The red cabbage indicator shows how a usual household product such as red cabbage can make a suitable indicator and be able find out if a chemical is either and acid, alkali or neutral. Acids are a chemical that reacts with an alkali neutralising it producing water and a salt. Acids are also commonly found to be sour tasting. Acids react with metals, releasing hydrogen gas and leaving behind a salt they also can conduct electricity. Acids also readily give off hydrogen ions and have a pH level lower than 7. Some more common laboratory acids are Hydrochloric, Sulphuric and Nitric Acids. Sulphuric acids and water are used in car batteries as the electrolyte.
Bases or alkali are a chemical that will react with acids and usually have a slimy or soapy feeling on contact with skin. Bases readily accept hydrogen ions and has a pH level that is higher the 7. Bases have a bitter taste and neutralise d by acids, producing water and a salt. Some common laboratory bases are Sodium Hydroxide, Potassium Hydroxide and Calcium Hydroxide. Stronger bases are commonly used today in many cleaning products.
Indicators help us find wether if a chemical is an acid or base. The scale that is used to find wether a chemical is an acid or a base is the pH scale. The pH scale gives us an indication of the amount of hydrogen ions and goes from 1 – 14, one being the strongest acid and 14 being the strongest base. Many plants and flowers have natural substances which have indicating properties that allow them to be used as indicators. The red colour of red cabbage comes from a molecule called an anthocyanin. Very acidic solutions will turn anthocyanin a red colour. Neutral solutions result in a purplish colour. Alkalis solutions appear in greenish-yellow. Therefore, it is possible to determine the pH of a solution based on the colour it turns the anthocyanin in red cabbage juice.
← Red cabbage leaves (or red flower petals such as carnation, rose or geranium)
← 250ml beaker
← Hotplate or Bunsen burner, tripod, gauze mat and bench mat
← Spotting tile
← Dilute (0.1M) Hydrochloric acid
← Dilute (0.1M) sodium hydroxide solution
← Distilled Water
← Cloudy Ammonia
← Sodium Chloride
← Lemon Juice
← Dish washing detergent
Part A: Making the indicator
1.The cabbage leaves were torn up and placed in the beaker
2.The beaker was heated until the water was gently boiling. The cabbage leaves continued to boil until the water has been strongly coloured red.
3.The cabbage leaves were allowed to cool and then to be filtered, strained or pick
Part B: Testing the indicator
4.The cabbage water was added to all wells of the spotting tile and split equally between them.
5.A known acid and base were placed on a spotting tile on the cabbage indicator. The colour was record.
6.The remaining chemicals were placed on the spotting tile and were recorded as in step 5
Hydrochloric acid (HCL) is a corrosive liquid
– Skin contact: Exposer for a short period/s of time may cause irritation and prolonged exposer may cause burns
– Eye Contact: Exposer for a short period of time may cause irritation and may cause burns.
– Permanent eye damage may result. To avoid any contact with the substance wear:
– Protective Clothing
– Safety Glasses
– Safety Gloves (Optional)
– Closed shoes
– Eye contact – immediately hold eyelids open and rinse eye continuously for five – ten minutes
– Skin contact – immediately rinse the affected area under water until there is none of the chemical left on the skin
– Contact with any other chemical should be treated as this one.
– All protective gear listed above should be used in the experiment in the same way.
– Hair tied back
– Jewellery to be taken off