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Gathering Data
Gathering Data
When we gather data there we generally look to write down important properties (traits or characteristics) or changes (processes that modify these properties in some way). This data can either be measured and therefore quantitative (such as time, distance traveled, temperature) or observed and therefore qualitative (such as color, changes observed when mixing 2 things, or that it's hot outside). When running an experiment it tends to be better to use quantitative data as much as possible to have measurable results to back any claims up.
Each row on the data table talks about the same thing but one is a quantitative observation and one is a qualitative observation!
We also want our observations to be both accurate and precise! If they aren't, then the experiment is inconclusive and the method of doing it needs to be looked at more to get more reliable results.
Accuracy is how close a value is to the value’s actual number.
Precision is how often repeating the process of finding this value gives the same results as before.
Data and Graphing
Data and Graphing
Knowing how to make and interpret a graph is important for all walks of life, otherwise someone is going to try and take advantage of your lack of knowledge. When making a graph you first need to know what type of graph to make:
Line graphs are usually used when tracking many small changes (For example, how temperature changes with time)
Bar graphs are usually used to compare different groups or amounts (For example, the grades of each student in a class)
To make a graph with enough good information, you then need to do the following:
Graphs need to be readable, well labeled (title and both axes, with units), and not misleading!
If multiple graphs are being compared, they need the same information on their axes.
If multiple data lines are on a single graph, use a key.
To make sure your graph is not misleading, check for the following:
Start and end points that don't show the whole picture should not happen. It's easy to blow things out of proportion by changing what boundaries are shown instead of starting at 0 (or another point that shows the full scope).
Sometimes the percentage numbers should be used and sometimes the actual values should be used when doing line graph comparison. Make sure something isn't becoming misleading based on which one was chosen.
Correlation does not imply causation. Just because 2 graphs look similar it doesn't mean they are related. Keep this in mind when comparing graphs with one another, you need to look at what the graphs are actually measuring.
Comparisons between 2 scales can also be a problem if done on a single graph. Make sure each graph only has 2 types of data being compared at once if possible.
Misleading 3D graphics look fancy but can skew graphs. Try to make the data on a graph as clear as possible.
Google Sheets
Google Sheets
Google Sheets is the often forgotten part of the main Google Suite, the part of it that allows data and information to more easily be displayed and manipulated. On Google Sheets, each box is known as a cell and has its own unique letter and number to define it. Clicking and typing in the cell will change what is said in that box. You can cut, paste, and copy cells just like you would a normal piece of text by using CTRL + X (Cut), CTRL + V (Paste), or CTRL + C (Copy). If you want to modify or do this to part of the stuff you typed into the cell you need to double click in the cell or modify it inside of the formula bar at the top of the sheet.
As a note, Google Sheets also has graphing functionality if you want to use it! Highlight all of the data you want to make a graph out of, then go to Insert->Chart, and pick what you want to graph.
Formulas are where the real strength of Google Sheets shines! By typing = as the first part of a cell it lets you enter a formula into the cell that will automatically be calculated. With this you can change information on the fly and do math quickly. When doing a math formula, the following characters are important:
+ is addition
- is subtraction
* is multiplication
/ is division
^ is power
( ) lets you put things in parenthesis so that stuff is calculated first
Error and Yield
Error and Yield
The world is not perfect! Because of this fact there are 2 different forms of error found within Chemistry:
When something is measured there is a bit of uncertainty in this measurement. This measurement error can get even larger after calculations are done. Uncertainty in measurement is (usually) okay in small amounts, depending on the process being done. For example, when placing water into a beaker to the 200mL line we aren't exact down to the molecule - there's error to it since our eyes can't actually measure things that closely. The range of acceptability for this is noted with the ± symbol (since it can be + or - that amount and still be an okay measurement to use).
If you have to calculate uncertainty instead of having it on your lab supplies, it should generally be equal to half the range of the smallest measured value:
Uncertainty Error = (One Measurement Mark - Measurement Mark Under the First One) / 2
The uncertainty on the beaker would be ± 5 mL if it wasn't given and needed to be calculated, for example.
