Chapter 9: Chemical Quantities

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Welcome to the Deep Dive, where we sift through information to bring you crucial nuggets of knowledge, tailored just for you.

Today we're diving into something fundamental, really underpinning so much of biology and medicine.

And we'll start with, well, a powerful story.

Imagine Michelle.

She had severe strep throat as a kid, and because of that, her kidneys failed.

Now, three times a week, her life literally depends on dialysis.

It sounds incredibly high tech, right?

It does, yeah.

But at its heart, dialysis is chemistry.

Specifically, the chemistry of solutions, saving her life.

It's a perfect real example.

So our mission today is to take that deep dive into solutions.

The core concept explaining, well, everything from the air we breathe to the fluids inside our bodies.

We want to unpack how things mix, how they interact, and why this basic chemistry is so critical, especially in health and life sciences.

Think of this as your shortcut to understanding the chemical dance happening all around us and inside us.

And what's really fascinating, I think, is how these principles are just constantly at play everywhere.

Whether it's within your cells, the tiny molecular machinery, or even the medications you might take,

understanding solutions connects that basic chemistry directly to our health.

OK, let's unpack this then.

When we talk about solutions,

it's more than just stirring sugar in coffee, isn't it?

What are we really getting at?

Exactly.

Fundamentally, a solution is what we call a homogenous mixture.

Meaning it's completely uniform throughout one substance, the solute that's usually the one in the smaller amount, like salt is perfectly dispersed in the other substance, the solvent, the one in the larger amount, like water.

It's not just mixed, it's evenly blended.

Every single part of that solution is identical.

Ah, OK.

Uniformity is key.

Absolutely critical, especially in health.

You need every drop of an IV fluid or medicine to have the exact same concentration.

You can't have stuff settling out.

Think about the air you're

in.

And the solvent determines the state, right?

Like liquid water means a liquid solution.

Precisely.

The overall physical state matches the solvent.

OK, that makes sense for air or salt water.

But why do some things mix so well and others just refuse?

Like the classic oil and water example.

Right.

That comes down to a really fundamental principle.

Like dissolves like.

Like dissolves like, OK.

It's all about polarity.

Think of molecules as having sort of electrical poles, positive and negative ends.

For a solution to form, the attractions between the solute particles and the solvent particles need to be strong enough, similar enough, to overcome the forces holding each substance together on its own.

Water, for instance, is super polar.

Its molecule is bent, and the electrons aren't shared equally.

This lets water molecules form strong attractions, especially hydrogen bonds, with other polar things or with charged ions.

So water can pull things apart.

Effectively, yes.

When you put something ionic like sodium chloride table salt in water,

the polar water molecules surround the positive sodium ions and the negative chloride ions.

They pull them apart, draw them into the solution.

We call that hydration.

OK.

And the same happens with other polar molecules like methanol.

But non -polar things like oil, grease, iodine,

they don't have those strong polar attractions.

Water molecules are more attracted to each other than they are to the oil molecules.

So there's no incentive for them to mix?

Exactly.

There's no energetic advantage, so they stay separate.

Oil floats on water.

So polarity isn't just some abstract chemistry idea.

It's literally how our bodies work, right?

Because water is the main solvent in us.

It absolutely is.

Our bodies are, what, about 60 % water for an adult, even higher for infants, maybe 75%.

And this water isn't static.

It's divided into the fluid inside your cells, intracellular and the fluid outside, like blood plasma extracellular.

And it's constantly moving, constantly being used and replenished.

Through drinking, obviously, but food, too.

Definitely.

You lose water daily breathing, sweating, urine,

maybe 1 ,500 to 3 ,000 milliliters.

But you gain it back not just from drinks, but also from food.

A carrot is like 88 % water.

Chicken, around 71%.

I never thought of it that way.

And this water acts as the solvent for countless vital substances, nutrients, waste products, ions.

It's essential for transport, for chemical reactions, life, basically.

That's a great point.

So once these things are dissolved, especially in water in our bodies, do they all act the same?

Particularly thinking about electricity, because you hear about electrical signals in nerves and muscles.

Ah, no, they definitely don't all act the same.

And this difference is crucial.

When substances dissolve, they either break apart into charged particles ions, or they stay as whole, neutral molecules.

The ones that break into ions are called electrolytes.

And because they form ions, their solutions can conduct electricity.

Think nerve impulses, muscle contractions.

That's electrolytes at work.

Right, conducting the body's electrical signals.

Exactly.

And then we classify them further.

You have strong electrolytes.

These dissociate, meaning break apart, almost 100%.

Things like sodium chloride, strong acids like hydrochloric acid.

