Study Guide: Water, Chemical Bonds, Molarity, and pH in Biology

Q1. What type of bond is joining the two hydrogen atoms?

Background

Topic: Chemical Bonds

This question tests your understanding of the different types of chemical bonds that can form between atoms, especially in biological molecules.

Key Terms:

• Ionic bond: Transfer of electrons between atoms.

• Covalent bond: Sharing of electrons between atoms.

• Hydrogen bond: Attraction between a hydrogen atom and an electronegative atom.

• Hydrophobic interaction: Nonpolar molecules grouping together to avoid water.

Step-by-Step Guidance

1. Recall that hydrogen atoms can form bonds by sharing electrons.

2. Consider the options: ionic bonds involve electron transfer, covalent bonds involve electron sharing, hydrogen bonds are weak attractions, and hydrophobic interactions are not true bonds.

3. Think about which bond is most likely between two hydrogen atoms in a molecule.

Try solving on your own before revealing the answer!

Final Answer: C. Covalent

Hydrogen atoms join by sharing electrons, forming a covalent bond.

Q2. Partial charges can occur when:

Background

Topic: Electronegativity and Partial Charges

This question tests your understanding of how partial charges arise in molecules, especially due to differences in electronegativity.

Key Terms:

• Electronegativity: The tendency of an atom to attract electrons.

• Partial charge: A small charge difference within a molecule due to unequal sharing of electrons.

• Covalent bond: Sharing of electrons between atoms.

Step-by-Step Guidance

1. Review what happens when atoms of different electronegativities form a covalent bond.

2. Consider whether partial charges can occur in ionic bonds or only covalent bonds.

3. Analyze the answer choices to see which situations lead to partial charges.

Try solving on your own before revealing the answer!

Final Answer: E. both (a) and (b)

Partial charges occur when a covalent bond links atoms of two different kinds and when atoms share electrons unequally.

Q3. Which atom in the pictured molecule will have the strongest partial negative charge?

Background

Topic: Electronegativity and Molecular Structure

This question tests your ability to identify which atom in a molecule will have the strongest partial negative charge based on its electronegativity and bonding environment.

Key Terms:

• Electronegativity: The ability of an atom to attract electrons.

• Partial negative charge: Occurs on atoms that attract electrons more strongly.

Step-by-Step Guidance

1. Identify the atoms in the molecule: H, N, C, O.

2. Recall that oxygen is more electronegative than nitrogen and carbon.

3. Look at the bonding environment: the O atom in C=O is double-bonded to carbon, which increases its electron density.

4. Compare the partial charges on each atom based on their electronegativity and bonding.

Try solving on your own before revealing the answer!

Final Answer: D. The O atom that's in C=O

The oxygen atom in the C=O group has the strongest partial negative charge due to its high electronegativity and double bond.

Q4. What hypothetical change would make water more polar?

Background

Topic: Polarity of Water

This question tests your understanding of what factors influence the polarity of water molecules.

Key Terms:

• Polarity: The distribution of electrical charge over the atoms in a molecule.

• Electronegativity: The tendency of an atom to attract electrons.

• Linear molecule: A molecule with atoms arranged in a straight line.

Step-by-Step Guidance

1. Recall that water is polar because of its bent shape and the difference in electronegativity between hydrogen and oxygen.

2. Consider how changing the shape (making it linear) would affect polarity.

3. Think about how increasing the electronegativity of hydrogen or oxygen would affect the charge distribution.

Try solving on your own before revealing the answer!

Final Answer: Increase the electronegativity value of oxygen

Making oxygen more electronegative would increase the polarity of water.

Q5. Hydrogen bonds: Which statements are true?

Background

Topic: Hydrogen Bonding

This question tests your understanding of hydrogen bonds, their formation, and their properties in biological molecules.

Key Terms:

• Hydrogen bond: A weak bond between a hydrogen atom and an electronegative atom (like N or O).

• Covalent bond: A strong bond formed by sharing electrons.

