Most substances we encounter are __mixtures__ - wood, gas, milk, champagne, air, steel, etc...

When the components of a mixture are __uniformly__ intermingled or mixed, the homogeneous mixture is a **solution**.

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**Solution Concentration**

Solutions can be __dilute__ or __concentrated__, but we need to define "solution composition" more precisely to do calculations.

There are several different ways to define a * solution's concentration*.

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**Types of Concentration**

Here are five types of concentration...

**Molarity****Molality****Mass Percent****Mole Fraction****Normality**

Let's take a closer look at each of these **5 types of concentration**, and their respective formulas.

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**Molarity Formula**

The __molarity__ of a solution is equal to the moles of solute per one liter of solution.

Visually, we have the molarity formula below:

* Molarity* is the most common way of determining (and providing) a solution's "composition" or concentration.

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**Molality Formula**

The __molality__ of a solution is equal to the moles of solute per one kilogram of solvent.

Here's how the molality formula looks:

Most solutions in General Chemistry are dissolved in water, which means the __solvent__ is H_{2}O.

So * molality* often represents the amount of solute (in moles) per kilogram of water.

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**Mass Percent Formula**

The __mass percent__ formula of a solution is equal to the mass of the solute divided by the mass of the entire solution (both solute + solvent), times 100%.

Here's the formula for mass percent:

This is just one chemistry teacher's opinion but, after molarity, **mass percent** is the second most common way to express the __concentration__ of a solution in General Chemistry.

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**Mole Fraction Formula**

The __mole fraction__ of a solution is equal to the moles of solute divided by the moles of the entire solution (moles of solute + moles of solvent).

Visually, the mole fraction formula looks like this:

* Mole fraction* is represented by an upper-case Greek letter "chi," which looks like a "wobbly X."

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**Normality Formula**

The __normality__ of a solution is equal to the number of equivalents of solute per one liter of solution.

The normality formula is here:

Quite often, but not always, the __normality__ of a solution is reserved for strong acid solutions and/or strong base solutions.

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**Mass Percent Calculations**

Molarity calculation examples and mole fraction calculations can be found in my other videos.

But today, let's examine a * mass percent calculation*, followed by a typical

*.*

**molality calculation**Here we go...

*ex:* A sulfuric acid solution is 3.75 M and has a density of 1.230 g/mL.

Calculate the mass percent and molality of the sulfuric acid.

_________**answer:**

➞ To find mass percent we need the **mass of solute** (H_{2}SO_{4}) and the **mass of the solution**:

__molarity__ = 3.75 moles H_{2}SO_{4} / 1 L solution,

and...

(1.230 g solution / 1 mL solution) x (1000 mL / 1 L)

= **1230. g/L**

➞ So, 1 L of solution contains * 1230. g of solution*.

➞ Hold that for a second.

➞ __Now__, let's find the mass of solute, H_{2}SO_{4}, followed by the mass percent of H_{2}SO_{4} .

We have:

(3.75 mol H_{2}SO_{4} / 1) x (98.1 g H_{2}SO_{4} / 1 mol H_{2}SO_{4})

= **368 g H _{2}SO_{4} (solute)**

➞ __Finally__,

**mass %** = [ (368 g H_{2}SO_{4}) / (1230. g solution) ] x 100%

= **29.9 % H _{2}SO_{4}**

You can see it clearly below:

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* REMEMBER,* we still have to do the second part of the problem:

__calculating the molality__...

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**Molality Calculations**

➞ To calculate molality, we need moles of solute (which we have) and __kg solvent__.

1230. g solution - 368 g solute = 862 g H_{2}O solvent

This is equal to = 0.862 kg H_{2}O

➞ **Molality** = (moles H_{2}SO_{4}) / (1 kg H_{2}O)

= 3.75 moles / 0.862 kg

= ** 4.35 m H _{2}SO_{4}**

Here's the above * molality calculation*, shown more visually:

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Stick around for my next post from **SECTION 11 - Solutions and Their Properties**.

We'll discuss the Three Factors that Affect the Solubility of a Solution.