Science Practice Questions — Set 7

Question 1

Why is H2O (water) a polar molecule?

Accepted Answer

Oxygen pulls electrons more strongly, creating uneven charge.

Answer

It contains hydrogen and oxygen atoms in fixed ratio.

Answer

It dissolves many substances, including some ionic compounds.

Answer

It is liquid at room temperature and pressure.

Question 2

Solution A has a pH of 2. Solution B has a pH of 4. This means:

Accepted Answer

Solution A is 100 times more acidic than Solution B.

Answer

Solution A is 2 times more acidic than Solution B.

Answer

Solution B is 2 times more acidic than Solution A.

Answer

Solution A is only slightly more acidic than solution B.

Question 3

When a 10kg log of wood is completely burned, it produces 1kg of ash. Where did the "missing" 9kg of mass go?

Accepted Answer

It was converted into gaseous compounds like CO2 and H2O.

Answer

It was converted directly into energy (heat and light).

Answer

It was destroyed, violating the Law of Conservation of Mass.

Answer

The smoke is absorbed by the soil beneath the fire.

Question 4

Why does evaporation make you feel cold?

Accepted Answer

Evaporation removes faster molecules, leaving cooler ones.

Answer

Cold air rushes in where evaporated water was.

Answer

The water adds coldness to your skin.

Answer

Water reacts with skin and absorbs heat chemically.

Question 5

An atom has 6 protons, 7 neutrons, and 6 electrons. What is this element?

Accepted Answer

An isotope of Carbon.

Answer

An isotope of Nitrogen.

Answer

A stable, neutral atom of Nitrogen.

Answer

An ion of Carbon.

Question 6

Why does salt (NaCl) conduct electricity when dissolved in water, but sugar (C12H22O11) does not?

Accepted Answer

Salt dissociates into mobile ions; sugar dissolves as neutral molecules.

Answer

Sugar is a non-polar molecule, while salt is polar.

Answer

Sugar molecules are too large to conduct electricity.

Answer

Salt is a white crystal, and all white crystals conduct electricity.

Question 7

Given the reaction N₂ + 3H₂ ⇌ 2NH₃ + heat. How could you increase the production of NH₃ (ammonia)?

Accepted Answer

Increase the pressure.

Answer

Remove some of the N₂ reactant.

Answer

Increase the temperature.

Answer

Add more NH₃.

Question 8

What is the fundamental difference between an ionic bond and a covalent bond?

Accepted Answer

Ionic bonds transfer electrons; covalent bonds share electrons.

Answer

Ionic bonds form molecules, while covalent bonds form crystals.

Answer

Ionic bonds occur only in liquids, covalent bonds only in gases.

Answer

Ionic bonds are stronger than covalent bonds in every case.

Question 9

What does "balancing a chemical equation" actually satisfy?

Accepted Answer

The Law of Conservation of Mass.

Answer

The Law of Conservation of Energy.

Answer

Balanced equations are written mainly for symmetry.

Answer

The ideal gas law principle.

Question 10

How do you increase the *solubility* of a solid, like sugar, in a liquid?

Accepted Answer

Increase the temperature of the liquid.

Answer

Add a different solid, like salt, to the liquid first.

Answer

Decrease the temperature of the liquid.

Answer

Stirring faster increases how much sugar can dissolve.