Which is True About the Dissolving Process in Water

3.3: The Dissolving Process

Learning Outcomes

• Define a solution and describe the parts of a solution.
• Describe how an aqueous solution is formed from both ionic compounds and molecular compounds.
• Recognize that some compounds are insoluble in h2o.
• Depict the differences amidst strong electrolytes, weak electrolytes, and nonelectrolytes.

Forming a Solution

When one substance dissolves into another, a solution is formed. A
solution

is a homogenous mixture consisting of a solute dissolved into a solvent.

The
solute

is the substance that is being dissolved,

while the
solvent

is the dissolving medium
. Solutions tin can be formed with many different types and forms of solutes and solvents. In this chapter, we will focus on solution where the solvent is h2o. An
aqueous solution

is h2o that contains 1 or more dissolved substance.

The dissolved substances in an aqueous solution may exist solids, gases, or other liquids.

In order to exist a true solution, a mixture must be stable. When carbohydrate is fully dissolved into h2o, it can stand for an indefinite corporeality of time, and the sugar volition non settle out of the solution. Further, if the sugar-water solution is passed through a filter, information technology will remain with the h2o. This is considering the dissolved particles in a solution are very small, usually less than $$ane \: \text{nm}$$ in diameter. Solute particles can exist atoms, ions, or molecules, depending on the type of substance that has been dissolved.

The Dissolving Process

Water typically dissolves most ionic compounds and polar molecules. Nonpolar molecules, such as those found in grease or oil, practise not dissolve in h2o. We will first examine the process that occurs when an ionic compound, such equally table common salt (sodium chloride), dissolves in h2o.

Water molecules move nigh continuously due to their kinetic energy. When a crystal of sodium chloride is placed into water, the water’s molecules collide with the crystal lattice. Call back that the crystal lattice is equanimous of alternating positive and negative ions. Water is attracted to the sodium chloride crystal because water is polar; it has both a positive and a negative end. The positively charged sodium ions in the crystal attract the oxygen end of the water molecules because they are partially negative. The negatively charged chloride ions in the crystal attract the hydrogen end of the water molecules because they are partially positive. The activeness of the polar water molecules takes the crystal lattice apart (see figure below).

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After coming apart from the crystal,
the individual ions are and then surrounded by solvent particles in a process called

solvation. Note in the figure in a higher place that the individual $$\ce{Na^+}$$ ions are surrounded by water molecules with the oxygen atom oriented near the positive ion. Also, the chloride ions are surrounded past water molecules with the opposite orientation.
Hydration

is the procedure of solute particles being surrounded by water molecules bundled in a specific manner
. Hydration helps to stabilize aqueous solutions by preventing the positive and negative ions from coming back together and forming a precipitate.

Table saccharide is made of the molecular compound sucrose $$\left( \ce{C_{12}H_{22}O_{11}} \correct)$$. Solid carbohydrate consists of individual sugar molecules held together by intermolecular attractive forces. When water dissolves saccharide, it separates the individual sugar molecules by disrupting the attractive forces, but it
does not suspension the covalent bonds
between the carbon, hydrogen, and oxygen atoms. Dissolved sugar molecules are too hydrated. The hydration shell around a molecule of sucrose is bundled and so that its partially negative oxygen atoms are well-nigh the partially positive hydrogen atoms in the solvent, and vice versa.

Insoluble Compounds

Non all compounds deliquesce well in water. Some ionic compounds, such equally calcium carbonate $$\left( \ce{CaCO_3} \right)$$ and silver chloride $$\left( \ce{AgCl} \right)$$, are nearly insoluble. This is considering the attractions between the ions in the crystal lattice are stronger than the allure that the water molecules have for the ions. Every bit a effect, the crystal remains intact. The solubility of ionic compounds can be predicted using the solubility rules equally shown in Table $$\PageIndex{ane}$$.

Tabular array $$\PageIndex{1}$$:
Solubility rules for ionic compounds in water.

Nonpolar compounds also do non dissolve in water. The attractive forces that operate between the particles in a nonpolar compound are weak dispersion forces. In order for a nonpolar molecule to dissolve in water, it would need to pause up some of the hydrogen bonds between next water molecules. In the case of an ionic substance, these favorable interactions are replaced past other bonny interactions between the ions and the partial charges on h2o. However, interactions between nonpolar molecules and water are less favorable than the interactions that water makes with itself. When a nonpolar liquid such as oil is mixed with water, two split up layers form, considering the liquids will not dissolve into each other (run across figure below). When a polar liquid like ethanol is mixed with water, they completely blend and deliquesce into one another.
Liquids that dissolve in one another in all proportions are said to be

miscible
.
Liquids that practice not deliquesce in one another are called

immiscible. The full general rule for deciding if one substance is capable of dissolving another is “like dissolves like”, where the property being compared is the overall polarity of the substance. For example, a nonpolar solid such every bit iodine will dissolve in nonpolar lighter fluid, but it will not deliquesce in polar h2o.

