Water, the SPECIAL Equilibrium

Transcription

1 THE ACID TEST

2 Water, the SPECIAL Equilibrium I. Characteristics of Water A. Water are highly. B. They are in continuous. C. Always. D. Water is dense in the solid phase than in the phase. i.e. ice floats in water. E. Water has a melting and boiling point than most other common liquids because of bonding. F. Polar and compounds are soluble in water but compounds are not. II. Transfer of Hydrogen Ions A. When some of these polar molecules collide, the contain enough that hydrogen are from one molecule to another. - + B. A water molecule that a hydrogen becomes a negatively charged ion (OH - ). C. A water molecule that a hydrogen ion becomes positively charged ion (H ). D. The reaction in which two molecules to give, is the - of water. E. This reaction can be written as a simple reaction. HOH H + + OH - Acid Packet Page 2

3 III. Self-Ionization of Water A. Self-ionization of water occurs to a very extent. B. Self-ionization of water occurs in water at 25 C. [OH - ] = [H + ] = 1 X 10-7 moles/liter C. Any solution in which the hydroxide and hydrogen ions both 1 X 10-7 moles/liter is described as a solution. IV. Applying Le Chatelier's Principle A. Le Chatelier's principle tells us how a system at reacts to applied stress. B. Stress is defined as a in the temperature or pressure of a system or a change in the of a component. C. Our focus will be on changing the of a solution. D. In the equation the [OH - ] and [H + ] are. E. As the concentration of [OH - ] the concentration of [H + ] will decrease and vice versa. [OH - ] and [H + ] are proportional to each other. F. If additional ions are to the solution, the will shift to the other type. This causes more molecules to be. V. Ion Product Constant for Water A. In all aqueous solutions the product of [OH - ] and [H + ] is: [OH - ] X [H + ] = 1 x moles/liter 2 B. The above equation is the ion-product for water. Acid Packet Page 3

4 Household Products PROCEDURE: In this exercise you will be testing household substances with different indicators. You will be testing food and cleaning substances that are either dissolved in water (e.g. grape juice, window cleaner) or can be ground up and easily dissolved in water (e.g. antacids, powdered cleansers). DATA: Record the substances used and the results in the table as you test at least six substances using each one of the following methods: SUBSTANCE Litmus paper color change ph paper color change ph paper number value from chart Universal indicator color change Red Cabbage juice color change Bromothymol Blue indicator color change Conclusion: 1. What is an indicator? What does it do? 2. Make a generalized statement about the ph of a substance and its possible household uses Acid Packet Page 4

5 Characteristics of acid/base Acids taste. and electrolytes. litmus paper turns. Turns red cabbage juice Turns universal indicator Turns bromothymol blue indicator Turns phenolphthalein indicator React with some to form React with to release carbon dioxide gas ion (proton) donor Bases taste and electrolytes litmus paper turns Turns red cabbage juice Turns universal indicator Turns bromothymol blue indicator Turns phenolphthalein indicator slippery ion donor or hydrogen ion (proton) acceptor. HCl H + + Cl - NaOH Na + + OH - or NH 3 + H + NH 4 + Acid + Base + HCl + NaOH + (Neutralization Reaction) Only those compounds which can form, when placed in water solutions can be acids or bases. The adjectives and have the same meanings as they did with electrolytes. A acid or base is one that ionizes completely in water solutions to form ions. When acids or bases dissolve in water, only a fraction of its molecules ionize. Acid Packet Page 5

6 Acid Rain Record all of your observations below: 1. Write an equation for the burning of sulfur in air. 2. When the gas produced by burning sulfur dissolved, what effect did it have on the acidity of the distilled water? Write an equation for the addition of this gas to water. 3. What was the actual ph of the new solution? What do think would happen to a lake as it collected acid rain within its banks? Research the web a find the optimum ph of water that trout will live in? What effect will the rain have on these fish? 4. Acids react with metals that are more reactive than hydrogen. What happens to the metal as the solution from the glass bottle is added? Write the reaction for this reaction. 5. Acids react with ionic compounds that contain carbonate ion. This causes a destructive action of acidic pollution on marble and limestone sculptures. What happens when some of the solution from the glass bottle is added to baking soda (sodium hydrogen carbonate)? Conclusions 1. In your own words describe the factors that lead to the production of acid rain. 2. Using the map of ph levels link on the web page, why do you think that Utah seems to have a relatively neutral ph compared to the east coast. 3. What are some ways to reduce acid rain? Include specific and personal solutions. Acid Packet Page 6

