Science 10-Bortolin Acids and Bases Chemistry. Acid-Base Chemistry

Transcription

1 Solutions can be: Acid-Base Chemistry Acidic (corrosive) examples: acetic acid (vinegar), ascorbic acid (vitamin c), (corrosive) Basic (alkaline) examples: cleaners, blood, (caustic) Neutral (neither acidic nor basic) example: pure water Acidity is measured using the ph scale. The ph scale ranges from 0-14 between 0 and 7 is ACIDIC between 7 and 14 is BASIC 7 is NEUTRAL Every whole number change on the ph scale is a ten times change in concentration. ** 0-14 on board with examples ** Examples: Grapes have a ph of 4, lemons have a ph of 3 the difference in their ph values is 1 (the whole number difference is the exponent with base 10) lemons are ten times more acidic than grapes grapes are ten times more basic than lemons

2 bleach is ph 12, eggs are ph 8 The difference in their ph values is 4 so bleach is 10 4 or more basic than eggs eggs are more acidic than bleach Small changes in ph have large effects! Acids vs. Bases When in solution, acids produce H + ions (hydrogen ions) When in solution, bases product OH - ions (hydroxide ions) ph measures the [H + ] (concentration of hydrogen ions) low ph is high concentration of hydrogen ions high ph is low concentration of hydrogen ions Why? H + and OH - readily react with each other to produce H2O Because they react so readily, there can only ever be a surplus of one or the other, or none at all. Fill in: An acid and a base will typically react to form a neutral solution.

3 Acids vs. Bases: Properties Property Acid Base Taste Sour Bitter Touch Burn Slippery Litmus Red Blue Reaction with metals Corrode No reaction Conductivity Conductive Conductive ph <7 >7 Ion Production H + OH - How Do We Tell? We use ph indicators to tell us the acidity of a solution. An indicator will be a different colour depending on the ph Example 1: Litmus paper (drawn on board) Blue litmus paper will turn red in acidic solutions Red litmus paper will turn blue in basic solutions If blue litmus stays blue and red litmus stays red, the solution is neutral A universal indicator contains many indicators and will be a specific colour for many given ph s A probe can measure the electrical properties to determine ph Indicators typically have a specific ph value where their colour changes. We use the appropriate indicator in experiments when trying to obtain a certain ph.

4 Examples of indicators: Indicator ph when change occurs Colour change (low to high ph) Methyl orange Red to yellow Methyl red Red to yellow Bromothymol blue Yellow to blue Litmus 7 Red to blue Phenolphthalein Colourless to pink Indigo carmine Blue to yellow In the middle of the range, they are a mixture of the 2 colours For example: indigo carmine - blue to yellow, around ph 12, the solution will be green. Using the chart in your data booklets, you can: 1. Determine what colour each indicator would be at a given ph a. Draw a straight line perpendicular to the ph scale at the ph you are curious about b. Look for the specific indicator and see where the line goes through its line i. The colour where the line crosses it will be the colour it is at that ph 2. Determine a range of ph when told the colour(s) of indicator(s) a. Determine where each indicator is the given colour b. See where every colour requirement is satisfied i. this will give you a range of possibilities

5 Try This: Using the chart, indicate the colour of each ph ph 3, ph 8, ph 10 Try This: What is the possible ph range for a solution if: methyl red is red and methyl orange is yellow? Phenolphthalein is pink and indigo carmine is blue? Types of Reactions with Acids and Bases 1. Acid-Base Neutralization An acid reacts with a base to product water and a salt What is a salt? -a class of ionic compounds -the ionic compound that is created by reacting an acid and a base 2. Metal Oxides (compounds with metals chemically bonded to oxygen) Metals react with oxygen to form oxides. These oxides then turn a solution basic when put into water Li2O + H2O -> 2LiOH MgO + H2O -> Mg(OH)2

6 3. Non-metal Oxides (compounds with non-metals chemically bonded to O) Non-metals react with oxygen to form oxides These oxides turn a solution acidic when put in water SO2+H2O->H2SO3 SO3+H2O->H2SO4 Acids and Metals Reactivity of metals increases as we move DOWN the periodic table and to the LEFT of the periodic table. Both alkali metals and alkaline earth metals react vigorously with water and acids Typically, a metal will react with an acid to form an ionic compound and hydrogen gas. Acids and Carbonates Carbonates (ionic compounds containing carbonates) will react with acids to produce a new ionic compound, water, and carbon dioxide. limestone contains carbonate naturally-this can help neutralize water that has become acidic artificial liming is performed as well H2SO4 + CaCO3 -> CaSO4 + H2O + CO2