Background Acids are solutions that lose hydrogen ions and usually taste sour. Some very common household solutions are acids, such as citrus fruit juices and household vinegar. Bases are solutions that pull hydrogen ions out of solution and onto themselves, "accepting" them, and usually feel slippery. Bases have many practical uses.
For example, "antacids" like TUMS are used to reduce the acidity in your stomach. Other bases make useful household cleaning products. To tell if something is an acid or a base, you can use a chemical called an indicator.
An indicator changes color when it encounters an acid or base. There are many different types of indicators, some that are liquids and others that are concentrated on little strips of "litmus" paper. Indicators can be extracted from many different sources, including the pigment of many plants. For example, red cabbages contain an indicator pigment molecule called flavin, which is a type of molecule called an anthocyanin.
Very acidic solutions will turn an anthocyanin red whereas neutral solutions will make it purplish and basic solutions will turn it greenish-yellow.
Consequently, the color an anthocyanin solution turns can be used to determine a solution's pH—a measure of how basic or acidic a solution is. If you do not want to grate the entire cabbage, grating half of a cabbage should be enough. Put the fine, pulpy grated cabbage into a large bowl or pot. Use caution when handling the boiling water. Pour the boiling water into the bowl with the cabbage pulp until the water just covers the cabbage. This should take at least half an hour. The liquid will become red or purplish-red in color.
Press down on the pulp in the strainer, such as by using a large spoon, to squeeze more liquid out of the pulp. This will be your indicator solution, which you will use to test the pH of different liquids.
What is the color of your indicator solution? Gently swirl the solution and make sure the color stays the same. Selection includes aquatic and classroom plants. Carolina's extensive assortment of compound and stereomicroscopes span virtually all grade levels and applications.
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You have questions-we have answers. Get general information, care guides, and product information here. Brush up on the latest instructional strategies and pedagogy with information from our teaching partners, instructional designers, and academic consultants. Feeling the pinch from the current economy? Carolina understands. In the laboratory, pH paper and chemicals are commonly used to indicate pH. In the homeschool, students can make their own pH indicator using red cabbage juice, which changes color in the presence of an acid or base.
The plant pigment anthocyanin is the active ingredient responsible for the color change. In this activity, students make a pH indicator from red cabbage juice and then use it to test various substances. Students can also make paper pH indicator strips using red cabbage juice.
First, cut strips from an unused paper coffee filter. Next, soak them in red cabbage juice for several hours. Finally, take the strips out of the juice and allow them to dry completely.
Once the indicator strips are dry, they are ready for use. The dried strips will be light violet or pale blue in color. Acids will turn the strips red and bases will turn them green. Red cabbage juice indicator changes color because its hydrogen ion concentration changes when a test substance is added to it. Acids produce hydrogen ions in aqueous solution and have a pH less than 7.
Bases contain hydroxide ions and have a pH greater than 7. At a pH of 7, a substance is neutral neither acid nor base due to equal numbers of hydrogen and hydroxide ions. Carolina offers a full line of kits, chemicals, and pH indicators to further your exploration of pH. We use cookies to provide you with a great user experience. Dropper bottles are ideal. Alternatively small beakers cm 3 with dropper pipettes could be used.
Students need to be able to pour the acid and alkali solutions easily and safely into test tubes. Additional information This is a resource from the Practical Chemistry project , developed by the Nuffield Foundation and the Royal Society of Chemistry. Level years years.
Use Practical experiments. Category Acids and bases. Investigate reactions between acids and bases; use indicators and the pH scale Leaving Certificate Chemistry 9. Environmental chemistry: water 9. Use of universal indicator paper or solution. Limitations of the pH scale - usefulness confined to dilute aqueous solutions. Theory of acid-base indicators Scotland National 5 SQA Chemistry Chemistry in society Chemical analysis Analytical methods An indicator is normally used to show when the end-point is reached.
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