0:04 What makes a pure substance pure? Is it
0:07 because it looks clean? Because it
0:09 tastes plain? Or is there something
0:13 deeper? Something invisible that defines
0:15 it? In this video, we're diving into
0:18 pure substances and what they really
0:26 Imagine [Music]
0:35 you're known for your voice, your style,
0:39 even your smile. These little things,
0:42 they make you uniquely you. You don't
0:44 randomly wake up with a new identity,
0:48 right? Well, in science, some materials
0:51 have an identity, too. We call them pure
0:54 substances made of just one kind of
0:58 building block. No surprises, no mixups.
1:00 And that's what makes them stand out in
1:03 chemistry. But what exactly is a pure substance?
1:05 substance?
1:08 It's a material made of only one kind of
1:10 particle, either single atoms or
1:14 particles made of atoms bonded together.
1:17 To understand this better, let's explore
1:20 two examples. a gold bar and a beaker of
1:23 water. If we can zoom in to observe the
1:26 gold bar, we'd see only gold atoms
1:30 packed closely, all exactly the same.
1:33 Now, let's examine the water. Every drop
1:36 contains identical particles, each made
1:40 of two hydrogen atoms joined to one
1:42 oxygen atom.
1:44 Gold and water may seem different, but
1:46 each one is stays the same all
1:50 throughout. The key is this. The
1:53 composition never changes.
1:56 That's what makes them pure.
1:58 When scientists say that a substance has
2:02 a fixed chemical composition, they mean
2:04 something very specific.
2:07 It means that every single sample of
2:10 that substance, no matter where you find
2:12 it, always contains the same kind of
2:16 atoms in the same ratio.
2:19 Take water for example. Pure water
2:23 always has two hydrogen atoms bonded to
2:28 one oxygen atom. That's what H2O means.
2:33 Not 2 and 1/2, not 3 and 1, always 2 to
2:37 1. No more, no less. That's what we mean
2:41 by fixed chemical composition.
2:44 So remember, pure substances have the
2:48 same kind of particles in the same ratio
2:50 every time.
2:53 So if both gold and water are pure substances,
2:54 substances,
2:57 what makes them different?
3:01 Well, pure substances come in two types,
3:03 elements and compounds.
3:06 Gold is an element. It's made of just
3:09 one kind of atom. Water, on the other
3:11 hand, is a compound made of different
3:15 atoms chemically bonded in a fixed ratio.
3:16 ratio.
3:19 Let's dive in on the first type, elements.
3:21 elements.
3:24 Elements are made of only one kind of
3:27 atom. All the particles are exactly the
3:30 same. Whether it's gold, oxygen, or
3:34 argon, an element never mixes in atoms
3:38 of a different kind, each atom type has
3:41 a unique number of protons. That's its
3:44 atomic identity.
3:46 And because every atom in an element is
3:50 the same, the substance stays consistent
3:52 all throughout.
3:54 So what makes a gold atom gold or an
3:58 oxygen atom oxygen? The answer is
4:01 protons. The number of protons in the
4:05 nucleus decides the element. Gold always
4:10 has 79 protons. Oxygen always eight.
4:15 Argon 18. That never changes. It's like
4:18 a fingerprint. If the proton count
4:21 changes, it's not the same element
4:24 anymore. So in a pure substance like
4:27 gold, every atom has the same number of
4:31 protons, 79. When all the atoms are the
4:34 same, you get a fixed composition. And
4:38 that's what makes it a pure substance.
4:41 Now let's talk compounds. Compounds are
4:44 pure substances too, but with a twist.
4:46 They are made of more than one kind of
4:49 atom. And those atoms are always
4:53 combined in a specific unchanging ratio.
4:56 Take salt also called sodium chloride.
5:00 Every unit is made of one sodium atom
5:04 and one chlorine atom. This atoms form a
5:07 chemical bond locking together in that
5:11 exact ratio. That ratio doesn't change.
5:14 No matter where you get it, table salt
5:17 is always an ACC.
