Chem AUG 2010 Regents

1. Which two factors must be equal when a chemical reaction reaches equilibrium?

The concentration of the reactants and the concentration of the products

The number of reactant particles and the number of product particles

The rate of the forward reaction and the rate of the reverse reaction

The mass of the reactants and the mass of the products

Rates of reactions in an equilibrium must be constant.

Explanation

Rates of reactions in an equilibrium must be constant.

2. Which compound has both ionic and covalent bonds

CO2

CH3OH

NaI

Na2CO3

A compound with both ionic and covalent bonds would be one that has Table E compounds as well as a metal.

Explanation

A compound with both ionic and covalent bonds would be one that has Table E compounds as well as a metal.

3. Which nuclide is listed with its half-life and decay mode?

K-37, 1.24 h, α

N-16, 7.2 s, β−

Rn-222, 1.6 × 10^3 y, α

U-235, 7.1 × 10^8 y, β−

The only one that matches is the Nitrogen...look at Table N.

Explanation

The only one that matches is the Nitrogen...look at Table N.

4. Which compound is insoluble in water?

KOH

NH4Cl

Na2SO4

PbSO4

Group 1 elements are ALWAYS soluble. Ammonium (NH4) is ALWAYS soluble. Pb (lead) is an exception to the sulfate rule.

Explanation

Group 1 elements are ALWAYS soluble. Ammonium (NH4) is ALWAYS soluble. Pb (lead) is an exception to the sulfate rule.

5. Which substance can not be broken down by a chemical change?

Methane

Propanal

Tungsten

Water

Tungsten (W) is an element. elements cannot be broken down by a chemical change.

Explanation

Tungsten (W) is an element. elements cannot be broken down by a chemical change.

6. Which element forms an ionic compound when it reacts with lithium?

K

Fe

Kr

Br

Kr is a noble gas, so it doesn't react. Br is a nonmetal and nonmetals form ionic bonds when reacted with metals.

Explanation

Kr is a noble gas, so it doesn't react. Br is a nonmetal and nonmetals form ionic bonds when reacted with metals.

7. Based on the results of testing colorless solutions with indicators, which solution is most acidic?

A solution in which bromthymol blue is blue

A solution in which bromcresol green is blue

A solution in which phenolphthalein is pink

A solution in which methyl orange is red

Methyl orange is red in acidic solutions.

Explanation

Methyl orange is red in acidic solutions.

8. According to one acid-base theory, water acts as an acid when an H2O molecule

Accepts an H+

Donates an H+

Accepts an H-

Donates an H-

Bronsted-Lowry acids donate H+.

Explanation

Bronsted-Lowry acids donate H+.

9. What is the minimum amount of heat required to completely melt 20.0 grams of ice at its melting point?

20.0 J

83.6 J

6680 J

45 200 J

Using the heat of fusion (melting and freezing), you will multiply 20 by 334 to get 6680

Explanation

Using the heat of fusion (melting and freezing), you will multiply 20 by 334 to get 6680

10. What is the total number of electrons shared in a double covalent bond?

1

2

3

4

one bond is two electrons...double bonds means 4 electrons.

Explanation

one bond is two electrons...double bonds means 4 electrons.

11. As the temperature of a chemical reaction in the gas phase is increased, the rate of the reaction increases because

Fewer particle collisions occur

More effective particle collisions occur

The required activation energy increases

The concentration of the reactants increases

Higher temperatures means more effective collisions...

Explanation

Higher temperatures means more effective collisions...

12. Which gas sample at STP has the same total number of molecules as 2.0 liters of CO2(g) at STP?

5.0 L of CO2(g)

2.0 L of Cl2(g)

3.0 L of H2S(g)

6.0 L of He(g)

All gases with the same volume have the same number of molecules, regardless of their molecular formula. In other words, 2.0 L of ANY gas has the same number of particles as 2.0 L of any other gas.

Explanation

All gases with the same volume have the same number of molecules, regardless of their molecular formula. In other words, 2.0 L of ANY gas has the same number of particles as 2.0 L of any other gas.

13. Which element is present in all organic compounds?

Carbon

Hydrogen

Nitrogen

Oxygen

organic chemistry deals with carbon...think about the unit.

Explanation

organic chemistry deals with carbon...think about the unit.

14. The table below shows the number of subatomic particles in atom X and in atom Z.

Atom X and atom Z are isotopes of the element

Aluminum

Carbon

Magnesium

Nitrogen

6 protons equals carbon. 'NUFF SAID.

