Chapter 6 Solutions and Other Mixtures

Chapter 6: Solutions and Other Mixtures A mixture is a combination of several substances that do not form a chemical reaction and can be separated into their individual parts. An example is this classroom. It is a mixture of boys, girls, age, ethnicity, etc. that could be physically separated.

Chapter 6: Solutions and Other Mixtures Heterogeneous mixtures are unevenly combined. The composition of these mixtures vary throughout the sample. If you have a box of Fruity Pebbles, you can separated it by size, color, shape etc. It is unevenly mixed.

Chapter 6: Solutions and Other Mixtures Many heterogeneous solutions are suspensions. Italian dressing, sand and water, some orange juices are examples. When agitated (stirred or shaken) everything mixes evenly, but if left alone, it settles into layers.

Chapter 6: Solutions and Other Mixtures The heavier (denser) the particle, the faster it settles. If the particles are smaller, they often do not settle into layers, but remain dispersed in another substance. These are called colloids or colloidal suspensions.

Chapter 6: Solutions and Other Mixtures An example is Jell-O. The particles are so small they do not settle out, but remain spread out. Paint is made of tiny particles of pigment (colored) solids suspended in a liquid. Blood is another example. It is made of many different types of solids.

Chapter 6: Solutions and Other Mixtures Some liquids form suspensions also. A common example is water and oil. If you mix water and oil they do not combine unless you keep shaking them.

Chapter 6: Solutions and Other Mixtures Often, if care is taken, liquid suspensions can be separated by carefully pouring off the less dense liquid and leaving the denser behind. Liquids that cannot be combined are called immiscible. Immiscible liquids will eventually separate.

Chapter 6: Solutions and Other Mixtures This is why Italian dressing needs to be shaken, not stirred before going on a salad and why many other things must be mixed well before being used.

Chapter 6: Solutions and Other Mixtures Sometimes, immiscible liquids can be forced to combine into an emulsion. An emulsion is any mixture of immiscible liquids in which the liquids are spread throughout one another. Mayonnaise, cream, butter, are examples.

Chapter 6: Solutions and Other Mixtures Mayonnaise is a mixture of vinegar and oil emulsified by egg yolk. Homemade mayonnaise is easy if done correctly. Add oil to vinegar and egg yolks slowly while whipping constantly. Other seasonings can be added to make unique flavors.

Chapter 6: Solutions and Other Mixtures Solutions-a homogeneous mixture of two or more substances uniformly spread out. Solute-the substance that dissolves, Solvent-the substance that dissolves the solute to make the solution.

Chapter 6: Solutions and Other Mixtures Homogeneous mixtures not only look uniform, but are uniform or evenly mixed. Sugar water or salt water are good examples. The solids (solutes) are so small that the liquid (solvent) keeps the particles constantly moving.

Chapter 6: Solutions and Other Mixtures According to Kinetic theory, molecules are always moving. As these molecules move, they collide with other molecules and impart some of their energy to those they hit. If water molecules hit a sugar molecule, they move that sugar.

Chapter 6: Solutions and Other Mixtures If the sugar is a large molecule, it takes many repeated hits to dissolve. Thus, the more surface area available, the faster something will dissolve. Loose sugar granules will dissolve faster than compact sugar cubes.

Chapter 6: Solutions and Other Mixtures Stirring a solution adds kinetic energy into the solution. By adding energy, the molecules move faster and collisions occur more often. As the collisions occur, they impart energy and speed the rate of dissolving.

Chapter 6: Solutions and Other Mixtures The more you stir or agitate as solution, the more solute will enter the solution. Temperature also affects the solubility rate of a solution. The warmer the solution, the more solute will be dissolved.

Chapter 6: Solutions and Other Mixtures Concentration is used to state how much solute in grams is dissolved into a given quantity of solvent in grams. grams(solute)/100 grams(solvent) A dilute solution is a small amount of solute in a large amount of solvent.

Chapter 6: Solutions and Other Mixtures A concentrated solution is a large quantity of dissolved solute. An unsaturated solution can dissolve more solute. A saturated solution cannot dissolve any more solute under the current conditions.

Chapter 6: Solutions and Other Mixtures Pressure affects how much solute can enter a solution. Some solutes require high pressure to enter into a solution, some require low pressure. An example that we see everyday is in carbonated beverages.

Chapter 6: Solutions and Other Mixtures The bubbles are CO2 molecules that have been dissolved into very cold liquid soda syrup. As the temperature increases, the ability of the syrup to hold the CO2 in solution decreases. Once the top is removed, the pressure tries to equalize.

Chapter 6: Solutions and Other Mixtures Water is sometimes called the universal solvent. Water is not an ionic compound, but it is polar. This means that it has a slightly positive charge at one end and a slightly negative charge at the other.

Chapter 6: Solutions and Other Mixtures This polarity helps explain why water can dissolve so many compounds. Most substances that dissolve in water have slight charges that line up with water without reacting.

Chapter 6: Solutions and Other Mixtures Chemists have a saying “like dissolves like” to decide if water will dissolve something. A polar molecule like methane will dissolve in water whereas a non-polar molecule like gasoline is immiscible.

Chapter 6: Solutions and Other Mixtures Gasoline will mix with oil whereas methane will not. The partial charges have their own symbols—lower case Greek delta (δ)—to indicates slight charge: positive= δ+ negative= δ-

Chapter 6: Solutions and Other Mixtures A solution is unsaturated if more solute can be dissolved. A saturated solution is in equilibrium. No more solute can be added.

