Q: A beaker contains 100 mL of water at 25°C. If you add 1,000 J of heat to the water, by how many degrees Celsius will the temperature increase? (Specific heat of water = $$1 \ \mathrm{cal}/(\mathrm{g} \ ^\circ\mathrm{C})$$, $$1 \ \mathrm{cal} = 4.184 \ \mathrm{J}$$, density of water = $$1 \ \mathrm{g}/\mathrm{mL})$$

$$1000 \ \mathrm{J} \times \frac{1 \ \mathrm{cal}}{4.184 \ \mathrm{J}} = 239 \ \mathrm{cal}$$; $$239 \ \mathrm{cal} / 100 \ \mathrm{g} = 2.39 ^\circ\mathrm{C}$$

Question 1

Which property of water is primarily responsible for the ability of some insects to walk on water surfaces?

Accepted Answer

Cohesion due to hydrogen bonding

Question 2

A beaker contains 100 mL of water at 25°C. If you add 1,000 J of heat to the water, by how many degrees Celsius will the temperature increase? (Specific heat of water = $$1 \ \mathrm{cal}/(\mathrm{g} \ ^\circ\mathrm{C})$$, $$1 \ \mathrm{cal} = 4.184 \ \mathrm{J}$$, density of water = $$1 \ \mathrm{g}/\mathrm{mL})$$

Accepted Answer

$$1000 \ \mathrm{J} 	imes \frac{1 \ \mathrm{cal}}{4.184 \ \mathrm{J}} = 239 \ \mathrm{cal}$$; $$239 \ \mathrm{cal} / 100 \ \mathrm{g} = 2.39 ^\circ\mathrm{C}$$

Question 3

Why does ice float on liquid water?

Accepted Answer

Ice is less dense than liquid water because hydrogen bonds keep water molecules farther apart in the solid state.

Question 4

Which of the following best explains why water has a high specific heat?

Accepted Answer

Hydrogen bonds between water molecules absorb heat when they break and release heat when they form.

Question 5

A solution has a pH of 4. What is the concentration of hydrogen ions $$[H^+] in $$this solution?

Accepted Answer

$$[H^+] = 10$$^{-4}$$ \ \mathrm{M}$$

Question 6

Which of the following best describes a buffer system in biological fluids?

Accepted Answer

A buffer minimizes changes in pH by accepting or donating hydrogen ions ($$H^+) as $$needed.

Question 7

If the pH of a solution changes from 7 to 5, what happens to the hydrogen ion concentration?

Accepted Answer

It increases by 100 times.

Question 8

Which of the following is an example of a hydrophobic substance?

Accepted Answer

Olive oil

Question 9

A marine biologist observes that coral reefs are declining in areas with increased atmospheric $$CO_2. $$Which chemical process best explains this phenomenon?

Accepted Answer

Ocean acidification reduces carbonate ion ($$CO_3$$^{2-}$$) concentration, making it harder for corals to form calcium carbonate ($$CaCO_3$$) skeletons.

Question 10

Which of the following statements about acids and bases is correct?

Accepted Answer

Acids increase the concentration of $$H^+$$ ions in solution.

Question 11

A scientist wants to prepare 1 liter of a 1 M sucrose solution. The molecular weight of sucrose ($$C_{12}H$$_{22}$$O_{11}$) is 342 g/mol. How many grams of sucrose should be dissolved in water to make this solution?

Accepted Answer

342 grams

Question 12

Which of the following best describes the difference between a solution and a mixture?

Accepted Answer

A solution is a homogeneous mixture where the solute is completely dissolved in the solvent.

Question 13

Which of the following equations correctly represents the dissociation of water?

Accepted Answer

$$2H_2O \rightleftharpoons H_3O^+ + OH^-$$

Question 14

Which property of water allows it to dissolve many ionic and polar substances?

Accepted Answer

Its polarity, which allows it to form hydration shells around ions and polar molecules.

Question 15

A solution has a $$[OH^-] of$$ $$1 	imes 10$$^{-9}$$ \ \mathrm{M}. $$What is the pH of the solution?

Accepted Answer

pH = 5

Question 16

Which of the following best explains why sweating cools the body?

Accepted Answer

Evaporation of water from the skin removes heat due to water's high heat of vaporization.

Question 17

Which of the following is true about electrolytes?

Accepted Answer

They are substances that form ions in water and conduct electricity.

Question 18

If you mix 0.5 moles of NaCl in enough water to make 2 liters of solution, what is the molarity of the solution?

Accepted Answer

$$0.25 \ \mathrm{M}$$

Question 19

Which of the following best describes the role of buffers in blood?

Accepted Answer

Buffers help maintain a stable pH by neutralizing excess acids or bases.

Question 20

Which of the following is a correct statement about the relationship between pH and $$[H^+]$$?

Accepted Answer

As pH decreases, $$[H^+]$$ increases.

Chapter 3: Water and Life – Properties, Chemistry, and Biological Importance

Guida di studio - Domande di pratica

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