Lots of ions mean they conduct electricity really well.

Okay, strong means full dissociation.

Right.

Then there are weak electrolytes.

They only partially dissociate.

Maybe only a few percent of the molecules break into ions.

Acetic acid vinegar is a classic example.

Most stays as molecules, a few form ions, so they conduct electricity, but poorly.

Got it.

And the last type.

Non -electrolytes.

These dissolve, but they stay as whole molecules.

No ions are formed.

Sugar, alcohol like methanol, urea, these are non -electrolytes.

Their solutions don't conduct electricity at all.

So like MgNO3 -2, magnesium nitrate, how does that break down?

Right, that's a strong electrolyte, an ionic salt.

When it dissolves, one magnesium nitrate unit breaks completely into one magnesium ion, which has a 2 plus charge, Mg2 plus O, and two nitrate ions, each with a one charge, 2 and O3.

Two nitrates, right, because of the formula.

Connecting this back to health,

what does this conductivity of these electrolytes mean for us practically?

It's absolutely vital.

In hospitals, we measure the concentration of specific ions in your body fluids, usually in units called milli -equivalents per liter,

or MEQL.

And these levels tell us a lot.

Think about key ions.

Sodium, NAF plus E, is crucial for regulating how much water is in your body, and for nerve signals.

Potassium, K plus A, is essential for electrical signals in the heart, keeping your heartbeat regular.

So imbalances would be serious.

Extremely serious.

Chloride, Cl, helps balance the positive charges and maintain fluid levels.

Bicarbonate, HCO3, is key for keeping your blood pH stable.

And how do imbalances happen?

Things like severe vomiting, diarrhea, even excessive sweating can throw these levels off drastically, can be life -threatening.

That's why IV solutions like normal saline, which is 0 .9 % sodium chloride, or lactated ringers, are so important.

They're carefully made with specific MEQL values to restore that critical balance.

That makes sense.

Now, moving from the how things dissolve to how much.

Is there a limit?

You can't just keep pouring salt into water forever.

At some point, it just sits there.

Exactly.

There's a limit, and we call that solubility.

Solubility.

It's the maximum amount of a solute that can dissolve in a specific amount of solvent, usually 100 grams of water at a particular temperature.

Great.

Temperature matters.

Big time.

So if you add less solute than the maximum, the solution is unsaturated.

If you add exactly the maximum amount, it's saturated.

Any more solute you add after that point just won't dissolve.

It'll settle at the bottom.

And I've heard of super saturated.

Right.

That's a tricky one.

Sometimes if you make a saturated solution at a high temperature and cool it very carefully, you can actually get it to hold more solute than it normally should at that lower temperature.

That's super saturated,

but it's unstable.

Unstable how?

Just disturb it slightly, tap the glass, add a tiny crystal, and boom, all the excess solute suddenly crystallizes out.

Wow.

Okay.

And the temperature effect.

You said it matters.

Yeah.

For most solid solutes, like sugar or salt in water, solubility increases as the temperature goes up.

That's why you can dissolve way more sugar in hot tea than in iced tea.

Makes sense.

But for gases dissolved in liquids, it's the opposite.

Gas solubility decreases as temperature increases.

Oh, okay.

Like the warm soda going flat.

Exactly.

Yeah.

The warmer it gets, the less carbon dioxide gas can stay dissolved, so it bubbles out faster.

This is also related to Henry's Law.

Henry's Law.

It states that the solubility of a gas in a liquid is directly proportional to the pressure of that gas above the liquid.

When you open a soda can, you release the pressure.

And the gas comes out.

Right.

The solubility decreases instantly and the CO2 bubbles out.

This pressure relationship is super important for how gases like oxygen and CO2 dissolve in our blood too.

Okay.

The solubility limit thing.

Yeah.

If things can only dissolve up to a certain point, what happens if they precipitate out, especially somewhere they shouldn't like inside the body?

That sounds like it could cause problems.

It definitely can.

While many ionic compounds dissolve well in water, especially those with ions like sodium, potassium, ammonium, nitrate, there are important exceptions.

Some ionic compounds are essentially insoluble.

Meaning they don't dissolve in water?

Pretty much.

Their internal ionic bonds are just too strong for water to break apart effectively.

Things like silver chloride, lead chloride are insoluble.

Is that ever useful?

Actually, yes.

Medically, think about barium sulfate, base 04.

It's used for x -rays of the digestive system.

Right.

You drink it.

You do.

Now, soluble barium compounds are highly toxic, but barium sulfate is safe because it's extremely insoluble.

It just passes through your system without dissolving and releasing those dangerous barium ions.

Ah, the insoluble makes it safe.