Step-by-Step Guidance

1. Recall that hydrogen bonds can form between H and N or H and O.

2. Consider whether hydrogen bonds occur within a water molecule or between molecules.

3. Think about whether hydrogen bonds involve sharing electrons or are covalent bonds.

Try solving on your own before revealing the answer!

Final Answer: A. can form between H and N

Hydrogen bonds can form between hydrogen and nitrogen (or oxygen), but they are not covalent bonds and do not occur within a single water molecule.

Q6. Which atoms can form hydrogen bonds with water molecules?

Background

Topic: Hydrogen Bonding in Water

This question tests your understanding of which atoms are capable of forming hydrogen bonds with water molecules.

Key Terms:

• Hydrogen bond: A weak bond between a hydrogen atom and an electronegative atom.

• Electronegative atom: Atoms like oxygen and nitrogen that attract electrons strongly.

Step-by-Step Guidance

1. Recall that hydrogen bonds form between hydrogen and electronegative atoms (O, N).

2. Identify which atoms in a water molecule can participate in hydrogen bonding.

3. Consider other molecules that can form hydrogen bonds with water.

Try solving on your own before revealing the answer!

Final Answer: Oxygen and nitrogen atoms

Atoms like oxygen and nitrogen can form hydrogen bonds with water molecules.

Q7. Water has surface tension because:

Background

Topic: Properties of Water

This question tests your understanding of why water exhibits surface tension, a property important for many biological phenomena.

Key Terms:

• Surface tension: The cohesive force at the surface of a liquid.

• Hydrogen bond: A weak bond between hydrogen and an electronegative atom.

• Cohesion: Attraction between molecules of the same substance.

Step-by-Step Guidance

1. Recall that surface tension is caused by cohesive forces between water molecules.

2. Consider how hydrogen bonds contribute to these cohesive forces.

3. Analyze the answer choices to determine which best explains surface tension.

Try solving on your own before revealing the answer!

Final Answer: C. surface water molecules form better hydrogen bonds

Surface tension arises because surface water molecules form stronger hydrogen bonds.

Q8. The open spaces in water's crystal structure make it possible for:

Background

Topic: Water's Structure and Properties

This question tests your understanding of how the structure of water in its solid form (ice) affects its properties and biological implications.

Key Terms:

• Crystal structure: The arrangement of atoms in a solid.

• Boiling point: The temperature at which a substance changes from liquid to gas.

Step-by-Step Guidance

1. Recall that water's crystal structure in ice creates open spaces, making ice less dense than liquid water.

2. Consider how this property allows aquatic life to survive in frozen ponds.

3. Analyze the answer choices for other implications of water's structure.

Try solving on your own before revealing the answer!

Final Answer: A. aquatic life to exist in a frozen pond

The open spaces in water's crystal structure allow ice to float, enabling aquatic life to survive beneath it.

Q9. What would happen to the temperature of a large lake if it contained water without hydrogen bonds?

Background

Topic: Hydrogen Bonds and Temperature Regulation

This question tests your understanding of how hydrogen bonds affect the temperature changes in large bodies of water.

Key Terms:

• Hydrogen bond: A weak bond between hydrogen and an electronegative atom.

• Specific heat: The amount of heat required to change the temperature of a substance.

Step-by-Step Guidance

1. Recall that hydrogen bonds give water a high specific heat, meaning it resists temperature changes.

2. Consider what would happen if water lacked hydrogen bonds.

3. Analyze the answer choices for the effect on temperature change.

Try solving on your own before revealing the answer!

Final Answer: A. It would heat up faster.

Without hydrogen bonds, water would heat up more quickly because it would have a lower specific heat.

Q10. Which property of water allows dogs to cool themselves by panting?

Background

Topic: Properties of Water and Biological Functions

This question tests your understanding of how water's properties are important for temperature regulation in living organisms.

Key Terms:

• Heat of vaporization: The energy required to convert water from liquid to gas.

• Surface tension: The cohesive force at the surface of a liquid.

Step-by-Step Guidance

1. Recall that panting helps dogs cool down by evaporating water from their tongue and respiratory tract.

2. Consider which property of water is involved in this process.

3. Analyze the answer choices for the property that enables cooling by evaporation.

Try solving on your own before revealing the answer!

