6/7(F): Chemistry Checkpoint #63

Which symbol has a nuclear charge of 4?

• Li

• Be

• Na

• Mg

Which atom has the lowest electronegativity?

• Nitrogen

• Oxygen

• Fluorine

• Neon

Which mixture can be separated by filtration? (listen to audio if you need help)

• NaCl(aq) and SiO₂(s)

• 
  NaCl(aq) and C₆H₁₂O₆(aq)

• 
  CO₂(aq) and NaCl(aq)

• CO₂(aq) and

  C₆H₁₂O₆(aq)

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.

Answer explanation

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

Oxidation is Loss of Electrons

Which pair of formulas represents two compounds that are electrolytes?

• HCl and CH₃OH

• HCl and NaOH

• C₅H₁₂ and CH₃OH

• C₅H₁₂ and NaOH

Answer explanation

Electrolytes are acids, bases, and salts. They can conduct an electric current when dissolved in water or melted (ionic compounds) due to the presence of mobile ions. HCl and NaOH are an acid and a base (Check acid+base tables).

CH₃OH and C₅H₁₂ are covalent compounds (an alcohol and a hydrocarbon) that do not form ions in solution/melted.

How many electrons are contained in an Au³⁺ ion?

• 76

• 79

• 82

• 197

Answer explanation

Since this is a cation (+ ion) there are 3 more protons than electrons.

All gold nuclei contain 79 protons.

A gold atom would contain 79 electrons. A gold ion would contain 3 fewer electrons.

Given the reaction for the corrosion of aluminum:

4 Al + 3 O₂ → 2 Al₂O₃

Which half-reaction correctly represents the oxidation that occurs?

• 4Al + 12e− → 4Al³⁺

• 3O₂ + 12e− → 6O²⁻

• 4Al → 4Al³⁺ + 12e−

• 3O₂ → 6O²⁻ + 12e−

Answer explanation

4Al → 4Al³⁺ + 12e− correctly shows the loss of electrons during oxidation (LEO)

• It is endothermic and entropy increases

• It is exothermic and entropy increases

• It is endothermic and entropy decreases

• It is exothermic and entropy decreases

Answer explanation

Energy is being added to the reaction and there are more particles in the products (which means more entropy)

A metal, M forms an oxide compound with the general formula M₂O. In which group on the Periodic Table could metal M be found?

• Group 1

• Group 2

• Group 15

• Group 17

Answer explanation

Group 1 are all metals with a +1 oxidation number so they all form +1 ions.