1. Accuracy, Precision, & Percent's

2. Precision vs. Accuracy
Precision- getting the same results again & again (reproducible)
Accuracy- getting results close to the accepted or standard value
Which do you think is better?

3. Precision vs Accuracy If the is the target or bulls-eye
Which does this represent?
High precision
Low accuracy

4. Precision vs Accuracy How about this one? lower precision
higher accuracy

5. Precision vs Accuracy
And this one?
high precision
high accuracy

6. Accuracy vs. Precision So which is better? Accuracy
Why? Well if you get the same results over and over but they are far off from the standard or accepted value then experiment is flawed. Percent Error shows accuracy.
However if there is no known standard then your experiment also needs to be precise so that other scientists who preform your experiment should be able to get the same results repeatedly.
A scientist’s goal is to be both accurate and precise.

7. Practice
The following data was collected. If the volume of the gas was known to be 2.20 L, the data has-
A) low precision and low accuracy
B) low precision and high accuracy
C) low accuracy and high precision
D) high accuracy and high precision

8. Percent Yield & Percent Error
3 main types we use in chemistry: Percent Yield, Percent Error and Percent Composition
Percent Yield tells you the percent of the product you obtained, the goal of course being 100% but we will have labs with as little as 10% and as much as 200% (trust me its possible but not good)
Percent Yield is calculated by dividing what you got- called Experimental or Actual Yield by the Theoretical Yield- what you should have gotten x 100.
% YIELD = Experimental Yield x 100
Theoretical Yield

9. Percent Error Percent Error tells you how accurate your results are.
Percent Error = (Measured Value - Accepted Value) x 100
Accepted Value
Now here is the confusing part. The measured value is the same thing as the experimental value & the accepted value can also be called the theoretical value. So to keep everything the same I tweak the 2 formulas to look like this

10. My fool-proof versions
% YIELD = What’cha Got x 100
What’cha Should’a Got
Percent Error = (What’cha Got - What’chaShould’a Got) x 100
This way they both similar and you are less likely to forget what goes where. I know it’s not very grammatically correct but trust me it works 

11. Practice:
During a reaction between sodium bicarbonate (baking soda) and acetic acid (vinegar) 23.4 grams of sodium acetate was collected. The theoretical yeild should have been 33.6 grams. What is your percent yeild?
During a density lab you got an experimental value of g/cm3 , if the actual density of Au (gold) = 19.3 g / cm3