Chemistry at home – Indicators

Potentially a series of experiments for parents to do over half term times.

 

The concept of acids and alkalis comes up in around Year 7 but I found that top set kids in particular didn’t get to do some of the more interesting practical work as they were too busy getting onto higher level skills such as word equations.  This is a fun experiment to do at home.

 

Risk Assessment-bit

Use of kettle for hot water – will your child need help?

Substances for testing – cleaning products tend to be corrosive, so Marigolds may be helpful

Indicators stain fabrics

 

What is an acid? An alkali? pH? an indicator?

pH is a way of measuring how acidic or alkaline a substance is.  It is a scale from 1 to 14, with 1 being very acidic, 7 being neutral (neither acidic nor alkaline), and 14 being very alkaline.

An acid is a substance that releases hydrogen ions.  An alkali is a substance which can accept hydrogen ions.  An indicator is a substance that changes colour if hydrogen ions are added or removed.

 

Making an indicator

Some old methods recommend kids collecting berries from trees.  Personally I’m not so keen – berries are so tempting to taste!  Better options include blackcurrant squash (diluted as directed on the bottle) or red cabbage.  For red cabbage, cut approx a handful into small pieces and put into a heatproof mug, add hot water and stir.  Allow to steep for 5 mins or so, then sieve to remove the pieces.  Allow the solution to cool.

 

Testing substances

At school, the first indicator students meet is called Universal Indicator.  Your Ribena or cabbage indicator will change colour in the same way as this so it links in nicely with the curriculum.  Add a few drops of your indicator to an acid and the indicator will turn reddish.  Add a few drops of your indicator to an alkali and the indicator will turn blueish.  If a substance is neutral, the indicator will stay purple (may look a bit diluted).

Suggested samples: vinegar, lemon juice, juice squeezed from fruit, toothpaste*, washing powder*, baking powder*, soap*

*Solid samples must be mixed with some water in order to be tested.

 

Extending your investigation

Pretty much any colourful natural substance will interact with acids and alkalis.  Your little chemist could try some of the following substances and see what colour they give in acidic, alkaline, and neutral conditions: herbal teas and infusions, petals of bright flowers, brightly coloured leaves.  Soak them in hot water as with the cabbage and test with water (neutral), lemon juice (acidic), and toothpaste solution (alkali).

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