Bath Bombs - Periodic Table of Videos

0:00 Brady set Neil and me a challenge.

0:04 He'd been shopping in a shop that sells bath bombs.

0:14 These are objects, mixtures of chemicals

0:19 and perfumes that people throw into their baths.

0:24 Much bubbling and they smell nice.

0:28 Have you ever used one?

0:29 No, I haven't used one.

0:30 I have baths, but I have more sense than to use bath bombs.

0:35 Do you have more baths or showers?

0:37 More baths.

0:38 I'm like Alimedes.

0:39 I have sometimes very good ideas in the bath.

0:43 In fact, I was thinking about your challenge in the bath.

0:46 Last night, Brady was in the shop and he

0:50 saw some bath bombs called the mad professor.

0:56 Now why he was interested in a mad professor I cannot guess but you might.

1:02 He sent me a challenge and Neil

1:05 to do something chemically interesting with these bath bombs.

1:10 There was a list of the ingredients some of which look chemically

1:15 a bit strange but the main ingredients was sodium bicarbonate and citric acid.

1:22 Citric acid is the acid that you find in lemons, oranges.

1:26 It's an organic acid.

1:28 Sodium bicarbonate is a very weak alkali.

1:32 So the idea is that acid will react with alkali,

1:38 liberate carbon dioxide, blow bubbles, and give you a sort of bubble bath.

1:44 So when you put it in a normal bath,

1:46 professor, it's not the bicarbonate reacting with the water.

1:50 Is the water helping the bicarbonate react with the acid?

1:53 Yes.

1:53 First of all, we just put one of the poor professors into water.

2:02 Or rather, we put him in an empty beaker and poured water over him.

2:08 And just to make things a bit more complicated,

2:11 the manufacturers had put some different colored

2:15 dyes in different chunks of the bomb.

2:20 So the professor had blue streaks and green streaks

2:23 and a red streak which came out at various times.

2:27 But chemically we think that these dyes are completely inert.

2:33 [music] Brady's you know has a thermal camera

2:38 which measures the temperature of whatever it's looking at.

2:43 So I suggested he should point the thermal camera

2:47 at the professor because Neil and I predicted that when

2:53 the acid and alkali reacted the professor would get

2:57 hot so-called exothermic reaction meaning heat is given out.

3:03 My reason was chemical.

3:06 Neil's reason was most reactions are exothermic.

3:11 On the other hand, Brady said he thought the temperature would drop,

3:16 so-called endothermic reaction,

3:20 and he has privileged information because he uses bath bombs and he's

3:25 noticed they get a bit cold when he uses them in his bath.

3:31 As it turned out, unfortunately, Raid was right.

3:45 The reason probably is that the dissolving of the salts is

3:52 the endothermic process and citric acid is a pretty weak acid.

3:58 So the acid alkali reaction doesn't produce

4:02 much heat but heat is needed to dissolve

4:06 the salt and the professor is quite tubby

4:10 so there's a lot to dissolve at that face.

4:21 So then I thought that because

4:24 sodium bicarbonate is slightly alkaline that perhaps

4:30 if we put an indicator so-called phenolthalene

4:35 which is colorless in acid and red in alkali if we poured some

4:42 colorless solution of phenolthalene over the professor

4:47 a new fresh sample it would go

4:49 red Because the professor would be slightly alkaline.

5:01 Nothing happened.

5:03 The professor wasn't out the line.

5:06 But Neil had a really historic sample so-called universal

5:12 indicator which changes different colors for acid and alkaline.

5:20 And this showed that the professor when you

5:25 pour the universal indicator over him is slightly acid.

5:30 It's acidic.

5:37 That's an old gold jar that one.

5:39 This probably reflects on the fact that citric acid

5:42 has three acid groups and therefore even when it's neutralized,

5:48 it still has some acid groups that have not reacted with the bicarbonate.

5:54 So I was beginning to feel a bit cheated.

5:58 There was Brady who was right once.

6:01 Neil was right once.

6:03 And I was completely wrong.

6:05 I then had the idea that we should try shining UV light onto the bath bomb.

6:12 Poor professor to see if there was any fluoresence.

6:17 Fluoresence is when a molecule takes in UV light and gives out visible light.

6:25 Oh yeah, well done prof.

