Mixtures and Solutions

Physical Science

Elements, Compounds and Mixtures

• Element – The purest substance that cannot be separated into simpler substances by phsyical or chemical means.

• Ex: a 5 gram (g) nugget of gold is like every other particle of gold. This is how you can identify gold found in rock.

Periodic Table of Elements

Identifying Elements by Their Properties

• Each element has its own characteristic properties, both physical and chemical. Look at the examples on page 83.

• Elements are grouped into categories according to their shared properties. For example, metals are not all alike, but they share enough in common to be grouped into the metals category.

Identifying Groups by Their Properties

• Metals – shiny, good conductors of heat and electrical energy, they are malleable and ductile. Examples: iron, copper, lead, tin.

• Nonmetals – dull, poor conductors of heat and electricity, tend to be brittle and unmalleable. Examples: sulfur, bromine, neon

• Metalloids – have properties of both metals and nonmetals. Some shiny or dull. Somewhat malleable and ductile. Some can conduct heat or electricity. Examples: silicon, antimony and boron.

Families of the Periodic Table

Atoms

• The smallest particle of a substance is an atom. Every element is made of its own unique atom (and every atom of that element looks the same).

• Atoms are the source of energy for each substance. Each atom has a “brain” (nucleus) that helps to control the behavior of the atom.

Parts of the Atom

• Inside the nucleus:• Protons – positive (+) charge, the number

can never change, because they can’t leave the nucleus.

• Neutrons – neutral charges inside the nucleus that 1) add mass to the atom, and 2) keep the protons from repelling.

Traveling Negative Charges

• Electrons – located in shells outside the nucleus, these are the only particles that can cause an atom to join with another atom.

• Electrons “hang around” the outside of the atom because they are attracted to the positive force of the protons. However, the further away an electron is from the protons, the more likely they are to leave.

Atoms

Molecules

• A molecule is formed when the atoms share an electron.

• Example:• H20 = 1 molecule of water

• 2H20 = 2 molecules of water

• NaCl = 1 molecule of table salt• 4NaCl = 4 molecules of table salt

Compounds

• A compound is a pure substance made of

two different elements that are chemically combined. There must be a reaction to create a substance different from the two elements.

• Examples: iron + oxygen = iron oxide (rust). Sodium + chlorine = sodium chloride (table salt).

Compounds: 2 Hydrogen + 1 Oxygen = Water

The Unique Properties of Compounds

• Just like elements, compounds have their own physical properties (melting point, boiling point, density, color, etc.). They can also be identified by their chemical properties.

• Because a compound is a different substance than the elements that make it up, then a compound has different properties. Chlorine by itself is poisonous, but not when it combines with sodium to become NaCl (table salt).

Iron Oxide (rust)

Compounds and Simpler Substances

• Unlike elements, compounds can be broken down into simpler substances, but only through chemical changes. For example adding energy (heat or electrical) can break down a substance into it’s original elements. Carbonic acid (in drinks like cola) can be added to water molecules, which then could be broken down into the elements of carbon, oxygen and hydrogen.

Mixtures

Mixtures

• A mixture is a combination of two or more substances that are not chemically bonded. Mixtures are a physical change:

- Mixtures retain their identity – Each substance in a mixture has the same chemical makeup it had before the mixture formed.

- Mixtures can be physically separated – It isn’t always easy, but you can separate the substances.

Mixtures (continued)

• The components of a mixture do not have a definite ratio – Since there is no chemical bonding, the components of a mixture do not have to combined into a definite ratio. For example, air is a mixture of gases, but not all a the same ratio.

Homogeneous Mixture

• Some mixtures look the same throughout (you can’t tell one ingredient from another.)

• Examples would be ice tea, chocolate milk, or anything that could dissolve into another liquid or gas.

Homogeneous Mixtures

Suspensions

• In some solutions, the particles in a mixture can settle out and been seen while in still in the solvent. They don’t dissolve, but are suspended in the liquid. For example: a snow globe.

• Heterogeneous mixture – you can see the different components in the mixture (salad dressing). The particles that separate are large enough to scatter or block light.

• These suspensions can be separated using a filtration system.

Heterogeneous Mixtures

Colloids• A colloid is a mixture that has properties of

both a solution and a suspension. The particles are dispersed throughout , but they aren’t heavy enough to settle out. The particles can’t settle, but they are large enough to scatter light. Unlike a suspension, a colloid cannot be separated by filtration. Milk, mayonnaise, Jello and whipped cream are examples of colloids.

Colloids

Compounds vs Mixtures

Compounds

- Are made up of elements

- They lose their original properties

- Can only be separated by chemical means

- Formed using a set mass ratio of components

Mixtures- Made up of elements,

compounds or both- These components

keep their original properties

- Separated by physical means

- Form using any ratio of components.

Compounds vs Mixtures

Solutions

Physical Science

Particles in a Solution

Solutions

• A solution is a mixture that appears to be a single substance but is composed of particles of two or more substances that are distributed evenly amongst each other.

• When dissolving, the solute is the substance that is dissolved, and the solvent is the substance in which the solute is being dissolved. Ex: Kool Aid (solute) dissolves in water (solvent). Water is called the universal solvent.

Solution of Ice Tea (Sugar, Tea and Water)

Different States of Solutions

Gas in gas: gasses in dry airGas in liquid: soft drinks (CO2 in water and

syrup)

Liquid in liquid: antifreeze (alcohol in water)

Solid in liquid: salt water

Solid in solid: alloys – metals and nonmetals dissolved in other metals. Example: brass (metal zinc melted in copper).

