If it is not reddish, add more drops, but be sure to count the total number of drops added. Ask students: What could you then add in order to make the indicator solution less acidic? Adding a base, like the sodium carbonate solution, will make the solution less acidic. Should you add one drop of sodium carbonate solution at a time or a few drops at once? You should add one drop at a time to better monitor how many more drops of the sodium carbonate solution should be added. How will you know when the solution is neutralized?
The color of the solution will be similar to the color of the control. Tell students that if the solution turns blue, it has gone from an acid, past neutral, and is now a base. If this happens, try adding one or more drops of citric acid until the color is close to neutral.
Be sure to keep track of the total number of drops of acid and base you add. Expected Results With each drop of sodium carbonate, the citric acid solution will move toward neutral, eventually becoming green. Table 1. How many drops of sodium carbonate does it take to neutralize your citric acid solution? Acidic solution Number of drops of citric acid solution added to the indicator Number of drops of sodium carbonate solution needed to neutralize the citric acid solution First citric acid solution 3 drops Second citric acid solution Discuss student observations.
How many drops of sodium carbonate did it take to bring the color back to the color of the control? Results will vary but it should take fewer drops of sodium carbonate than drops of citric acid to neutralize the solution. Does the solution become more acidic or less acidic as each drop of sodium carbonate is added to the indicator?
The solution becomes less acidic. How do you use the color of the control to help you neutralize an acid? When the color of the universal indicator solution becomes near green, the acidic solution has been neutralized.
Project the animation Neutralizing an Acidic Solution. Explore Have students compare how many more drops of a base it takes to neutralize a more concentrated acidic solution. Question to Investigate How many more drops of sodium carbonate solution will it take to neutralize a more concentrated citric acid solution? Materials for Each Group Citric acid Citric acid solution Sodium carbonate solution Universal indicator solution 2 flat toothpicks 3 droppers Spot plate Neutralize a citric acid solution Use a flat toothpick to add two scoops of citric acid to your citric acid solution to make it even more acidic.
Add universal indicator solution to a clean well in the spot plate. Add 3 drops of the more concentrated citric acid solution to the indicator and stir with a clean toothpick. Ask students: Do you think it will take more, less, or the same amount of sodium carbonate solution to neutralize this more concentrated citric acid solution?
It will take more drops of the base to neutralize the more concentrated citric acid solution. Thinking about the animation, why will you need more drops of sodium carbonate solution? So it takes more molecules of the base to accept the extra protons and move more toward neutral. Neutralize a more concentrated citric acid solution Add single drops of sodium carbonate solution to the same well in which you added the acid. Extend Have students neutralize two basic solutions to determine which is most concentrated.
Materials for each group Universal indicator solution Citric acid solution Solution A Solution B At least 6 toothpicks Spot plate 3 droppers Teacher Preparation Make two mystery solutions using different amounts of sodium carbonate. Label two cups Solution A and Solution B for each group.
Make a class set of solutions A and B. Solution A: 50 mL of water and 5 toothpicks of sodium carbonate Solution B: 50 mL of water and 10 toothpicks of sodium carbonate Place about 5 mL of each solution in their labeled cups. Ask students: Solutions A and B are both basic solutions made with sodium carbonate and water. One of these solutions has more sodium carbonate than the other. How can you figure out which solution is more concentrated?
Students should describe a procedure very similar to the one they used to neutralize the two citric acid solutions. They should suggest that they neutralize each sodium carbonate solution with drops of citric acid and count how many drops it takes to neutralize each solution.
When the color of the solution is close to the color of the control, the solution is neutralized. How will you know which solution is the most concentrated? The solution that requires the greatest number of drops of citric acid to become neutral is the most basic. When we have heartburn, it feels better if we reduce the excess acid in the esophagus by taking an antacid. As you may have guessed, antacids are bases. One of the most common antacids is calcium carbonate, CaCO 3.
The reaction,. Milk of Magnesia is a suspension of the sparingly soluble base magnesium hydroxide, Mg OH 2. It works according to the reaction:. The hydroxide ions generated in this equilibrium then go on to react with the hydronium ions from the stomach acid, so that :. This reaction does not produce carbon dioxide, but magnesium-containing antacids can have a laxative effect.
Several antacids have aluminum hydroxide, Al OH 3 , as an active ingredient. The aluminum hydroxide tends to cause constipation, and some antacids use aluminum hydroxide in concert with magnesium hydroxide to balance the side effects of the two substances.
Cooking is essentially synthetic chemistry that happens to be safe to eat. There are a number of examples of acid-base chemistry in the culinary world. Neutralisation is the reaction of an acid with a base that results in the pH moving towards 7. It is a useful process that occurs in everyday life such as in the treatment of acid indigestion and the treating of acidic soil by adding lime.
Neutralisation also moves the pH of an alkali down towards seven. Several different bases can neutralise acids, and water is always produced as a result of these reactions. Metal oxides and alkalis are two types of base. Basic substances neutralise acids, resulting in the pH of the acid increasing towards 7, and water being produced.
Helmenstine, Todd. How to Neutralize a Base With an Acid. Acids and Bases: Titration Example Problem. Calculating the Concentration of a Chemical Solution. How to Calculate the pH of a Weak Acid. Calculating Concentrations with Units and Dilutions. What Is Muriatic Acid? Facts and Uses. Arrhenius Acid Definition and Examples.
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