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Chemistry – Review for 1st Semester Exam
Part I: Measurement and Calculations
1.Demonstrate understanding of the use of measurements in science. You should be able to apply the rules of significant figures to choose answer with the correct number of significant figures.
Express the answer in the correct number of significant figures. Label with appropriate units.
a. 21.3 g = 16.38461516 g/cm3
1.3 cm3
b. 6.34 cm2 x 1.2 cm = 6.2514376.3 cm2
1.217 cm
c. 13.21m x 61.5 m = 812.415812 m2
d. 21.50 cm = 2.5294117652.53 cm/in
8.50 in
You should also be able to measure the length of an object or volume of a liquid to the appropriate number of significant figures based upon the measuring instrument.
Which of the following best expresses the width of the business card?
a.5 cmb. 5.0 cmc. 5.05 cmd. 5.50 cm
Which of the following best expresses the volume of the liquid in the graduated cylinder?
a. 40 mL
b. 43 mL
c. 43.0 mL
c. 44.0 mL
d. 43.01 mL
2. Demonstrate proficiency in the use of scientific notation and use of dimensional analysis in metric conversions. Know the meaning of the following metric prefixes and be able to make conversions utilizing them: milli-, centi-, kilo-
Example:
Complete the indicated conversions:
a. 37 g x = 37000 mgc. 138 m x= 0.138 km
b. 4.7 kg x = 4700____ gd. 4021 mm x = 4.021 m
3.Be able to convert standard (decimal) notation to scientific notation and vice versa.
standard:scientific:
13001.3 x 103
0.001551.55 x 10-3
16800001.68 x 106
0.02732.73 x 10-2
4.What is the Law of Conservation of Mass?
Mass can not be created nor destroyed. Mass does not change unless particles enter or leave a system.
Study the mass and change lab. Under what conditions will you observe a decrease in mass? Where do the particles go? Under what conditions will you observe an increase in mass? Where do the particles come from?
Take notes below for each part of the lab.
See Lab #1 in Lab Book and notes taken in class
5. Determine the density of an object from a data table or from a graph of mass v volume.
Volume (cm3) / Mass (g)1.5 / 11.7
3.0 / 24.0
4.5 / 35.1
6.0 / 48.0
7.5 / 58.5
9.0 / 70.0
Plot the data above and determine the density of the substance.
What volume would 150g of the substance occupy? Show work; use labels.
Density is the slope. Calculate the slope using two data points above (8.2 g/1 cm3).
Once you know slope, set up dimensional analysis to convert g to cm3 (18 cm3).
Part II: The Role of Energy in Physical Change
1.Describe the ways energy is stored in solids, liquids and gases (thermal, phase, chemical). Also describe ways energy is transferred (working, heating, radiating).
Thermal energy – energy of motion – related to the absolute temperature
- Hotter molecules move more rapidly than slower ones; for a given volume the gas will have a greater pressure due to the greater number of collisions
Phase energy – energy due to attractions between molecules; the stronger the attractions, the lower the energy of the system of particles
- Lowest for solids, greater in liquids, greatest in gas phase
2.Heat is the transfer of energy into or out of a system due to molecular collisions.
Energy is transferred from hotter (faster) molecules to colder (slower) molecules.
Explain why the alcohol level in a thermometer rises when it is placed in a warmer fluid. (3-step process)
The warm fluid particles are moving fast and colliding with the glass particles resulting in a transfer of energy to the glass. The glass particles are also colliding with the alcohol particles resulting in another transfer of energy. As the alcohol particles gain more energy through this process, they speed up. As they speed up, expansion occurs due to the more frequent and the harder collisions.
Describe what happens (at the molecular level) when a glass of cold water warms up to room temperature.
Warm air particles collide with the cold water particles resulting in energy being transferred to the water. As the water gains energy, the water particles speed up (speed = temperature).
Be able to draw energy bar graphs to account for energy storage and transfer in all sorts of changes. (Review worksheet 1 and 2, quiz in unit 3)
Complete the energy bar chart for the following scenario: An ice cube tray of water at room temperature is placed into the freezer and the liquid changes to solid.
When energy is transferred to a sample of matter, either the particles speed up (temperature increases) or they get pulled apart (phase change), but not both at the same time. This helps account for the shape of the warming curve you got in the Icy Hot lab.
On the graph above label which phases are present in each portion of the curve.
1) solid only 2) solid and liquid 3) liquid only 4) gas and liquid
Label the sections in which the thermal energy (Eth) of the sample is changing. Label the sections where the phase energy (Eph) is changing.
