Chem Second Semester Exam
If water is added to magnesium nitride, ammonia gas is produced when the mixture is heated M3N2 (s) + 3H2O (l) --> 3MgO (s) + 2NH3 (g) If 10.3 g of mg nitride is treated w/water, what volume of ammonia gas would be collected @ 24 degrees celcius and 752 mmHg?
5.03 L (dry volume)
At what temp does 16.3 g of nitrogen gas have a pressure of 1.25 atm in a 25.0 - L tank?
654 K
What is it meant by the term "colligative property"?
are properties of a solution that depend only on the #, not the identity of the solute particles
Calculate the [H+] in the solutions and tell if it's acidic or basic [OH-]= 2.32 x 10^-4 M [OH-]= 4.34 x 10^-4 M
basic basic
Nonmetals form negative ions by (losing/gaining) enough electrons to achieve the electron configuration of the next noble gas.
gaining
Why type of intermolecular forces is active in the liquid state of each of the following substances? CH3OH
hydrogen bonding and london dispersion forces
If an electron moves from the 1s orbital to the 2s orbital, its energy (increases/decreases)?
increases
The forces that connect two hydrogen atoms to an oxygen atom in a water molecule are (intermolecular/intramolecular), but the forces that hold water molecules close together in an ice cube are (intermolecular/intramolecular)
intramolecular; intermolecular
What type of bonding requires the complete transfer of an electron from one atom to another? What type of bonding involves the sharing (either equally or unequally) of electrons between atoms?
ionic; covalent
The label "concentrated H2SO4" on a bottle means that there is a relatively __________ amount of H2SO4 present in the solution.
large
In both of the following sets of elements, which element shows the least ability to gain or lose electrons? Li, C, O Ra,Ca,Mg
- O -Mg
Calculate molarity 55.0 mL of water to the 25.0 mL of 0.119 M NaCl solution 550 mL of water added to 125 mL of 3.01 M KOH solution
0.0372 0.0557
An alcoholic iodine solution ("tincture" of iodine) is prepared by dissolving 5.15 g of iodine crystals in enough alcohol to make a volume of 225 mL. Calculate the molarity of iodine in the solution.
0.0902 M
How many moles of each ion are present per liter, in a solution that is labeled "0.22 M CaCl2"?
0.221 mol Ca^2+, 0.442 mol Cl-
Supposed 1.01 g of FeCl3 is placed in a 10.0-mL volumetric flask, water is added, the mixture is shaken to dissolve the solid, and then water is added to the calibration mark on the flask. Calculate the molarity of each ion present in ghe solution.
0.623 M Fe^3+; 1.87 M Cl^-
The molar heat of fusion of aluminum metal is 10.79 kJ/mol, whereas its heat of vaporation os 293.4 kJ/mol. What quantity of heat would be required to vaporize 1.00 g of aluminum at its normal boiling point? What quantity of heat would be required to melt 0.105 mole of aluminum at its normal melting point?
10.9 kJ; 1.13 kJ
Calculate new volume of the gas sample after the pressure change is made. Assume the tempature and the amount of gas stay the same V=291 mL at 1.07 atm; V=? at 2.14 atm
121 mL
Combustion of propane C3H8 (g) + O2 (g)---> CO2 (g) + H2O (g) What volume of oxygen gas @ 25 degrees celcius and 1.04 atm is needed for the complete combustion of 5.53 g of propane?
14.7 L O2
A sample of gas in a balloon has an initial tempature of 18 degrees celcius and a volume of 1340L. If the temp changes to 87 degrees celcius and there is no overall change of pressure or amount of gas, what is the new volume of the gas?
1660L
Calculate the missing quantity after the change is made V= 2.03 L at 24 degrees celcius, V=3,.01 L at ? degrees celcius
167 celcius
Calculate unknown quantity p= 732.4 mm Hg; V=?; n= 0.1021 mol; T=26.2 degrees celcius
2.44 L
Explain why a solution is homogeneous mixture. Give two examples of homogeneous mixtures.
