Regents Chemistry Exam Explanations June 2002

Questions

Answer

Explanations

41 The gram formula mass of NH₄Cl is

(1) 22.4 g/mole (3) 53.5 g/mole
(2) 28.0 g/mole (4) 95.5 g/mole

NH₄Cl=53.5g/mol

N=14

H= 4(1)=4

Cl=35.5

42 What is the molarity of a solution that contains 0.50 mole of NaOH in
0.50 liter of solution?

(1) 1.0 M (3) 0.25 M
(2) 2.0 M (4) 0.50 M

M=	0.50moles
	0.50 Liters

1-compound

2-mixture of elements

3-element

4-diatomic element

44 Which process is accompanied by a decrease in entropy?

(1) boiling of water
(2) condensing of water vapor
(3) subliming of iodine
(4) melting of ice

45 If 5.0 milliliters of a 0.20 M HCl solution is required to neutralize exactly
10. milliliters of NaOH, what is the concentration of the base?

(1) 0.10 M (3) 0.30 M
(2) 0.20 M (4) 0.40 M

Ma	Va	=	Mb	Vb
0.20M	5.0mL	=	M	10mL

46 Exactly how much time must elapse before 16 grams of potassium-42
decays, leaving 2 grams of the original isotope?

(1) 8 × 12.4 hours (3) 3 × 12.4 hours
(2) 2 × 12.4 hours (4) 4 × 12.4 hours

16->8->4->3

= 3 (1/2 lives) x12.4h

47 Which mass measurement contains four significant figures?

(1) 0.086g (3) 1003g
(2) 0.431g (4) 3870g

48 Which pair of compounds are alcohols?

Look for -OH and no other functional groups

49 The process of joining many small molecules into larger molecules is called

(1) neutralization (3) saponification
(2) polymerization (4) substitution

Definition-polymerization

50 The diagram below represents a portion of a 100-milliliter graduated cylinder.

What is the reading of the meniscus?

(1) 35.0 mL (3) 44.0 mL
(2) 36.0 mL (4) 45.0 mL

estimate the last decimal place