1) thermal increasing 2) phase increasing 3) thermal increasing
4) phase increasing
Use the equations to determine the energy transferred to or from water during a phase change. Use to determine the energy transferred to or from water during heating or cooling.
Draw a heating curve and mark on the curve your beginning and ending points. Using the appropriate equations and values answer the following:
How much energy would be required to bring 100. g of ice at 0.0°C to its boiling point?
Q=mc ΔT
Q= 100.g x 4.18J___ x 100.°C = 41800 J41800+ 33400 = 75200 J
1g 1°C
Q=mΔHf
Q= 100.g x334 J = 33400 J
1g
Part III: Gases and Kinetic Theory
1. Demonstrate knowledge of the relationships that exist among the pressure, volume, temperature, and number of molecules of a gas. You should be able to determine the pressure of a sample of gas in a flask connected to a manometer.
You should be able to identify the correct graphic representation of the relationships between volume, temperature, and pressure.
Which graph describes the relationship between gas pressure and volume?
D
Which graph describes the relationship between gas pressure and the Kelvin temperature?
A
Solve problems given volume, pressure, or temperature of gases (PVTn charts).
A sample of carbon dioxide has a volume of 2.0 L at a temperature of –10˚C. What volume will this sample have when the temperature is increased to 110˚C. Assume that the pressure does not change and that no carbon dioxide leaks from the sample.
Remember to convert temp to Kelvin scale! Set up PVTn chart and then solve. Final calculation looks like this:
2.0L x 383 K = 2.9L
263 K
A 12.7 L sample of gas is under a pressure of 740 mm Hg at 20°C. What will be the volume of the gas if the pressure increases to 1.00 atm and the temperature drops to 0.0°C?
Convert temp to Kelvin scale and set up a PVTn chart. Final calculation looks like this:
12.7 L x 740 mmHg x 273K = 11.5 L =11.2L
760 mmHg 293K
Based on the height of a column of mercury in an open U-tube manometer, be able to compare pressures on both sides of the tube.
Determine the pressure in each of the flasks.
A= 787 mmHgB=660 mmHg
Part IV: Matter and Atomic Theory
1.Describe how matter is organized.
You should be able to identify diagrams and distinguish between atoms, molecules, compounds, mixtures, gases, and solids.
a. What is represented in Figure A? Atoms of an element
b. Does Figure B represent a compound or an element? Explain.
An element; all atoms are identical
c. Which diagrams show only molecules? What is different about the molecules represented by the diagrams?
B, C, and D. B= molecules of an element; C= molecules of a compound; D= mixture containing compound molecules and element molecules
2. Demonstrate knowledge of separation techniques for mixtures and compounds. Distinguish between the separation techniques required for mixtures and compounds. List and describe a few examples below.
Mixtures- Distillation, filtration, use of magnet, etc. (Describe each)
Compounds- Hydrolysis (Describe use of Hoffman apparatus)
3. Demonstrate knowledge of the meaning of a chemical formula in terms of atoms and molecules.
Given the formula of a compound, identify the number of atoms present.
Example: Identify the number of atoms of each kind in each compound.
Pb(NO3)2Na3PO4Al2(SO4)3
9817
IV. The mole concept and chemical reactions
Recognize that atoms are too small to count directly. We determine how many there are in a sample by finding their mass. We use the mole to determine the number of atoms and molecules. Molar mass (on Periodic Table) is relative mass, based originally on hydrogen (lightest element).
- Be able to determine the molar mass of a compound.
Example: Determine the molar masses (using correct SFs and giving unit of measurement!).
Pb(NO3)2BaSO4
331.2 g/mole233.4 g/mole
2.Determine the number of atoms or moles using Avogadro’s number and the molar mass of a compound.
Example: use molar mass
12 g MgCl2 x = molesMgCl2
A= 0.13 moles
use Avogadro’s number
3 moles Clx= atoms Cl
A= 2 x 1024 atoms
3. Determine the empirical and molecular formulas from data.
A compound is composed of 7.20 g of carbon, 1.20 g of hydrogen, and 9.60 g of oxygen. The molar mass of the compound is 180 g. Find the empirical and molecular formulas for this compound.
Empirical Formula = CH2O
Molecular Formula = C6H12O6
Additional Terms/Concepts: Law of Definite Proportions, Law of Multiple Proportions, Empedocles, Democritus, and Dalton’s Atomic Theory, percent composition