GOB Chemistry Study Guide: Molecules for Life Quiz 4 Sample Questions

Q1. Which of the following substances contains only covalent bonds (i.e., is a molecular substance)?

Background

Topic: Chemical Bonding

This question tests your ability to distinguish between ionic and covalent compounds based on their chemical formulas.

Key Terms:

• Covalent bond: A chemical bond formed by the sharing of electrons between atoms.

• Ionic bond: A bond formed by the transfer of electrons from one atom to another, resulting in oppositely charged ions.

• Molecular substance: A compound made up of molecules held together by covalent bonds.

Step-by-Step Guidance

1. Examine each formula and identify whether it is composed of only nonmetals (which typically form covalent bonds) or contains metals (which typically form ionic bonds).

2. Recall that compounds containing only nonmetals are usually molecular substances with covalent bonds.

3. For each option, determine if the substance is ionic or covalent based on the elements present.

4. Eliminate any options that contain metal ions or polyatomic ions with ionic bonds.

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Q2. Which of the following substances is a nonelectrolyte?

Background

Topic: Electrolytes and Nonelectrolytes

This question tests your understanding of which substances conduct electricity in solution and which do not.

Key Terms:

• Electrolyte: A substance that produces ions when dissolved in water and conducts electricity.

• Nonelectrolyte: A substance that does not produce ions in solution and does not conduct electricity.

Step-by-Step Guidance

1. Identify which substances are ionic and which are molecular.

2. Recall that ionic compounds and strong acids/bases are typically electrolytes.

3. Consider which substance is molecular and does not dissociate into ions in water.

4. Eliminate options that are known to dissociate or ionize in water.

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Q3. Which of the following correctly identifies the principal intermolecular attractions for the given compound?

Background

Topic: Intermolecular Forces

This question tests your knowledge of the types of intermolecular forces present in different compounds.

Key Terms:

• Hydrogen bonding: Strong attraction between molecules containing N, O, or F bonded to H.

• Dipole-dipole forces: Attractions between polar molecules.

• London dispersion forces: Weak attractions present in all molecules, especially nonpolar ones.

Step-by-Step Guidance

1. For each compound, determine if it is polar or nonpolar.

2. Identify if the compound contains N, O, or F bonded to H (for hydrogen bonding).

3. Recall that nonpolar molecules have only London dispersion forces.

4. Match each compound to its principal intermolecular force.

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Q4. Which of the following molecules is non-polar?

Background

Topic: Molecular Polarity

This question tests your ability to determine whether a molecule is polar or nonpolar based on its structure and symmetry.

Key Terms:

• Polar molecule: Has an uneven distribution of charge due to differences in electronegativity and molecular shape.

• Nonpolar molecule: Has an even distribution of charge, often due to symmetry.

Step-by-Step Guidance

1. Draw or visualize the Lewis structure for each molecule.

2. Assess the symmetry and the presence of polar bonds.

3. Determine if the dipoles cancel out, resulting in a nonpolar molecule.

4. Eliminate options that are clearly polar based on their structure.

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Q5. When the ionic salt Na3PO4 dissociates in aqueous solution, it forms the ions ______.

Background

Topic: Dissociation of Ionic Compounds

This question tests your understanding of how ionic compounds dissociate in water.

Key Terms:

• Dissociation: The process by which an ionic compound separates into its constituent ions in solution.

• Polyatomic ion: An ion composed of more than one atom.

Step-by-Step Guidance

1. Write the formula for Na3PO4 and identify the ions it contains.

2. Recall that sodium ion is Na+ and phosphate ion is PO43–.

3. Determine the ratio of ions produced upon dissociation.

4. Eliminate options with incorrect charges or formulas.

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Q6. The melting point of a fatty acid will increase as the length of its carbon chain _______ and the number of C=C bonds ________.

Background

Topic: Properties of Fatty Acids

This question tests your understanding of how molecular structure affects physical properties like melting point.

Key Terms:

• Fatty acid: A carboxylic acid with a long hydrocarbon chain.

• Melting point: The temperature at which a substance changes from solid to liquid.

• C=C bond: Double bond in the carbon chain; affects packing and melting point.

