- Sit with, or near, your group & take out your sig figs worksheet - Talk to group members to see where you want to sit - Remember your number! #Group AGroup BGroup CGroup DGroup EGroup FGroup G 1ANNA G.NICOLABERNICEJASMINEKOMALMANISHABEN 2IVANVIVIANNA Z.IVYNICOLETIANWING 3TOMMYECKHAMSIMRANANGELAKIANADOMNANCY 4DEBORAHHUSNRAFAYAUTUMNVERONICAJONATHANFELIPE & AMY

Hand in Course Outline, Safety Agreement, Contact Lens Letter on the overhead please New students: measurement lab at lunch today, safety quiz tomorrow at lunch Was it helpful to post up the notes a day beforehand? I will try to do this every class so you can print, take notes or read it over before class

Today’s Groups When I ask you to go into groups to try questions today, discuss the solution in your group Make sure everyone understands the steps I pick a number, that number from every group stands up, I pick one (or more) to write answers on the board No notes allowed when you come up to write Get into your groups and remember your numbers

Mixed Operations with Sig Figs Follow the rules for each operation Do NOT round off after every step Do keep track of the decimal places and sig figs every calculation you make Try: 9.34 x – 6.88 x

Mixed Operations with Sig Figs 9.34 x – 6.88 x = –

Mixed Operations with Sig Figs 9.34 x – 6.88 x = – =

Mixed Operations with Sig Figs 9.34 x – 6.88 x = – = = Try Hebden p.40 #59 c, f, g Work with your groups!

Dimensional Analysis (Unit Conversions)

Conversion Factors

Same Quantity, Different Units

Sig Figs in Conversion Factors

Exact/Defined/Counting Numbers

Warning: not all conversion factors are exact Can you think of an example of an inexact conversion factor?

Exact/Defined/Counting Numbers Warning: not all conversion factors are exact Can you think of an example of an inexact conversion factor? Conversions between metric & imperial units E.g. 1 m = ft This number is rounded to 5 sig figs but goes on forever There is uncertainty so the number of sig figs matter

Exact/Counting or Measured (Inexact)? 29 students in the classroom $20.48 in my pocket 100,000 hairs on my head

Exact/Counting or Measured (Inexact)? 29 students in the classroom - exact $20.48 in my pocket 100,000 hairs on my head

Exact/Counting or Measured (Inexact)? 29 students in the classroom - exact $20.48 in my pocket - exact 100,000 hairs on my head

Exact/Counting or Measured (Inexact)? 29 students in the classroom - exact $20.48 in my pocket - exact 100,000 hairs on my head - exact

Solving Unit Conversion Problems Step 1: identify the initial amount – what info are you given? Step 2: identify the unknown amount – what are you looking for? Step 3: identify the conversion factor – how are 1 & 2 related? Overall: unknown amount = initial amount x conversion factor

Example 1 How many min are there in 3480 s? Step 1: Step 2: Step 3:

Example 1 How many min are there in 3480 s? Step 1: initial = 3480 s Step 2: Step 3:

Example 1 How many min are there in 3480 s? Step 1: initial = 3480 s Step 2: unknown = min Step 3:

Example 1

How many min are there in 3480 s? Overall: unknown = initial x conversion factor

Example 1 How many min are there in 3480 s? Overall: unknown = initial x conversion factor ? min = 3480 s x conversion factor Want to leave min and cancel s so use the c.f. with min on top (numerator) and s below (denominator)

Example 1

Example 2 (don’t copy, just try) The automobile gas tank of a Canadian tourist holds L of gas. If 1 L of gas is equal to gal in the US (“gal” is the symbol for “gallon”), and gas is $1.26/gal in Dallas, Texas, how much will it cost the tourist to fill his gas tank in Dallas?

Example 2 Initial = Unknown = Conversion factors:

Example 2 Initial = L Unknown = Conversion factors:

Example 2 Initial = L Unknown = $ (cost) Conversion factors:

Example 2 Initial = L Unknown = $ (cost) Conversion factors: L  gal: gal  $:

Example 2

Unknown = initial x c.f. x c.f.

Example 2 $ ? = L x c.f. x c.f. First c.f. must cancel out litres Must have L in the denominator (below)

Example 2

Tips to Avoid Rounding Errors Write only one equation for the entire question If you must do more than one equation, do not round before you get to the final answer Instead, write down as many digits as you can or use the memory function on your calculator (M+) This is the difference b/t right and wrong answers!

SI Units The International System of Units (Le Système International d’Unités) Modernized version of the metric system used in science Any SI prefix can be used with any SI base unit

SI UnitsSI Prefixes Quantity Unit name Unit Symbol Lengthmetrem Masskilogramkg VolumelitreL Timeseconds TemperaturekelvinK Amount of Substance molemol Electric current ampereA Written Prefix Prefix Symbol Equivalent Exponential megaM10 6 kilok10 3 hectoh10 2 dekada decid10 -1 centic10 -2 millim10 -3 microμ10 -6

SI Prefixes 5 Mm = 5x10 6 m 5 m = 5x10 -6 Mm 12 ms = 1.2x10 -3 s 12 s = 1.2x10 3 ms Written Prefix Prefix Symbol Equivalent Exponential megaM10 6 kilok10 3 hectoh10 2 dekada decid10 -1 centic10 -2 millim10 -3 microμ10 -6

Other Units & Equivalences 1 t = 1 tonne = 10 3 kg 1 mL = 1 cm 3 (cubic centimetres, cc) 10 3 L = 1 m 3

Derived Units A unit made by combining two or more other units Speed = distance/time = km/h Density = mass/volume = g/L

Group Activity Closed book, open notes I give questions 5 min to discuss the solution in your group Make sure everyone understands the steps I pick a number, that number from every group stands up, I pick one (or more) to write answers on the board No notes allowed when you come up to write Get into your groups and remember your numbers

Question 1 Express 905 in 2 sig figs

Question 1 Express 905 in 2 sig figs = 9.0 x 10 2

Question x x 10 2 = ?

Question x x 10 2 = ? Always convert smaller exponent to the bigger one x x 10 4 = x 10 4

Question x – x

Question x – 16 x = – = = 0.8

Question 4 If there are 6.02 x atoms in 1 mol of atoms, how many atoms are there in 5.5 mol of atoms?

Question 4 If there are 6.02 x atoms in 1 mol of atoms, how many atoms are there in 5.5 mol of atoms?

Question 5 Sugar costs $0.980/kg. 1 t = 1000 kg. How many tonnes (“t”) of sugar can you buy for $350?

Guiding Questions for the Video What are the differences between exact and measured numbers? What are the two kinds of 0’s and how do we tell them apart? Are there disagreements between the video and your notes?

Hand in tomorrow: sig figs worksheet, Hebden p. 14 #2-10 Practice: Hebden p #11-18 Start studying for unit 1 test on Monday Tomorrow will be a fun review activity