We're the Grade 11s in Mr. Doktor's chemistry 11 class.
We're in Block A, Day 1.
We are
Theresa Nguyen
Dominika Skibicki
Charles Perea
Tim Pang
This is our blog.

DAY 1C - 09/15/09

Expressing Errors

1. Error is a fundamental part of science
2. There are usually 3 reasons for error

• Physical errors in the measuring device
• "Sloppy" Measuring
• Changing ambient conditions

3. Error is taken to be half the smallest division on your measuring device

Calculated Errors

1. 2 Different Possibilities

Absolute Error

• Measured value minus accepted value

ABSOLUTE ERROR = MEASURED - ACCEPTED

• Positive number means you're over the accepted value
• Negative number means you're under the accepted value

Percent Error

• Most common
• Percent error = Absolute Error/Accepted Value

% ERROR = (MEASURED - ACCEPTED/ACCEPTED) x 100
= (OBSERVED - THEORETICAL/THEORETICAL) x 100

Ex: You measure the weight of an orange to be 15 N. The actual weight is 17.5 N. What is the percent error?

• % ERROR = (MEASURED - ACCEPTED/ACCEPTED) x 100
• = (15 - 17.5/17.5) x 100
• = - 14.28
• = 14
  

* ABSOLUTE = I DON'T CARE IF IT'S (-) or (+) *

Dimensional Analysis

• Want to know what 100 km/h is in miles/hr?
• Just like converting between currencies in chem it is usually necessary to convert between unites
• This process is called DIMENSIONAL ANALYSIS

Steps:
There are only 4 steps

1. Find a unit equality
2. Find the conversion factors
3. Apply conversion factors
4. Cancel units

Ex: How many miles are equal to 120 km?
1m = 1.6 km 1 = 1m/1.6 km (120 km)(1 m/1.6 km)
use conversion factor to cancel units

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