Clever.

But when things that should stay dissolved precipitate out inside the body because their concentration exceeds their solubility limit, that causes diseases.

Like what?

Gout and kidney stones are prime examples.

In gout, uric acid, a waste product, builds up.

Its solubility in blood plasma at body temperature is pretty low, maybe 7 milligrams per 100 mil out.

If the concentration gets higher than that, it crystallizes out, forming these sharp needle -like crystals, often in joints like the big toe.

Very painful.

Ouch.

And kidney stones?

Similar idea.

They form when compounds like calcium phosphate or calcium oxalate become too concentrated in the urine, exceeding their solubility, and they crystallize into hard stones.

Diet, hydration levels, they all play a role.

So understanding solubility is key to understanding and treating these conditions.

Absolutely.

It's all about managing those concentration levels.

Okay.

So we know what solutions are, how they form, solubility limits, but how do we actually measure the strength?

How do we quantify concentration precisely?

Especially in medicine, precision must be everything.

It really is.

We use different units for concentration, which is just the amount of solute in a given amount of solution.

In health sciences, probably the most common you'll see are mass, volume, percent written as MV and molarity, symbol M.

Mass, volume, percent.

It's super practical.

It's just the grams of solute divided by the milliliters of solution

100%.

So a 5 % MV glucose solution, common in IVs, means there are five grams of glucose in every 100 milliliters of that solution.

Easy to calculate doses from.

Okay.

Grams per 100 milliliter and molarity.

Molarity is more fundamental for chemists.

It's defined as the moles of solute per liter of solution.

Moles tell us about the actual number of particles, which is crucial for understanding chemical reactions.

So M equals moles divided by liters.

Moles per liter.

Got it.

Both of these and others like mass percent or volume percent MV act as conversion factors.

They let us figure out, say, how many grams of an antibiotic are in a certain volume of an IV bag or how much solution we need to get a specific dose.

Right.

Crucial for calculations.

And what if you have a solution that's too strong, like a stock solution in a lab and you need something weaker for an experiment or a patient?

Ah, then you perform a dilution.

Dilution, just adding water.

Usually, yes.

Dilution is simply adding more solvent to a solution.

This increases the total volume, which naturally decreases the concentration, spreads the solute out more.

Okay.

But the key thing to remember during dilution is that the amount of solute doesn't change.

You start with a certain amount, you end with the same amount.

It's just in a bigger volume.

Like adding water to frozen orange juice concentrate.

Perfect analogy.

The amount of orange stuff stays the same, but the juice gets less concentrated, less strong.

So there's a calculation for that.

Yep.

A simple one.

C1V1 times the initial volume equals the final concentration times the final volume.

Because the amount of solute concentration times volume is constant.

C1V1 equals C2V2.

Okay.

This is done constantly in labs, pharmacies, hospitals.

Preparing weaker solutions from stronger stock solutions is a fundamental skill.

Right.

Now, we've mostly talked about true solutions, but not all mixtures look like salt water, right?

Some are cloudy, some settle out.

Exactly.

We need to distinguish true solutions from colloids and suspensions.

It all comes down to particle size.

Particle size.

Solutions have the smallest particles, ions, small molecules.

They're transparent, they don't settle, and the particles pass right through filters and also through special membranes called semi -permeable membranes.

Colloids have larger particles.

Think big molecules like proteins or small clumps.

Examples are milk, fog, blood, plasma.

They often look cloudy or opaque.

The particles are big enough to scatter light, but usually small enough not to settle out quickly.

They'll pass through ordinary filters.

But not semi -permeable membranes.

Correct.

They get held back by semi -permeable membranes.

That's a key difference.

And suspensions.

Suspensions have the largest particles.

Things you can often see, like sand and water or certain liquid medications you have to shake well, like some antibiotics or kaopectate.

These particles will settle out over time, if left undisturbed, and they get trapped by both regular filters and semi -permeable membranes.

Okay.

Solutions, colloids, suspensions.

Different particle sizes, different behaviors with membranes.

That membrane part sounds important, especially for biology.

Hugely important.

It leads us straight to osmosis.

Osmosis.

I remember that from biology class.

Movement of water.

Precisely.

Osmosis is the movement of water molecules across a semi -permeable membrane.

And the key is water moves from an area where the solute concentration is lower.

Meaning more water.

Right.

Higher water concentration.

To an area where the solute concentration is higher.

So less water.

Water moves to dilute the more concentrated side.

You got it.

It's trying to equalize the concentration on both sides.

The pressure that this movement generates, or the pressure needed to stop it, is called osmotic pressure.

And it depends on the total concentration of solute particles, ions, molecules, doesn't matter what they are, just how many.

