Chemistry 11 Unit III – Matter / Scientific Method / Lab Reports Notes
Everyone approaches problems in a different way. Some people jump right in, others think for a while, everyone is different.
Scientists rely on a process called the scientific method to solve and approach problems.
Although several different versions of the scientific method exist, all begin with the identification of a problem or a question that needs to an answered. Based on observation, experimentation, data analyze and if necessary re-testing, the answer to the question or problem may be found.
Look at the chart to the right for the steps involved in the scientific method.
A hypothesis is a single, unproven assumption or idea which attempts to explain a behavior.
When creating an experiment you must remember to be safe and ensure that you develop a proper procedure to obtain useful data.
Experiments should be designed to test for a limited number, or just one, condition or variable. A variable is the condition that is changed during an experiment. Variables that are left unchanged are called controlled variables.
Example: Does microwaved water affect plant growth?
The variable in this case is the water.
The controlled variables will be the type of plant, pot size, sun exposure, soli, amount of soil etc. You want to ensure that outside of the water (in this case), the plants are identical.
When writing up an experiment and presenting your results, there is certain format that we use here at Clayton Heights.
Below you will find the correct way to submit a laboratory report. If you any questions, please ask!
Title (underlined) First and Last name
Introduction: Brief introduction into the lab. Somebody with no / little science knowledge should be able to read the introduction and understand what you will be doing.
Purpose: State the questions you have about the experiment.
Example: We will attempt to explain changes in mass during a chemical reaction that produces a gas.
(Purpose can usually be found in the first few lines on a lab)
Hypothesis: What you think will happen. Your prediction.
Materials: Copy the list (Sometimes it will acceptable to write, “Please refer to pages… I will let you know when this is OK.)
Procedure: Write out Procedure in your own words. . Can be done in point form. Graphs and Diagrams must be done in pencil. Use blue or black ink for tables. (Again, sometimes you will be able to write, “Please refer to pages…”)
I will tell you when this is allowed.
Safety Notes: Write anything that you should be cautious of.
Observations: State observations as you see, hear, smell, feel etc. e.g. I saw bubbles coming from the reaction e.g. I heard a ‘pop’.
Please remember, NEVER taste any chemicals or specimens!!!!
Data: Record any data that you have collected. Tables must be in ink (blur or black). The data being recorded must also be in ink.
Questions: Answer the activity or discussion questions.
Conclusion: Provide the explanation from the purpose. Use the information collected in the lab (observations, data etc.) to help you.
Submission: Use a separate sheet of plain paper for the title page. Staple all sheets together, with the title page in front. You will be marked on neatness, completeness and accuracy.
***A sample title page is shown on the next page***
Observations are an important component of the scientific method. Chemists make observations and analyze them to find patterns or relationships that exist between substances.
Observations are either classified as qualitative or quantitative.
Qualitative observations are general, and use words, not numbers to describe and event or object. Think Qualities.
Examples: Clayton Heights has lots of students
My chemistry 11 mark is great
Pepsi slurpee’s from 7-11 are relatively inexpensive
Quantitative observations are more specific and usually describe an object or event using numbers. There are more useful in science since they tend to be more specific.
Examples: Clayton Heights has 1275 students
My chemistry mark is 95% (You wish ☺)
Pepsi slurpee’s from 7-11 cost $1.67
Look at the double bubble gum in front of you? Can you think of 5 qualitative and 5 quantitative observations?
Measuring is an extremely important aspect of science. If measurements are not read or recorded accurately, calculations based off the data will likely be wrong and thus the
conclusion may be wrong.
When measuring the volume of a liquid, you have to be especially careful. You have to look at the BOTTOM of the meniscus. The meniscus is the curvature of the water at ‘beaker level’.
Below you will some questions to practice measuring liquids.
Measuring mass is also an important skill, but one that is a little easier. In chemistry we usually measure mass in grams (g) or kilograms (kg) using either a digital scale of a triple beam balance.
Digital scales are easy to read, but a triple beam takes a little practice. Look below and try to read the scales. Watch your sig figs!
Chemistry is the study of matter and its transformations. Matter is anything that has mass and occupies space.
Properties are the qualities common to a thing or group of things. The relationship between matter and its properties is a very important aspect of chemistry. Properties can be classified as physical or chemical. Physical properties can be sub divided into extensive or intensive.
