Unit 1 AP Chem
b) The molar masses of X and Z
A student obtains a mixture of the Fluorides of two unknown metals, X and Z . The percent by mass of X and the percent by mass of Z in the mixture is known. Which of the following additional information is most helpful in calculating the mole percent of XF(s) and of ZF(s) in the mixture? a) The number of isotopes of F b) The molar masses of X and Z c) The density of either XF (s) or ZF(s) d) The percent by mass of F in the mixture
a) The molar mass of each gas
A vessel contains a mixture of gases. The mass of each gas used to make the mixture is known. Which of the following information is needed to determine the mole fraction of each gas in the mixture? a) The molar mass of each gas b) The density of the gases in the vessel c) The total pressure of the gases in the vessel d) The number of atoms per molecule for each gas
*got wrong* (the valence electrons in Rb are in a higher energy level than those of K or the outer orbitals have a higher principal quantum number in rb than in K or the valence electrons of Rb are less attracted to the nucleus than those of K.)
Answer the following questions related to Rb. a) In terms of atomic structure, explain why the atomic radius of Rb is larger than K.
Rb's atomic structure is larger than K's atomic structure, this means that the IE is lower since the far distance weakens the attraction. (The response indicates that the first ionization energy of Rb is less than that of K because the electron removed from Rb is less strongly attracted to (and thus more easily removed from) the Rb nucleus, which has fewer protons than K.)
Answer the following questions related to Rb. b) In terms of atomic structure, explain why the first-ionization energy Rb is less than that of K.
*got wrong* (M: Li, Na, K, Cs, or Fr the element chosen is in the same group/family/column of the periodic table as Rb OR that an atom of the element the student chose has the same number of valence electrons as an Rb atom)
Answer the following questions related to Rb. c) Rb forms the compound Rb2O, which is an ionic compound that is brittle. Identify another element, M, that is likely to form a brittle, ionic compound with the formula M2O. Justify your answer in terms of periodic trends.
Yes, because they are both pure. When they are both in their pure state, they are different. (YES, the chemist can determine the identity of the compound.if the mass of Rb in a sample of the compound is determined, then the percent mass of Rb in the compound can be calculated and the compound identified because the percent mass is different (or known) for the two compounds.)
Answer the following questions related to Rb. d) The compound Rb2O2 also exists. A chemist can determine the mass of Rb in a sample of known mass that consists of either pure Rb2O or Pure K2O2. From this information, can the chemist answer the question of which compound is in the sample? Indicate yes or no, and explain.
a) 0
1s2 2s2 2p6 3s2 3p6 How many unpaired electrons are in the atom represented by the electron configuration above? a) 0 b) 1 c) 2 d) 3
d) H2C4O4
A 1.0 mol sample of which of the following compounds has the greatest mass? a) CO b) CO2 c) HCO3 d) H2C4O4
*got wrong* correct answer is: d) What is the empirical formula of the compound?
A 52.0g sample of compound containing only C and H was analyzed. The results showed that the sample contained 45.0g of C and 7.0g of H . Which of the following questions about the compound can be answered using the results of the analysis? a) What was the volume of the sample? b) What is the molar mass of the compound? c) What is the chemical stability of the compound? d) What is the empirical formula of the compound?
b) Mass Percent of Na
A jar labeled NaCl contains a powder. The table above contains information determined by analyzing a sample of the powder in the laboratory. What information in the table is the most helpful in determining whether the powder is pure NaCl? a) Mass b) Mass Percent of Na c) Density d) Color
3 (The response indicates that there are three isotopes represented in the mass spectrum.)
A sample of a pure element is analyzed using a mass spectrometer. The results are shown below. a) how many different Isotopes of the element were in the sample?
Find the average by adding up all of the masses and dividing by the number of isotopes there are. *on right track but kinda wrong* (The response indicates that the weighted average must be calculated by finding the sum of three terms, each of which is the product of the proportional abundance of each isotope and the mass of each isotope(ex: (0.79)(24)+(0.10)(25)+(0.11)(26), or (0.80)(24)+(0.10)(25)+(0.10)(26))
A sample of a pure element is analyzed using a mass spectrometer. The results are shown below. b)Describe how to use the information from the mass spectrum to determine the average atomic mass of the element.
Mg (The response indicates that the element is Mg.)
A sample of a pure element is analyzed using a mass spectrometer. The results are shown below. c) Identify the element.
Mg: 1s2 2s2 2p6 3s2 (The response indicates the following e configuration: 1s2 2s2 2p6 3s2)
A sample of a pure element is analyzed using a mass spectrometer. The results are shown below. d) Write the ground-state electron configuration of an atom of the element that you identified in part (c).
b) What is the molar mass of M?
A student measures the mass of a sample of a metallic element, . Then the student heats the sample in air,where it completely reacts to form the compound . The student measures the mass of the compound that was formed. Which of the following questions can be answered from the results of the experiment? a) What is the density of M? b) What is the molar mass of M? c) What is the melting point of M? d) What is the melting point of MO?
b) Is the BaCl2(s) used in the experiment pure?
