FE Review Chemistry. Heather J. Shipley Assistant Professor Civil and Environmental Engineering UTSA

Transcription

1 FE Review Chemistry Heather J. Shipley Assistant Professor Civil and Environmental Engineering UTSA

2 Basic Concepts Nucleus of atom Proton: positively charged particle, amu Neutron: neutral particle, amu Electron: negatively charged particle, amu neutron proton electron

3 Definitions Atomic mass: the total mass of protons, neutrons, and electrons in a single atom Atomic number: the number of protons in the nucleus Element: a substance only composed of one type of atom Isotope: element with the same number of protons but different atomic masses

4 Electron Configuration

5 Periodic Trends Electronegativity Ionization Energy Atomic Radius

6 Electronegativity: is a chemical property that describes the tendency of an atom or a functional group to attract electrons (or electron density) towards itself. Ionization energy: is the energy required to remove electrons from atoms or ions. Atomic radius: the size of the atom

7 Molecular Bonding E.g. CaCl 2 = (35.45) = g/mole Elements combine to form molecules in order to fill their shells. Usually an element has 8 electrons around it, except H which is 2 and B which is 6

8 Formed by sharing a pair of electrons formed by electrostatic attraction between positive and negative ions

9 Gas Laws Ideal Gas law PV= nrt No intermolecular forces Gas molecules occupy no specific volume Standard Temperature and Pressure 0 C and 1atm 22.4L/mole

10 Gas Laws cont. P = Pa +Pb +Pc+ Henry s Law: relates gases and solutions K H =P gas /C = partial pressure of a gas (atm)/ concentration in solution (M)

11 Solution Chemistry

12 Solution Chemistry

13 Equilibrium aa + bb = cc +dd K = [C] c [D] d / [A] a [B] b = products/reactants

14 ph Water dissociates into H + and OH - H 2 O = H + + OH - Equilibrium Kw = [H + ][OH - ]/[H 2 O] = [H + ][OH - ] Kw = 1x10-14 ph = log(1/[h + ]) ph >7: alkaline ([OH - ]>[H + ]) ph < 7: acidic ([OH - ]<[H + ]) poh = log(1/[oh - ]) ph+poh = 14

15 Example Calculate the ph of 10g/L NaOH solution [NaOH] = 10g/L*1mol/40g = 0.25M [OH-] = 0.25M * 1mol OH/1mol NaOH = 0.25M poh = log(1/0.25) = ph = =

16 Chemical reactions In chemical reactions elements or molecules rearrange themselves to form more stable molecules. The reaction is highly favored if electrons are transferred from an element which loosely binds electrons to an element that tightly binds electrons. The element which donates the electrons is the reducing agent and the element which receives is the oxidizing agent.

17 Reactions Precipitation/Dissolution Reactions Dissolved ions react with other ions to form insoluble compounds A a B b (s) = aa b+ + bb a- Ksp = [A] a [B] b Undersaturated if [A] a [B] b < Ksp Saturated if [A] a [B] b = Ksp Super-saturated if [A] a [B] b > Ksp Acid/Base reactions Substances that influence ph, see earlier slides Complexation Reaction Occurs when 2 or more atoms, molecules, or ions combine and form a stable product E.g. Fe(H 2 O) 6 2+

18 Reactions Oxidation and Reduction Reactions (Redox) Involves transfer of e-; one compound gives up e- the other takes them up Compound giving up e- is being oxidized, so reducing agent Compound accepting e- is being reduced, oxidizing agent Ex. Corrosion of Fe Fe 0 = Fe 2+ +2e- 2H + + 2e- = H 2 (g) Overall Fe 0 + 2H + = Fe 2+ +H 2 (g) Combustion Reaction: burning of fuel with oxygen

19 Electrochemical cells

20 Balancing Equations 2 rules Mass must be conserved The number of atoms of an element on the left hand side of the rxn needs to equal the amount on the right The atoms can change what they associate with but not be created or destroyed Charge must be conserved charge on the left must equal the charge on the right

