Biol 1510 : Recitation 1 (lectures Jan. 6 - Jan 10)

1. An atom has 9 neutrons, 9 protons and 9 electrons . What is its approximate atomic

mass (or weight) in amu

a) 9 b) 18 c) 27 d) need more information to calculate its approximate atomic mass

2. What is the minimum amount of information you would have to be given in order to

calculate the exact atomic mass (or weight) in amu of a naturally occurring element.

Assume that the exact masses (in amu) of a proton, neutron and electron are known

a) atomic number (element and isotopes), mass number (element and isotopes), number of

neutrons (element and isotopes), mass defect (element and isotopes), isotope ratio

b) atomic number (element), mass number (element and isotopes), mass defect (element

and isotopes), isotope ratio

c) atomic number (element), number of neutrons (element and isotopes), mass defect

(elements and isotopes).

d) atomic number (element and isotopes), mass number (isotopes), mass defect (element

and isotopes), isotope ratio

3. Deuterium (atomic number =1 mass number=2)

a) is an element b) is formed in the upper atmosphere

c) is an isotopic form of an element d) exists only in ionic form

4. Sr-90 (atomic number=38, number of neutrons=52, number of protons+number of neutrons

= 90) is formed through a -decay in an nuclear reaction. Which element is the a - emitter?

a) Kr-86 (atomic number = 36) b) Nb-93 (atomic number = 41)

c) Zr-94 (atomic number = 40) d) Mo-94 (atomic number = 42)

5. I-131 has a half life of 8 days. After 16 days an initial amount of 8 g I-131 has degraded to

a) 4 g, b) 2 g c) 1 g d) 0.8 g

Nt = No e - (0.693 / t[half life]) t No=8g, t{half life} = 8days , t =16 ays

6. What is formed when an atom loses an electron

a) isotope b) anion c) cation d) molecule

7. A neutral Na atom becomes positively charged by : a) gaining an electron, b) gaining a

proton c) losing an electron d) Na is a metal it can not become positively charged

8. Which statement is correct

a) C-14 is formed from nitrogen in a nuclear reaction

b) C-14 is a naturally occurring isotope of C-12

c) C-14 has a half life time of approximately 10 mio years

d) all are incorrect

9. A neutral CL atom becomes negatively charged by

a) gaining an electron b) loosing a proton c) loosing an electron d) forming an ionic bond

with a Na atom e) two answers are correct

10. What is the electron configuration of Silicon (atomic number = 14) ?

a) 2s2 , 2p6, 3s2, 3p4 b) 1s2, 2s2 , 2p6, 3s1 , 3p3

c) 3s2, 3p6, 3d6 d) 1s2, 2s2 , 2p6, 3s2, 3p2

11 . What is the electron configuration for the potassium ion (K+) (atomic number of K = 19)

a) 3s2, 3p6, 3d10, 4s1 b) 1s2, 2s2, 2p6, 3s2, 3p6, 3d1

c) 1s2, 2s2, 2p6, 3s2, 3p5, 4s2 d) 1s2, 2s2 , 2p6, 3s2, 3p6, 4s1

e) 1s2, 2s2 , 2p6, 3s2, 3p6,

12. The element magnesium (Mg) has two electrons in it’s outermost s-orbital . In its componds Mg tends to:

A) gain six electrons to become the Mg -6 ion.

B) lose 2 electrons to become the Mg ++ ion.

C) form 4 bonds, like carbon.

D) None of the above.

13. What is the three dimensional orientation of carbon’s four hybrid orbitals?

a) they are overlapping spheres. b) they point to the three principals axes (X, Y and Z).

c) they point towards the corners of a tetrahedron. d) they point toward the 2s orbital.

14. Because of the electron configuration of O (2s2, 2p4) the water molecule should have a

bond angle of 90 ° C between O and the two H atoms, however, it is 104 ° because

a) repulsion of the H-atoms b) attraction of the lone electron pair to the H-atoms

c) sp3 hybridization of the oxygen d) all of the above

15. The hybridization state of carbon in C2H2 is

a) sp3 b) sp2 c) sp d) 2s2, 2p2

16. The electrostatic attraction between two ions of opposite charge is called a:

A) chemical bond B) polar covalent bond. C) covalent bond. D) an ionic bond.

17. A polar covalent bond forms between hydrogen (H) and oxygen (O). As a result of

this bond, there is:

A) a partial positive charge associated with the H and a partial negative charge associated with the O.

B) equal sharing of electrons between these two atoms.

C) an ionic bond between the H and the O.

D) a partial negative charge associated with the H and a partial positive charge associated with the O.

18. The interactions are arranged according to decreasing strength. Which sequence is correct

a) ionic bonds, covalent bonds, H-bonds, polar interactions,

b) covalent bonds, H-bonds, ionic bonds, polar interactions, hydrophobic interactions

c) covalent bonds, ionic bonds, H-bonds, hydrophobic interactions

d) covalent bonds, ionic bonds, hydrophobic interactions, polar interactions, H-bonds

19. H-bonds (dotted line) can only be formed between

a) C=O ....... H-C=O b) -N ......... O=C c) O-H ...... N- d) N-H ........ H-O-

20. The pH of a 10-5 molar NaOH solution is

a ) approximately neutral b) 5 c) 9 d) need dissociation constant to calculate pH

21 : Which of the following would not be used in connection with the word acid?

a) H+ ion concentration = 10-5 M b) OH- ion concentration = 10-4 M

c) CH3COOH d) pH less than 7

22. What is the pH of a solution that contains 0.5 mol CH3COOH and 0.05 mol CH3COO-

(pK of CH3COOH is 4.72) pH = pK - log acids/base

a) 3.72 b) 5.72 c) 4.72 d) 4.62 e) none of the above

23. Which of the following is a good buffer for pH= 7

a. H2CO3/HCO3- pk = 6.2   b. CH3COOH/CH3COO- pK= 4.72

c. citic acid/citrate pK =5.2   d. H2PO4--/HPO4 pK = 7.1