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Acidic, Basic and Neutral Solutions

Acidic, Basic and Neutral Solutions. Chapter 9, Lesson 2. Acids. An acid is a substance that releases a positively charged hydrogen ion, H + , in water. Acids taste sour and turn blue litmus paper red.

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Acidic, Basic and Neutral Solutions

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  1. Acidic, Basic and Neutral Solutions Chapter 9, Lesson 2

  2. Acids • An acid is a substance that releases a positively charged hydrogen ion, H+, in water. • Acids taste sour and turn blue litmus paper red. • The hydrogen ion from an acid combines with a water molecule in solution to form a hydronium ion, which has the formula H3O+ • Because acid solutions contain ions, they conduct electricity.

  3. Hydrogen ion Water molecule Hydronium ion Hydronium ion • When an acid dissolves, it releases a hydrogen ion. • The H+ ion combines with water to form H3O+, the positively charged hydronium ion.

  4. What is a hydronium ion?

  5. Uses of Acids • Acids are important in several body processes, including breaking down food in the stomach. • Acids are also used in making many products, such as fertilizers, detergent, and cleaners.

  6. Bases • A base is a substance that produces hydroxide ions when dissolved in water. • The formula for the hydroxide ion is OH- • Bases feel slippery on your skin, taste bitter, and turn red litmus paper blue. • Most bases are ionic compounds.

  7. Hydroxide ion • In water, bases separate into a positive ion and the hydroxide ion (OH–). • All the properties of bases are a result of the presence of hydroxide ions that form when the base is dissolved in water.

  8. Uses of Bases • Common bases include baking soda and cleaning agents. • Bases are also used to produce new products, such as soap, paper, and plaster. Acids and Bases

  9. What is pH? • pH is a numerical scale used to indicate how acidic or basic a solution is. • The pH scale runs from 0 to 14. • Acids are below 7; strong acids are near 0. • Bases are above 7; strong bases near 14. • Neutral solutions have a pH of 7.

  10. pH and Hydronium ion Concentration • The higher the concentration of hydronium ions, the more acidic a solution is. • All acid and base solutions contain both hydronium ions and hydroxide ions. • In a neutral solution (pH=7) the hydronium and hydroxide ion concentrations are equal. • A change in one pH unit represents a tenfold change in the acidity or alkalinity (how basic) of a solution.

  11. Neutralization • When an acid and a base are mixed, a neutralization reaction occurs. • A neutralization reaction produces water and a salt. • Stomach acid reacts with magnesium hydroxide in the following equation: 2HCl + Mg(OH)2 → MgCl2 + 2H2O • Neither of the products is acidic or basic.

  12. How is pH measured? • An indicator is a compound that changes form one color to another within a particular pH range. • Indicators can be used to determine approximate pH, simply whether something is acidic or basic.

  13. How is pH measured?

  14. pH strips • Litmus is one of the simplest indicator test papers but also the least accurate. • pH testing strips are a quick way of determining the approximate pH of a solution.

  15. pH Meters • pH meters are electronic instruments with an electrode that is sensitive to hydronium ions present in a solution. • Accurately measures pH • Requires an electric source to operate

  16. pH Meters (cont’d)

  17. Lesson Review 9-2 1. An acid with a pH of 3 is contains how many times as many hydronium ions as an acid with a pH of 6? A 1000 B 3 C 30 D 100

  18. Lesson Review 9-2 2. When an acid and base are mixed, the products are ____ and ____. A water; a base B water; ammonia C water; salt D ammonia; salt

  19. Lesson Review 9-2 3. Red litmus paper is dipped in a solution. The paper turns blue. The solution must have been ____. A acidic B homogeneous C basic D polar

  20. Lesson Review 9-2 4. Blue litmus paper turns ____ in acid solutions. A red B orange C green D blue

  21. Lesson Review 9-2 5. Which of the following is a hydroxide ion? AH3O+ BH+ COH– D NH4+

  22. Lesson Review 9-2 6. Which is a property of a base? A sour taste B produces OH–in water Cproduces H+ in water D reacts with metal to produce hydrogen gas

  23. Lesson Review 9-2 7. What ions are present in the greatest amount in a solution with a pH of 2.5? A hydroxide B hydrogen C hydronium D oxygen

  24. Lesson Review 9-2 8. What is the symbol for the hydrogen ion? AH3O+ BH2O CH+ DOH–

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