21 Example Balance the equation? SO H + + CH 2 O HS - + CO 2 + H 2 O 1SO H + + 2CH 2 O 1HS - + 2CO 2 + 2H 2 O

22

23 Speed of a reaction Kinetics Zero order: rxn proceeds at a rate independent of the conc. of any reactant C-C 0 = -kt First Order: rxn proceeds at a rate directly proportional to the concentration of one reactant C = C 0 e -kt Half life t 1/2 = ln2 / k Second order: proceeds at a rate proportional to the square of the conc. of 1 reactant or the product of 2 reactants 1/C-1/C 0 = kt

24 Alkanes Organic Chemistry

25 Organic Chemistry

26 Practice problems FE Exam: Chemistry 1. Which statement is incorrect? a) solutions may be homogeneous or heterogeneous b) matter may be homogeneous or heterogeneous c) Both elements and compounds are composed of atoms d) All substances contain atoms e) substances are always homogeneous 2. Which statement is incorrect? a) An element may be separated into atoms b) An element may be a gas, a liquid, or a solid c) A compound can be separated into its elements by chemical means d) An element is always heterogeneous e) A compound may be a gas, a liquid, or a solid 3. In relation to the proton, the electron is a) about the same mass and of opposite charge b) about the same mass and of the same charge c) about the same mass and with no charge d) much lighter and of opposite charge e) much heavier and with no charge 4. A negative ion of a certain element can be formed by a) subtraction of a proton from and atom of that element b) subtraction of a electron from and atom of that element c) subtraction of a neutron from and atom of that element d) addition of a electron from and atom of that element e) addition of a neutron from and atom of that element 5. Metallic conduction involves a) migration of cations towards a positively charged electrode b) migration of cations towards a negatively charged electrode c) passage of electrons from one atom of a metal to another d) migration of anion towards a negatively charged electrode 6. Which of the following statement is true? a) within a group of elements in the periodic table, the largest atom has the highest ionization potential b) within a period of elements in the periodic table, the noble gas has the highest ionization potential c) when all valence p orbitals of an atom are half filled the ionization potential of that atom is lower than the ionization potential of an atom with only 2 electrons in valence p d) it is easier to form a 2+ ion than a 1+ ion e) ionization potential is the same as Electronegativity

27 7. Which one of the following elements has the largest atomic radius? a) Li b) Na c) Be d) Mg e) P 8. In the series of elements B, Al, Ga, In a) Electronegativity increases from B to In b) metallic character increases from B to In c) ionization energy increases from B to In d) nonmetallic character increases from B to In e) none of the above 9. Which of the following lists contains only nonmetals? a) Be, H, Os b) Ge, Pd, Si c) C, S, F d) Ca, Cl, B e)zn, Ga, Ge 10. In an element a) the atomic number is equal to the number of neutrons in the atom b) the number of protons always equals the number of neutrons in the atom c) the mass number is equal to the number of electrons in the atom d) the atomic number is equal to the number of protons in the atom e) the number of electrons can never equal the number of neutrons in the atom 11. What is the ground state electron configuration of Al, Z = 13 a) 1s 2 2s 2 2p 5 3s 2 3p 1 b) 1s 2 2s 2 2p 6 3s 2 3p 1 c) 1s 2 2s 2 2p 6 3s 2 4s 1 d) 1s 2 2s 2 2p 6 3s 2 3p 2 e) 1s 2 2s 2 2p 6 3s 2 3d Which of these electron configurations is found in periodic Group VI a) ns 2 b) np 6 c) ns 4 d) ns 2 np 4 e) ns 4 np From a consideration of electron configuration which of the following elements would you expect to be most similar in chemical properties to Sr a) Rb b) Y

28 c) Sc d) Ba 14. How many electrons does a phosphorus atom have in its set of valence shell p orbitals a) 0 b) 1 c) 2 d) 3 e) An atom of an unknown element Q as a mass number of 31 and the nucleus contains 15 protons. The element is a) Ga b) S c) P d) Pd e) Sc 16. An ion of an unknown element has an atomic number of 15 and contains 18 electrons. The ion is a) P 3- b) Ar c) O 2- d) Si 3- e) S What one of the following compounds is classified as an alkane? a) ethylene b) benzene c) propane d) acetylene e) ethanol 19. Which one of the following bonds is most covalent? a) MgCl b) AlP c) NaCl d) MgS e) NaP 20. The sum of the oxidation states of all the atoms in a neutral molecule a) must be a small positive number b) must be a small negative number c) must be zero d) can be either positive or negative, but not zero e) can have any value, including zero

