Acids and Bases Measuring ph Experiment Part 2

Transcription

1 Acids and Bases Measuring ph Experiment Part 2 Aim: To measure the ph of various substances Materials: Substances to test: Sodium Hydroxide (NaOH) solution Hydrochloric acid (HCl) Sodium Bicarbonate (NaHCO3) solution Antacid Vinegar Lemon Juice Distilled water Equipment: Spotting tile Red litmus paper Blue litmus paper Universal indicator solution Safety glasses Instructions: 1. Place a few drops of the solution you are testing in a cavity on the spotting tile. 2. Dip a piece of blue litmus paper into the solution. Record your observations. 3. Dip a piece of red litmus paper into the solution. Record your observations. 4. Add 1 drop of universal indicator solution to the solution you are testing. Use the chart to determine the ph of the solution. Record your observations. 5. Repeat steps 1 4 for all 8 solutions. Ensure you record your observations after every test. Note: The antacid is given to you as a tablet. You will need to break the tablet up and add a few drops of distilled water.

2 Observations Solution to be tested Sodium Hydroxide (NaOH) Prediction Observations after adding blue litmus paper Observations after adding red litmus paper Observations after adding universal indicator (ph) Strong acid, weak acid, neutral, weak base or strong base? Hydrochloric Acid (HCl) Sodium Bicarbonate (NaHCO3) Antacid Vinegar Lemon Juice Distilled Water

3 Discussion: 1. For which substances did your observations match what you had predicted? 2. For which substances did your observations NOT match what you had predicted? Explain why you now think your prediction/s were incorrect. 3. Which was the most acidic substance you tested (lowest ph)? Which was the most basic (highest ph)? List the 8 substances from the most acidic to the most basic. Challenge 1: Predict what will happen to the ph of an acid when you dilute it with distilled water. Will it be more or less acidic? Explain your thinking.

4 Acids and Bases Measuring ph Experiment Part 1 Let s review what we know: An acid is a substance that releases hydrogen ions (H + ) into an aqueous solution (water). Common examples of acids include hydrochloric acid (which is found in your stomach) and acetic acid (which is found in vinegar). Acids are corrosive (meaning they will burn our skin), have a sour taste and turn blue litmus paper red. A base is a substance that releases hydroxide ions (OH - ). If a base can be dissolved in water it is known as an alkali. The solution it forms is called an alkaline solution. Common examples of bases include sodium hydroxide which is used in soap and ammonia which is used for household cleaning. Bases are caustic (meaning they will burn our skin), have a soapy feel, have a bitter taste and turn red litmus paper blue. We use the ph scale to measure the strength of acids and bases. Pure water has a ph of 7. It is in the middle of the ph scale meaning it is neutral. Acidic solutions have a ph below 7 (1 being the most acidic). Basic, or alkaline, solutions have a ph above 7 (14 being the most basic). For this experiment you will be working in groups of 3 4 (no more). We are now going to break into our groups to complete the next activity. Predictions: We are going to be testing 8 substances to determine if they are strong acids, weak acids, neutral, weak bases or strong bases. Sodium Hydroxide (NaOH) solution Hydrochloric acid (HCl) Sodium Bicarbonate (NaHCO3) solution Antacid Vinegar Lemon Juice Distilled water Before we begin our experiment we are going to make predictions about the substances we are testing. Sodium Hydroxide (NaOH) solution:

5 Hydrochloric acid (HCl): Sodium Bicarbonate (NaHCO3) solution Antacid:

6 Vinegar: Lemon Juice: Distilled Water: