Intro to Acids, Bases, & Salts

1. Intro to Acids, Bases, & Salts

2. Word Origins • ‘Acid’ comes from the Latin word ‘acidus’ meaning sour. • ‘Base’ comes from the Arabic word ‘alqili’ or ‘alkali’ meaning the ashes of the Kali plant. • ‘Salt’ comes from the Latin word ‘salarium’. Roman soldiers were paid in salt which they used to preserve food. Intro to Acids, Bases, & Salts

3. Familiar Examples • Acids, bases, and salts are part of our daily lives. The orange juice we drink contains citric acid; soap is made using sodium hydroxide, a base; and we flavor our foods with sodium chloride, table salt. • Stronger acids and bases are also part of our daily life, but must be handled carefully (e.g. car battery acid, and base used for cleaning drains). Intro to Acids, Bases, & Salts

4. Acids • Have a sharp sour taste (vinegar, lemon). • Dissolve many metals. • Turn blue litmus paper red in an aqueous solution. • Contain hydrogen ions (H+) and can be recognized by the ‘H’ that appears in their formulas. • Acids neutralize bases. Properties of Acids, Bases, & Salts

5. Acids Properties of Acids, Bases, & Salts

6. Bases • Have a bitter taste; are slippery to the touch. • Dissolve many metals. • Turn red litmus paper blue in an aqueous solution. • Contain hydroxide ions (OH-) and can be recognized by the ‘OH’ that appears in their formulas. • Bases can neutralize acids. Properties of Acids, Bases, & Salts

7. Bases Properties of Acids, Bases, & Salts

8. Salts • Common salts are made up of sodium (Na) or potassium (K) combined with a halogen. • Solutions of acids, bases, and salts all contain ions, and thus can conduct electricity. • When an acid and base react, water and a salt are produced. • This reaction is called a neutralization, therefore, a salt is neither an acid nor a base. • HCl (aq) + NaOH (aq)  NaCl(aq) + H2O • (acid) (base) (salt) (water) Properties of Acids, Bases, & Salts

9. Salts Properties of Acids, Bases, & Salts

10. pH • Chemist use a pH scale to indicate the strength of an acid or a base. The number is usually on a scale of 0 to 14, measured with a pH meter. • A pH below 7 indicates a solution is acidic. • A pH above 7 indicates a solution is basic. • A pH of 7 indicates a neutral solution (such as pure water). Strength of Acids & Bases

11. pH Strength of Acids & Bases 2, stomach acid 7, pure water 10, sea water 14, NaOH

12. pH • pH level can be measured with special dyes called acid-base indicators: • ‒ litmus paper contains several indicators that change color at different pH’s level. • ‒ When dipped into a solution, the paper’s color indicator the approximate pH of the solution. Strength of Acids & Bases

13. pH Strength of Acids & Bases Acid Base

14. pH • Another indicator is phenolphthalein: a colorless liquid which turns pink in basic solutions, but remains colorless in acidic and neutral solutions. • ‒ Turns pink above a pH of 9, and at very high pH values, it is again colorless. • ‒ To avoid high pH values, thus ruining the phenolphthalein test, avoid making solutions too concentrated or too dilute. Strength of Acids & Bases

15. pH Strength of Acids & Bases phenolphthalein

16. pH • Two other indicactors: • ‒ Methyl orange; red in acid; yellow in base. • ‒ Bromothymol Blue; for weak acids and bases, yellow below pH 6 and blue above pH 7.6 • Note: Indicators work only when placed in an aqueous solutions thus solids must first be dissolved in a solution (water, HCl, …) Strength of Acids & Bases