mixtures,solutions, and acids and bases

Categories of Matter

Substances matter always made up of same combination of atoms

Elements – always one type of atom

Ex: on periodic table

Compounds- matter made of 2 or more elements, always in the same combination

Ex: water is always H2O

Mixtures 2 or more substances which are physically blended(mixed, dissolved) but not chemically bonded

The composition can vary

Ex: Tap water, the air, cement, granite

There are 2 types of mixtures heterogeneous and homogeneous

Heterogeneous unevenly mixed; the parts can usually be seen with the eye (or a microscope)

Ex: granite, blood, a salad

Colloid – undissolved particles within the mixture, cannot be seen but scatter light (so not clear)

Suspension – undissolved particles within the mixture, larger, can be seen, will settle out

Homogenous also called a solution

evenly mixed, cannot see the individual parts, looks the same throughout

Ex: air, salt water

Compounds vs Mixtures compounds are chemically bonded; properties are different from the individual parts

Mixtures are physically bonded; maintain properties of individual parts, can be separated

using physical means – filtering, boiling, magnet, centrifuge, distillation

Parts of a Solution Solvent Solute solutions are evenly mixed at the atomic level

the greatest part of the solution; does the dissolving

what is dissolved; other than the solvent

solutes raise the boiling point of a solution above that of the solvent

lower the freezing point of a solution below that of the solvent

solutes increase the density of a solvent

Types of Solutions Can be liquids, gases or solids

Ex: Gas Air- nitrogen is the solvent, oxygen, carbon dioxide, etc are solutes

Liquid salt water- water is solvent, salt and other minerals are solutes

Solid Brass – copper is the solvent and zinc is the solute

Water one of few substances that exists on Earth in all 3 states of matter

Known as the universal solvent; usually exists in nature as a solution

Dissolving A covalent compound – held together by shared pairs of electrons; not shared equally

Polar - Oxygen end is slightly positive and Hydrogen end is slightly negative;

uneven distribution of charges

the water molecules surround the solute because the oppositely charged ends attract one

another and separate the molecules – dissolving it but not breaking the bonds

polar solvents can dissolve polar and ionic substances – ‘like dissolves like”

Likewise with ionic solutes, the polar ends of the solvent attract the oppositely charged ions

of the solute and pulls the solute apart.

Concentration a measure of the amount of solute in a given amount of solution; similar to density

measured qualitatively – not an exact amount; a relative amount

concentrated – means solution has a significant amount of solute

dilute - means solution has a small amount of solute

quantitatively – the exact amount of solute in a given amount of solution

the concentration of a solute effects the properties of the solvent (see above)

solid dissolved in liquid Formula: mass of solute/volume of solution

mass is usually measured in grams (g) or kilograms (kg)

volume is usually measured in liters (L) or milliliters (mL)

containing only liquids Formula: volume of solute/volume of solution X 100

called percent by volume

and/or gasses liquids and gases can be measured more easily by volume (Liters or milliliters)

since the units for solute and solution will be the same the concentration can be

given as a percent

Solubility maximum amount which can dissolve

In a given amount of solvent

At a given temperature and pressure

High Solubility a lot can dissolve

Saturated Solutions holding the maximum amount of solute that solvent can hold at given temp & pressure

Unsaturated more will dissolve

Supersaturated holding more solute than the solvent typically holds at given temp and pressure

Changing Solubility If you change temperature and/or pressure you can change solubility

solubility increases for many solids in liquids when you increase temperature

particles of solvent are moving faster/more energy so break up solute faster

solubility of gas in liquid decreases if you increase temperature

particles are already moving freely so moving faster causes them to escape

ex: CO2 in soda O2 in water

solubility of a gas in liquid decreases if pressure is decreased

ex: CO2 dissolved in soda is released (leaves the solution) when can is opened

Solute will dissolve faster if temp is increased – particles speed up/more collisions

crushed – more surface area

stirred/agitated – more collisions

stirring and crushing only increase how fast (rate) not how much (solubility) dissolves

Reading a Solubility Curve

The Y-axis shows the grams of solute.

The X-axis shows the temperature.

The line indicates how much solute has dissolved at a given temperature.

At the line (curve) the solution is saturated.

Below the line the solution is unsaturated.

If material dissolves above the amount of the line than the solution is supersaturated.

Note that solubility increases when temp is increased for some substances and decreases for other substances.

What are acids and bases? Acid and Base Solutions

Description of solutions indicating the relative amount of hydrogen.

Acids Most acids contain one or more hydrogen atoms. (HCl, H2SO4, CH3COOH, etc.)

When dissolved in water this hydrogen atom combines with the water molecule and

creates a hydronium ion.

They give up/donate hydrogen atoms to the water molecule.

Characteristics

Have a pH of less than 7; the lower the pH the stronger the acid.

Taste sour

Can damage skin and eyes

React with metals to produce hydrogen gas

Conduct electricity when dissolved in water

React with bases to form salts (neutral solutions)

Turn blue litmus paper red

Bases Contain Hydroxide ions (OH-) which separate from the rest of the compound when in water,

Or create Hydroxide ions by stealing or accepting Hydrogen atoms from water molecules.

Characteristics Have a pH of greater than 7; the higher the pH the stronger the base

Taste bitter

Can damage skin and eyes

Slippery when mixed with water

Conduct electricity in water

React with acids to form salts/neutral solutions

Turn red litmus paper blue

Potential of Hydrogen

pH Is an inverse measure of the concentration of hydronium ions in a solution.

As pH decreases, acidity increases; As pH increases acidity decreases

In neutral solutions pH = 7, indicating concentrations of hydronium and hydroxide ions are equal

If there is a greater concentration of hydronium ions the solution is an acid.

If there is a greater concentration of hydroxide ions the solution is a base.

[ ] means concentration of

pH scale Ranges from 0 to 14; 0 is most acidic and 14 is most basic.

A change of 1 unit on the scale represents a 10 X change in concentration.

A change of 2 units on the scale represents 100X change in concentration.

Measuring pH Indicators are chemicals which change color at different pH values

Testing strips contain an indicator which changes color at different pH values.

pH Meters have an electrode sensitive to hydronium concentration. They are the most accurate.