Water, pH & Buffer

During a science class, Emma asked her classmates to identify the importance and chemical properties of water.

• Water is primarily used for industrial purposes only.

• Water has no role in temperature regulation.

• Water is not essential for any living organisms.

• Water is vital for life due to its solvent properties, high specific heat, and role in biochemical reactions.

Answer explanation

Water is essential for life due to its unique properties: it acts as a solvent for many substances, has a high specific heat that helps regulate temperature, and is crucial in biochemical reactions, making it vital for all living organisms.

Abigail and Rohan are studying the differences between polar and non-polar molecules in their chemistry class.

• Polar molecules are always gases; non-polar molecules are always liquids.

• Polar molecules have partial positive and negative charges; non-polar molecules do not.

• Polar molecules have equal distribution of charge; non-polar molecules have unequal distribution.

• Non-polar molecules can form hydrogen bonds; polar molecules cannot.

Answer explanation

Polar molecules have partial positive and negative charges due to unequal sharing of electrons, while non-polar molecules have an even distribution of charge, resulting in no partial charges.

Priya is conducting an experiment in the lab to understand the differences between strong and weak acids and bases. Can you help her?

• Weak acids completely dissociate in solution; strong acids do not.

• Strong acids fully dissociate in solution; weak acids partially dissociate. Strong bases fully dissociate; weak bases partially dissociate.

• Strong bases do not react with water; weak bases do.

• Strong acids are always safe to handle; weak acids are dangerous.

Answer explanation

Strong acids and bases fully dissociate in solution, meaning they break down completely into ions. In contrast, weak acids and bases only partially dissociate, resulting in a mixture of undissociated molecules and ions.

In a chemistry class, Kai is explaining the pH levels of different substances. He mentions that strong acids have low pH, while weak acids have moderate pH. He also talks about strong and weak bases. Can you summarize his explanation?

• Strong acids have low pH (<3), weak acids have moderate pH (3-7); strong bases have high pH (>11), weak bases have moderate pH (7-11).

• Weak acids and bases have the same pH range (3-11)

• Strong bases have moderate pH (3-7), weak bases have low pH (<3)

• Strong acids have high pH (>11), weak acids have low pH (<3)

Answer explanation

Kai explains that strong acids have low pH (<3) and weak acids have moderate pH (3-7). For bases, strong bases have high pH (>11) and weak bases have moderate pH (7-11), making the first answer choice correct.

What is the significance of the equivalence point in acid-base titrations?

• The equivalence point indicates the point at which the solution is neutralized, with no excess acid or base remaining.

• It is the point where the pH is always 7, regardless of the acids or bases used.

• The equivalence point is irrelevant in determining the concentration of the solutions involved.

• It marks the end of the titration process, after which no further measurements are needed.

Answer explanation

The equivalence point is crucial in acid-base titrations as it signifies complete neutralization, meaning no excess acid or base remains. This allows for accurate determination of concentrations.

What is the role of buffers in biological systems?

• Buffers are only found in laboratory settings.

• Buffers help to stabilize pH levels in living organisms.

• Buffers are ineffective in maintaining pH.

• Buffers can only be made from strong bases.

Answer explanation

Buffers play a crucial role in biological systems by helping to stabilize pH levels, which is essential for proper cellular function and metabolic processes. This makes the correct choice: Buffers help to stabilize pH levels in living organisms.

What is the significance of water in biological systems?

• It is the main solvent for biological systems.

• It is not involved in transportation.

• It does not help in temperature regulation.

• It has no role in excretion.

Answer explanation

Water is crucial in biological systems as it serves as the main solvent, facilitating chemical reactions and transport of nutrients and waste. The other options incorrectly state its roles in transportation, temperature regulation, and excretion.

What is the pH of pure water?

• 7

• 0

• 14

• 1

Answer explanation

The pH of pure water is 7, which is considered neutral. Values below 7 indicate acidity, while values above 7 indicate alkalinity. Therefore, the correct answer is 7.

What is a buffer?

• A solution that resists changes in pH.

• A solution that changes pH rapidly.

• A solution that has no effect on pH.

• A solution that only contains strong acids.

Answer explanation

A buffer is a solution that resists changes in pH when small amounts of acid or base are added. This property is crucial in many biological and chemical processes, making the first choice the correct answer.

What happens if the pH of the body drops below 6.8?

• Death may occur.

• The body functions normally.

• It leads to increased energy levels.

• It has no significant effect.

Answer explanation

A drop in body pH below 6.8 indicates severe acidosis, which disrupts cellular functions and can lead to organ failure and death. Therefore, the correct answer is that death may occur.