A homogeneous mixture is a combination of 2 (or more) pure substances that is uniform in composition and appearance throughout. Examples include rubbing alcohol (70% isopropyl alcohol and 30% water) and gasolin (a mixture of hydrocarbons)
How are the three states of matter similar and how do they differ?
A solid is rigid and incompressable and has a definite shape of its container. A gas has no fixed volume or shape; it takes the volume and shape of its container and is affected more by changes in pressure and tempature than is a liquid or a solid
On the basis of their electron configurations, predict the formula of the simple binary ionic compound likely to form when the following pairs of elements react with each other Aluminum, Al, and Sulfur, S Calcium, C, and Fluorine, F
Al2S3 CaF2
In the Arrhenius definition, what characteristics an acid? What characteristics a base? Why are the Arrhenius definitions too restrictive?
An acid is a substance that produces H2 ions (H^+) when dissolved in H2O. An Arrhenius base produces hydroxide ions (OH^-) when dissolved in H2O. These definitions are not complete because they limit the bases to compounds with a hydroxide ion and the allowable solvent in water
Arrange the following sets of elements in order of increasing atomic size S, Al, Ar, Na
Ar, S, Al, Na
Potatoes and other veggies often require longer cooking times at higher elevations. Explain why it takes longer to cook something at higher elevations.
At higher temperatures of liquids are lower because there is less atmospheric pressure above the liquid. The temperature at which food cooks is determined by the temperature to which the water in the food can be heated before it escapes as steam. By boiling at a lower temperature, the food will have to cook longer.
What simple ion does each of the following elements most commonly form? Calcium, Z=20 Bromine, Z=35
Ca^2+ Br^-
How do the components of a conjugate acid-base pair differ from one another? Give and example of a conjugate acid-base pair.
Differs by on hydrogen ion H^+. For example. HC2H3O2 (acetic acid) differs from its conjugate base C2H3O2^- (acetate ion) by a single hydrogen ion.
How is the strength of dipole-dipole interactions related to the distance between polar molecules? Are dipole-dipole forces short-range or long-range forces?
Dipole-Dipole forces are stronger at shorter distances; they are relatively short-range forces
When an atom in an excited state returns to its ground state, what happens to the excess energy of the atom?
Emitted as photon
In hydrogen fluoride, HF, which end of the molecule is positive relative to the other end?
H
Show how the following species behaves as a base when dissolved in H2O. HClO4 HSO3
HClO4+H2O—> ClO4^- + H3O^+ HSO3^- + H2O both arrows SO3^2- + H3O^+
Indentify conjugate acid-base pairs HF (aq) + H2O (l) (arrows going both ways F^- (aq) +H3O^+ (aq) HCO3^- (aq) +H2O (l) both ways H2OCO3 (aq) + OH (aq)
HF (acid) + H2O (base) arrows F^- (base) +H3O^+ (acid) HCO3^- (base) +H2O (acid) arrows H2CO3 (acid) + OH^- (base)
Write and complete orbital diagram for each of the following elements, using boxes to represent orbitals and arrow to represent electrons: Helium Z=2, Krypton: Z=36
Helium- 1s (^|) Krypton- 1s (^|) 2s (^|) 2p (^|)(^|)(^|) 3s(^|) 3p(^|)(^|)(^|) 4s (^|) 3d (^|)(^|)(^|)(^|)(^|) 4p (^|)(^|)(^ )
What does it mean to say that an acid is weak in aq solution what does tis reveal about the ability of the acid's anion protons?
If an acid is weak in aq solution, it does not easliy transfer protons to water (and does bot fully ionize) Thus the anion of the acid must attract protons rather strongly
Compare and contrast the bonding found in H2 (g) and HF (g) molecules with that found in NaF (s).
In H2 and HF, the bonding in covalent in nature, with an electron pair being shared between the atoms. In H2, the two atoms are identical (the sharing is equal); in HF the two atoms are different (the sharing is unequal) and as a result the bond is polar. Both of these are in marked contrast to the situation in NaF; NaF is an ionic compound--an electron has been completely transferred from sodium to fluorine, producing separate ions.
