you wish to
discover something about its internal workings. You have no
tools and cannot open the box. You pull on rope B, and it
moves rather freely. When you pull on rope A, rope C appears
to be pulled slightly into the box. When you pull on rope C,
rope A almost disappears into the box.*
a) Rope A and C are the same rope, and the rope is attached to a pulley system. When rope A is pulled, there is more tension, preventing too much of rope C to be pulled back. The opposite applies to rope A where there is less tension. Rope B is it’s own rope.
An experiment was performed in which an empty 100-mL graduated cylinder was weighed. It was weighed once again after it had been filled to the 10.0-mL mark with dry sand. A 10-mL pipet was used to transfer 10.00 mL of methanol to the cylinder. The sand–methanol mixture was stirred until bubbles no longer emerged from the mixture and the sand looked uniformly wet. The cylinder was then weighed again. Use the data obtained from this experiment (and displayed at the end of this problem) to find the density of the dry sand, the density of methanol, and the density of sand particles. Does the bubbling that occurs when the methanol is added to the dry sand indicate that the sand and methanol are reacting?
Answer more questions in Chapter 1 regarding significant figures, density, temperature, etc. (ChemWorks)
Read CH 2 and answer questions
| CHAPTER 3: Stoichiometry
[Include Assignment 3 questions and answers]
[challenge problems]
[target objective problems]