Water is SO special!• Ocean water is a solution

of many substances: solids, liquids, and gases all dissolved in water.

• Your blood and body fluids are water solutions of sugars, ions, and minerals.

• Water dissolves so many more things than other solvents that it is called the universal solvent.

Concentration: How Much Solute is Dissolved?

• Concentration is the amount of solute dissolved in a solvent.

• This can be expressed in grams/milliliters (yep, it’s the density of the solution!)

• Solutions can be concentrated, a high amt of g per ml (g/ml) - or diluted, a low amt of g per ml (g/ml)

• EX: Adding 5 pkgs of Kool Aid to 1 quart water is highly concentrated (too strong!) Adding 4 gallons of water to it would dilute the solution (and make it very weak!)

Solubility

Solubility

• The amount of a substance that can be dissolved is its solubility. For example, if you add too much sugar to water, then the extra sugar won’t dissolve (but will drop to the bottom of the glass).

• Most solids increase solubility in liquids when heat energy is added (adding sugar to hot water dissolves more sugar).

What affects how fast solids will dissolve?

• Temperature! If you increase temperature, solids will dissolve faster.

Movement! If you stir them, solids will dissolve faster!

Particle size! The smaller the particles, the greater the surface area so the faster they will dissolve.

What affects how much will dissolve?

• Solubility of most solids in a liquid increases when you raise the temperature!

• Solubility of a gas in a liquid decreases when you raise the temperature!

• Gases are also affected by pressure. As you increase the pressure, more gas will dissolve. Soft drinks are canned or bottled under pressure so more CO2 can be dissolved in the solution.

Saturation Levels

• In a saturated solution, the maximum amount of solute that can be dissolved in a solvent at a given temperature.

• When a solution is unsaturated, then the solution can dissolve more solute at a given temperature. This happens every time you increase the temperature of the solvent.

• A supersaturated solution happens when the solvent contains more solute than when it is saturated at a given temperature.

Concentration and Solubility

Particles with a Charge

• Electrical charges are everywhere (including your nerve endings!) These charged particles are called ions.

• In order for conduction to occur, solutions have to contain ions. Ions are particles that can be positively or negatively charged. These solutions are called electrolytes.

Ionization

Ionic solutions form in 2 ways. Some electrolytes are molecules that are made up of neutral atoms. The molecule breaks up into atoms take on a charge. An example would be hydrogen chloride (see page 676.)

Particles with a Charge

• Example, when hydrogen chloride (HCl) is neutral, but, when water (H20) is added, the HCl molecule is broken up. The H20 becomes positively charged, and the HCl becomes negatively charged. (see page 676)

• Solutes that can be broken down into ions are considered to be polar materials.

Particles with a Charge

• Sometimes, when a charged (ionic) solid dissolves into a solvent, the solvent breaks it apart into different charged particles. This is called dissociation.

• When sodium chloride (Na+Cl-) is dissolved in water, the water molecules pull the compound ions from the crystal (Na+ and Cl- .) The sodium chloride solution will then be able to conduct electricity. (see page 677)

Effects of Solute Particles

• Solutes (like salt) affect physical properties of the solvent by changing the number of particles per gram of the solute – it doesn’t change the chemical properties of the solute.

• Some solute particles can change the freezing and boiling points of a solvent (ex: salt and antifreeze do both to water.)

Effects of Solute Particles

• Fish living in polar regions have a natural antifreeze solution called glycoprotein.

• As solution particles freeze, they begin to arrange in orderly patterns.

Dissolving Without Water

• Solvents, such as water, can break down solutes and cause them to become ionic.

• However, if water can’t break down a solute (such as oil), then the oil is considered to be nonpolar materials. This is why you have to shake oil and vinegar for salad dressing.

Oil and Water

Acids (High School)

• Acids are substances that produce extra H+ ions when in a water solution.

• Acids have a pH less than 7.0.

• Acids have a sour taste.

• Acids turn blue litmus paper red.

• Acids react with metals to form H2 gas.

• Acids may be strong or weak.

• Acids react with bases in a neutralization reaction to form a salt and water.

• Weak acids are found in many foods.

• Many acids have H in their chemical formulas.

1) HCl

2) HNO3

3) H2SO4

Bases• Bases are

substances that produce extra OH- ions when put in a water solution.

• Bases have a pH greater than 7.0.

• Bases taste bitter.• Bases turn red

litmus paper blue. • Bases feel slippery

when you touch them and are found in soaps and drain cleaners.

• Many bases contain OH- ions in their chemical formulas.

1) NaOH2) KOH

3) Ca(OH)2

The pH scale• The pH scale goes from 0

to 14 and tells how acidic or basic a solution is.

• Acids have a pH below 7.0 but greater than 0.

• The lower the pH, the stronger the acid.

• Stomach acid has a pH of 2.0 and weak acids like vinegar or apple juice have a pH above 4.0 but less than 7.0.

• Pure water is neutral and has a pH of exactly 7.0.

• Bases have a pH above 7.0 but below 14.0.

• The higher the pH, the stronger the base.

• Drano has a pH of 12.0 but shampoos have a pH range of 8.0 to 9.0.

Strong Acid Weak Acid Neutral Weak Base Strong Base

0.0 2.0 4.0 6.0 7.0 8.0 10.0 12.0 14.0