CHEM 114 Exam 1 Study Guidance

Q1. What is the correct formula for the oxide ion?

Background

Topic: Ions and Ionic Compounds

This question tests your understanding of how ions are formed, specifically the oxide ion, which is derived from oxygen.

Key Terms and Concepts:

• Ion: An atom or molecule with a net electric charge due to the loss or gain of electrons.

• Oxide ion: The ion formed when oxygen gains electrons.

• Charge: Oxygen typically gains two electrons to achieve a stable electron configuration.

Step-by-Step Guidance

1. Recall that oxygen is in Group 16 (6A) of the periodic table and has 6 valence electrons.

2. Determine how many electrons oxygen needs to gain to achieve a full octet (8 valence electrons).

3. Write the symbol for oxygen and add the appropriate charge based on the number of electrons gained.

Try solving on your own before revealing the answer!

Final Answer: O2-

Oxygen gains two electrons to form the oxide ion, resulting in a 2- charge: O2-.

Q2. What is the formula for aluminum nitrate?

Background

Topic: Naming and Writing Formulas for Ionic Compounds

This question tests your ability to write the correct chemical formula for a compound formed between aluminum and the nitrate ion.

Key Terms and Formulas:

• Aluminum ion: $\mathrm{Al^{3+}}$

• Nitrate ion: $\mathrm{NO_3^-}$

• Formula writing: Use the criss-cross method to balance charges.

Step-by-Step Guidance

1. Write the symbols and charges for aluminum and nitrate: $\mathrm{Al^{3+}}$ and $\mathrm{NO_3^-}$.

2. Balance the charges so the total positive and negative charges equal zero.

3. Determine how many nitrate ions are needed to balance the charge of one aluminum ion.

4. Write the formula, using parentheses if more than one polyatomic ion is needed.

Try solving on your own before revealing the answer!

Final Answer: Al(NO3)3

Three nitrate ions are needed to balance the 3+ charge of aluminum, so the formula is Al(NO3)3.

Q3. A serving of fish contains 50 g protein and 4 g of fat. If protein has a caloric value of 4 kcal/g and fat has 9 kcal/g, how many kcal are in the serving?

Background

Topic: Caloric Content Calculations

This question tests your ability to calculate the total caloric value of a food serving based on the mass and caloric value per gram of its macronutrients.

Key Terms and Formulas:

• Caloric value: The amount of energy provided per gram of nutrient.

• Formula: $\text{Total kcal} = (\text{grams protein} \times 4) + (\text{grams fat} \times 9)$

Step-by-Step Guidance

1. Multiply the grams of protein by its caloric value per gram: $50 \times 4$.

2. Multiply the grams of fat by its caloric value per gram: $4 \times 9$.

3. Add the two results to find the total calories in the serving.

Try solving on your own before revealing the answer!

Final Answer: 236 kcal

Protein contributes 200 kcal and fat contributes 36 kcal, for a total of 236 kcal.

Q4. The main type of intermolecular forces between particles of ammonia (NH3) are ________.

Background

Topic: Intermolecular Forces

This question tests your understanding of the types of intermolecular forces present in molecules, specifically ammonia.

Key Terms and Concepts:

• Hydrogen bonding: A strong type of dipole-dipole attraction between molecules containing H bonded to N, O, or F.

• Dipole-dipole attractions: Forces between polar molecules.

• Dispersion forces: Weak forces present in all molecules, especially nonpolar ones.

• Ionic bonds: Forces between ions, not present in NH3.

Step-by-Step Guidance

1. Identify the elements present in ammonia and their bonding.

2. Determine if ammonia is a polar molecule and if it contains hydrogen bonded to N, O, or F.

3. Recall which intermolecular force is strongest in molecules with H-N, H-O, or H-F bonds.

Try solving on your own before revealing the answer!

Final Answer: Hydrogen bonds

Ammonia exhibits hydrogen bonding due to the presence of N-H bonds and its molecular polarity.

Q5. Why is it important that radioisotopes used in diagnostic tests have short half-lives?

Background

Topic: Nuclear Chemistry and Medical Applications

This question tests your understanding of why short half-lives are preferred for radioisotopes in medical diagnostics.

Key Terms and Concepts:

• Radioisotope: An unstable isotope that emits radiation.

• Half-life: The time required for half of a radioactive sample to decay.

• Diagnostic tests: Medical procedures that use radioisotopes to image or study organs/tissues.

