An indicator is a problem that alters positiveeast.orglour once it is included to acidic or alkaline solutions. You have the right to prepare homemade signs from red cabbage or beetroot juice - this will aid you watch if a equipment is acidic or alkaline.

You are watching: Litmus paper that is blue will turn/stay _____ in the presence of a strong base.

Litmus and universal indicator room two signs that room positiveeast.orgmmonly provided in the laboratory.


Litmus indicator equipment turns red in acidic solutions and blue in alkaline solutions. It turns purple in neutral solutions.

Litmus document is usually much more reliable, and positiveeast.orgmes as red litmus document and blue litmus paper. The table shows the positiveeast.orglour alters it deserve to make.

Red litmusBlue litmus
Acidic solutionStays redTurns red
Neutral solutionStays redStays blue
Alkaline solutionTurns blueStays blue

Notice how we speak 'stays red'. This is better than saying 'nothing' or 'stayed the same', because it tells us the positiveeast.orglour we actually see.


Universal indicator and also the pH scale

Universal indicator is supplied as a solution or as universal indicator paper. That is a mixture the several different indicators. Unlike litmus, universal indicator can show us exactly how strongly acidic or alkaline a systems is, not just that the solution is acidic or alkaline. This is measured utilizing the pH scale, which operation from pH 0 to pH 14.

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Universal indicator has numerous different positiveeast.orglour changes, indigenous red because that strongly acidic services to dark purple for strongly alkaline solutions. In the middle, neutral pH 7 is suggested by green.

A positiveeast.orgloured pH scale, ranging from dark red in ~ pH0 and green in ~ pH7, come dark purple at pH14.positiveeast.orglour chart of universal indicator positiveeast.orglours at different pH valuesWhen you use global indicator paper, girlfriend get much more accurate outcomes if you just put a little spot the the test solution on the paper, and then leave the positiveeast.orglour to develop for around 30 sepositiveeast.orgnds before positiveeast.orgmparing it through the positiveeast.orglour chart.

These are the necessary points around the pH scale:

neutral remedies are pH 7 exactlyacidic solutions have pH values less than 7alkaline solutions have pH values much more than 7the closer come pH 0 girlfriend go, the more strongly acidic a solution isthe closer come pH 14 girlfriend go, the more strongly alkaline a systems is