Step-by-Step Guidance

1. Recall that longer carbon chains generally increase melting point due to stronger van der Waals forces.

2. Consider how the presence of double bonds (C=C) affects the packing of molecules and melting point.

3. Compare the effect of increasing or decreasing chain length and number of double bonds.

4. Eliminate options that do not match the expected trends.

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Q7. A solution is prepared by dissolving 6.31 g of glycerol (C3H8O3) in enough water to give 275 mL of solution. The molarity of this solution is equal to _______.

Background

Topic: Solution Concentration (Molarity)

This question tests your ability to calculate molarity from mass and volume.

Key Formula:

$\text{Molarity (M)} = \frac{\text{moles of solute}}{\text{liters of solution}}$

$\text{Moles of solute} = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}}$

Step-by-Step Guidance

1. Calculate the moles of glycerol using its mass and molar mass.

2. Convert the volume of solution from mL to L.

3. Set up the molarity formula using the calculated moles and volume in liters.

4. Plug in the values but stop before calculating the final molarity.

Try solving on your own before revealing the answer!

Q8. A 4% starch solution and a 10% starch solution are separated by a semi-permeable cell membrane. Which of the following will occur?

Background

Topic: Osmosis

This question tests your understanding of osmosis and the movement of water across membranes.

Key Terms:

• Osmosis: The movement of water across a semi-permeable membrane from low solute concentration to high solute concentration.

• Semi-permeable membrane: Allows water but not solute to pass through.

Step-by-Step Guidance

1. Identify which solution has the higher solute concentration.

2. Recall the direction of water movement during osmosis.

3. Determine whether water will move toward the 4% or 10% solution.

4. Eliminate options that do not match the principle of osmosis.

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Q9. Which one of the following solutions would have the highest osmotic pressure?

Background

Topic: Colligative Properties (Osmotic Pressure)

This question tests your understanding of how solute concentration and dissociation affect osmotic pressure.

Key Formula:

$\pi = iMRT$

• $\pi$ = osmotic pressure

• $i$ = van't Hoff factor (number of particles produced per formula unit)

• $M$ = molarity

• $R$ = gas constant

• $T$ = temperature in Kelvin

Step-by-Step Guidance

1. For each solution, determine the van't Hoff factor ($i$) based on how many particles it produces in solution.

2. Recall that higher $i$ and $M$ lead to higher osmotic pressure.

3. Compare the $i$ values for each compound at the same molarity.

4. Eliminate options with lower $i$ values.

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Q10. What is the total concentration of dissolved particles in a 0.142 M solution of Na2SO4?

Background

Topic: Colligative Properties (Particle Concentration)

This question tests your ability to calculate the total concentration of ions produced by dissociation.

Key Formula:

$\text{Total particle concentration} = \text{molarity} \times \text{number of particles per formula unit}$

Step-by-Step Guidance

1. Write the dissociation equation for Na2SO4 in water.

2. Count the number of ions produced per formula unit.

3. Multiply the molarity by the total number of ions produced.

4. Set up the calculation but stop before computing the final value.

Try solving on your own before revealing the answer!

Q11. Which of the following is an example of a triprotic acid?

Background

Topic: Acids and Bases

This question tests your knowledge of acids that can donate three protons (H+).

Key Terms:

• Triprotic acid: An acid that can donate three protons.

• Monoprotic acid: Can donate one proton.

• Diprotic acid: Can donate two protons.

Step-by-Step Guidance

1. Examine the formula for each acid and count the number of hydrogen atoms that can be donated.

2. Recall which acids are known to be triprotic.

3. Eliminate options that do not have three ionizable hydrogens.

4. Identify the acid with three protons to donate.

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Q12. A 5.0 x 10-3 M aqueous solution of HCl has a pH of ______.

Background

Topic: pH Calculations

This question tests your ability to calculate pH from the concentration of a strong acid.

Key Formula:

$\text{pH} = -\log_{10}[\text{H}^+]$

Step-by-Step Guidance

1. Recognize that HCl is a strong acid and dissociates completely, so $[\text{H}^+] = 5.0 \times 10^{-3}$ M.

2. Set up the pH formula using the given concentration.

3. Plug the value into the formula but stop before calculating the logarithm.

4. Compare the possible answers to see which is closest to your setup.

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Q13. A technician wishes to prepare 225 mL of a 1.5 M solution of NaOH from a 12 M stock solution. The volume of the stock solution which should be used is equal to ______.

