catalyst: 1. open all handouts on the website. 2. turn chapter 1 homework in. 3. how many...
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It’s Time to Start Cooking!Catalyst:1. Open all handouts on the website.2. Turn Chapter 1 homework in.3. How many significant figures are in
0.50004. (0.24567)(0.034) = ? (GIVE CORRECT SIG
FIGS)5. 4.5 + 0.01434 = ? (GIVE CORRECT SIG
FIGS)
Lecture 0.3 – Sig Figs, Dimensional Analysis, and Cooking Protocol
Every Chef Needs Proper Tools
Just like chefs do in the kitchen, chemists use tools to take exact measurements of the substances they interact with.
Sometimes cooking can be an art, but chemistry is a science.
We want to be precise and accurate.
Precision and Accuracy
Precision – Measure of how close individual measurements agree with one another A standard deviation tells
someone how precise you were during a laboratory.
Accuracy – How close individual measurements agree with the “true” value.
Significant Figures
There is always uncertainty in the last digit of any quantity that we report.
Significant Figures – All digits of a measured quantity
The number of digit reported represent the number of significant figures a number has
Determining the Number of Sig Figs The most important rule is that all nonzero
digits in any measurement are significant:1. Zeros between nonzero digits are always
significant. For example, 1005 has ______ sig figs.
2. Zeros at the beginning of a number are never significant. For example, 0.005 has _____ sig fig.
3. Zeros at the end of a number are significant only if there is a decimal. For example, 3.0 has ____ sig figs, but 30 has _______ sig fig.
A Note on Scientific Notation
Recall that we can write a number like 10,300 in scientific notation as 1.03 x 104
This number would have _____ sig figs
Sig Figs for Calculations
Determine sig figs only after a calculation is complete.
Sig Fig for Addition/Subtraction When you add/subtract numbers, the
answer has the same number of decimal places as the number with the least decimal places.
Round off to one decimal place since 83.1 has the least number of decimal
places!Final answer you report is 104.9
Sig Figs for Multiplication/Division
When you multiply or divide numbers, the answer has the same number of sig figs as the number with the fewest sig figs.
4 sig figs
2 sig figs, so the answer needs 2 sig
figs 32 cm2
When does this translate to the kitchen?
Cooking is more of an art – often times the same dish will never be made using the exact same quantity of ingredients.
Baking, however, is much more like science. Exact quantities and ratios are necessary to ensure that desired product is achieved!
Why are precision/accuracy important here?
Kitchen Knowledge:Three Important Macromolecules
Carbohydrates Lipids Proteins
Food contains a large number of things, but these are the essential ones:
When I get in the kitchen, what do I eat? Though they vary in caloric content, they
are all essential to human life in specific ways.
A low-fat diet alone won’t help dieting citizens, as the hormone insulin is a key player in weight regulation, among others.Biological Molecule
Number of Calories Per 1 Gram
Proteins 4
Carbs 4
Fats 9
When I get in the kitchen, what do I eat? It’s actually possible to estimate food
content just by knowing a few easily identifiable facts.Food Grams Calories Calories per
gramMost likely contains…
Beef Jerky 28 116 4 Proteins
Popcorn 8 31 3.8 Carbs
Butter 10 70 7 Fats
Bacon 12 50 4 Proteins
Whole Wheat Bread
28 70 2.5 Carbs
Setting Up Conversion Factors To make calculations like this, we have to use
conversion factors. We know that certain quantities are equal to one
another. For example, we know that in fats:1 gram = 9 calories
Just as we food, we know conversions for measurement:
1 in = 2.54 cm
For example convert 6 in to cm:
Table Talk
How many gallons of milk are in 1500 L? (1 gal = 3.79 L)
Kitchen Fact:
You’ll need to know your volume conversions for measurements!
Two or More Step Conversions Often times, you need to do multiple
conversions in order to complete the desired conversion.
For these problems, you should plot out the units you will need to convert between to get to your final answer.
Hours Minutes Seconds1 hour = 60 minutes
1 minute = 60 seconds
Kitchen Fact:
You’ll need to know your time conversions for recipes!
Convert 3 hours to seconds
1 hour3 hours
10,800 sec60 min
1 min
60 sec
Class Example
You want to run to your favorite restaurant, but it’s 15.2 miles away! How many inches is this? (1 mi = 5280 ft and 1 ft = 12 in)
Table Talk
It takes you 15,250 s to slow-braise pork shoulder for carnitas. How many days did it take you to complete this?
Conversions and the Metric System
Recall, that the metric system is based on the power of 10.
These powers of 10 will convert you back to the base unit. Once you are at the base, you can convert to the desired unit.
Memorize these prefixes and conversion!
Prefix Factor
Milli- (m) 10-3
Centi- (c) 10-2
Deci- (d) 10-1
Base 100
Deka- (D) 101
Hecto- (H) 102
Kilo- (k) 103
How to Remember the OrderKing Henry Died By Drinking
Chocolate Milk
Converting is like a Staircase
Metric Conversion Example You have 425 cg of enriched flour, how many kg
do you have?
Sig. Fig Practice
Complete Problem Set 0.1 Be sure to use the appropriate units!
Quiz
Closing Time
Have all supplies by Thursday/Friday Quiz on Ch. 1 on Wednesday Complete Pre-lab for Lab 0. MUST BE
DONE BEFORE CLASS Focus on metric system, sig figs,and
dimensional analysis!