Final Answer: A. water’s high heat of vaporization

Water's high heat of vaporization allows dogs to cool themselves efficiently by panting.

Q11. Why do you think a needle floats on water? Would the needle have an easier time floating on warm or cold water?

Background

Topic: Surface Tension and Water Properties

This question tests your understanding of surface tension and how temperature affects it.

Key Terms:

• Surface tension: The cohesive force at the surface of a liquid.

• Temperature: Affects the strength of surface tension.

Step-by-Step Guidance

1. Recall that surface tension is caused by hydrogen bonds between water molecules.

2. Consider how temperature affects the strength of hydrogen bonds and surface tension.

3. Think about whether warm or cold water would have stronger surface tension.

Try solving on your own before revealing the answer!

Final Answer: Cold water

A needle floats more easily on cold water because surface tension is stronger at lower temperatures.

Q12. How would you make 1 liter of 1M solution of glucose? The molecular mass of glucose is 180 g/mol

Background

Topic: Molarity and Solution Preparation

This question tests your ability to calculate the amount of solute needed to prepare a solution of a given molarity.

Key Terms and Formula:

• Molarity (M): Number of moles of solute per liter of solution.

• Molecular mass: Mass of one mole of a substance.

Step-by-Step Guidance

1. Recall the formula for molarity: $M = \frac{\text{moles of solute}}{\text{liters of solution}}$

2. Calculate the number of moles needed for a 1M solution in 1 liter: $1 \text{ mole}$

3. Multiply the number of moles by the molecular mass of glucose to find the grams needed: $1 \text{ mole} \times 180 \text{ g/mol}$

Try solving on your own before revealing the answer!

Final Answer: 180 grams of glucose

To make 1 liter of 1M glucose solution, dissolve 180 grams of glucose in water and bring the total volume to 1 liter.

Q13. How would you make 1 liter of 2M solution of glucose? The molecular mass of glucose is 180 g/mol

Background

Topic: Molarity and Solution Preparation

This question tests your ability to calculate the amount of solute needed for a higher molarity solution.

Key Terms and Formula:

• Molarity (M): Number of moles of solute per liter of solution.

• Molecular mass: Mass of one mole of a substance.

Step-by-Step Guidance

1. Recall the formula for molarity: $M = \frac{\text{moles of solute}}{\text{liters of solution}}$

2. Calculate the number of moles needed for a 2M solution in 1 liter: $2 \text{ moles}$

3. Multiply the number of moles by the molecular mass of glucose: $2 \text{ moles} \times 180 \text{ g/mol}$

Try solving on your own before revealing the answer!

Final Answer: 360 grams of glucose

To make 1 liter of 2M glucose solution, dissolve 360 grams of glucose in water and bring the total volume to 1 liter.

Q14. How would you make 2 liters of 1M solution of glucose? The molecular mass of glucose is 180 g/mol

Background

Topic: Molarity and Solution Preparation

This question tests your ability to scale up solution preparation for a larger volume.

Key Terms and Formula:

• Molarity (M): Number of moles of solute per liter of solution.

• Molecular mass: Mass of one mole of a substance.

Step-by-Step Guidance

1. Recall the formula for molarity: $M = \frac{\text{moles of solute}}{\text{liters of solution}}$

2. Calculate the number of moles needed for a 1M solution in 2 liters: $2 \text{ moles}$

3. Multiply the number of moles by the molecular mass of glucose: $2 \text{ moles} \times 180 \text{ g/mol}$

Try solving on your own before revealing the answer!

Final Answer: 360 grams of glucose

To make 2 liters of 1M glucose solution, dissolve 360 grams of glucose in water and bring the total volume to 2 liters.

Q15. How many grams of hydrogen chloride (HCl) are required to prepare 4 liters of 5M HCl in water?

Background

Topic: Molarity and Solution Preparation

This question tests your ability to calculate the mass of solute needed for a specific volume and molarity.

Key Terms and Formula:

• Molarity (M): Number of moles of solute per liter of solution.

