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    Home » Science Experiments for Kids » Chemistry » How to make pH indicator with a poinsettia

    How to make pH indicator with a poinsettia

    December 29, 2022 By Emma Vanstone Leave a Comment

    Do you know you can make a pH indicator with the red leaves from a poinsettia plant? Red poinsettia leaves contain anthocyanins which change colour in the presence of acids or alkalis.

    Acids have a low pH ( below 7 ), and alkalis have a high pH ( over 7 ).

    Poinsettia with red and green leaves
    Red leaves on a poinsettia plant

    If it’s not the season for red poinsettia leaves, red cabbage also makes a brilliant pH indicator.

    You’ll need

    A handful of poinsettia leaves

    Pan

    Water

    Scissors

    Sieve

    Beaker

    Test tubes or small transparent containers

    Substances to test – lemon juice, vinegar, baking soda in water, water

    Coffee filter – optional

    two beakers of poinsettia indicator. One is pink after the addition of an acid

    Instructions

    Place about 200ml of water in a pan and heat gently.

    Cut a handful of red poinsettia leaves with the scissors and drop them into the pan.

    Bring the water and poinsettia leaf mixture to the boil and then leave to stew for about 20 minutes.

    Let the indicator cool and pour through the sieve into a beaker.

    Pour a little indicator into two test tubes or small containers.

    Add a couple of drops of your test substance and watch as the indicator changes colour.

    The poinsettia indicator should turn pink/red in the presence of an acid and green if mixed with an alkali. I struggled to get my mixture to turn green, but I plan to try it again.

    Poinsettia indicator strips

    To make indicator strips with filter paper, soak a piece of filter paper or a coffee filter in the indicator mix and leave it to dry.

    Cut the filter paper into strips and drop some test substances onto each. The strips should change colour.

    What is a pH indicator?

    Indicators are used to measure the pH of a substance. They change colour in the presence of an acid or alkali. The pH scale goes from 0 to 14.

    Scientists commonly use Universal Indicator to measure pH. Universal indicator is a mixture of dyes that gives the colours below when an acid or alkali is added.

    universal indicator

    Examples of weak acids

    Milk

    Coffee

    Tomato Juice

    Examples of strong acids

    Hydrochloric acid

    Sulphuric acid ( found in car batteries )

    Examples of weak alkalis

    Washing up liquid

    Examples of strong alkalis

    Ammonia

    Sodium hydroxide

    All about acids and alkalis

    Acids have a low pH ( below 7 )

    Strong acids can be corrosive.

    Acids are neutralised by bases ( alkalis ).

    When acids react with some metals, they release hydrogen.

    Alkalis have a pH above 7.

    Alkalis can also be corrosive.

    Alkalis neutralise acids to make salts and water.

    An alkali is a soluble base!

    poinsettia pH indicator science experiment

    Last Updated on December 30, 2022 by Emma Vanstone

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    Safety Notice

    Science Sparks ( Wild Sparks Enterprises Ltd ) are not liable for the actions of activity of any person who uses the information in this resource or in any of the suggested further resources. Science Sparks assume no liability with regard to injuries or damage to property that may occur as a result of using the information and carrying out the practical activities contained in this resource or in any of the suggested further resources.

    These activities are designed to be carried out by children working with a parent, guardian or other appropriate adult. The adult involved is fully responsible for ensuring that the activities are carried out safely.

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