Often times processes don't go 100% to completion. This leads to Percent Error, comparing how much was made compared to what would be expected at 100% efficiency.
Percent Error = | (Calculated Value - Measured Value / Calculated Value) | * 100
Note the absolute value bars in the formula. This should almost always give a number that is both positive and a decimal. Since we express it as a percent, it then needs to be multiplied by 100.
Theoretical Yield is the expected amount of something that should be made by a process. This could be a material, an amount of energy released, how much of something changes phase, or the like. Practically nothing is 100% efficient (we'll cover why later for multiple cases), so when we make the process happen the stuff that comes out of that process is known as the Actual Yield.
Crime Scenes and Evidence (PSA)
Crime Scenes and Evidence (PSA)
When setting up a crime scene, there are seven steps that are generally followed:
Secure the Scene: Find the center of the crime and make a perimeter large enough to contain as much relevant evidence as possible. The perimeter should be restricted with tape and law enforcement so no evidence or witnesses are lost or tampered with. Safety is top priority when securing a scene before preserving evidence.
Separate the Witnesses: Witnesses shouldn't be allowed to talk to each other as they can influence one another's testimony. When collecting evidence from witnesses each one of them should be asked questions such as "When did this happen?", "Who contacted law enforcement?", "Who is the victim?", "What did you see happen?", "Who is the perpetrator?", "Where were you?", and more.
Scan the Scene: Figure out all scenes related to the crime, how and where to take photos of the crime scene and evidence, and where all the evidence and relevant locations are.
See the Scene: Take the photos outlined in the previous step. Evidence should be shot both close up and afar and photos both with and without measuring devices (rulers, surveying tape, etc) should be taken to better recreate the scene later.
Sketch the Scene: The crime scene is sketched as accurately as possible, including all evidence and large landmarks (trees, furniture, doors, windows, houses, vehicles). This can even be improved through computer programs later.
Search for Evidence: Make sure no evidence has been left unseen using a search pattern of the contained area.
Secure and Collect Evidence: Properly collect, seal, and label evidence for further analysis.
There are different search patterns available when looking for evidence in an area!
Usually this evidence is considered Trace Evidence, small but measurable amounts of substances found at a crime scene. Some examples include:
Paint: breaking & entering or car accidents often leave traces of paint.
Explosives: chemical tests determine unknown powders and types of explosive.
Glass: embeds itself in hair and clothing, found in breaking and entering, car accidents, etc. Can be reconstructed to see the direction of impacts and where the glass came from.
Dust/Dirt: chemical analysis can reveal where someone has been, where they live, where they work, and if they have pets.
Fluids: can be found in splatters, drops, or stains. Each fluid has its own collection method and can be tested for things like poison or drugs.
Tool Marks: can show trace substances as to what the tool has come into contact with or if it was used for a task.
Shoe/Tire Prints: Identification based on car type/shoe type and the walking style of a suspect (each person wears their shoes down differently).
Fractured/Ripped Materials: Can be put back together and analyzed.
Documents: Handwriting is unique, printing style is (mostly) unique based on type of printer used.
Hairs: DNA evidence, usually transfers from suspects to victims fairly easily.
Fibers: Can be more closely looked at to see things like what fabric/clothing the suspect is wearing. It usually transfers from suspects to victims fairly easily.
Blood: the shape of blood and location at a scene provides clues as to what happened and can eliminate suspects based on blood type and the way the blood's pattern has turned out.
Fingerprints: Everyone’s fingerprint is unique, letting us identify who has touched what in a room.
Fingerprints (PSA)
Fingerprints (PSA)
We identify fingerprints of individuals based on both primary patterns (The main pattern on fingerprint. This may be an arch, whorl, or loop) and ridge characteristics (The smaller patterns, such as a bridge between 2 parts of a fingerprint or a defining scar).
Additional Resources
Additional Resources
Interesting Links
Interesting Links
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