Background

Topic: Solution Dilution

This question tests your ability to use the dilution equation to prepare a solution of desired concentration.

Key Formula:

$M_1V_1 = M_2V_2$

• $M_1$ = initial concentration (stock solution)

• $V_1$ = volume of stock solution to use

• $M_2$ = final concentration

• $V_2$ = final volume

Step-by-Step Guidance

1. Identify the known values: $M_1 = 12$ M, $M_2 = 1.5$ M, $V_2 = 225$ mL.

2. Set up the dilution equation to solve for $V_1$.

3. Plug in the values but stop before calculating $V_1$.

4. Check units to ensure consistency (mL or L).

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Q14. Which of the following species can readily act as either an acid or a base, according to the Bronsted-Lowry definition?

Background

Topic: Bronsted-Lowry Acids and Bases

This question tests your understanding of amphiprotic species (can act as acid or base).

Key Terms:

• Bronsted-Lowry acid: Proton donor.

• Bronsted-Lowry base: Proton acceptor.

• Amphiprotic: Can act as both acid and base.

Step-by-Step Guidance

1. Identify which species can both donate and accept a proton.

2. Recall common amphiprotic ions (e.g., HSO4-, HCO3-).

3. Eliminate options that can only act as acid or base.

4. Choose the species that fits the amphiprotic definition.

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Q15. Solution A contains 0.1 M NaCl and solution B contains 0.1 M glucose (C6H12O6). Which of the following statements about these two solutions is correct?

Background

Topic: Osmosis and Tonicity

This question tests your understanding of isotonic, hypotonic, and hypertonic solutions.

Key Terms:

• Isotonic: Solutions with equal concentrations of dissolved particles.

• Hypotonic: Lower concentration of dissolved particles compared to another solution.

• Hypertonic: Higher concentration of dissolved particles compared to another solution.

Step-by-Step Guidance

1. Determine if NaCl dissociates into ions, increasing the number of dissolved particles.

2. Compare the total particle concentration in each solution.

3. Recall that glucose does not dissociate, so its particle concentration equals its molarity.

4. Eliminate options that do not match the calculated particle concentrations.

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Q16. The pH of a solution changes from 7 to 5. Which of the following correctly describes the change in [H3O+]?

Background

Topic: pH and Hydronium Ion Concentration

This question tests your understanding of how pH relates to [H3O+].

Key Formula:

$[\text{H}_3\text{O}^+] = 10^{-\text{pH}}$

Step-by-Step Guidance

1. Calculate [H3O+] at pH 7 and pH 5 using the formula.

2. Compare the two concentrations to determine the change.

3. Recall that a decrease in pH means an increase in [H3O+].

4. Set up the ratio but stop before calculating the numeric value.

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Q17. Which of the following is the conjugate base of HSO4-?

Background

Topic: Acid-Base Chemistry

This question tests your ability to identify conjugate acids and bases.

Key Terms:

• Conjugate base: Formed when an acid loses a proton.

• Conjugate acid: Formed when a base gains a proton.

Step-by-Step Guidance

1. Write the formula for HSO4- and remove one H+ to find the conjugate base.

2. Recall the charge and formula after losing a proton.

3. Eliminate options that do not match the expected formula.

4. Choose the correct conjugate base.

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Q18. Briefly explain why a solution of table salt (NaCl) in water conducts electricity strongly, but a solution of sugar or glucose (C6H12O6) does not conduct an electric current at all.

Background

Topic: Electrolytes and Conductivity

This question tests your understanding of why ionic compounds conduct electricity in solution and molecular compounds do not.

Key Terms:

• Electrolyte: Produces ions in solution, conducts electricity.

• Nonelectrolyte: Does not produce ions, does not conduct electricity.

Step-by-Step Guidance

1. Recall that NaCl is an ionic compound and dissociates into Na+ and Cl- ions in water.

2. Glucose is a molecular compound and does not dissociate into ions.

3. Explain how the presence or absence of ions affects conductivity.

4. Summarize the difference in behavior between the two solutions.

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Q19. A technician dissolves 0.625 g of glucose (C6H12O6; molar mass = 180.2 g/mol) in sufficient water to give 355 mL of solution.