How do the physical properties of ionic solids, in general, differ from the properties of molecular solids? Give an example of each to illustrate your discussion.
Ionic solids tend to be harder and have higher melting and boiling points. Table salt (NaCl) to table sugar (sucrose)
What does it mean to say that an acid is strong in an aq solution? What does fhis reveal about thr ability of acid's anion to attract protons?
It means it is losing a proton making it an anion acid's anion attracts H+ ions and this means the weaker the acid, stronger conjugate base
Write the full electron configuration (1s^2s^2, etc.) for Mg Z=12 and O2 Z=8
Magnesium- 1s^2s^2p^63s^2 Oxygen- 1s^2s^2p^4
For the following pair, indicate which species is smaller. Explain M²+ or Mg
Mg⁺2; The nuclear charge is more effective for a positively charged ion (vs the neutral form of that atom), thus drawing the electrons in closer to the nucleus.
Write a Lewis Structure for the following molecules, Show all bonding, valence electrons pairs as lines and nonbonding valence electron pairs as dots NH3 NCl3
On study sheet
A tank contains a mixture of 3.0 moles of N2, 2.0 moles of O2, and 1.0 mole of CO2 at 25 degrees celcius and a total pressure of 10.0 atm. Calculate the partial pressure (in torr) of each gas in the mixture?
Po2= 732 torr, 1.98 x 10^⁻2
On the basis of electronegetivity values given in Fig 12.4 indicate whether each of the following bonds would be expected to be ionic, covalent, or polar covalent? S-S S-H
S-S: covalent S-H: polar covalent
Figure 14.2 presents the cooling curve for water. Discuss the meaning of the different portions of this curve (for example, explain what each flat section and each sloping section represents)
Sloped portions represent changes in temperature. The flat portions represent phase changes
How are the different types of electromagnetic radiation similar? How do they differ?
The different forms of electromagnetic radiation all exhibit the same wavelike behavior and move through space at the same speed (speed of light). The types of electromagnetic radiation differ in their frequency and wavelength and in the resulting amount of energy carried per photon
What types of ions do the metals and the nonmetallic elements form? Do the metals lose or gain electrons in doing this? Do the nonmetallic elements gain or lose electrons in doing this?
The metallic elements lose electrons and form positive ions (cations); the nonmetallic elements gain electrons and form negative ions (anions)
Explain how the properties of a metal may be modified by alloying the metal with some other substance. Discuss, in particular, how the properties of iron are modified in producing the various types of steel.
The presence of a second metal's atoms in a metal's lattice changes the properties (usually making the alloy stronger because irregularities arise, keeping the crystal from being easily deformed). Steels with relatively high carbon content are exceptionally strong. Steels produced by alloying iron with nickel, chromium, and cobalt are more resistant to corrosion (rusting) than iron itself.
Chem student needs 125 mL of .150 M NaOH solution for an experiment, but the only solution available in the lab is 3.02 M. Describe how the student could prepare the solution he needs.
Transfer 6.21 mL of the 3.02 M solution to a 125- mL volumetric flask and add the H2O to the calibration mark.
What is the geometric structure of the ammonia molecule? How many pairs of electrons surround the nitrogen atom in NH3? What is the approximate H-N-H bond angle in ammonia?
Trigonal Pyramid structure with 4 electron pairs, (three bonding pairs and one lone pair.) Bond is somewhat less than 109.5 degrees (due to lone pair)
What is vapor pressure? On a microscopic basis, how does a vapor pressure develop in a closed flask containing a small amount of liquid? What processes are going on in the flask?
Vapor pressure is the pressure of vapor pressure present at equilibrium above a liquid in a sealed container at a given temperature. Molecules in the liquid evaporate, but as the number of molecules in the vapor state increases, some of these rejoin (condense). Eventually dynamic equilibrium is reached between evaporation and condensation.
A solution that has not reached its limit of dissolved solute is said to be what?
unsaturated
