Liquids and Solutions - College Chemistry

Most salts containing halogens are soluble. Carbonates, phosphates, sulfides, oxides, and hydroxides are insoluble except for cations containing alkaline earth metals and hydroxides of calcium, strontium, and barium, which are slightly soluble.

Start by writing the equation for the dissolution of calcium hydroxide.

Next, set up the following table to show the equilibrium concentrations of the ions:

| | \[ \] | \[\] | | | -------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------- | ---- | | Initial | 0.00 | 0.00 | | Change | +S | +2S | | Equilibrium | S | 2S |

Now substitute in the values of the concentrations of the ions into the expression to find .

Now, plug in the given value and solve for , the molar solubility.

For this question, we're told that an aqueous solution of magnesium fluoride is saturated. We're then told that the fluoride concentration in the solution is reduced by a factor of two, and we're asked to find how the magnesium concentration would need to change in order to keep the solution saturated.

First, it's important to recall what saturation means. Some substances cannot dissolve in water, whereas others can dissolve readily. In other words, different substances will dissolve to differing degrees in water. The dissolution of a compound in a solvent such as water can be represented by an equilibrium expression. When there is a relatively small amount of solute added, the solution is said to be unsaturated. This means that all of the added solute will dissolve. As more and more solute is added to the water, there will eventually reach a point at which so much solute is present that it can no longer dissolve. When this happens, any additional solute will not dissolve and will instead form a precipitate in the solution. This condition is referred to as supersaturated. Saturation is the "sweet spot" so to speak; it is the point in between unsaturated and supersaturated where the maximum amount of solute has been added to the solution where all of the solute can be in the dissolved form. In other words, saturation refers to the maximum concentration of added solute where there is NO precipitation.

In order to set up an equilibrium expression, we can first write out the reaction in which magnesium fluoride dissolves.

Knowing the reaction, we can now write an equilibrium expression. Remember that pure solids and liquids don't appear in equilibrium expressions! Thus, this expression will only contain the products of the above reaction.

In the above expression, refers to the solubility product constant, which is just a quantitative way of expressing the degree to which a given compound can dissolve within a given solvent.

Since the equilibrium expression tells us the concentrations necessary to have a saturated solution, we can determine how a change in fluoride concentration would affect the equilibrium. Then, we can determine what changes to magnesium are needed.

If the fluoride concentration were to be cut in half, the value would be decreased by a factor of . This means that in order to maintain the value, we would have to increase the magnesium concentration by a factor of in order to compensate for the loss of fluoride.

In this question, we're asked to identify an answer choice that would be expected to give us a solution with the greatest osmotic pressure. Remember that osmotic pressure is proportional to the total number of dissolved solute particles in solution, regardless of the identity of those solute particles.

When looking at the answer choices, we need to keep in mind two things. First, we need to recognize the numerical value given for the concentration of the compound given. Secondly, we need to identify if the compound shown is capable of dissociating in solution to give rise to even more solute particles. This is important, as it would affect the osmotic pressure.

would be expected to have the largest osmotic pressure because, in total, this would be a solution after dissociation occurs.

Colligative properties are properties of solutions which depend on the number of dissolved particles in solution. The four main colligative properties are:

1. Freezing point depression: The presence of a solute lowers the freezing point of a solution as compared to that of the pure solvent.

2. Boiling point elevation: The presence of a solute increases the boiling point of a solution as compared to that of the pure solvent.

3. Vapor pressure depression: The vapor pressure of a pure solvent is greater than that of a solution containing a non-volatile liquid. The lowering of vapor pressure leads to boiling point elevation.

4. Osmotic pressure: The osmotic pressure of a solution is the pressure difference between the solution and pure solvent when the two are in equilibrium across a semipermeable membrane. Because it depends on the concentration of solute particles in solution, it is a colligative property.

Electronegativity is not a property of solutions reliant on the number of dissolved particles, but a property of atoms themselves.

This question is asking us to identify a solution that increases the boiling point of water by the greatest amount.

To answer this, we need to understand the concept of colligative properties. When a solute dissolves in a solvent such as water, various physical properties are affected. The four colligative properties that change as a result of the addition of solute are freezing point, boiling point, vapor pressure, and osmotic pressure.

