The fake blood chemical reaction is an eye-catching and useful chemical reaction that forms a blood red iron complex. It’s a sensitive test for the presence of iron(III), plus it lends itself to three chemistry demonstrations that are particularly popular around Halloween. The reaction also finds use as a special effect in movies and television for simulating injuries.
Fake Blood Chemical Reaction Materials
For this reaction, you need a water-soluble iron(III) compound and potassium thiocyanate. If desired, use sodium fluoride to instantly decolorize the fake blood.
- iron(III) chloride (FeCl3) or iron(III) nitrate [Fe(NO3)3]
- potassium thiocyanate (KSCN)
- sodium fluoride (NaF) – optional
All you do is make aqueous (water-based) solution of the iron compound and potassium thiocyanate. Either mix the solutions and form a blood red complex or else paint a surface with the potassium thiocyanate solution and draw across it with the iron solution, instantly making “blood.”
Prepare separate solutions. Exact amounts are not critical, but saturated solutions yield the deepest color:
- Add a few milliliters of water to a small container. Stir in iron(III) chloride until no more dissolves. If you like, add the chemical until you see a bit of solid at the bottom of the container and filter out the crystals using a paper towel or coffee filter. You only need the liquid.
- Add a few milliliters of water to a second container. Prepare a saturated potassium thiocyanate solution by stirring the solid into the water until no more dissolves.
- If you like, dissolve a bit of sodium fluoride in water in a third container.
3 Fake Blood Chemistry Demonstrations
Here are three simple chemistry demonstrations featuring the fake blood chemical reaction:
Water Into Blood Color Change Chemistry Demonstration
The usual “water into wine” or “water into blood” chemistry demonstration uses a pH indicator. But, the fake blood chemical reaction works great, too.
- Pour the potassium thiocyanate solution into a clear container.
- Instantly turn the liquid blood red by adding the iron(III) solution.
- If desired, clear the solution with sodium fluoride.
Invisible Ink and Bloody Messages
The potassium thiocyanate solution is a type of invisible ink. The iron(III) solution reveals messages that appear written in blood.
- Write a message using the potassium thiocyanate solution as ink.
- Dampen a cotton ball or dip a paintbrush into the iron(III) solution and swipe across the message to reveal it.
Alternatively, write a message in fake blood:
- Coat paper using the potassium thiocyanate solution and let it dry.
- Write a message using the iron(III) solution.
Messages written on goldenrod paper also appear like blood. But, goldenrod paper is yellow and the color change results from a pH indicator.
Bloody Knife Chemistry Trick
In the bloody knife chemistry trick, a butter knife (or even a spoon) coated with the iron chloride solution leaves a bloody trail across skin or another surface pre-treated with the potassium thiocyanate solution.
- Dampen a paintbrush or cotton ball with the potassium thiocyanate solution and paint over the affected area.
- Dip the dull edge of knife, axe, scythe (etc.) in the iron chloride solution.
- Drawing the damp edge of the treated dull blade appears to cause a bloody injury.
As you might guess, this demonstration isn’t for the squeamish and may be inappropriate in a classroom setting. However, you see it all the time in television and movies when a character appears to cut their hand to make some unholy pact or uses a weapon for inflicting close-up harm to another character. It’s also popular for Halloween haunted houses. Now you know how it’s done!
Safety Info: The chemicals do irritate skin, so immediately rinse the affected area with water. Avoid long contact with the chemicals and don’t apply them near the eyes, nose, or mouth.
How the Fake Blood Chemical Reaction Works
Both the iron(III) compound and potassium thiocyanate are soluble in water. They break into their ions. The important players in the reaction are the Fe3+ from the iron compound and the K+ and SCN2+ from the potassium thiocyanate. These ions form a red-colored iron(III) thiocyanate complex [KSCN=Fe(SCN)₃ ]. It’s red like the iron-based hemoglobin complex that gives real blood its color, minus any injury.
The color of iron thiocyanate depends on pH. In acidic solutions, the color is yellow rather than red. Try wiping off the fake blood with vinegar (dilute acetic acid) and see what happens.
Adding sodium fluoride breaks apart the complex, forming colorless iron cyanate, hexafluoroferrate(III) ions, and sodium cyanate:
Fe(SCN)₃ + 6NaF=Na₃[FeF₆] + 3NaSCN
- Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
- Guy, R. G. (1977). “Syntheses and Preparative Applications of Thiocyanates”. In Patai, S. (ed.). Chemistry of Cyanates and Their Derivatives. 2. New York: John Wiley.
- Lawrance, Geoffrey A. (2010). Introduction to Coordination Chemistry. Wiley. ISBN 9780470687123. doi:10.1002/9780470687123
- Lewin, Seymour A.; Wagner, Roselin Seider (1953). “The nature of iron(III) thiocyanate in solution”. Journal of Chemical Education. 30 (9): 445. doi:10.1021/ed030p445