Acid and Bases. pH

Acids

Bases

Indicator An indicator is a compound which shows by means of a colour change whether a substance is acidic or basic.

Litmus indicator Acid turn litmus from blue to red Base turns litmus form red to blue.

Exp: To test a variety of solutions with litmus. Method: Place a variety of solutions on the appropriate places on the acetate sheet. Dip a piece of blue litmus into each, note colour change. Dip a piece of red litmus into each, note colour change. Result: (Fill in table). Conclusion:Acids turn litmus blue- red, bases turn litmus red to blue, neutral substances have no effect on litmus.

Sample Colour change Acid or base Lemon Juice Finish Powerball detergent Baking soda Vinegar Water

Acids and Bases Corrosive

The pH Scale The pH scale indicates the level of acidity or basicity in a solution A solution that has a pH of 7 is neutral A solution that has a pH less than 7 is acidic A solution that has a pH greater than 7 is alkaline

Universal Indicator

Exp: To investigate the pH of a variety of materials using the pH scale. Method: Place a variety of solutions on the appropriate places on the acetate sheet. Add a few drops of universal indicator to each, note colour change. Result: (Fill in table). Conclusion:Universal indicator can be used to tell the pH of a variety of materials.

Acids Acids have a sour taste. They turn blue litmus red. They have a pH below 7.

Examples of ACIDS Everyday Acids? Lab Acids Hydrochloric acid HCl Sulfuric acid H SO

Bases Bases are the opposite to acids. They turn red litmus blue. They have a pH above 7. An alkali is a base which is soluble in water.

Examples of BASES Everyday Bases? Lab Bases Sodium hydroxide NaOH Calcium hydroxide Ca(OH)

Acid + base  salt + water Neutralisation When an acid is mixed with a base they cancel each other out and form a salt and water. Acid + base  salt + water

Examples of Neutralisation hydrochloric acid + sodium hydroxide  sodium chloride + water HCl + NaOH  NaCl + H O hydrochloric acid + calcium carbonate  calcium + carbon + water chloride dioxide HCl + Ca CO  Ca Cl + CO + H O 2 3 2 2 2

Exp: To titrate HCl against NaOH, and prepare sample of NaOH. Method: Using a pipette, place 25cm of sodium hydroxide in a conical flask. Add a few drops of indicator e.g. methyl orange. Fill the burette with dilute hydrochloric acid. Slowly add acid to the base until a colour change occurs. Note the volume of acid added. Repeat the experiment twice, noting volume of acid added. Get an average reading for the amount of acid added in the three experiments. Repeat the expriment without adding any indicator, adding the exact volume of acid needed to neurtalise the base. Pour some of the salt solution into an evaporating dish and heat until the water evaporates leaving behind sodium chloride. Result: Conclusion:An acid and a base react to form a salt and water.

Exp: To investigate the reaction between zinc and hydrochloric acid. Method: Place a piece of zinc into a test tube of dilute hydrochloric acid. Place your thumb over the top of the test tube and when you fell the pressure build up, test with a lighted splint. Result: The splint burns with a ‘popping sound’. Conclusion: Hydrogen gas burns with a ‘pop’. This is the test for hydrogen gas.

zinc + hydrochloric acid  zinc chloride + hydrogen Zn + HCl  ZnCl + H 2 2

Skoool acids and bases