Question 1

A student heats a sample of CuSO$$_4$$ hydrate and collects the following data: Mass of empty crucible = 23.56 g, Mass of crucible + hydrate (before heating) = 25.84 g, Mass of crucible + anhydrous salt (after heating) = 24.48 g. What is the mass of water lost during heating?

Accepted Answer

$$1.36\ \mathrm{g}$$

Question 2

Using the data from the previous question, calculate the moles of water lost during heating. (Molar mass of H$$_2O$$ = $$18.02\ \mathrm{g/mol})$$

Accepted Answer

$$0.0755\ \mathrm{mol}$$

Question 3

After heating, the mass of anhydrous CuSO$$_4 is $$found to be $$0.92\ \mathrm{g}$$ less than the hydrate. What is the empirical formula of the hydrate? (Molar mass of CuSO$$_4$$ = $$159.61\ \mathrm{g/mol})$$

Accepted Answer

$$\mathrm{CuSO}_4 \cdot 5\mathrm{H}_2\mathrm{O}$$

Question 4

If some of the hydrate splatters out of the crucible during heating, how will the calculated number of moles of water lost compare to the actual value?

Accepted Answer

It will be less than the actual value because some hydrate (and thus water) is lost.

Question 5

Write the complete ground-state electron configuration for a krypton (Kr) atom.

Accepted Answer

$$1s^2$$\ $$2s^2$$\ $$2p^6$$\ $$3s^2$$\ $$3p^6$$\ $$4s^2$$\ $$3d^{10}$$\ $$4p^6$$

Question 6

The Rb$$^+$$ ion has the same electron configuration as a neutral Kr atom. Which has the larger radius and why?

Accepted Answer

Kr atom, because it has fewer protons and thus a weaker effective nuclear charge according to Coulomb’s law.

Question 7

Given the following isotopic composition of rubidium: 32.5% Rb-83 (mass = 83 amu), 50.8% Rb-85 (mass = 85 amu), and 16.7% Rb-87 (mass = 87 amu), what is the average atomic mass of Rb in this sample?

Accepted Answer

$$84.8\ \mathrm{amu}$$

Question 8

Over time, Rb-83 decays into gaseous Kr-83 and leaves the solid sample. How will the average atomic mass of the remaining solid sample change?

Accepted Answer

It will increase because the lighter isotope (Rb-83) is lost.

Question 9

A rock sample from another planet contains Mg isotopes with the following abundances: 20% Mg-25 and 40% Mg-26. What percent abundance must Mg-24 have?

Accepted Answer

40%

Question 10

Using the mass spectrum provided (20% Mg-25, 40% Mg-26, 40% Mg-24), calculate the average atomic mass of Mg in the sample.

Accepted Answer

$$24.2\ \mathrm{amu}$$

Question 11

If the first ionization energy of Mg on Earth is $$736\ \mathrm{kJ/mol}$$, and the rock sample from another planet has a higher average atomic mass, how would you expect the first ionization energy to compare? Explain.

Accepted Answer

It would be about the same, because ionization energy depends mainly on nuclear charge and electron configuration, not isotopic mass.

Question 12

Given a photoelectron spectrum with four peaks, the highest binding energy peak corresponds to which electrons?

Accepted Answer

The 1s electrons, which are closest to the nucleus.

Question 13

Based on the photoelectron spectrum with peaks at approximately 1000, 100, 10, and 1 MJ/mol, what is the complete electron configuration of the element?

Accepted Answer

$$1s^2$$\ $$2s^2$$\ $$2p^6$$\ $$3s^2$$

Question 14

If the element to the right of the one identified in the previous question is analyzed, where would you expect its valence electron peak to appear on the photoelectron spectrum?

Accepted Answer

To the left, because the additional proton increases nuclear charge, increasing binding energy.

Question 15

Which of the following best explains why the 1s electrons have the highest binding energy in a photoelectron spectrum?

Accepted Answer

They are closest to the nucleus and experience the greatest effective nuclear charge, as described by Coulomb’s law.

Question 16

A student is given a photoelectron spectrum with three main peaks. If the element has one more proton than the unknown element, how would the spectrum change?

Accepted Answer

A new peak would appear at a higher binding energy, corresponding to the additional valence electron.

Unit 1 FRQ Practice – General Chemistry Study Guidance

Guida di studio - Domande di pratica

Study guide - Flashcard