5:22 Never Na2 CL or N A C2.
5:24 Now, not all compounds are as simple as
5:28 salt. Let's look at two more examples.
5:31 Carbon dioxide and ammonia. Carbon
5:35 dioxide or CO2 is always made of one
5:38 carbon atom and two oxygen atoms. Ammonia
5:40 Ammonia
5:43 or NH3 is always made of one nitrogen
5:47 atom and three hydrogen atoms. Even
5:49 though they're made of different atoms,
5:52 the rule stays the same. They're always
5:56 bonded in a fixed ratio. And that's what
5:58 makes them pure substances just like
6:02 water, salt, and gold.
6:05 Now, not everything around us has this
6:08 fixed recipe. Let's clear things up by
6:12 comparing pure substances to mixtures.
6:14 A pure substance has particles that are
6:17 all the same, whether it's a single
6:21 element or a compound. A mixture, on the
6:23 other hand, combines different particles
6:26 and the ratio can change.
6:30 Think of salt water. When salt dissolves
6:33 in water, it doesn't disappear. It
6:36 breaks apart into ions.
6:38 Inside the mix, you'll find water
6:41 molecules, sodium ions, and chloride
6:45 ions all swimming around together.
6:47 They're not held together by chemical
6:51 bonds, it's just a physical mix. And
6:52 because there's more than one kind of
6:56 particle, salt water is a mixture, not a
6:59 pure substance.
7:02 All right, now that you've seen what
7:04 makes something a pure substance, let's
7:06 put your eyes and your brain to the
7:10 test. Can you tell which ones are truly
7:12 pure and which are just clever mixtures
7:15 in disguise? Let's test your science
7:18 instincts. Are these materials pure
7:21 substances or not?
7:25 Take a look at each one. Just drink air
7:30 in a balloon, ethanol, medical oxygen,
7:33 and vinegar. Think carefully, then get
7:36 ready for the answers. This lemon drink
7:39 might look uniform, but it's actually a
7:44 mixture. Sugar, water, flavoring, maybe
7:46 even coloring, all blended, not
7:49 chemically bonded.
7:53 Air seems invisible and even, but it's a
7:55 mix of gases.
7:58 Nitrogen, oxygen, carbon dioxide, and
8:04 more. So, nope, not a pure substance.
8:06 Ethanol, on the other hand, is a
8:10 compound. It's made of carbon, hydrogen,
8:13 and oxygen atoms. And every molecule has
8:18 the same formula C2 H5O.
8:21 That fixed structure makes ethanol a
8:23 pure substance.
8:26 Medical oxygen is a pure substance too.
8:30 And it's an element. It contains only
8:33 oxygen molecules, nothing else. That's
8:37 why it's safe for patients who need it.
8:40 Now, vinegar, it often tricks people.
8:42 Some think it's a compound, but it's
8:46 actually a mixture. Why? Because it's
8:48 just water and acetic acid mixed
8:51 together, not chemically bonded.
8:54 Each part keeps its identity. So,
8:58 vinegar is a mixture.
9:00 So, remember pure substances have only
9:03 one kind of particle.
9:05 Mixtures have different particles
9:07 physically combined, not chemically bonded.
9:09 bonded.
9:12 All right, quick recap. Pure substances,
9:14 they're made of just one kind of
9:16 particle, either an element or a
9:20 compound. Their makeup always the same.
9:22 No surprises.
9:24 Elements, they've got only one kind of
9:28 atom like gold or oxygen. Compounds made
9:31 of different atoms chemically bonded in
9:35 a fixed ratio like water or salt.
9:38 Now mixtures, that's a totally different
9:40 story. They're just physically combined
9:43 and the ratio can change. Think salt
9:46 water, lemon drink, or even the air you
9:48 breathe. So next time you're holding
9:51 something and thinking, is this pure?
9:54 Just remember what you've learned today.
9:56 Science is all about asking the right questions.
9:59 questions.
10:01 This is Learning with G. Stay tuned for
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