6:29 And much to my pleasure of the three dyes, the red,

6:34 the green, and the blue, the green dye fluess very strongly.

6:40 It looked a completely different color,

6:42 but it was emitting this sort of bluish light.

6:46 Then we decided to be a bit more chemically vicious.

6:52 We tried using concentrated sulfuric acid.

6:57 Concentrated sulfuric acid has the property

7:01 of removing the elements of water from compounds.

7:08 And both citric acid and the so-called rice powder or rice starch that was

7:16 being used as one of the ingredients in the bomb contain the elements of water.

7:23 And if you extract those, you form carbon.

7:26 and carbon is black.

7:29 So, having had a whole series of boring experiments where nothing much changed,

7:35 we poured on the sulfuric acid and we noticed two quite different effects.

7:58 The first effect was looking through the thermal

8:02 camera and this time with the con sulfuric acid, the professor really lit up.

8:11 There was a lot of heat.

8:14 Partly this may have been the water

8:17 being extracted and reacting with sulfuric acid

8:21 because sulfuric acid releases a lot of heat [music] when it's mixed with water.

8:28 And secondly, it may be because the reaction of sulfuric

8:31 acid with the ingredients of the bath bomb were inherently exothermic.

8:40 But either way, the professor lit up.

8:44 [music] [music] [music] [music] [music] Secondly,

9:10 and quite surprisingly, there wasn't much color change.

9:15 I'd expected the professor to go coal black straight away,

9:21 and there was perhaps some slight discoloring,

9:26 but that could have come from traces of the dye as it dissolved out of the bomb.

9:32 But it did fizz in a really quite satisfying way.

9:37 Heat.

9:38 Heat.

10:14 And then when Neil doused it all in the sink,

10:18 the heat from the water going into the sulfuric acid caused

10:24 really quite a lot of bubbling and a big temperature rise.

10:28 Then, as you know, Neil loves burning things.

10:34 So, we decided to burn the poor professor.

10:40 Neil had a gas torch and he also had a tube with a supply

10:47 of oxygen coming out of essentially a needle which he could point at things.

10:55 So when he played the flame on the face of the poor professor,

11:00 the face went black presumably because things were decomposing to carbon.

11:16 So that's a good change.

11:18 It's gone black.

11:20 He then thought he would jazz it up by blowing

11:25 oxygen on it and it should get much hotter.

11:28 Oxygen makes combustion go faster.

11:40 But really surprisingly, the jet of oxygen cooled things down.

11:48 You could see on the thermal imaging camera,

11:50 it got cooler and visibly the flames got less.

11:58 This doesn't mean that you should use oxygen as a fire extinguisher,

12:04 but it means the blast of gas was enough to cool things down.

12:13 And presumably the oxygen diffused away so fast

12:17 that it didn't really add to the combustion.

12:19 So Neil got a bigger and better burner.

12:27 And then when he put the big flame on the poor professor,

12:32 when he added the oxygen, it really started burning.

12:52 By the end, the poor professor had sort of become a black and white owl.

12:59 I thought it looked rather elegant and artistic.

13:02 Professor, were you worried about how much Neil

13:04 seemed to enjoy setting fire to a professor?

13:08 Well, I was concentrating so much on the experiment

13:13 that I didn't notice the smirk on Neil's face.

13:17 Otherwise, I might have got a bit worried.

13:20 Anyway, we then thought it would be interesting to see

13:24 what happened if we poured some water on this owl.

13:30 Unfortunately, part of the owl's face fell off before we got the water there.

13:37 But what I thought was really interesting is that when we added water,

13:43 the charred bits of the figure fell off and inside it

13:50 was still completely white and had been largely unaffected by the heat.

13:56 which demonstrates that these materials are very

14:01 poor conductors of heat and also the material

14:04 is sufficiently dense that the oxygen cannot

14:10 really reach the middle so they can't burn.

14:14 So after just a few minutes it looked just the same as the unburnt professor.

14:21 Do you think the bombs have to be dense like that so that they last

14:24 a long time in the bath and the water can't get in as easily as well?

14:28 I think that's almost certainly the reason.

14:31 And also, you'd be very disappointed if your expensive bath toy,

14:36 and I assume it was expensive, falls to bits as soon as you put it in the bath.

14:42 So, it has to have a certain strength like

14:45 the old professor and doesn't fall to bits immediately.

14:53 [music]