Physical property of a substance is a property that can be found without creating a new substance. Most physical properties describe relationships or interactions between matter and energy.
Chemical Change: Is a change in which new substances are formed. A chemical change produces a set of chemicals with is different from the set of chemicals, which existed before the change.
Physical Change: Is a change in the phase of a substance, such that no new substances are formed. A physical change does not change the set of chemicals involved.
Kinetic energy (KE) is ‘moving’ energy, cannot be stored. The greater an objects speed and mass, the greater it’s kinetic energy .
Potential energy (PE) is stored energy, related to an objects position. See the picture to the right.
Particles of matter possess a type of KE called mechanical energy because of their continuous motion. There are three (3) forms of mechanical energy:
Translational – movement from place to place (line)
Rotational – movement about an axis
Vibrational – repetitive back and forth movement.
Thermal energy, an extensive property, is the total mechanical energy of an object’s particles. There is a normal distribution of K.E among its particles. Think bell curve…some have high energy…some have low energy.
What has more thermal energy, a bathtub full of cold water or a cup of hot coffee? Explain.
Temperature, an intensive property, is the average mechanical energy of the particles that compose a material.
Heat is the energy transferred from one body to another because of a difference in temperature. An object immersed into a fluid will transfer energy with the fluid until both arrive at the same temperature.
This can cause a problem with thermometer’s and experiments. Why should you begin an experiment with a thermometer in as opposed to introducing it later? Hmmmmm….
Matter exists in three (3) common phases: solid, liquid or gas. Each common phase has a unique set of properties. You MUST be able to describe each phase and list its properties.
The Kinetic Molecular Theory (KMT) helps us understand how matter behaves…
1.) All matter is made up of very small particles.
2.) These particles are in constant motion (Have kinetic energy)
3.) There are spaces between particles.
4.) The particles and spaces are so small that they can’t be seen.
5.) Solid – particles are close and move so slowly that they can only vibrate.
6.) Liquids – particles are farther apart and move slightly faster than those found in a solid.
7.) Gas – particles are far apart and move very quickly.
8.) Add heat to these – particle gain kinetic energy so move faster.
Solids:
• Has a fixed shape and volume
• Very small changes in volume when heated or subjected to pressure.
• Least compressible of all
• Molecules held in fixed positions; very slow diffusion
• Molecules display vibrational energy
• All the particles are packed into a given volume in a highly organized and rigid manner, which requires particles to be in direct contact with each other. (This is way solids are not compressible)
Liquids:
• Has a fixed volume, but takes the shape of its container
• Volume changes only slightly under pressure
• Only slightly compressible
• Molecules are able to flow past each other; slow diffusion
• Molecules are close together, but are able to tumble over top of one another.
• Molecules display both vibrational and rotational energy. (
• The particles remain in close contact with each other but have sufficient room to slide past one another easily and prevent organized packing. Because of the close contact between particles, liquids are not compressible.
• Volume is drastically changed by changes in temperature and pressure
• Spaces between molecules is very large
• Molecules move at random everywhere; rapid diffusion
• Molecules display vibrational, rotational and translational energy.
• The particles are widely separated and only contact each other during collisions. Because the wide separation of particles can be decreased, gases are compressible.
Note: Liquids share some properties with both solids and gases and thus can be seen as an “intermediate” between a solid and a gas when you consider that:
• Both solids and liquids undergo only slight changes in volume when heated or subjected to pressure.
• Both liquids and gases conform to the shape of their containers
The table and picture summarizes the properties of solids, liquids and gases with respect to volume and movement.
Solid Liquid Gas
Volume Occupied Small Small Large
Movement allowed in substance Small Small Very Large
In general, continued heating of a solid produces the following temperature behaviour.
Melting temperature: temperature at which a solid changes into a liquid.
Freezing temperature: temperature at which a liquid changes into a solid.
***At both the melting and freezing temperature the solid and liquid phase exist***
Boiling temperature: temperature at which liquid changes into a gas.
Condensation temperature: temperature at which a gas changes into the liquid phase.
***At both the boiling and condensation temperature the solid and liquid phase exist***
As heat is added to the substance, we see two distinct portions of the graph.
• On the sloping portion of the graph – all heat is used to warm the substance so the temperature rises.
