Understanding Solutions 7-1

What is a Solution? Solution Solvent Solute Well-mixed mixture that contains a solvent and at least one solute Solvent Part of a solution present in the largest amount Solute Substance that is present in a solution in a smaller amount and is dissolved by the solvent Water is the universal solvent; because it dissolves so many substances.

http://www.wwk.in/chemistry/states-of-matter/solutions

Colloids Mixture containing small, undissolved particles that do not settle A colloid contains larger particles than a solution The particles are too small to be easily seen, but large enough to scatter a light beam http://chemwiki.ucdavis.edu/Physical_Chemistry/Physical_Properties_of_Matter/Solutions_and_Mixtures/Colloid

Suspensions Mixture in which particles can be seen and easily separated by settling or filtration Suspensions do not have the same properties throughout Contains visible particles that are larger than those in solutions or colloids

Particles in Solution When a solution forms, particles of the solute leave each other and become surrounded by particles of the solvent Ionic and molecular solutes Ionic solutes break into ions when they dissolve Molecular solutes break into individual neutral molecules Solutes and Conductivity Solution of ionic compounds conducts electricity Solution of molecular compounds doesn’t conduct electricity

Effects of Solutes on Solvents Solutes lower the freezing point and raise the boiling point of a solvent What are examples of how we use this property? We put salt on roads to prevent ice from forming or to melt it We add salt to water when making pasta, increases the boiling temperature so water is hotter when pastas is cooked

Concentration and Solubility 7-2

Concentration Dilute solution Concentrated solution A mixture that has only a little solute dissolved in it Concentrated solution A mixture that has a lot of solute dissolved in it You can change the concentration of a solution by adding more solute You can add more water to make a more diluted solution

Measuring Concentration To measure concentration, you compare the amount of a solute to the amount of solvent or to the total amount of the solution Measurement is in grams

Sample Problem Rubbing alcohol sold in grocery stores is a mixture of isopropyl alcohol and water. The concentration of a 473.0mL is 70% alcohol by volume. Find the volume of alcohol in the solution. 0.7 x 473.0mL = 331.1 mL

Practice problem #1 What is the concentration of a solution that contains 45 grams of sugar in 500 grams of solution?

Practice Problem #2 How much sugar is dissolved in 500 grams of a solution if the solution is 70 percent sugar by mass?

Solubility Definition: the measurement of how will a solute can dissolve in a solvent at a given temperature Saturated and Unsaturated solutions Saturated: contains as much solute as possible at a given temperature Unsaturated: the solution does not hold as much solute as is possible at the given temperature

http://www.youtube.com/watch?v=mxO9rtVjoR4 http://www.youtube.com/watch?v=1y3bKIOkcmk

Working with Solubility Solubility tells you how much solute you can add before a solution becomes saturated Solubility is a characteristic property of a compound It helps you identify a compound

Changing Solubility Solublities can change depending on conditions Temperature In solids increasing temperature, increases solubility When heated a solute can hold more solute than it can hold at cooler temperatures Supersaturated solution- a mixture that has more dissolved solute than is predicted by its solubility at the given temperature Gases-become less soluble when the temperature goes up

Pressure The higher the pressure, the more gas can dissolve

Which person’s tea will dissolve the sugar faster?

Solvents Ionic and polar covalent compounds usually dissolve Polar and non-polar compounds do not mix very well

Describing Acids & Bases 7-3

Properties of Acids Acids- a substance that tastes sour, reacts with metals and carbonates, and turns blue litmus paper red Sour taste Fruits, tea, spoiled milk Some acids are hard to identify, or may not be safe to eat Not a good way to identify if a solution is an acid

Reactions with carbonates Reactions with indicators Reactions with metals Acids react with certain metal to produce hydrogen gas When reaction takes place, the metals seem to disappear (corrode) Reactions with carbonates Gas forms from adding carbon and an acid Reactions with indicators Litmus paper is an indicator in which changes color If the litmus paper turns red, it is an acid

http://www.youtube.com/watch?v=s0CyLbiwHkg

Properties of Bases Bases- a substance that tastes bitter, feels slippery, and turns red litmus paper blue Bitter tastes: tonic water Slippery feel- think of how your hands feel with water and soap on them Reactions with indicators- bases turn litmus paper blue Reactions of bases-does not react with carbon to form a gas

Uses of Acids and Bases What are some ways we use them? Bases: cleaners, baking Acids: food (tomatoes & oranges), fertilizer, batteries

Acids and Bases in Solution Acids: any substance that produces hydrogen ions in water Produces one or more hydrogen ions and a negative ion in solution of water Hydrogen or hydronium ion: atom of hydrogen that has lost its electron Negative ion: nonmetal or polyatomic ion

Example of reaction in water:

Bases: any substance that produces hydroxide ions in water Made of positive ions combined with hydroxide ions Hydroxide ions: negative ion made of oxygen and hydrogen Produces a positive ion and a hydroxide ion in a solution of water

Example reaction in water:

Measuring pH pH scale: range of values from 0-14 pH of 7 is neutral Expresses the number of hydrogen ions in a solution Low pH tells you that the concentration of hydrogen ions is high. In contrast, a high pH tells you the concentration of hydrogen ions is low pH of 7 is neutral Can determine pH by using an indicator

Acid-Base Reactions Reaction between an acid and a base is called a neutralization Example reaction:

Reactants Final pH depends on the volumes, concentrations, and identities of the reactants Products Salt: ionic compound that can be made from neutralization reaction Positive ion of base and negative ion of acid Water: the other product of a neutralization reaction

In a neutralization reaction, an acid reacts with a base to produce a salt and water Example:

Digestion and pH 7-5

What is digestion? Food must be broken down into simpler substances that your body can use for raw materials and energy Digestion: breaks down the complex molecules of foods into smaller molecules Mechanical digestion Physical process in which large pieces of food are torn into smaller pieces Size of food is reduced, but food isn’t changed into other compounds

Chemical digestion Breaks large molecules into smaller ones Using help from enzymes (catalyst that speed up reactions) Enzymes require the right conditions to work (temperature and pH)

pH in the Digestive System Your mouth Teeth chew and mash food (mechanical digestion) Food is mixed with saliva Saliva contains enzyme, amylase that works best at pH of 7

Stomach Mechanical continues Chemical digestion begins for foods containing protein (meat, fish, & beans) Cells release enzymes (ex. Pepsin) and hydrochloric acid (pH of 2)

Small Intestine Chemical digestion continues Digestive fluid containing bicarbonate ions surrounds the food (pH of 8) Contains enzymes that breakdown carbohydrates, fats, and proteins Large food molecules have been broken down into smaller ones and they pass through the wall of the small intestine into the bloodstream and carried to cells that need them