7 OHconcentration H + concentration Drano Detergents Milk of magnesia Seawater Eggs Blood Pure water Milk Rainwater Tomatoes Oranges Soft drinks Vinegar Lemons Stomach Acid The ph Scale The acidic, basic, or neutral character of a solution can be measured and reported using the scale. PH is short-hand for the of the hydrogen ion. PH values commonly range from to although some very basic or acidic solutions may be outside this range. A ph of is a neutral solution. PH values than 7 indicate acids; the lower the ph the more acidic the solution. PH values than 7 indicate bases; the higher the ph the more basic the solution. Most acid and base solutions occur in water, therefore we must consider the. HOH H + + OH - As a solution becomes more acidic ( in [H + ]) the [OH - ] must decrease. As a solution becomes more basic ( in [H + ]) the [OH - ] must increase. ph values Examples Acid Packet Page 7

8 Environmental Bees In this scenario, you will determine the source of groundwater pollution by measuring phs of well samples and plotting these on a topographical map. DATA Monitoring well # Water level (m) Groundwater elevation (m) ph REPORT OF RESULTS Acid Packet Page 8

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10 The Math of PH PH is defined as the log of the hydrogen ion concentration PH = -log [H + ] Because H + is always in equilibrium with water and proportional to OH - concentration (as one increases the other decreases). HOH H + + OH - We can also have the " of the hydroxide ion" value, or poh: POH = -log [OH - ] Also remember the ion product constant for water? [H + ] x [OH - ] = 1x10-14 moles/liter 2 With some mathematical manipulation this also means that: PH + poh = 14 With all this information, you can solve problems involving ph: PROBLEMS 1. What is the ph of a solution with a [H + ] of 1 x 10-8? 2. What is the [H + ] of a solution with a ph of 3? 3. What is the poh of a solution with a ph of 5? 4. What is the [OH - ] of a solution with a ph of 4? 5. If you wanted to change the ph of a solution from 3 to 5, how many times would you dilute it? Finish the [H + ] or the [OH - ] and ph calculations for the "Colormetric ph Meter" lab. Acid Packet Page 10

11 Your Basic Acid-Base Titration When acids and bases are mixed together, they will the effect of each other. Acid + Base Water + Salt This fact can be used to determine the H + or OH - concentration of an solution. This process is done by means of titration. is the incremental addition of acid (or base) to a solution of base (or acid) so the progress of then neutralization reaction can be monitored with an indicator. After titrating until the ph of (neutral) is reached, you can calculate the amount of acid or base in an unknown sample if you know the and concentration of the solution you titrate the unknown sample with: Volume acid x Molarity acid = Volume base x Molarity base Record your observations: ACID/BASE TITRATION Conclusion: 1. What indicates the titration is compete? 2. Calculate the molar concentration of the hydrochloric acid from the results of the demonstration. 3. What is the equivalance point of the titration? Acid Packet Page 11

12 How Much Vinegar? Beginning buret reading ml End buret reading ml Amount of 1M NaOH used to titrate vinegar ml What is the % concentration of vinegar found in your samples? Show ALL your calculations. What is your % error? Show your calculations. Practice: Calculating ph etc. [ H + ] [ OH - ] ph Acid/Base/Neutral 1 x x x x x x Titrations 1. How many milliliters of 4.5 M HCl are needed to neutralize 25 ml of.8 M NaOH? 2. What is the concentration of acetic acid, given it takes 22 ml of.02 M NaOH to neutralize a 52 ml sample of the acids? 3. If 75 ml of 2.8 M KOH is needed to neutralize a 35 ml sample of nitric acid, what is the concentration of the acid? 4. What volume of 5 M NaOH is needed to neutralize 200 ml of 3.0 M HCl? 5. Given that 40 ml of sulfuric acid are neutralized b 22 ml of.6m Ca(OH)2, what is the concentration of the acid? Acid Packet Page 12