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!