Chemistry Unit 1 Test

Scientific Law

a concise statement that summarizes the results of a broad spectrum of observations and experiments

Nitrogen

N

Sodium

Na

Oxygen

O

Solutions

(special type of homogenous mixture) made up of two components: Solute- the dissolved material Solvent- the material that the solute dissolves into. For example, in salt water salt is the solute and water is the solvent

Steps & definition to the Scientific Method

1) identify a problem/ ask a question 2) make a hypothesis 3) design an experiment 4) perform experiment 5) analyze data 6) draw conclusions/repeat experiment an approach to the solution of scientific problems, which involves making observations and trying to explain them

Explain the difference between a homogeneous mixture and a heterogeneous mixture. Your answer should include a definition for each term and two examples of each type.

A homogeneous mixture is a combination of at least two different substances that is uniform (all the same) throughout the mixture. If you took two small samples from a homogenous mixture and analyzed them, you would find that both samples have the same composition (same amounts of each substance in the mixture). Homogeneous mixtures are also called solutions. Saltwater and bleach and air are examples of homogeneous mixtures. Other examples include: Sprite® (mostly water with sugar, flavors and carbon dioxide dissolved in it), 14k gold (a solid phase solution of gold and silver) and air (a solution of gases - mostly nitrogen and oxygen). A heterogeneous mixture is a combination of two or more substances that is not uniform throughout the mixture. If you took two small samples from a heterogeneous mixture, each sample would not be made up of the same amounts of each substance - the two samples might even be different substances from the mixture. Italian salad dressing and muddy water are examples of heterogeneous mixtures.

Carbon

C

Physical Properties of Water

Colorless Odorless Liquid at room temp. Boiling point = 100oC Freezing point = 0oC Is an excellent solvent for a lot of other substances

Copper

Cu

Distillation

Distillation relies on the difference in the boiling points of the components in a solution to separate the mixture. Watch Vid For Explanation: http://www.youtube.com/watch?v=xxNfJLMNS4E

True or False: It's easy to remove dissolved salt from water using a filter.

False. It's impossible to remove salt from water with an ordinary filter, you would have to distill the solution. The water would boil at 100oC, becoming a vapor you could cool off and condense back to a liquid while the salt is left behind.

True or False: The hydrogen and oxygen that make up water molecules can be easily separated by a physical change.

False. When water forms, the hydrogen and oxygen are chemically combined to form a new substance. If you wanted to separate them, it would require a chemical change.

Iron

Fe

Hydrogen

H

Potassium

K

Phosphorus

P

Explain the difference between a physical change and a chemical change and give an example of each.

Physical: an alteration of a substance that does not change its chemical identity. Examples: phase changes (boiling, freezing, melting, evaporating), crushing, breaking, dissolving Chemical: an alteration of a substance that changes its chemical identity. Examples: combustion (burning), reaction with acid, oxidation (rusting), rotting, cooking

Vapor

Refers to the gas phase of a substance that is normally a solid or liquid at room temperature

Sulfur

S

2 main types of heterogeneous mixtures

Suspension: a mixture containing large particles that can settle out or be separated by filtration Colloid: a mixture containing particles that are small enough to remain suspended. Examples: milk, fog ** heterogenous mixtures exhibit the Tyndall effect when a light is shined through them

State the Law of Conservation of Mass. Explain what really happens when acetone seems to "disappear" when it burns.

The Law of Conservation of Mass states that, in a chemical or physical change,matter can never be created or destroyed, it can only change form. Remember the hexane that I lit on fire on the countertop? Even though it seems like the hexane "disappeared" when it burned, the law of conservation of mass says it couldn't have. In reality, it combined with oxygen from the air and formed new, invisible substances(mostly carbon dioxide gas and water vapor) that are products of the reaction. The carbon and hydrogen atoms that made up the hexane are still here, they're just chemically combined with the oxygen.

Why is it almost impossible to create a sample of pure water?

Water is an excellent solvent. Most substances will dissolve in water (at least a little). Water in nature is never pure - it always contains some amount of dissolved material Distillation is a great way to remove impurities from water and distilled water is probably the "purest" water you can create, but even freshly distilled water will contain dissolved gases from the air.

Chemical Reaction

a change in matter which involves the formation of new substances from other substances, they involve reactants and products

Mixture (2 types heterogenous and homogenous)

a combination of substances in which each substance remains its own separate identity.

Chemical Symbol

a letter or two letters used to represent an element

Experiment

a means of testing a hypothesis

Substance

a particular type of matter that has a uniform and definite composition. matter can be called a pure _____ if it is made up of particles that are all identical. Elements and compounds are pure _____ . Examples: water, copper, sugar, salt If a sample of matter is made up of different type of particles it is not a pure ______. Examples: orange juice, granite milk, blood

Hypothesis

a proposed reason for what is observed- an "educated guess"

Aqueous solution

a solition in which water is the solvent

Theory

a well tested hypothesis

Matter

anything that has mass and takes up space

Chemistry is the study of the ____ of ______ and the ____ they undergo.

composition, substances, changes

Chemical properties

characteristics of a substance that can only be observed or measured by changing the identity of the substance examples: flammability, corrosion, reactivity, with oxygen, reactivity with acid

Examples of Physical Properties

color, odor, solubility, density, boiling point, freezing point

Solid

definite shape (rigid), definite volume

Liquid

definite volute, no definite shape (flood takes shape of container)

In a chemical equation reactants are written on the ___ side of the arrow, and products are written on the ___ side of the arrow

left, right

Gas

no definite shape, no definite volume ( fills its container)

5 Major Categories: _____= substances containing carbon _____= all others substances-ones not containing carbon _____= the composition of substances _____= theories and experiments that describe the behavior of substances _____= study of living things

organic carbon inorganic analytical physical biochemistry

Reactants

starting substances in a chemical reaction

Products

substances produced during a chemical reaction

Compounds

substances that can be separated into simpler substances by chemical reactions Examples: water, salt, glucose. _____ are made up of two or more different types of elements chemically combines. any sample of matter can be classified as an element, compounds, or mixture

Subscript

tells you how many atoms of that element are in that molecule

Elements

the simplest forms of matter that can exist under normal laboratory conditions Examples: carbon, oxygen, iron, or any other element listed on the periodic table

Chemical Formula

uses symbols and subscripts to represent a chemical compound

List at least three (3) observations that might indicate that a chemical change has occurred.

• A change in color • A change in odor • Fizzing (formation of a gas) • A noticeable change in energy (heat or light being given off, a dramatic change in temperature)