Solutions

What is a solute?

when liquids make weak intermolecular bonds to chemically different molecules

What is a solvent?

the liquid that solutes are dissolved in

What is a solution?

When solutes dissolve in the solvent when they are mixed together (the solvent dissolves the solute)

What does the power of the solvent to dissolve the solute depend on?

the attraction and chemical properties:

• solute-solvent attraction, the molecules can easily move around each other and therefore easily dissolved

• solute-solute and solvent-solvent attraction, the molecules are harder to break apart so it is difficult to dissolve in

What is concentration?

It is the amount of substance there is per volume in the solution

What is molarity?

Number of moles/volume (M or mol / dm³)

What is molality?

number of moles of solute dissolved per one kilogram of solvent (m or mol / kg)

When do we use molality?

when we are testing in different temperatures since density and volume is not constant. However, mass is always constant

What is percentage by weight?

Usually used for solid solutes, it measures the weight of solute as a percentage of weight of solution

What is percentage by volume?

Usually used for liquid solutes, it measures the volume of the solute as a percentage of volume of solution

What is parts per million (ppm)?

used for very small concentrations

Difference between concentrated and dilute?

Concentrated is when a solution has a lot of solute, diluted is when a concentration has little solute. These terms are relative so it would depend on the solution

What is a saturated solution?

It is a solution that cannot dissolve anymore

What is solubility?

The ability of a solute to dissolve in a solvent

Difference between soluble and insoluble?

Soluble is when a solute can easily dissolve into a solvent, insoluble is when a solute cannot easily dissolve into a solvent. These terms are relative, so it depends what they mean

When will a solution be saturated?

For each solute, they have a maximum solubility and when this maximum solubility is reached they cannot dissolve anymore. (e.g. sucrose has a maximum solubility of 130 g / dm³ so once this is reached, it cannot dissolve anymore)

What is a precipitate?

When a solution has already reached maximum solubility, and some solvent is evaporated or taken away, the solute will form a precipitate so that the solution can maintain its maximum concentration. (the solvent can only hold a maximum concentration so if that is exceeded, some of the solute forms a solid which is the precipitate)

What are the solubility implications of using CO2?

CO2 easily dissolves in water to create H2CO3 (carbonic acid) which can decrease the pH and make water more acidic

What are the solubility implications of using calcium carbonate (CaCO3)?

CaCO3 are found in limestones, coral reefs and concrete. CaCO3 does not dissolve well in pure water, but when it reacts with carbonic acid, it forms calcium bicarbonate (Ca(HCO3)2) which dissolves easily in water

What are solubility implications in limestone caves?

The limestones are made of CaCO3 and rainwater contains H2CO3 to form stalactites and stalagmites. However, the CO2 of people visiting can mix with the CaCO3 which dissolve these formations and could create sinkholes

What are the solubility implications of coral reefs?

Coral reefs are made of CaCO3 and the increasing CO2 in our atmospheres makes the sea more acidic due to the formation of H2CO3 and dissolve the coral reefs

What are the solubility implications of concrete?

Concrete can often have CaCO3 in the structure and the carbonic acid can weaken this structure often making sinkholes

At a higher temperature, do solids have a higher solubility?

Yes, solid solutes are more likely to dissolve to a more disordered state

At a higher temperature, do gases have a higher solubility?

No, gas solutes are less likely to dissolve as they are already in a disordered state

Why are there some random changes in solubility?

This means that a chemical reaction most likely happened and it has changed states or phases

How is pressure related to solubility?

Increasing pressure increases solubility, however, it mostly only happens in gaseous solutions (higher pressure means more opportunity for the molecules to collide and react with each other)

Why do solutions have elevated boiling points?

When a pure liquid is boiling, the solvent molecules can get into the air and have a set vapor pressure. When solutes dissolve into a solvent, they take the energy of solvent molecules so the solvent molecules cannot dissolve into the air meaning lower vapor pressure and therefore takes longer for the solution to reach boiling point

Why do solutions have depressed melting points?

Normally, pure solvent would line up to create a solid crystal, however, the solutes get in the way and prevent this from happening needing it to be colder for the solution to freeze. In the end, the solutes don’t freeze and only the pure solvent does, the solute stays in the liquid

What happens in osmosis?

A semi-permeable membrane only allows water molecules to go through. However, one side has more solute concentration and the other is lesser solute concentration. The water moves from high concentration (low solute) to low concentration (high solute). This is because in low solute concentration, more water is touching the surface of membrane thus can pass to other side. The water then keeps moving till it is equal.

What is an emulsion?

A mixture of oil and water that normally wouldn’t mix

What are the parts of a surfactant?

It has a hydrophilic head that likes water and a hydrophobic tail that hates water but likes oil and dirt. When washing oil of a pan, the oil sticks to the tails and the head cover the tail inside so that the outside is only the hydrophilic head (this circular structure is called micelle) which then get washed away.