29 21. The oxidation state of sulfur (S) in the ion SO 3 2- is a) 1+ b) 2+ c) 3+ d) 4+ e) An empty Al Coke can weighs 50g. How many moles of Al does one Coke can contain? a) 1350 b)1.85 c) 1.0x10 25 d) A 27g sample of OF 2 contains how many molecules? a) 3.0x10 23 b) 2 times 6.0x10 23 c) 12.0x How many grams are there in 0.01mole of Na 2 SO 4? a) 7.1g b) 14.2g c) 9.6g d) 1.42g e) 0.71g 26.What is the volume at standard temperature and pressure of 16g of gaseous SO 2? a) 22.4L b) 11.2L c) 5.6L d) 16.8L e) 64L 27. What is the percentage by weight of Al in Al 2 O 3? a) 63 b) 37 c) 23 d) What is the expression for the equilibrium constant for the following systems? 2NOCl = 2NO + Cl 2 a) K = [NO] 2 [Cl 2 ]/[NOCl] 2 b) K = 2[NO][Cl 2 ]/2[NOCl] c) K = [NO] 2 [Cl 2 ] 2 /[NOCl] 2 d) K = [NO] 2 [Cl 2 ] 2 /[NOCl] 2

30 30. For the reaction of solid BaO with CO 2 according to the equation BaO(s) + CO 2 (g) = BaCO 3 (s), the equilibrium expression is expressed a) [BaCO 3 ]/[BaO] b) 1/[CO 2 ] c) [BaO][CO 2 ]/[BaCO 3 ] d) [BaCO 3 ]/[BaO][CO 2 ] 31. Assume excess oxygen reacts with methane to form 14g of carbon monoxide according to the equation 2CH 4 +3O 2 = 2CO+4H 2 O. How many moles of the methane will be consumed? a) 2.0 moles methane b) one third mole methane c) 0.25 mole methane d) 0.5 mole methane e) 4.0 moles of methane 32. What coefficient is required for NO 2 in order to balance the equation? 2Pb(NO 3 ) 2 = 2PbO + NO 2 + O 2 a) 0.5 b) 1 c) 1.5 d) What coefficient is required for H 2 O in order to balance the equation? Be 3 N 2 + H 2 O = 3Be(OH) 2 + 2NH 3 a) 1 b) 2 c) 3 d) In the following reaction determine the change if any that occurs in the oxidation number of the underlined element and the whether the element is oxidized, reduced, or unchanged. 3Mg + N 2 = Mg 3 N 2 a) from 0 to +3, oxidized b) from 0 to -3, oxidized c) from +3 to +5, oxidized d) from 0 to -3; reduced 35. According to the equation 2Al + 6HCl = 2AlCl 3 + 3H 2 a) production of 1 mole of H 2 requires 3 mole of HCl b) production of 1 mole of AlCl 3 requires 3 moles of HCl c) production of 2 moles of H 2 requires 2 moles of HCl d) production of 2 moles of H 2 requires 5 moles of HCl

31 38. The rate of most chemical reactions increase as the temperature increases primarily because at higher temperatures a) the ionic charge is higher b) the pressure is higher c) there are increases in the average distances between atoms within molecules d) there are more collisions involving molecules with sufficient energy for reaction 39. In electrolysis, the anions migrate to the anode. Which of the following ion migrates to the other electrode? a) acidic ions b) basic ions c) neutral ions d) zwittweions e) cations 40. The reaction of 1 mole of As 2 O 3 with carbon will result in the formation of As 2 O 3 + 3C = 3CO + 2As a) 1 gram of CO b) 1 gram of As c) 28grams of CO d) 150 grams As 42. Which of the following elements would not be expected to form a positive ion? a) Li b) S c) Mg d) As C

32 D B C C D

33 B A B