• Molecular mass of HCl: 36.5 g/mol

Step-by-Step Guidance

1. Calculate the total number of moles needed: $5 \text{ M} \times 4 \text{ L} = 20 \text{ moles}$

2. Multiply the number of moles by the molecular mass of HCl: $20 \text{ moles} \times 36.5 \text{ g/mol}$

Try solving on your own before revealing the answer!

Final Answer: 730 grams of HCl

To prepare 4 liters of 5M HCl, dissolve 730 grams of HCl in water and bring the total volume to 4 liters.

Q16. A solution contains 2g of glucose in 500 mL of water. What is its molarity, and how does that compare to the normal fasting blood glucose level in humans (4-6 mM)? The molar mass of glucose is 180 g/mol

Background

Topic: Molarity Calculation and Biological Comparison

This question tests your ability to calculate molarity and compare it to physiological values.

Key Terms and Formula:

• Molarity (M): Number of moles of solute per liter of solution.

• Mole: $\text{moles} = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}}$

Step-by-Step Guidance

1. Calculate the number of moles of glucose: $\frac{2 \text{ g}}{180 \text{ g/mol}}$

2. Convert 500 mL to liters: $0.5 \text{ L}$

3. Calculate molarity: $\frac{\text{moles}}{\text{liters}}$

4. Convert the molarity to mM (millimolar): $1 \text{ M} = 1000 \text{ mM}$

5. Compare your calculated value to the normal fasting blood glucose level (4-6 mM).

Try solving on your own before revealing the answer!

Final Answer: 22.2 mM

The solution is 22.2 mM, which is higher than the normal fasting blood glucose level in humans.

Q17. Neutral water has the H+ concentration of 10^-7 M. What does this mean?

Background

Topic: pH and Hydrogen Ion Concentration

This question tests your understanding of pH and what the hydrogen ion concentration indicates about a solution.

Key Terms and Formula:

• pH: $\text{pH} = -\log [\text{H}^+]$

• Neutral solution: Equal concentrations of H+ and OH- ions.

Step-by-Step Guidance

1. Recall that neutral water has equal concentrations of H+ and OH- ions.

2. Calculate the pH using the formula: $\text{pH} = -\log [\text{H}^+]$

3. Interpret what a pH of 7 means in terms of acidity and neutrality.

Try solving on your own before revealing the answer!

Final Answer: Neutral water has a pH of 7

This means the solution is neither acidic nor basic.

Q18. What is the difference between H+ concentration in an acidic solution such as lemon juice (pH 2) and a basic solution such as household bleach (pH 13)?

Background

Topic: pH Scale and Hydrogen Ion Concentration

This question tests your understanding of the logarithmic nature of the pH scale and how it relates to hydrogen ion concentration.

Key Terms and Formula:

• pH: $\text{pH} = -\log [\text{H}^+]$

• Logarithmic scale: Each unit change in pH represents a tenfold change in H+ concentration.

Step-by-Step Guidance

1. Recall that a lower pH means higher H+ concentration.

2. Calculate the difference in H+ concentration between pH 2 and pH 13: $10^{13-2} = 10^{11}$

3. Interpret what this difference means in terms of acidity.

Try solving on your own before revealing the answer!

Final Answer: The H+ concentration of lemon juice is higher than household bleach by a factor of 10^11

Lemon juice is much more acidic than household bleach.

Q19. If a buffered solution has an acid added to it, what will the buffer do in response?

Background

Topic: Buffers and pH Regulation

This question tests your understanding of how buffers work to maintain pH in biological systems.

Key Terms:

• Buffer: A solution that resists changes in pH when acids or bases are added.

• Hydrogen ion (H+): Increases with added acid.

• Hydroxide ion (OH-): Increases with added base.

Step-by-Step Guidance

1. Recall that buffers work by neutralizing added H+ or OH- ions.

2. Consider what happens when an acid (H+) is added to a buffered solution.

3. Analyze the answer choices for the buffer's response.

Try solving on your own before revealing the answer!

Final Answer: A) Decrease hydrogen ions

The buffer will decrease the concentration of hydrogen ions to maintain pH.