Chapter 6: Solutions and Other Mixtures Solubility is the greatest quantity of solute that will dissolve in a given amount of solvent to produce a saturated solution. If you heat a saturated solution, you can add more solute. As it cools, the excess solute remains in the solution. This is called a supersaturated solution.

Chapter 6: Solutions and Other Mixtures However, it is often unstable and adding more solute can have impressive affects. If you have a supersaturated solution of sodium acetate and add a tiny amount of solute, the sodium acetate drops from solution in a brilliant, crystalline form.

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Chapter 6: Solutions and Other Mixtures Dilute, concentrated, unsaturated, saturated, or supersaturated are often not as accurate as you need.

Chapter 6: Solutions and Other Mixtures Exact amounts of solute in the solvent often needed for many experiments. Molarity is used to figure out precisely the ratio of solute to solvent. Molarity= moles of solute/liters of solution M= mol/ L

Chapter 6: Solutions and Other Mixtures A 1.0 M (1 molar) solution of NaCl contains 1.0 mol of dissolved NaCl for every 1.0 L of solution. Chemists prefer molarity since it expresses the molar amount of solute present.

Chapter 6: Solutions and Other Mixtures Acids are substances that donate hydrogen ions to form hydronium ions when dissolved in water. H+ + H2O  H3O+ Bases are substances that either contain OH- or react with water to form OH- ions.

Chapter 6: Solutions and Other Mixtures Acids turn blue litmus paper red, bases turn red litmus paper blue. Litmus paper is an pH indicator. pH is the concentration of hydronium ions in the solution. Acids taste sour and bases taste bitter.

Chapter 6: Solutions and Other Mixtures All acids conduct electricity because of hydronium ions. Strong acids fully ionize in water. The reaction is one way. Weak acids do not fully ionize in water and the reaction goes both ways.

Chapter 6: Solutions and Other Mixtures Acids and bases can be dangerous. All bases conduct electricity because of hydroxide ions. Strong bases ionize fully in water. The reaction is one way. Weak bases do not fully ionize in water and the reaction goes both ways.

Chapter 6: Solutions and Other Mixtures Strong acid: HNO3 + H2O  NO3- + H3O+ nitric acid water nitrate ion hydronium ion Weak acid: CH3COOH + H2O CH3COO- + acetic acid water acetate ion H3O+ hydronium ion Strong base: KOH  K+ + OH- potassium hydroxide potassium ion hydroxide ion Weak base: NH3 + H2O NH4+ + OH- ammonia water ammonium ion hydroxide ion

Chapter 6: Solutions and Other Mixtures The pH of a solution indicates the concentration of hydronium ions, but it also can indicate the concentration of hydroxide ions. Using a pH indicator can tell you if something is an acid, base, or neutral solution.

Chapter 6: Solutions and Other Mixtures Typically pH ranges from 0 to 14 with neutral being 7. Acids range from 0 to 6.9 and bases range from 7.1 to 14.

Chapter 6: Solutions and Other Mixtures Each whole number unit of pH represents a factor of 10. Thus an acid of 4 is ten times stronger than an acid of 5. A universal pH indicator strip will show a color coded pH scale.

Chapter 6: Solutions and Other Mixtures A neutralization reaction is a reaction between hydronium ions and hydroxide ions to create water molecules. The resulting solution is more neutral than the reactants.

Chapter 6: Solutions and Other Mixtures Strong acids and bases react to form water and salts. HCl + H2O  H3O+ + Cl- NaOH  Na+ + OH- H3O++ Cl- + Na++ OH-  Na++ Cl- + 2H2O The Na+ and Cl- ions did not react, only the hydronium and hydroxide ions reacted.

Chapter 6: Solutions and Other Mixtures If you excluded the non-reactants, the equation is much simpler: H3O+ + OH-  2H2O Salts are ionic compounds that are often soluble in water.

Chapter 6: Solutions and Other Mixtures Some acid-base reactions do not neutralize because of pH differences or quantity differences. Strong bases/weak acids or strong acids/ weak bases only partially neutralize. A strong acid/weak base may have a higher pH and still be acidic. A large quantity of a weak base would be to added to neutralize a strong acid.

Chapter 6: Solutions and Other Mixtures Because of the reactivity between acids and bases, never combine household cleaners. Soaps are emulsifiers. They have glycerol chain (—COO-) that is negatively charged that can combine with oils and greases and water. They allow immiscible substances to dissolve. This is why soaps clean.

Chapter 6: Solutions and Other Mixtures Detergents are non-soap water-soluble cleaners that remove dirt and oils. They have a sulfonate group (—SO3-) that can combine with dirt and oil and water to clean.

Chapter 6: Solutions and Other Mixtures Ammonia cleaners have ammonia gas dissolved into solution to remove grease and oils. NH3 + H2O NH4+ + OH- ammonia water ammonium ion hydroxide ion Disinfectants are substances that kill bacteria.

Chapter 6: Solutions and Other Mixtures Bleach is a solution of sodium chlorite. NaClO2, or sodium hypochlorite, NaOCl, in water. Antacids are weak bases that neutralize excess stomach acids. Shampoos are pH balanced hair cleaners.

Chapter 6: Solutions and Other Mixtures Common kitchen acids: apple juice, lemon juice, orange juice, vinegar Common kitchen bases: milk, baking soda, baking powder