Explanation

6 protons equals carbon. 'NUFF SAID.

15. Which unit can be used to express the concentration of a solution?

L/s

J/g

Ppm

KPa

Table T shows the correct answer...ppm is parts per million.

Explanation

Table T shows the correct answer...ppm is parts per million.

16. Which isotope is used to treat cancer?

C-14

U-238

Co-60

Pb-206

C-14 is used to date organic substances.
U-238 is used to date minerals (rocks).
Pb-206 is harmful (think lead paint).

That leaves cobalt.

Explanation

C-14 is used to date organic substances.
U-238 is used to date minerals (rocks).
Pb-206 is harmful (think lead paint).

That leaves cobalt.

17. The entropy of a sample of CO2 increases as the CO2 changes from

Gas to liquid

Gas to solid

Liquid to solid

Solid to gas

Entropy is randomness, gases are the most random.

Explanation

Entropy is randomness, gases are the most random.

18. An atom of which element has the largest atomic radius?

Fe

Mg

Si

Zn

This one's a bit tricky...magnesium has fewer orbitals, but it also has only two valence electrons, which makes it the largest.

WHEN IN DOUBT, CHECK OUT TABLE S!!!

Explanation

This one's a bit tricky...magnesium has fewer orbitals, but it also has only two valence electrons, which makes it the largest.

WHEN IN DOUBT, CHECK OUT TABLE S!!!

19. Each of four test tubes contains a different concentration of HCl(aq) at 25°C. A 1-gram cube of Zn is added to each test tube. In which test tube is the reaction occurring at the fastest rate?

Higher concentrations make a reaction go faster.

Explanation

Higher concentrations make a reaction go faster.

20. In the formula X2(SO4)3, the X represents a metal. This metal could be located on the Periodic Table in

Group 1

Group 2

Group 13

Group 14

Group 13 has oxidation states of +3, SO4 has an oxidation of -2. Switch the numbers.

Explanation

Group 13 has oxidation states of +3, SO4 has an oxidation of -2. Switch the numbers.

21. Which subatomic particles are located in the nucleus of an He-4 atom?

Electrons and neutrons

Electrons and protons

Neutrons and protons

Neutrons, protons, and electrons

electrons are in orbitals around the nucleus.

Explanation

electrons are in orbitals around the nucleus.

22. Given the balanced equation representing a reaction: 2NaCl(l) → 2Na(l) + Cl2(g) A 1170.-gram sample of NaCl(l) completely reacts, producing 460. grams of Na(l). What is the total mass of Cl2(g) produced?

355 g

710 g

1420 g

1630 g

Do the math. 1170 - 460 = 710 g.

Explanation

Do the math. 1170 - 460 = 710 g.

23. Given the formula representing a hydrocarbon:

The molecular formula and the empirical formula for this hydrocarbon are

C5H10 and CH2

C5H10 and CH3

C4H8 and CH2

C4H8 and CH3

the compound is for pentENE, and the formula is C5H10. The empirical formula (simplest form) is CH2.

Explanation

the compound is for pentENE, and the formula is C5H10. The empirical formula (simplest form) is CH2.

24. Which energy conversion occurs during the operation of an electrolytic cell?

Chemical energy to electrical energy

Electrical energy to chemical energy

Nuclear energy to electrical energy

Electrical energy to nuclear energy

Chemical energy exists in the electrodes (the aqueous solutions and the solid blocks) and it is converted to electrical energy.

Explanation

Chemical energy exists in the electrodes (the aqueous solutions and the solid blocks) and it is converted to electrical energy.

25. Which compound is an Arrhenius acid?

CaO

HCl

NaOH

NH3

Arrhenius acid has H+ as the only positive ion in the solution.

Explanation

Arrhenius acid has H+ as the only positive ion in the solution.

26. The percent composition by mass of nitrogen in NH4OH (gram-formula mass = 35 grams/mole) is equal to

calculating percent composition is the mass of the part divided by the mass of the whole.

In this example, 14/35

Explanation

calculating percent composition is the mass of the part divided by the mass of the whole.

In this example, 14/35

27. In the late 1800s, experiments using cathode ray tubes led to the discovery of the

Electrons

Neutrons

Protons

Positrons

Using the cathode ray tube enabled the scientists to discover that negatively charged particles exist outside the nucleus.

Explanation

Using the cathode ray tube enabled the scientists to discover that negatively charged particles exist outside the nucleus.

