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UA / Chemistry / CHEM 1103 / What are theree sources of exact numbers?

# What are theree sources of exact numbers? Description

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● BC Notes Week 2

## What are theree sources of exact numbers?

○ Learn about scientific notation, significant figures, and how to report and calculate scientific measurements to the correct digit of uncertainty. ■ The last number of a measurement is estimated while the other digits are certain.

■ Precision in how close our measurements are to one another

■ Accuracy is how close our measurements are to the actual value of what we are measuring

■ Random error has the same probability of causing an error higher and lower than the actual measurements. With many repetitions the

errors should average out of our measurement

## How can i calculate the density of a substance?

■ Systematic error is a consistent error that happens every experiment, and it would not average out

○ Learn about scientific notation, significant figures, and how to report and calculate scientific measurements to the correct digit of uncertainty. ■ All nonzero digits are significant Don't forget about the age old question of How is histogram different from a bar graph?

■ To determine if a zero is significant, check if it is an interior zero, or between two non zero digits

■ Leading zeros are not significant because they are only placeholders. ■ Trailing zero

● If after a decimal it is significant

## How are changes quantified in energy?

● If before a decimal it is significant Don't forget about the age old question of What is the function of lipids in biology?
If you want to learn more check out How does angular distance measure?

● If it doesn’t have a decimal then the trailing zeros are

ambiguous and therefore cannot be determined to be

significant or not.

○ To avoid this ambiguity, report the number in scientific

notation

■ There are three sources of exact numbers

● Counting discrete objects (can’t have only part)

● In conversion factors

● Integral numbers (radius=diameter/2)

■ The answer of a multiplication or division problem should only have as many significant digits as the factor with the fewest significant

digits.

● NOTE:Your calculator will not keep track of significant

figures!

○ Learn about density and how to calculate and use the density of a substance ■ Density= mass/ volume Don't forget about the age old question of What is the inferior part of the thorax?
We also discuss several other topics like What is the modern development in microbiology?

● This is an intensive property, which is a property that does not

depend on the quantity of the substance

● An extensive property such as mass and volume depend on

quantity

○ Learn to quantify changes in energy

■ Energy is the capacity to do work

● Work is a force acting over a distance

■ Kinetic energy- the energy of motion

■ Potential energy- the energy of position or composition Don't forget about the age old question of What are the four d’s to describe abnormality?

● Systems with high potential energy tend to change in ways to

lower their potential energy

■ The law of conservation of energy states that energy can be neither created nor destroyed, only change it from one form to another

■ The Joule is the SI unit for energy (1 joule = 1 kg meter^2/second^2) ■ Other common units for energy

● Calorie= 1000 calories (lowercase)

○ A calorie is the amount of energy required to raise the

temperature of 1 gram of water by one degree celsius.

■ If our system increases in energy then that energy had to come from our surroundings

● A positive change in energy is when energy is transferred

from the surroundings into a system

● A negative change in energy is when energy is transferred

from the system into the surroundings

■ If a thermal system has a negative change in energy, it is exothermic (it gives off heat)

■ If a thermal system has a positive change in energy, it is exothermic (it takes heat)

○ Use the unit-conversion method, applying conversion factors to calculations. ■ Dimensional analysis is a method of solving problems using units to guide the process

● We can use conversion factors, which relate two equivalent

quantities with different units

○ Ex: 1m=100cm

● In word problems, sort through the information given and find

standalone pieces of information (usually quantitative), and

conversion factors (1ft=12in)

○ NOTE:there are 3 example problems on Blackboard

under LO 13 & 14 that will further explain the

conversion and calculation process.

○ To help with conversion homework problems on

MasteringChemistry, click on the ‘Constants’ tab on

the left side of the page, then scroll down to

conversions.

● SI Drill Week 2 (First Meeting)

○ A law tells you something, a theory explains why a law happens ■ Difference between an element and a compound

○ Matter

■ Pure substances

● Elements & compounds

■ Mixtures

● Heterogeneous & homogeneous

○ Dalton’s Atomic Theory

● Lecture 3, August 28

○ Isotopes are the same element with different numbers of neutrons ■ The percentage of certain isotopes is called the natural abundance ○ Atomic Mass= SUM(fraction of isotope n)x(mass of isotope n) ○ Know the SI prefix multipliers from 10^12 through 10^-12

○ Measurement

■ Quantitative observation has two parts- number and unit.

● Number tells comparison

● Unit tells scale

○ Scientific notation can be represented by Exp, EE, E, 10^n

○ When reading an instrument, read from the bottom of the meniscus ○ NOTE- ON TEST

■ Boron has two naturally occurring isotopes:

10B with an isotopic mass of 10.013

11B with an isotopic mass of 11.009

Calculate the percent abundance of 10 b.

** ALL LECTURE POWERPOINTS CAN BE FOUND ON BLACKBOARD

● Lecture 4, August 30

○ Significant figures and mathematical operations

■ Multiplication and Division

● The least precise measured value (the fewest numbers)

determines the number of significant significant figures that

can be used in the answers.

■ Addition and Subtraction

● Value with the smallest decimal (decimal’s only, don’t count

the whole numbers) determines the number of significant

significant figures that can be used in the answers.

○ Volume

■ Measure the amount of 3-D space occupied by a substance

■ SI unit= cubic meter (cm^3)

■ Commonly measure solid volume in cm^3

● 1mL=1cm^3

● 1L=1dm^3

■ Mass of a substance per unit volume of the substance

● Common units are g/cm^3 or g/mL

● Density= mass/volume

○ Density is an intensive property

○ Energy terminology

■ Energy of the universe is conserved

● First law of thermodynamics, all matter possesses energy ■ System (phase change or chemical reaction)

● The area or location under study

■ Surroundings

● Area or location around the study

■ Universe

● System + surroundings

○ Use when converting a given result from one system of units to another. ■ To convert from one unit to another, use the equivalence statement that relates the two units

■ Choose the appropriate conversion factor by looking at the direction of the required change

■ Multiply the quantity to be converted by the conversion factor to give the quantity with the desired units

■ Check that you have the correct number of sig figs

■ Make sure your answer makes sure

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