Making a red cabbage indicator

I took some red cabbage

 I chopped it quite finely and boiled it in a little water.

 Then I crushed it with the potato masher for a minute or two.

 Then I strained it.

When it cooled I used sherry glasses because I don't have any test tubes at home.

I tried it with lemon juice, vinegar, bicarbonate of soda and toothpaste. The little pot on the end is to show the colour of untested red cabbage juice. So acids tend to be pink and alkalis like bicarbonate of soda go green. What I hadn't realised is that the red cabbage is like a universal indicator in that it not only tells you whether it is acid or alkali but also how strong an acid it is. Strength of acid is given as a pH number. The full colour scale is shown here (scroll down when you get there) https://www.compoundchem.com/2017/05/18/red-cabbage/ pH 8 for toothpaste is probably not far off the mark (I'd expect 7.5) , lemon juice as pH 2 is about right, as is vinegar. I used bicarbonate of soda powder so I might have got a different result if I'd watered it down more.