Week 2 Quiz

Which of these is a molecule rather than a single atom?

Select one.

• H, one hydrogen on its own
• O, one oxygen on its own
• H₂O, two hydrogens bonded to an oxygen
• N, one nitrogen on its own

In a grain of table salt, sodium gives up an electron to chlorine, and the resulting Na⁺ and Cl⁻ hold together. Which bond is this?

Select one.

• An ionic bond: one atom transfers an electron and the ions attract
• A covalent bond: the two atoms share a pair of electrons
• A hydrogen bond: a weak pull between two separate molecules
• A polar bond: oxygen pulls the electrons toward itself

Why is a water molecule polar?

Select one.

• The molecule carries an overall negative charge from extra electrons
• Each hydrogen pulls the shared electrons away from the oxygen
• Oxygen and hydrogen are held together by ionic bonds
• Oxygen pulls the shared electrons closer, so it is δ− and each hydrogen is δ+

The corner of a paper towel is dipped in water, and the wet line climbs up the towel. Which two properties of water work together to move the water upward? Select all that apply.

Select every option that applies.

• Adhesion, water clinging to the towel's fibers
• High specific heat, water resisting a change in temperature
• Cohesion, water clinging to other water molecules
• Evaporative cooling, fast molecules escaping as vapor

Why does ice float on liquid water?

Select one.

• Freezing removes the hydrogen atoms, so ice weighs less
• Hydrogen bonds hold frozen molecules farther apart, so ice is less dense
• Ice is lighter because cold water has fewer molecules
• Air from the surface is trapped in every ice crystal

On the pH ladder (approximate household values), which liquid is the most acidic: lemon juice at about pH 2, white vinegar at about pH 3, tap water at about pH 7, or baking-soda solution at about pH 9?

Select one.

• Baking-soda solution, because it has the highest pH number
• Tap water, because pure water is the reference point
• Lemon juice, because it has the lowest pH number
• White vinegar, because it sits closest to neutral

How many times more hydrogen ions does a solution at pH 4 have than a solution at pH 7?

Select one.

• 3 times, because 7 minus 4 is 3
• 1,000 times, because three steps give 10³
• 30 times, because each step adds ten
• 10,000 times, because four steps give 10⁴

True or false: a buffer, such as the carbonic acid / bicarbonate system in blood, prevents any change in pH.

True or false.

• True
• False

In the Red-Cabbage pH Indicator lab, you add the same amount of cabbage indicator to five household liquids and record the color each one turns. Which is the dependent variable?

Select one.

• Which household liquid goes in each cup
• The amount of indicator added to every cup
• The tap-water cup used as the neutral reference
• The color the indicator turns in each liquid

In the illustrative penny experiment, a penny held an average of 30 drops of plain water and 14 drops of soapy water. Which conclusion fits this week's chemistry and Week 1's honest verbs?

Select one.

• The data prove soap destroys every hydrogen bond in the water
• The evidence supports that soap lowers water's surface tension
• Soapy water is the control group, so it should hold more drops
• Soap makes each water molecule heavier, so drops spill sooner