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ACIDS and BASES.

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Properties/characteristics of Acid and Base.
Understanding the pH scale.
Acid-Base Indicator.
Neutralization.
Example of acids and bases

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ACIDS and BASES.

  1. 1. ACIDS AND BASES Prepared by: Mrs Analiza B. Secillano
  2. 2. ACIDS and BASES Determine the acidity and basicity of mixtures. Properties of acids and bases. Examples of acids and bases. The pH scale. Acid- base Indicator Neutralization.
  3. 3. ACIDS • An acid is a substance that releases H+ ions in an aqueous solution – Aqueous means water • Example: when hydrochloric acid is dissolved in water, the compound separates into chlorine ions (Cl-) and hydrogen ions (H+)
  4. 4. When we think of acids and bases we tend to think of science labs and chemicals…but did you know Acids cause:  Lemons to be sour  Acid rain to eat away at sculptures  Framed paintings to be damaged  Cavities in your teeth  Food to digest in your stomach  Ants and bees use it to sting
  5. 5. STRONG ACIDS • A strong acid breaks down completely in water and gives off many H+ ions
  6. 6. WEAK ACID • A weak acid only partially breaks down. It gives off much less H+ than a strong acid.
  7. 7. Characteristics of Acids • Acids have a sour taste • Acids react with metals & carbonates to produce gas • Acids contain hydrogen H
  8. 8. Characteristics of Acids: Taste Sour • Acids in foods taste sour and produce a burning or prickling feeling on the skin
  9. 9. Characteristics of Acids • Since tasting or touching an unknown chemical is extremely dangerous, other methods are needed to tell whether a solution is an acid
  10. 10. Characteristics of Acids: Reacts with Carbonate • A safe way to test to see if a solution is an acid is to place a few drops on a compound that contains a carbonate (CO3) • Example: limestone is a rock that contains calcium carbonate (CaCO3) When an acid touches a piece of limestone, a reaction occurs that produces carbon dioxide gas
  11. 11. Characteristics of Acids: Reacts with Metal • Acids also reacts with most metals • The reaction produces hydrogen gas, which you can see as bubbles
  12. 12. Characteristics of Acids: Contain Hydrogen
  13. 13. BASES • A base is a substance that releases hydroxide (OH-) ions in an aqueous solution • Example: When sodium hydroxide (NaOH) is dissolved in water, the compound separates into sodium ions (Na+) and hydroxide ions (OH-)
  14. 14. Characteristics of Bases  Turn red litmus  taste bitter  Negatively charged hydroxide ions (OH–)  Feel slippery  Bases neutralize acids  Poisonous and can cause severe burns  Strong Bases are Caustic.
  15. 15. Characteristics of Bases: Taste Bitter • Example: Baking soda
  16. 16. Characteristics of Bases: Taste Bitter • Mild bases in foods taste bitter and feel slippery, but as with acids, tasting and touching are not safe ways of testing whether a solution is a base • In fact, some strong bases can burn the skin as badly as strong acids
  17. 17. Characteristics of Bases: Feel Slippery • Bases feel soapy or slippery because they react with acid molecules in your skin called fatty acids
  18. 18. Characteristics of Bases: Feel Slippery • In fact, this is exactly how soap is made. Mixing base- usually sodium hydroxide – with fatty acids produces soap • So when a base touches your skin, the combination of the base with your own fatty acids actually makes a small amount of soap
  19. 19. Characteristics of Bases: Contain Sodium Hydroxide (OH-) Strong Bases The Formula Lithium hydroxide LiOH Sodium hydroxide NaOH Potassium hydroxide KOH Rubidium hydroxide RbOH Caesium hydroxide CsOH Barium hydroxide Ba(OH) 2 Calcium hydroxide Ca (OH) 2 Strontium hydroxide Sr(OH) 2
  20. 20. Properties of Acids & Bases • Similarities between acids and bases – Dissolve in water – Conduct electricity in aqueous solution – Can irritate or burn skin
  21. 21. Properties of Acids and Bases
  22. 22. Acid-Base Strength • pH stands for “potential hydrogen” and is a measure of how many H+ ions there are in solution. • The strength of an acid or base is usually measured using a pH scale • The more H+ there are, the lower the pH will be
  23. 23. Properties of Acids and Bases Acids  turn blue litmus red  taste sour  Acids corrode metals  positively charged hydrogen ions (H+) Bases  turn red litmus blue  taste bitter  Negatively charged hydroxide ions (OH–)  Feel slippery  Most hand soaps and drain cleaners are bases  Strong bases are caustic
  24. 24. Understanding the pH Scale  pH stands for (presence of Hydrogen)  Numbered from 0 to 14.  The lower the pH number – the higher Acid  That means more Hydrogen Ions (H+)  The higher the pH - the higher the Base  That means less Hydrogen Ions (H+)
  25. 25. Acid-Base Strength • The numbers of the pH scale usually range from 0 – 14, but numbers outside this range are possible • The middle number, 7, represents a neutral solution • A neutral substance is neither an acid nor a base. Pure water has a pH of 7
  26. 26. Acid-Base Strength pH < 7 indicate acidic solution pH = 7 indicate neutral solution pH > 7 indicate basic solution A concentrated strong acid has a low pH value A concentrated strong base has a high pH value
  27. 27. Acid-Base Indicators • An acid-base indicator is a compound that will change color in the presence of an acid or base • Litmus is a plant extract that can be blue or red (pink) – Litmus turns red/pink in an acidic solution – Litmus turns blue in a basic solution
  28. 28. Acid-Base Indicators  Example of plants that can be use as an acid-base indicator.
  29. 29. Acid-Base Indicators • It would be impossible to determine the pH of all solutions using just one indicator, such as litmus • Several other acid-base indicators exist, each producing a color change at a specific pH level
  30. 30. Acid-Base Indicators • A universal indicator is a mixture of chemicals that changes color through a wide range of pH values
  31. 31. Acid-Base Indicators • An even more precise way of determine pH is to use a pH meter
  32. 32. Acids and Bases Neutralize Each Other • When an acid and base react with each other, the characteristic properties of both are destroyed. This is called neutralization.
  33. 33. Acids and Bases Neutralize Each Other • The salts formed may be soluble in water or can be insoluble • If the salt is insoluble, a precipitate will form • Recall: a precipitate is a suspension of a small, solid particles formed during a chemical reaction
  34. 34. Acids and Bases Neutralize Each Other • General formula for acid base reaction Acid + Base → H2O + Salt • Salt means any ionic compound formed from an acid/base reaction HCl + NaOH → H2O + NaCl
  35. 35. Acids and Bases Neutralize Each Other • A common example of neutralization reaction occurs when you swallow an antacid tablet to relieve an upset stomach. • The acid in your stomach has a pH of about 1.5 due to mostly hydrochloric acid produced by the stomach lining
  36. 36. Acids and Bases Neutralize Each Other • An antacid tablet contains a base, such as sodium bicarbonate, magnesium hydroxide or calcium carbonate. The base reacts with the stomach acid and produces a salt and water. • This reaction lowers the acidity and raises to pH to its normal value (about 2)

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