Unit Test 7: Aqueous Solutions

Which property of an unsaturated solution of sodium chloride in water remains the same when more water is added to the solution?

• density of the solution

• boiling point of the solution

• mass of sodium chloride in the solution

• percent by mass of water in the solution

Answer explanation

The mass of sodium chloride in the solution remains constant regardless of the amount of water added. Adding water dilutes the solution but does not change the amount of solute present.

Under which conditions of temperature and pressure is a gas most soluble in water?

• high temperature and low pressure

• high temperature and high pressure

• low temperature and low pressure

• low temperature and high pressure

Answer explanation

A gas is most soluble in water at low temperatures and high pressures because lower temperatures reduce kinetic energy, allowing more gas to dissolve, while higher pressures increase the gas's solubility by forcing more gas into the liquid.

A change in pressure would have the greatest effect on the solubility of a

• solid in a liquid

• liquid in a liquid

• gas in a liquid

• liquid in a solid

Answer explanation

A change in pressure significantly affects the solubility of gases in liquids due to the gas law, which states that increasing pressure increases gas solubility. Solubility of solids and liquids is less affected by pressure.

Compared to distilled water, an aqueous salt solution has

• better electrical conductivity

• poorer electrical conductivity

• a lower boiling point at standard pressure

• a higher freezing point at standard pressure

Answer explanation

An aqueous salt solution contains ions that enhance its ability to conduct electricity, making it a better conductor than distilled water, which lacks these ions.

Which phrase describes the molarity of a solution?

• liters of solute per mole of solution

• liters of solution per mole of solution

• moles of solute per liter of solution

• moles of solution per liter of solution

Answer explanation

Molarity is defined as the number of moles of solute per liter of solution. Therefore, the correct phrase is 'moles of solute per liter of solution', which accurately describes how molarity is calculated.

The concentration of a solution can be expressed in

• milliliters per minute

• parts per million

• grams per kelvin

• joules per gram

Answer explanation

The concentration of a solution is commonly expressed in parts per million (ppm), which indicates the amount of solute in a million parts of solution. Other options like milliliters per minute or joules per gram do not represent concentration.

Tags

NGSS.HS-PS1-5

Two substances in a mixture differ in density and particle size. These properties can be used to

• separate the substances

• chemically combine the substances

• determine the freezing point of the mixture

• predict the electrical conductivity of the mixture

Answer explanation

The differing density and particle size of the substances allow for physical separation methods, such as filtration or sedimentation, making 'separate the substances' the correct choice.

A solution consists of 0.50 mole of CaCl₂ dissolved in 100. grams of H₂O at 25°C. Compared to the boiling point and freezing point of 100. grams of H₂O at standard pressure, the solution at standard pressure has

• a lower boiling point and a lower freezing point

• a lower boiling point and a higher freezing point

• a higher boiling point and a lower freezing point

• a higher boiling point and a higher freezing point

Answer explanation

The presence of CaCl₂ increases the boiling point (boiling point elevation) and decreases the freezing point (freezing point depression) of the solution compared to pure water. Thus, the solution has a higher boiling point and a lower freezing point.

A mixture consists of sand and an aqueous salt solution. Which procedure can be used to separate the sand, salt, and water from each other?

• Evaporate the water, then filter out the salt.

• Evaporate the water, then filter out the sand.

• Filter out the salt, then evaporate the water.

• Filter out the sand, then evaporate the water.

Answer explanation

To separate the components, first filter out the sand, which is solid and insoluble. Then, evaporate the water to obtain the salt, which dissolves in the water. This method effectively separates all three components.

According to Reference Table F, which of these compounds is most soluble at 298 K and 1 atm?

• AgNO₃

• AgCl

• PbCrO₄

• PbCO₃

Answer explanation

AgNO₃ is highly soluble in water, while AgCl, PbCrO₄, and PbCO₃ have low solubility. Therefore, AgNO₃ is the most soluble compound at 298 K and 1 atm.