Question

A scientist adds heat to each of the following substances. Which will probably absorb the most heat before its temperature changes significantly?
50 g of solid copper

50 g of solid iron

50 g of liquid water

50 g of sand

A scientist discovers a new substance. The molecules of the substance form hydrogen bonds with each other. When the molecules lose a lot of energy, the hydrogen bonds hold them relatively far apart. Based on this information, what can the scientist infer about the substance?

It expands when it freezes.╖

It is highly colored.

It exists only as a gas.

It does not dissolve ionic compounds.

Which of these best explains why a paper clip can float on water?

Water has a very high specific heat.

Water molecules at the surface experience fewer hydrogen bonds than water molecules within the liquid.

The metal in the paper clip has a lower mass than the water.

Water molecules near the surface produce more buoyant force than water molecules within the liquid.

Which of these best explains why the hydrogen atoms in a water molecule are attracted to Cl− ions in sodium chloride (NaCl)?

The hydrogen atoms have +1 charges.

The hydrogen atoms share electrons equally with the oxygen atom.

The hydrogen atoms have partial positive charges.

The hydrogen atoms form covalent bonds with the chloride ions.

Answer 1

1) The answer is: 50 g of liquid water.

The quantity of heat that is required to raise the sample’s temperature by 1°C (or Kelvin) is specific heat.

Heat capacity of a sample is expressed in units of thermal energy per degree temperature (J/K).

Heat capacity is often defined relative to a unit of mass (J/kg·K or J/g·K), prefixed with the term specific  heat.

cp(H₂O) = 4.184 J/g·K, specific heat capacity of water.

Since the mass is same for all the given substances, the higher is the specific heat of a substance more heat is needed to raise the temperature.

2) The answer is: It expands when it freezes.

When molecule frezes, it lose energy. When molecules are far apart, it means the volume is greater and it expands.

For example, ice expands when water is freezing.

Hydrogen bond is an electrostatic attraction between two polar groups that occurs when a hydrogen atom (H), covalently bound to a highly electronegative atom such as flourine (F), oxygen (O) and nitrogen (N) atoms.

3) The answer is: Water molecules at the surface experience fewer hydrogen bonds than water molecules within the liquid.  

The water molecules at the surface do not have other water molecules to form hydrogen bonds, only below and to either sides, like other water molecules that hydrogen bond with other water molecules on all sides.

Surface water molecules attract more strongly to the water molecules around them and create a high surface tension with smaller surface area of a water.

4) The answer is: The hydrogen atoms have partial positive charges.

Dissociation of sodium chloride in water:  

NaCl(aq) → Na⁺(aq) + Cl⁻(aq).

Solvation is the interaction of solvent (water) with molecules or ions (in this example Na⁺ and Cl⁻) in a solute.  

Anion Cl⁻ has negative charge, so positive end (hydrogen atoms) of a water molecul attracts them.

Solvent (usually a liquid, but can also be a solid or a gas) is a substance that dissolves a solute.

Answer 2

A scientist adds heat to each of the following substances. Which will probably absorb the most heat before its temperature changes significantly?

50 g of liquid water 


A scientist discovers a new substance. The molecules of the substance form hydrogen bonds with each other. When the molecules lose a lot of energy, the hydrogen bonds hold them relatively far apart. Based on this information, what can the scientist infer about the substance?

It expands when it freezes.╖



Which of these best explains why a paper clip can float on water?


Water molecules near the surface produce more buoyant force than water molecules within the liquid.


Which of these best explains why the hydrogen atoms in a water molecule are attracted to Cl− ions in sodium chloride (NaCl)?


The hydrogen atoms have partial positive charges.