• On the level portions (plateaus) of the graph – substance contains so much heat energy that is cannot absorb more heat energy and stay in the same phase. The added heat is used to ‘break up’ the current phase and change into a new one. All the heat is used to change phase, thus the temperature does not go up.
Currently we classify everything as a form of energy or a form of matter.
Below you will see the classification system used to distinguish between various chemical species. Chemists refer to all the particles of matter collectively as chemical species.
Although the flow chart is very common, there are variations, particularly with the mixtures. Colloids and Suspensions may have different definitions or examples.
Pure Substances: Constant composition. All samples have the same proportion of
components. One set of properties.
Mixture: Variable composition. Same components may be mixed in different proportions. Composed of more than one substance.
Element: Composed of only one type of atom, cannot be decomposed. (e.g. Silver, gold, potassium, cobalt etc)
Compounds: Composed of MORE than one type of atom, CAN be decomposed (e.g. H2O, NaCl)
Homogenous: appears to be the same throughout. Any region of a homogeneous solution will be chemically identical to any other region
Heterogeneous: does NOT appear to be the same throughout. A.K.A mechanical mixture. Can separate by picking/shaking/sifting/spinning etc.
Solutions: Chemical species DO NOT aggregate to form particles. Can be aqueous (dissolve in water). Solute is the minor component of the mixture, solvent is the major component (what the solute is dissolved in).
Is a homogeneous mixture of two or more substances.
There are several different types of solutions:
Colloids: Particles between 1nm and 1μm dispersed throughout a continuous medium. Unlike a solution, can be in a different phase than the dispersion medium in which they are suspended. (e.g. jelly, butter, Styrofoam, whipped cream)
Suspensions: Particles bigger than 1 μm are spread through a liquid, but do not dissolve. Can have solid in liquid, liquid in liquid (emulsion e.g. milk). Liquid in a gas is an aerosol.
Big difference between a colloid and a suspension is that colloids will remain suspended indefinitely, suspensions will settle out, or sediment, upon standing.
Atom: Smallest possible unit of an element which retains the fundamental properties of the element.
Molecule: Molecules can consist of more than one type of atoms. • Molecules can have only one type of atom (an element). • Molecules can have more than one type of atom (a compound).
Ion: Atom or molecule, which possesses an electrical charge.
On the microscopic level, matter consists of atoms and molecules. Atoms combine to form molecules.
As we see for the picture below, molecules may consist of the same type of atoms or different types of atoms.
*** In these models, we use red to represent oxygen, white to represent hydrogen,
and gray to represent carbon.***
Separation of Mixtures
Compounds can be decomposed into elements.
Elements cannot be decomposed any further.
Heterogeneous mixtures are not uniform throughout and thus are easily separated.
Homogeneous mixtures can be separated by physical means.
Various methods exist to separate mixtures. These include hand separation, filtration, distillation, solvent extraction, recrystallization, gravity separation and chromatography.
Homogeneous liquid mixtures can be separated by distillation.
• Requires the different liquids to have different boiling points.
• In essence, each component of the mixture is boiled and collected.
Mechanical mixtures can be separated by hand (hand separation) as the various components can be easily seen.
Filtration can be used to separate a mechanical mixture of liquids and solids. A filtering apparatus is set up and the liquid is passed through a filter. The liquid which passes through the filter paper is called the filtrate. The material which remains in the filter paper is called the residue.
Evaporation is used to separate a solid in liquid solution. The liquid is evaporated and the solid residue will remain in the flask.
Solvent extractions are used to separate a solid from a mechanical mixture or a dissolved liquid from a liquid solution. Solvent extractions use the varying solubility’s of the different substances to start the separation process. If two or more liquids are used, the liquids will be miscible. Miscible means two liquids are mutually soluble (will mix) and immiscible means they are not mutually soluble (will NOT mix). A separatory funnel is used to mix the various substances.
Gravity separation separates substances based on their densities, for example, a gold pan. Gold is denser than rock or gravel and thus will stay in the bottom of the pan. Another type of gravity separation involves using a centrifuge. A centrifuge spins around very rapidly causing the solid materials to collect in the bottom of the test tube.
Paper Chromatography Is a method for analyzing complex mixtures (such as ink) by separating them into the chemicals from which they are made. Chromatography is used to separate and identify all sorts of substances in police work. Drugs from narcotics to aspirin can be identified in urine and blood samples, often with this method