And this has big consequences for our cells.

Enormous consequences for red blood cells, for example.

They have semi -permeable membranes if you put them in an isotonic solution.

ISO meaning same.

Yes.

Same osmotic pressure as the fluid inside the cells.

A 0 .9 % MV sodium chloride solution or a 5 % MV glucose solution are isotonic to red blood cells.

In these solutions, water moves in and out at the same rate so the cells maintain their normal shape and volume.

Okay, that's the ideal state.

What about other solutions?

If you put red blood cells in a hypotonic solution, hypo, meaning lower solute concentration than inside the cell.

So more water outside.

Right.

Water will rush into the cells following that concentration gradient.

The cells swell up and they can eventually burst.

That's called hemolysis.

Think of a raisin dropped in pure water.

It swells up.

Hemolysis.

Got it.

And the opposite.

The opposite is a hypertonic solution,

meaning higher solute concentration outside the cell than inside.

So water leaves the cell.

Exactly.

Water flows out of the red blood cells into the more concentrated surrounding solution.

The cells shrivel up.

They shrink.

This is called crenation.

Think about making pickles.

You put cucumbers in very salty brine, a hypertonic solution, and they shrivel as water leaves them.

Crenation.

Okay.

Isotonic, hypotonic, hypertonic.

Crucial for cell survival.

Absolutely.

Maintaining the right osmotic balance is fundamental.

Which brings us full circle.

Back to Michelle on dialysis.

How does this life -saving procedure fit into all this chemistry of solutions, membranes, osmosis?

Dialysis is essentially an artificial application of these very principles, designed to mimic kidney function.

It uses a special dialyzing membrane.

Like a semi -permeable membrane.

Similar, but slightly different.

A dialyzing membrane allows not just water, but also small solute particles, ions, small molecules like glucose,

and crucially waste products like urea to pass through.

However, it retains larger colloidal particles like proteins and blood cells.

So it filters based on size, letting small waste out, but keeping important big stuff in.

Precisely.

Your natural kidneys do this constantly.

Millions of tiny filters called nephrons clean your blood, removing waste products like urea and excess salts and water, while reabsorbing vital things your body needs.

But if kidneys fail, like Michelle's.

Then waste products build up to toxic levels and fluid balance goes haywire.

That's where hemodialysis, the artificial kidney machine, comes in.

How does the machine work?

The patient's blood is pumped through tubing made of or containing a dialyzing membrane.

This tubing is immersed in a special fluid called the dialysate.

The dialysate.

What's in that?

It's carefully controlled.

It has normal, healthy concentrations of essential electrolytes like sodium and potassium.

But importantly, it has no waste products like urea.

So there's a concentration gradient for the waste.

Exactly.

Waste products like urea are highly concentrated in the patient's blood, but absent in the dialysate.

So they naturally diffuse across the dialyzing membrane from the blood into the dialysate, following the concentration gradient.

Excess electrolytes and excess water also move out of the blood.

Cleaning the blood.

Effectively, yes.

And because kidney failure patients often retain a lot of fluid, the process is also designed to remove significant amounts of excess water, maybe two to 10 liters in a single session, which usually lasts several hours, three times a week.

Wow.

That's a lot of fluid.

It is.

And managing this whole process, ensuring the dialysate is correct, monitoring the patient, that's the critical job of dialysis nurses, it's a life -sustaining chemical balancing act performed outside the body.

It really puts it all together.

We've journeyed through this unseen world of solutions, haven't we?

From just mixing salt and water to the really complex chemical balancing inside us, and even machines that replicate it.

Understanding why salt dissolves, how an IV works, how dialysis keeps someone like Michelle alive.

It really drives home that chemistry isn't just abstract.

It's the language of life, the language of health.

It absolutely is.

And this deep dive, I hope, shows how these foundational chemical ideas,

polarity, solubility, concentration, osmosis, they aren't just textbook terms.

When you grasp them, you unlock the why behind so many critical biological processes and medical treatments.

You start to see the chemistry in every sip of water, every breath you take, even the rhythm of your heartbeat.

It's all connected.

So here's a thought for you, listening.

The next time you encounter a simple mixture, maybe your morning coffee, or you hear about a medical condition or treatment, challenge yourself.

Think about the solutions involved.

What solutes might be hidden in there?

What role is the solvent playing?

How might concentration or solubility be affecting the world around you, or even the world within you, in ways you hadn't considered before?

Thank you for joining us on this deep dive into solutions, where we aim to turn complex chemistry into clear, usable insights.

This deep dive was custom -tailored for you, brought to you with a warm thank you from the last -minute lecture team.