Step-by-Step Guidance

1. Consider the effects of radiation exposure on the human body.

2. Think about what happens to the radioisotope after the diagnostic test is completed.

3. Relate the duration of radioactivity to patient safety and side effects.

Try solving on your own before revealing the answer!

Final Answer: This minimizes the harmful side effects of the radiation.

Short half-lives ensure the radioisotope decays quickly, reducing the patient's exposure to radiation.

Q6. An anion always ________.

Background

Topic: Ions and Ionic Compounds

This question tests your understanding of the definition and properties of anions.

Key Terms and Concepts:

• Anion: An ion with a negative charge, formed when an atom gains electrons.

• Cation: An ion with a positive charge, formed when an atom loses electrons.

Step-by-Step Guidance

1. Recall the definition of an anion and how it is formed.

2. Consider the charge on an anion and how it differs from a cation.

3. Eliminate options that do not match the definition of an anion.

Try solving on your own before revealing the answer!

Final Answer: Has a negative charge

An anion is always negatively charged because it has gained one or more electrons.

Q7. A patient has a temperature of 38.5 °C. What is the temperature in degrees Fahrenheit?

Background

Topic: Temperature Conversions

This question tests your ability to convert temperatures from Celsius to Fahrenheit using the appropriate formula.

Key Formula:

$F = (1.8 \times C) + 32$

Step-by-Step Guidance

1. Identify the given temperature in Celsius: $C = 38.5$.

2. Multiply the Celsius temperature by 1.8: $1.8 \times 38.5$.

3. Add 32 to the result to convert to Fahrenheit.

Try solving on your own before revealing the answer!

Final Answer: 101.3 °F

Using the formula, $F = (1.8 \times 38.5) + 32 = 101.3$ °F.

Q8. Which of the following is a homogeneous mixture?

Background

Topic: Classification of Matter

This question tests your ability to distinguish between homogeneous and heterogeneous mixtures.

Key Terms and Concepts:

• Homogeneous mixture: A mixture with uniform composition throughout (also called a solution).

• Heterogeneous mixture: A mixture with non-uniform composition.

Step-by-Step Guidance

1. Review the definitions of homogeneous and heterogeneous mixtures.

2. Consider the composition of each option and whether it is uniform throughout.

3. Identify which option is a solution or appears the same throughout.

Try solving on your own before revealing the answer!

Final Answer: Eye drops

Eye drops are a homogeneous mixture because their composition is uniform throughout.

Q9. The shape of the ammonia molecule (NH3) is ________.

Background

Topic: Molecular Geometry (VSEPR Theory)

This question tests your understanding of molecular shapes based on the number of bonding and lone pairs around the central atom.

Key Terms and Concepts:

• VSEPR Theory: Valence Shell Electron Pair Repulsion theory predicts molecular shapes.

• Bonding pairs: Shared pairs of electrons between atoms.

• Lone pairs: Non-bonding pairs of electrons on the central atom.

Step-by-Step Guidance

1. Draw the Lewis structure for NH3 and count the number of bonding and lone pairs on nitrogen.

2. Use VSEPR theory to determine the molecular geometry based on these pairs.

3. Recall the name for a molecule with three bonding pairs and one lone pair on the central atom.

Try solving on your own before revealing the answer!

Final Answer: Trigonal pyramidal

NH3 has three bonding pairs and one lone pair, resulting in a trigonal pyramidal shape.

Q10. How many calories are required to increase the temperature of 13 g of ethanol from 11 °C to 23 °C? The specific heat of ethanol is 0.59 cal/g °C.

Background

Topic: Heat Calculations (Specific Heat)

This question tests your ability to use the specific heat formula to calculate the energy required to change the temperature of a substance.

Key Formula:

$q = m \times c \times \Delta T$

• $q$ = heat (calories)

• $m$ = mass (g)

• $c$ = specific heat (cal/g °C)

• $\Delta T$ = change in temperature ($T_{final} - T_{initial}$)

Step-by-Step Guidance

1. Calculate the change in temperature: $\Delta T = 23 - 11$.

2. Multiply the mass by the specific heat: $13 \times 0.59$.

3. Multiply the result by the temperature change to find the heat required.

Try solving on your own before revealing the answer!

Final Answer: 92 cal

Using $q = m \times c \times \Delta T$, you find the energy required is 92 calories.