28. The reaction between an organic acid and an alcohol produces

An aldehyde

A ketone

An ether

An ester

The COOH and OH react to "pop off" a water (HOH) and leaves a -COO- (which is an ester).

Explanation

The COOH and OH react to "pop off" a water (HOH) and leaves a -COO- (which is an ester).

29. Which formula represents a mixture?

C6H12O6 (l)

C6H12O6 (s)

LiCl (aq)

LiCl (s)

Process of elimination: (l) means liquid, (s) means solid, and (aq) means aqueous. AQUEOUS means dissolved in water. Dissolved in water is a mixture.

Explanation

Process of elimination: (l) means liquid, (s) means solid, and (aq) means aqueous. AQUEOUS means dissolved in water. Dissolved in water is a mixture.

30. Which element requires the least amount of energy to remove the most loosely held electron from a gaseous atom in the ground state?

Bromine

Calcium

Sodium

Silver

sodium only has one valence electron, which is NOT held very strongly.

WHEN IN DOUBT, CONSULT TABLE S.

Explanation

sodium only has one valence electron, which is NOT held very strongly.

WHEN IN DOUBT, CONSULT TABLE S.

31. Petroleum can be separated by distillation because the hydrocarbons in petroleum are

Elements with identical boiling points

Elements with different boiling points

Compounds with identical boiling points

Compounds with different boiling points

The compounds have different boiling points, which is distillation.

Explanation

The compounds have different boiling points, which is distillation.

32. Which sample has particles with the lowest average kinetic energy?

1.0 g of Br2 at 50.°C

2.0 g of Br2 at 30.°C

7.0 g of Br2 at 40.°C

9.0 g of Br2 at 20.°C

Average kinetic energy is TEMPERATURE. The lowest temperature is 20C.

Explanation

Average kinetic energy is TEMPERATURE. The lowest temperature is 20C.

33. What is the total number of valence electrons in a calcium atom in the ground state?

8

2

18

20

the last number of the configuration is the valence electrons

Explanation

the last number of the configuration is the valence electrons

34. In which type of reaction is an atom of one element converted to an atom of a different element?

Decomposition

Neutralization

Transmutation

Saponification

transmutation is a nuclear reaction that converts one element to another element.

Explanation

transmutation is a nuclear reaction that converts one element to another element.

35. A gas sample is at 25°C and 1.0 atmosphere. Which changes in temperature and pressure will cause this sample to behave more like an ideal gas?

Decreased temperature and increased pressure

Decreased temperature and decreased pressure

Increased temperature and increased pressure

Increased temperature and decreased pressure

HIGH temperature and LOW pressure is an ideal gas.

Explanation

HIGH temperature and LOW pressure is an ideal gas.

36. At STP, which element is solid, brittle, and a poor conductor of electricity?

Al

K

Ne

S

Neon is a gas, so the answer cannot be Ne. Sulfur is a nonmetal, which makes it brittle.

Explanation

Neon is a gas, so the answer cannot be Ne. Sulfur is a nonmetal, which makes it brittle.

37. Object A at 40.°C and object B at 80.°C are placed in contact with each other. Which statement describes the heat flow between the objects?

Heat flows from object A to object B.

Heat flows from object B to object A.

Heat flows in both directions between the objects.

No heat flow occurs between the objects.

Heat flows from higher temperature to lower temperature.

Explanation

Heat flows from higher temperature to lower temperature.

38. A cylinder with a movable piston contains a sample of gas having a volume of 6.0 liters at 293 K and 1.0 atmosphere. What is the volume of the sample after the gas is heated to 303 K, while the pressure is held at 1.0 atmosphere?

9.0 L

6.2 L

5.8 L

4.0 L

Combined gas law problems. Plug in the digits...6.2 L.

Explanation

Combined gas law problems. Plug in the digits...6.2 L.

39. Which Group 15 element exists as diatomic molecules at STP?

Phosphorus

Nitrogen

Bismuth

Arsenic

HOFBrINCl

Explanation

HOFBrINCl

40. The atomic mass of titanium is 47.88 atomic mass units. This atomic mass represents the

Total mass of all the protons and neutrons in an atom of Ti

Total mass of all the protons, neutrons, and electrons in an atom of Ti

Weighted average mass of the most abundant isotope of Ti

Weighted average mass of all the naturally occurring isotopes of Ti

atomic mass equals the weighted average of the naturally occurring isotopes.