Background

Topic: Solution Concentration (Molarity)

This question tests your ability to calculate molarity from mass and volume.

Key Formula:

$\text{Molarity (M)} = \frac{\text{moles of solute}}{\text{liters of solution}}$

$\text{Moles of solute} = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}}$

Step-by-Step Guidance

1. Calculate the moles of glucose using its mass and molar mass.

2. Convert the volume of solution from mL to L.

3. Set up the molarity formula using the calculated moles and volume in liters.

4. Plug in the values but stop before calculating the final molarity.

Try solving on your own before revealing the answer!

Q20. Glucose is a non-dissociating solute. Why is glucose non-dissociating? How would the osmotic pressure of a 1 M solution of glucose compare with the osmotic pressure of a 1 M solution of NaCl? Explain your answer.

Background

Topic: Colligative Properties and Dissociation

This question tests your understanding of why some solutes dissociate and how this affects osmotic pressure.

Key Terms:

• Non-dissociating solute: Does not break into ions in solution.

• Osmotic pressure: Depends on the number of dissolved particles.

• Van't Hoff factor ($i$): Number of particles produced per formula unit.

Step-by-Step Guidance

1. Explain why glucose does not dissociate (molecular structure, covalent bonds).

2. Compare the number of particles produced by glucose and NaCl in solution.

3. Recall that osmotic pressure increases with the number of dissolved particles.

4. Set up the comparison but stop before stating the final relationship.

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Q21. The following represents an acid-base reaction at equilibrium: HCO3- (aq) + CN- (aq) ⇌ CO32- (aq) + HCN (aq) + heat

Background

Topic: Acid-Base Equilibrium and Conjugate Pairs

This question tests your ability to identify conjugate acid-base pairs in a reaction.

Key Terms:

• Conjugate acid-base pair: Two species that differ by one proton.

Step-by-Step Guidance

1. Identify which species act as acids and bases on each side of the equation.

2. Label the pairs that differ by one H+.

3. Write the formula for the conjugate acid of HCO3-.

4. Stop before listing all pairs and formulas.

Try identifying the pairs on your own before revealing the answer!

Q22. Physiological saline, containing 0.90% m/v NaCl, is isotonic with red blood cells. Describe, with explanation, what will happen to a red blood cell which is placed in a 0.50% m/v solution of NaCl.

Background

Topic: Osmosis and Tonicity

This question tests your understanding of how cells respond to hypotonic and hypertonic solutions.

Key Terms:

• Isotonic: Equal concentration of solute inside and outside the cell.

• Hypotonic: Lower concentration of solute outside the cell.

• Hypertonic: Higher concentration of solute outside the cell.

Step-by-Step Guidance

1. Compare the concentration of NaCl in the solution to that inside the cell.

2. Recall the direction of water movement in hypotonic solutions.

3. Describe the effect on the red blood cell (swelling, bursting, etc.).

4. Stop before stating the final outcome.

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Q23. A technician wishes to prepare 1.25 L of a 0.90% solution of NaCl, using a stock solution that contains 5.2% m/v. What volume of the stock solution must be used? Show all your work.

Background

Topic: Solution Dilution (Mass/Volume Percent)

This question tests your ability to use the dilution equation for mass/volume percent solutions.

Key Formula:

$C_1V_1 = C_2V_2$

• $C_1$ = concentration of stock solution

• $V_1$ = volume of stock solution to use

• $C_2$ = final concentration

• $V_2$ = final volume

Step-by-Step Guidance

1. Identify the known values: $C_1 = 5.2\%$, $C_2 = 0.90\%$, $V_2 = 1.25$ L.

2. Set up the dilution equation to solve for $V_1$.

3. Plug in the values but stop before calculating $V_1$.

4. Check units to ensure consistency (L or mL).

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Q24. Complete and balance each of the following neutralization equations.

Background

Topic: Acid-Base Neutralization Reactions

This question tests your ability to write and balance equations for reactions between acids and bases.

Key Terms:

• Neutralization: Reaction between an acid and a base to form water and a salt.

Step-by-Step Guidance

1. Write the products for each reaction (water and salt).

2. Balance the equation for each reactant and product.

3. Check the charges and formulas for the salts formed.

4. Stop before writing the fully balanced equations.

Try completing and balancing on your own before revealing the answer!