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Electrolytes and Nonelectrolytes

An
electrolyte
is a compound that conducts an electrical current when it is dissolved in water or melted.
In order to comport a current, a substance must contain mobile ions that can move from one electrode to the other. All ionic compounds are electrolytes. When ionic compounds deliquesce, they intermission apart into ions, which are then able to conduct a electric current. Fifty-fifty insoluble ionic compounds, such as $$\ce{CaCO_3}$$, are considered electrolytes considering they can behave a current in the molten (melted) state.

A
nonelectrolyte

is a chemical compound that does not conduct an electric electric current in either aqueous solution or in the molten land.

Many molecular compounds, such a carbohydrate or ethanol, are nonelectrolytes. When these compounds dissolve in water, they exercise not produce ions. Illustrated beneath is the difference betwixt an electrolyte and a nonelectrolyte.

Dissociation

Earlier, you saw how an ionic crystal lattice breaks autonomously when it is dissolved in h2o.
Dissociation
is the separation of ions that occurs when a solid ionic compound dissolves. But undo the crisscross method that y’all learned when writing chemical formulas for ionic compounds, and you are left with the components of an ionic dissociation equation. The subscripts for the ions in the chemical formulas become the coefficients of the respective ions on the product side of the equations. Shown below are dissociation equations for $$\ce{NaCl}$$, $$\ce{Ca(NO_3)_2}$$, and $$\ce{(NH_4)_3PO_4}$$.

\begin{marshal} &\ce{NaCl} \left( s \right) \rightarrow \ce{Na^+} \left( aq \right) + \ce{Cl^-} \left( aq \correct) \\ &\ce{Ca(NO_3)_2} \left( southward \correct) \rightarrow \ce{Ca^{2+}} \left( aq \correct) + 2 \ce{NO_3^-} \left( aq \right) \\ &\ce{(NH_4)_3PO_4} \left( s \right) \rightarrow three \ce{NH_4^+} \left( aq \right) + \ce{PO_4^{three-}} \left( aq \right) \end{align}

1 formula unit of measurement of sodium chloride dissociates into 1 sodium ion and one chloride ion. The calcium nitrate formula unit of measurement dissociates into one calcium ion and 2 nitrate ions, because the $$2+$$ accuse of each calcium ion requires two nitrate ions (each with a charge of $$ane-$$) to form an electrically neutral chemical compound. The ammonium phosphate formula unit dissociates into three ammonium ions and one phosphate ion.

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Do non confuse the subscripts of the atoms within the polyatomic ion for the subscripts that result from the crisscrossing of the charges that brand the original chemical compound neutral. The 3 subscript of the ntirate ion and the 4 subscript of the ammonium ion are role of the polyatomic ion and remain a role of the ionic formula after the chemical compound dissociates. Detect that the compounds are solids $$\left( s \correct)$$ that become ions when dissolved in water, producing an aqueous solution $$\left( aq \right)$$.

Nonelectrolytes do non dissociate when forming an aqueous solution. An equation can all the same be written that merely shows the solid going into solution. For example, the process of dissolving sucrose in h2o can be written as follows:

$\ce{C_{12}H_{22}O_{11}} \left( s \right) \rightarrow \ce{C_{12}H_{22}O_{eleven}} \left( aq \right)$

Potent and Weak Electrolytes

Some polar molecular compounds are nonelectrolytes when the are in their pure state merely get electrolytes when they are dissolved in h2o. Hydrogen chloride $$\left( \ce{HCl} \right)$$ is a gas in its pure molecular land and is a nonelectrolyte. However, when $$\ce{HCl}$$ is dissolved in water, it conducts a current well because the $$\ce{HCl}$$ molecule ionizes into hydrogen and chloride ions.

$\ce{HCl} \left( grand \right) \rightarrow \ce{H^+} \left( aq \right) + \ce{Cl^-} \left( aq \right)$

When $$\ce{HCl}$$ is dissolved into water, information technology is called hydrochloric acid. Ionic compounds and some polar compounds are completely broken apart into ions and thus conduct a electric current very well. A
potent electrolyte
is a solution in which about all of the dissolved solute exists every bit ions.

Another polar molecular compounds become electrolytes upon being dissolved into water but do non ionize to a very great extent. For example, nitrous acid $$\left( \ce{HNO_2} \right)$$ only partially ionizes into hydrogen ions and nitrite ions when dissolved in water. Aqueous nitrous acrid is composed of only virtually $$5\%$$ ions and $$95\%$$ intact nitrous acrid molecules A
weak electrolyte
is a solution in which just a minor fraction of the dissolved solute exists as ions. The equation showing the ionization of a weak electrolyte utilizes an equilibrium arrow, indicating an equilibrium between the reactants and products.

$\ce{HNO_2} \left( aq \right) \rightleftharpoons \ce{H^+} \left( aq \right) + \ce{NO_2^-} \left( aq \correct)$

Contributors and Attributions

• Allison Soult, Ph.D. (Department of Chemistry, University of Kentucky)

Which is True About the Dissolving Process in Water

Source: https://chem.libretexts.org/Courses/Brevard_College/CHE_104%3A_Principles_of_Chemistry_II/03%3A_Solutions_and_Colloids/3.03%3A_The_Dissolving_Process