A student obtains a 10.0g sample of a white powder labeled as BaCl2 . After completely dissolving the powder in 50.0mL of distilled water, the student adds excess Na2SO4(s) , which causes a precipitate of BaSO4(s) to form, as represented by the equation above. The student filters the BaSO4(s) , rinses it, and dries it until its mass is constant. Which of the following scientific questions could best be answered based on the results of the experiment? Ba2(+)(aq)+SO4(2−)(aq)→BaSO4(s)? a) Is the Na2SO4(s) used in the experiment pure? b) Is the BaCl2(s) used in the experiment pure? c) What is the molar solubility of BaCl2 in water? d) What is the molar solubility of BaSO4 in water?
a fixed composition
What do all pure substances have?
A technique used to identify the isotopes of an element and their relative abundance in nature. It's used to calculate average atomic mass.
What is Mass Spectroscopy and what is it used for?
It's used to calculate the force between two charged particles
Explain Coulomb's law.
As you move down, the IE decreases. As you move right, the IE increases.
Explain the trend of Ionization Energy on the periodic table.
An outer shell electron. The 8 periods on the periodic table shows the number of valence electrons in the elements in that period.
Explain a valence electron.
It helps us see how electrons are arranged in atomic orbitals for a specific element.
Explain electron configuration.
As you move down, the radius increases. As you move to the right, the radius decreases.
Explain the trend of Atomic Radius on the periodic table.
c) 186.3 amu
Based on the mass spectrum of a pure element represented above, the average atomic mass of the element is closest to which of the following? (65% abundance of 187; 37% abundance of 185) a) 185.7 amu b) 186.0 amu c) 186.3 amu d) 186.9 amu
As you move down, the EA decreases. As you move right, the EA increases.
Explain the trend of Electron Affinity on the periodic table.
As you move down, the electronegativity decreases. As you move right, the electronegativity increases.
Explain the trend of Electronegativity on the periodic table.
?
Cs reacts with S in a mole ration of 2 to 1, forming the ionic compound Cs2S. Which of the following elements will reaction with S in a mole ration of 2 to 1, forming an ionic compound and why? a) O, Because its in the same group as S. b) Rb, because it is in the same group as Cs . c) Sr , because it is in the same period as Rb . d) Ba , because the atomic mass of Br is similar to that of Cs
c) The Molar Mass of Fe
In a lab a student is given a 15.3 g sample of pure Fe metal. Which of the following pieces of information is most useful for determining the number of Fe atoms in the sample? Assume that the pressure and temperature in the lab are 1.0 atm and 25 C. a) The density of Fe at 25 C b) The Volume of the Fe sample c) The Molar Mass of Fe d) the ratio of the two main isotopes found in pure Fe
c) The attractive force between the valence electrons and the nuclei of the atoms decreases.
The atomic radii of the elements in the nitrogen group in the periodic table are given in the table below. Which of the following best helps explain the trend of increasing atomic radius from N to Bi? a) The number of particles in the nucleus of the atom increases. b) The number of electrons in the outermost shell of the atom increases. c) The attractive force between the valence electrons and the nuclei of the atoms decreases. d) The repulsive force between the valence electrons and the electrons in the inner shells decreases.
*got wrong* correct answer is: a) Peak X, because 1s electrons have the strongest attractions to the nucleus.
The complete photoelectron spectrum of an element is given above. Which labeled peak corresponds to the 1s electrons and why? *Y is shorter in relative number of electrons and closer to 0 in binding energy* a) Peak X, because 1s electrons are the easiest to remove from the atom b) Peak X, because 1s electrons have the strongest attractions to the nucleus. c) Peak Y , because electrons in the 1s sublevel are the farthest from the nucleus d) Peak Y, because there are fewer electrons in an s sublevel than in a p sublevel
Atomic radii, IE, electronegativity, and electron affinity.
What are the 4 periodic trends?
*got wrong* answer is c) The valence electron of K experiences a lower effective nuclear charge than the valence electrons of Ca.
Which of the following best helps explain why the first ionization energy of K is less than that of Ca? a) The electronegativity of K is greater than that of Ca. b) The atomic radius of the K atom is less than that of the Ca atom. c) The valence electron of K experiences a lower effective nuclear charge than the valence electrons of Ca. d) The nucleus of the K atom has fewer neutrons, on average, than the nucleus of the Ca atom has.
c) 1s2 2s2 2p6 3s2
Which of the following is the correct electron configuration for a ground-state atom of magnesium (atomic number 12 ) ? a) 1s2 2s2 2p8 b) 1s2 2s2 3s2 3p6 c) 1s2 2s2 2p6 3s2 d) 1s2 2s2 3s4 3p4
*got wrong* correct answer is: b) 5.3g/(58 g/mol)
Which of the following numerical expressions gives you the number of moles in 5.3g of NaCl? a) 5.3g x 58g/mol b) 5.3g/(58 g/mol) c) (58g/mol)/5.3g d) (1/5.3g) x (1/(58g/mol))
