SOLUTIONS - SOLIDS SOLUBILITY AND IONS IN WATER

Question 1

Define:

1. Solute
2. Solvent
3. Solution

Answer 1

1. The substance that dissolves in a solvent to produce a homogeneous mixture
2. The substance in which a solute dissolves to produce a homogeneous mixture
3. A solution is a homogenous mixture in which one substance (the solute) is dispersed in another substance (the solvent)

Question 2

Describe saturated, unsaturated, and supersaturated solutions

Answer 2

Saturated solution: Any solution which contains the max amount of solute for that given solvent at a given temp, additional solute will not dissolve

Unsaturated solution: Any solution containing less than the max amount of solute at a given temp, will also appear as a dissolved solution

Supersaturated solution: Any solution which contains more than the max amount of solute at a given temp, precipitate in solution will be observed

Question 3

Why is water an effective solvent?

Answer 3

Water is the most common convent, it is polar (dissolves other polar solutes)

Good at dissolving ionic substances and polar covalent but poor at dissolving non-polar substances

Polar covalent molecules dissolve because they are solvated by H-bonds or by dipole-dipole forces

Because of + and – charges, they will readily dissolve in water as the positive regions of the ion lattice will attract the negative oxygens in the water molecules

Similarly, negative regions of the ion lattice will attract the + H atoms in the water molecule

Question 4

Explain endothermic and exothermic processes in solubility

Answer 4

In exothermic reactions, heat energy from bonds breaking and forming is released and so adding more energy (heat) will cause the system to favour the reverse reaction (Le Chatelier’s Principle) and the solubility will decrease

In endothermic reactions, heat energy from the bonds breaking and forming is absorbed. Thus, adding heat will increase the solubility

Question 5

What is solubility and how is it expressed?

Answer 5

Dissolving a solid depends on the collisions between the solvent molecules and the solid molecules. Solubility is the maximum amount of a solid which will dissolve in a given amount of a particular solvent

Solubility is usually expressed in g of solute per 100g of solvent (e.g., 6g/100g)

If a substance is not soluble in something else, we say it is insoluble

Question 6

Describe the effects of temperature and pressure on solubility

Answer 6

Temperature:
Solubility of solids in liquids generally increases as the temp increases. Solubility of gases in liquids almost always decreases as temp increases

Pressure:
Has little effect on solubility of solids and liquids but it has a considerable effect on the solubility of gas in liquids. The solubility of gas in liquid increases as the pressure increases (Henry’s law)

Question 7

Are all salts soluble?

Answer 7

No, salts are all ionic compounds (they are all composed of an ionic structure of cations and anions)

Mostly salts are soluble but there are a few exceptions

Only a salt containing a soluble cation or anion will dissolve in water

Question 8

What are electrolytes?

Define normal, weak and strong

Answer 8

Ions dissolved in water can migrate from one place to another, maintaining their charge as they migrate

Electrolyte: a substance that conducts electric current when dissolved in water. A substance that does not conduct electricity is called a non-electrolyte

Strong Electrolyte: A compound that dissociates completely to ions in an aqueous solution

Weak Electrolyte: A compound that only partially dissociates to ions in an aqueous solution

Question 9

What is an equivalent?

Answer 9

The amount of + or - ion that supplies 1 mole of electrons electrical charge

Question 10

What is a colloid?

Answer 10

Colloid particles have very large surface areas, they appear turbid, cloudy, or milky

They form stable dispersions,

Question 11

What is the Tyndall effect

Answer 11

A phenomenon in which light passing through a colloid or suspension is scattered by colloidal-sized particles

Question 12

Brownian motion

Answer 12

The random motion of colloid-size particles. Examples of Brownian motion are the motion of dust particles in the air

Question 13

What are suspensions?

Answer 13

Suspensions have the largest particles, the particles are too large to be stable and dispersed through the solution and so they often settle as a heterogenous layer

They have unstable dispersions

Question 14

How do you work out the percent composition of a solution?

Answer 14

% comp = amount of solute / amount of solution x100

Question 15

How do you work out molarity?

Answer 15

Molarity and concentration = moles of solute (n) / volume of solution (v)

Question 16

How can you use molarity to conduct accurate dilutions?

Answer 16

We can use molarity to conduct accurate dilutions, moles (n) = concentration (c) x volume (v)

If we dilute a solution, the number of moles of solute remains the same after dilution. This results in the following relationship:
Moles (n) = concentration of initial solution (c1) x initial volume of solution (v1) = concentration of final solution (c2) x final volume of solution (v2)

Question 17

What is tonicity?

Answer 17

The ability of a solution to make water move in and out of a cell using osmosis is referred to as the tonicity of the solution

A hypertonic solution is one which contains a greater concentration of particles

A hypotonic solution contains a lower concentration of particles

An isotonic solution is when the concentration of particles remains the same