With regards to boiling point, as more solute is added to a solution, the boiling point increases. This is due to the fact that addition of solute makes it more difficult for the solute molecules to gain enough kinetic energy at the solution's surface to escape as a gas.

Furthermore, the identity of the solute does not matter. Thus, we need to look only at the number of dissolved solute particles rather than their identity. A compound such as sucrose will not dissociate in solution, which means that the osmotic pressure of the solution is the same as the concentration of sucrose.

Compounds that can dissociate into two or more particles will increase the osmolarity of the solution further. In this case, will double the stated osmolarity. , on the other hand, will dissociate completely because it is a strong acid, however the protons will not contribute to the osmolarity.

is able to dissociate into three equivalents of particles in solution. Thus, its initial concentration will be tripled, which gives it the highest osmolarity of any of the choices shown and will thus increase the boiling point by the greatest amount.

Recall how to find the molality of a solution:

First, start by finding the moles of glucose that we have. The molar mass of glucose is .

Next, convert the grams of water into kilograms.

Now, plug in the moles of glucose and kilograms of water into the equation for molality.

Start by assuming that we have of this solution. Recall that hydrogen peroxide has a molecular formula of .

Use the given density to find the mass of the solution.

Next, find the mass of the hydrogen peroxide present in the solution.

Convert the mass of hydrogen peroxide into moles of hydrogen peroxide.

Recall how to find the molarity of a solution:

Since we have of solution, the molarity is .

sodium hydrogen carbonate dissolved in a solution has .

The first step is to calculate how many moles of are present.

We calculate molarity with the following equation:

of solution are needed to prepare of .

We can use the formula

Therefore,

The relative concentrations of aluminum sulfate are

Molarity moles of solute per liter of solution.

We are given that there are of and of solution.

First lets convert the of solution to liters. It is easiest to use scientific notion in all calculations for easy simplification:

=

Now we must convert of to moles to get moles of solute per liter of solution.

This is done by dividing by its molecular weight which is . Once again we can use scientific notion to simplify calculations:

Now we can divide by solution to get the molarity.

Molality () is defined as moles of solute per kg of solvent.

is the solute (it is what is being dissolved) and water is the solvent (what is doing the dissolving).

Let’s start converting of to moles by dividing by its molecular weight using scientific notion through the entire molality calculations as necessary to simplify calculations.

Now we must convert the of water to then divide by it to get the molality:

Molality of solution:

=

In order to solve for the volume of water needed we must use this equation:

solve for since we are looking for the final volume of water needed to dilute the existing solution:

Molarity, molality, and normality are all units of concentration in chemistry. Molarity () is defined as the number of moles of solute per liter of solution. Molality () is defined as the number of moles of solute per kilogram of solvent. Normality () is defined as the number of equivalents per liter of solution. Molality, as compared to molarity, is also more convenient to use in experiments with significant temperature changes. This is because the volume of a solution increases with temperature, and heating causes molarity to decrease; however, since molality is based on masses rather than volumes, molality remains unchanged.

By definition, viscosity is the measure of a liquid's resistance to flow. If a liquid has a low viscosity, it has a low resistance to flow. It may not necessarily always have a low boiling point, melting point, and/or vapor pressure due to this characteristic. Viscosity is just a way to measure and describe one physical characteristic (resistance to flow) of a liquid. The volume of a liquid does not say anything about its physical properties.

Start by writing out the the chemical formulas for the reactants:

In order to figure out the possible products, combine the cation of one molecule with the anion of the other molecule.

For this reaction, the possible products are and .

Next, use solubility rules to figure out if any precipitate is formed. Since compounds with are soluble, is soluble. Since is only soluble when paired with , is insoluble.

Thus, we can write the final chemical equation:

Recall the solubility rules:

is generally soluble, except when paired with .

Solubility rules can help us find the answer to this question.

First, solubility rules state that all compounds of Group 1A elements on the periodic table are soluble in aqueous solution. This means that all of the alkali metals, including potassium, form compounds which are soluble in aqueous solution; thus, is soluble in aqueous solution.

Solubility rules also tell us that all ammonium salts (salts of ) are soluble. This means that is soluble.

Next, solubility rules tell us that all bromide salts are soluble, except for those of , , and . Thus, is not soluble in aqueous solution. However, as lithium is not included in that list, is soluble in aqueous solution.