AP Chemistry - Unit 1 Review

22.0 g of carbon tetrafluoride is equivalent to how many moles?

• 4.00 moles

• 0.250 moles

• 0.500 moles

• 132 x 10^23 moles

Answer explanation

When converting from mass to mole, divide by the compound's molar mass. Carbon tetrafluoride (CF4) has a molar mass of 88.01 g/mol. Therefore, 22.0 g is equivalent to 0.25 moles of CF4.

Tags

NGSS.HS-PS1-7

Using the mass spectrum, determine the element's average atomic mass and likely identity.

• 20.9 amu, Fluorine

• 20.9 amu, Neon

• 20.19 amu, Neon

• 20.19 amu, Calcium

Answer explanation

To calculate the average atomic mass, multiply the mass of each isotope by its relative/percent abundance. Then, add up all isotopes (3 from this mass spectrum).

(20 x 0.9) + (21 x 0.01) + (22 x 0.09) = 20.19 amu

Which of the following is NOT classified as a pure substance?

• Carbon

• Carbon dioxide

• Carbon monoxide

• Carbonated water

Answer explanation

Remember, both elements and compounds are classified as pure substances due to their uniform composition.

• 305% C

• 30.5% C

• 216 % C

• 21.6% C

• 70.8% C

Answer explanation

Percent composition is calculated by dividing the mass of an element by the compound's molar mass (mass of the part/total mass)

• True

• False

Answer explanation

These two formulas will have the same percent composition of all three elements as they are molecular and empirical formulas. (This means that they share the same ratio of each element, they just have different numbers of atoms).

The ionization energies for random elements in Period 3 is given at left. What element is most likely Magnesium?

• Element 1

• Element 2

• Element 3

• Element 4

Answer explanation

The third ionization of element 3 is dramatically higher, indicating the removal of an inner shell electron. Because Magnesium has 2 valence electrons, you would expect to see a significant jump between IE2 and IE3.

Tags

NGSS.HS-PS1-1

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What is the most likely identity of this element?

• Aluminum

• Magnesium

• Carbon

• Not enough information is given to determine this

Answer explanation

When interpreting a photoelectron spectrum, read the data from left to right. The first peak you'll see (closest to the origin), represents the innermost electrons while the peak furthest to the right represents the valence electrons.

In this spectrum, the electron configuration is 1s2 2s2 2p6 3s2 3p1.

Tags

NGSS.HS-PS1-1

Would you predict the first ionization energy of atoms of iodine to be less than, equal to, or greater than that of atoms of fluorine? Pick the correct answer and best justification.

• Less than because iodine's electrons are farther from the nucleus and therefore experience less effective nuclear charge.

• Less than because the IE decreases down a group.

• Equal to because iodine and fluorine are both halogens.

• Greater than because iodine atoms experience a greater nuclear effective charge.

• Greater than because the trend increases down a group.

Answer explanation

NEVER give a justification as "because it follows this trend." Always explain your reasoning in terms of the atomic radius (size of the atom) and effective nuclear charge (attractive force between the positive charges in the nucleus and negatively-charged electrons).

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NGSS.HS-PS1-1

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Write the chemical formula for magnesium phosphate.

• MgP

Answer explanation

Memorize the polyatomics... yesterday! I promise it's worth putting in the effort now!

Tags

NGSS.HS-PS1-1

Answer explanation

First, determine the charge of Scandium. (Nitrate has a charge of -1. There are 3 nitrates, so the total negative charge is -3. Therefore, scandium must have a charge of +3).

+3 charge indicates the loss of 3 electrons, so the electron configuration will now look like an atom of argon.

Tags

NGSS.HS-PS1-1