Chemistry EOC Review

Which of the following isotopes has 18 neutrons?

• ⁴⁰Ar

• ³⁵Cl

• ¹⁸F

• ²⁴Mg

Answer explanation

To find the number of neutrons, subtract the atomic number from the mass number. For 35Cl, the atomic number is 17, so 35 - 17 = 18 neutrons. Thus, 35Cl has 18 neutrons.

What is the correct name of Pb(CO₃)₂?

• Lead carbonate

• Lead (II) carbonate

• Lead (IV) carbonate

• Lead dicarbonate

Answer explanation

The correct name for Pb(CO3)2 is Lead (II) carbonate, as lead can have multiple oxidation states. In this case, the lead is in the +2 oxidation state, making 'Lead (II) carbonate' the accurate choice.

What is the most likely result of nitrogen and chlorine reacting based on their dot diagrams?

• Three chlorine atoms will each steal one electron from nitrogen

• Five chlorine atoms will each steal one electron from nitrogen

• Three chlorine atoms will each share one electron with nitrogen

• Five chlorine atoms will each share one electron from nitrogen

Answer explanation

Nitrogen has five valence electrons and needs three more to achieve stability. Chlorine has seven valence electrons and needs one more. Therefore, three chlorine atoms will share one electron each with nitrogen, forming covalent bonds.

Tags

NGSS.HS-PS1-1

NGSS.HS-PS1-2

As the number of protons increases across a period, while electrons are added to the same energy level, all of the following are true EXCEPT:

• the effective nuclear charge increases

• the electron shielding increases

• the atomic radius decreases

• the ionization energy increases

Answer explanation

As protons increase across a period, effective nuclear charge rises, atomic radius decreases, and ionization energy increases. However, electron shielding does not increase significantly since electrons are added to the same energy level.

Tags

NGSS.HS-PS1-1

NGSS.HS-PS1-2

If the number of protons changes, but the neutrons and electrons remain the same, which of the following is FALSE?

• The identity of the element will change

• The mass of the particle will change

• The electron configuration of the particle will change

• The charge of the particle will change

Answer explanation

Changing the number of protons alters the element's identity and charge, and affects mass. However, the electron configuration remains unchanged if electrons stay the same, making the statement about electron configuration false.

Tags

NGSS.HS-PS1-7

What is the percent composition by mass of nitrogen in Ca(NO₃)₂?

• 8.5 %

• 17 %

• 24 %

• 59 %

Answer explanation

To find the percent composition of nitrogen in Ca(NO3)2, calculate the molar mass: Ca=40.08, N=14.01 (2 N), O=16.00 (6 O). Total mass = 164.10 g. Nitrogen mass = 28.02 g. Percent = (28.02/164.10) x 100 = 17%. Thus, the answer is 17%.

Tags

NGSS.HS-PS1-7

What is the name of N₂O₅?

• nitrate

• dinitrogen pentoxide

• nitrogen pentaoxide

• dinitrogen pentoxygen

Answer explanation

The correct name for N2O5 is dinitrogen pentoxide, which indicates two nitrogen atoms and five oxygen atoms. The other options do not accurately reflect the chemical composition.

What is the pressure of 0.50 mol of argon gas trapped in a 3.0 L container at 400 K?

• 0.18 atm

• 5.5 atm

• 28 atm

• 49 atm

Answer explanation

Using the ideal gas law, PV = nRT, we can calculate pressure (P). Here, n = 0.50 mol, R = 0.0821 L·atm/(K·mol), T = 400 K, and V = 3.0 L. Plugging in the values gives P = 5.5 atm, which is the correct answer.

Which of the following solutions would be considered unsaturated at 50°C given the amount of solute added to 100 g of water?

• 100 g NaNO₃

• 80 g KNO₃

• 60 g NH₄Cl

• 40 g KCl

Answer explanation

At 50°C, the solubility of NaNO3 in 100 g of water is about 100 g, making it saturated. Therefore, 100 g NaNO3 is not unsaturated. The other options (80 g KNO3, 60 g NH4Cl, 40 g KCl) are below their saturation points.

Which of the following molecules would you expect to be polar if the non-central atoms are more electronegative than the central atom? Assume all non-central atoms shown in the picture are of the same element.

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