Explanation

atomic mass equals the weighted average of the naturally occurring isotopes.

41. The isotopes K-37 and K-42 have the same

Decay mode

Bright-line spectrum

Mass number for their atoms

Total number of neutrons in their atoms

Bright-line spectrum deals with electrons. Electrons are not different between two different isotopes.

Explanation

Bright-line spectrum deals with electrons. Electrons are not different between two different isotopes.

42. Every water molecule has two hydrogen atoms bonded to one oxygen atom. This fact supports the concept that elements in a compound are

Chemically combined in a fixed proportion

Chemically combined in proportions that vary

Physically mixed in a fixed proportion

Physically mixed in proportions that vary

the molecule is chemically combined. The proportion is fixed, meaning two hydrogens and one oxygen.

Explanation

the molecule is chemically combined. The proportion is fixed, meaning two hydrogens and one oxygen.

43. Given the balanced equation representing a reaction: Br2 +energy→Br+Br Which statement describes the energy change and bonds in this reaction?

Energy is released as bonds are broken.

Energy is released as bonds are formed.

Energy is absorbed as bonds are broken.

Energy is absorbed as bonds are formed.

To break a bond, energy must be added. Br2 is diatomic and the bonds are broken. Energy must go in to make the bonds break.

Explanation

To break a bond, energy must be added. Br2 is diatomic and the bonds are broken. Energy must go in to make the bonds break.

44.

The greatest composition by mass in an atom of oxygen-18 is due to the total mass of its

Electrons

Neutrons

Protons

Positrons

oxygen-17 has 8 protons. oxygen-17 has 9 neutrons. More of the mass is from the neutrons.

Explanation

oxygen-17 has 8 protons. oxygen-17 has 9 neutrons. More of the mass is from the neutrons.

45. Which balanced equation represents a redox reaction?

AgNO3(aq)+NaCl(aq)→AgCl(s)+NaNO3(aq)

H2CO3(aq) → H2O(l) + CO2(g)

NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)

Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)

QUICK TIP: Look for the elements (Mg and H2)...they have oxidation states of ZERO...one increases (Mg) and one decreases (H)...hence the oxidation/reduction.

Explanation

QUICK TIP: Look for the elements (Mg and H2)...they have oxidation states of ZERO...one increases (Mg) and one decreases (H)...hence the oxidation/reduction.

46. Which formula represents an unsaturated hydrocarbon?

C5H12

C6H14

C7H16

C8H14

3 of them are alkanes. One is an alkyne (C8H14), which makes is unsaturated.

Explanation

3 of them are alkanes. One is an alkyne (C8H14), which makes is unsaturated.

47. A balanced equation representing a chemical reaction can be written using

Chemical formulas and mass numbers

Chemical formulas and coefficients

First ionization energies and mass numbers

First ionization energies and coefficients

Chemical formulas are the atomic symbols and the coefficients are the numbers in front of the symbols.

Explanation

Chemical formulas are the atomic symbols and the coefficients are the numbers in front of the symbols.

48. Given the formula representing a molecule:

The molecule is

Symmetrical and polar

Symmetrical and nonpolar

Asymetrical and polar

Asymmetrical and nonpolar

The molecule is symmetrical, which makes it nonpolar overall.

Explanation

The molecule is symmetrical, which makes it nonpolar overall.

49. A solution with a pH of 2.0 has a hydronium ion concentration ten times greater than a solution with a pH of

1.0

0.20

3.0

20.

2.0 is ten times greater than 3.0. As you go from a whole number to the next lowest (i.e., 3.0 to 2.0), the hydronium (H+ or H3O+) increases ten times...a pH of 4.0 vs. a pH of 2.0 is different by a factor of 100 times.

Explanation

2.0 is ten times greater than 3.0. As you go from a whole number to the next lowest (i.e., 3.0 to 2.0), the hydronium (H+ or H3O+) increases ten times...a pH of 4.0 vs. a pH of 2.0 is different by a factor of 100 times.

50. The bond between which two atoms is most polar?

Br and Cl

Br and F

I and Cl

I and F

Iodine is the least electronegative of the Group 17 elements listed...Fluorine is the most electronegative of the Group 17 elements. The electronegativities of the two elements is the farthest apart, meaning the most polar.

Explanation

Iodine is the least electronegative of the Group 17 elements listed...Fluorine is the most electronegative of the Group 17 elements. The electronegativities of the two elements is the farthest apart, meaning the most polar.

Chem Aug 2010 Regents