Most Missed/Difficult Chemistry Regents Questions

Systems in nature tend to undergo changes toward

• lower energy and lower entropy

• higher energy and lower entropy

• lower energy and higher entropy

• higher energy and higher entropy

Answer explanation

Energy disperses and spreads out, more chaos or

higher entropy is what happens in nature all the time.

At STP, solid carbon can exist as graphite or diamond. These two forms of carbon have

• the same properties and same crystal structure

• the same properties and different crystal structure

• different properties and same crystal structure

• different properties and different crystal structure

Answer explanation

The vocabulary word here is ALLOTROPES, when different forms of a pure element exist. They have different forms or structure, different properties. Examples are carbon atoms, diamonds, and graphite. Other allotropes are oxygen and ozone.

Compared to a 0.1 M aqueous solution of NaCl, a 0.8 M aqueous solution of NaCl has a

• higher boiling point and a higher freezing point

• higher boiling point and a lower freezing point

• lower boiling point and a higher freezing point

• lower boiling point and a lower freezing point

Answer explanation

This is colligative properties. Adding a solute to water and making a solution results in a solution with a raised boiling point and a lowered freezing point.

Which equation represents a fusion reaction?

• 
• 
• 
• 

Answer explanation

Here the aluminum and alpha particle fuses into a larger Phosphorous atom, and gives off a neutron at the same time. Fusion requires 2 smaller atoms or particles to combine into something larger, in this case P-30.

Tags

NGSS.HS-ESS1-1

NGSS.HS-PS1-8

Answer explanation

Sulfur has 16 electrons as an atom. As an anion it gains 2 electrons to gain that coveted octet of electrons in the valence shell. It is ISOELECTRIC to Argon the noble gas. Isoelectric means having the same electron configuration as something else (usually but not always a noble gas).

Tags

NGSS.HS-PS1-1

NGSS.HS-PS1-2

Which molecule contains a non-polar covalent bond?

• 
• 
• 
• 

Answer explanation

Bromine molecules share equally their electrons in the bond.

They have NO DIFFERENCE in their electronegativity values (Table S). Since neither has a greater or lesser desire to gain the electrons in a bond, neither gets that electron more or less. Thus, the bond is perfectly balanced, or NON-P0LAR. All the other molecules were slightly to strongly polar.

Tags

NGSS.HS-PS1-2

According to reference table G, which substance forms an unsaturated solution when 80 grams of the substance is dissolved into 100 grams water at 10ºC?

Answer explanation

At 10°C 100 mL (1g = 1mL) water can hold much more KI than this.

Answer explanation

Here the zinc atoms become cations, by losing 2 electrons each.

Oxidation is Loss of Electrons

Tags

NGSS.HS-PS1-1

NGSS.HS-PS1-2

What is the half life of sodium-25 if 1.00 grams of a 16.00 gram sample

remains unchanged after 237 seconds?

• 47.4 sec

• 59.3 sec

• 79.0 sec

• 118 sec

Answer explanation

That took 4 half lives (16 to 8 to 4 to 2 to 1 gram) 237 seconds = 4 half lives

Tags

NGSS.HS-PS1-8

Proposed models of the atom:

Model A: protons in nucleus, electrons in specific shells

Model B: protons in nucleus, electrons in regions of most probably location

Model C: protons dispersed throughout the atom, electrons in specific shells

Model D: protons dispersed throughout the atom, electrons in regions of most probably location

Which model correctly describes the locations of protons and electrons in the

wave-mechanical model of the atom?

• A

• B

• C

• D

Answer explanation

modern model or wave mechanical have central protons (with the neutrons) with the electrons flying around in “clouds” or zones of likelihood.