Lab 2

Which atom in a water molecule is electronegative?

Oxygen.

What does it mean for an atom to be electronegative?

It means the atom is "greedy" with electrons and attracts them more strongly.

How is a covalent bond different than a hydrogen bond?

A covalent bond involves the sharing of electrons within a molecule, while a hydrogen bond is a weak attraction between water molecules.

What type of bond occurs within a water molecule?

Covalent bond.

What type of bond occurs between water molecules?

Hydrogen bond.

Contrast the terms: hydrophilic vs. hydrophobic.

Hydrophilic means "water-loving" and interacts with water; hydrophobic means "water-fearing" and repels water.

Contrast the terms: cohesion vs. adhesion.

Cohesion is the attraction between like substances, while adhesion is the attraction between unlike substances

Which activity demonstrated each of the following properties of water: imbibition, surface tension, capillary action, adhesion?

• Imbibition: Seeds soaking up water and swelling

• Surface tension: Paper clip floating on water

• Capillary action: Water moving up a capillary tube or paper towel

• Adhesion: Glass slide–water–glass slide

Which substance has a lower heat of vaporization – ethanol or water?

Ethanol.

Which substance has a higher specific heat – ethanol or water?

Water.

Which substances readily dissolved in water in this week's lab?

Salt and sugar.

Contrast the terms: electrolyte vs. non-electrolyte.

: Electrolytes release ions in water and conduct electricity; non-electrolytes do not release ions and do not conduct electricity.

List the electrolytes mentioned in the lab.

NaCl (salt), HCl, and NaOH.

As acids dissociate in water, what type of ions are released?

H⁺ (hydrogen) ions.

As bases dissociate in water, what type of ions are released?

OH⁻ (hydroxide) ions.

Which substance responded more rapidly to the heat applied – ethanol or water?

Ethanol.

Which term best refers to the “attraction of like substances”?

Cohesion.

Which term best refers to substances that repel water? Give an example.

Hydrophobic; example: oil.

At what temperature (in Celsius) does water boil?

100°C.

At what temperature (in Celsius) does ethanol boil?

78°C

Contrast the terms: solvent vs. solute.

A solvent is the substance doing the dissolving, while a solute is the substance being dissolved.

Do polar substances dissolve in water?

Yes, polar substances dissolve in water

What ions are released when salt dissociates in water?

Na⁺ and Cl⁻ ions.

What term refers to positively charged ions? To negatively charged ions?

Positively charged ions are cations; negatively charged ions are anions.

How does pH vary with H⁺ ion concentration?

As H⁺ ion concentration increases, pH decreases (the solution becomes more acidic).

What does it mean that the pH scale is on a logarithmic scale? For example, how many more times acidic is a pH of 4 compared to a pH of 7?

Each whole-number change in pH represents a 10-fold change in acidity. A pH of 4 is 1,000 times more acidic than a pH of 7.