Mastering Chemistry Chapters 2 & 3.1-2
Intensive (intrinsic) & Extensive (extrinsic) Properties
Intensive Property - can be used to identify a substance. It does not change as the amount of substance changes
Ex. Smell, color, density, flammability, reactivity, acidity,
Extensive Property - cannot be used to identify a substance. It does change as the amount of the substance changes.
Ex. - Length, mass, weight, and volume
2.2 Measured Numbers & Significant Figures
Important Terms:
Measured Numbers - a number obtained when a quantity is determined by using a measuring device
For example, height, weight, or temperature
Significant Figures - the numbers recorded in a measurement
Significant figures show precision of the measurement
Nonzero numbers are always significant figures
A zero may or may or be significant depending on its position
Rules of Significant Figures
Nonzero numbers are always significant figures
11 has 2 significant figures
Zeros between other non-zero digits are significant
303 has 3 significant figures
60103 has 5 significant figures
Zeros that put the decimal in the right place are not significant
200 and 0.002 have 1 significant figure
Zeros to the right of a number and to the right of the decimal are significant
2.00 has 3 significant digits
Zeros between significant zeros and a number are significant
60.0040 has 6 significant figures
50.0 has 3 significant digits
Exact Numbers -numbers obtained by counting items or by using a definition that compares two units in the same measuring system
They are not measures, do not have a limited number of significant figures and do not affect the number of significant figures in a calculated answer
Ex: a friend asks you how many classes you are taking - you would answer by counting the number of classes
Ex: there are 60 seconds in one minute
2.3a Significant Figures in Calculations
In science, measurement is crucial. The number of significant figures in measured numbers determines the number of significant figures in the calculated answer.
Rounding is important. If you multiply 5.52 meters and 3.58 meters to determine the answer in meters squared, you get an answer (for example, on a calculator) that shows 19.7616 (six significant figures). Since both of the original measurements had three significant figures, you should round 19.7616 to three significant figures - 19.8.
Rules for Rounding Off:
If the first digit to be dropped is 4 or less, it and all following digits are dropped from the number.
If the first digit to be dropped is 5 or greater, the last retained digit of the number is increased by 1.
Multiplication and Division with Measured Numbers:
In multiplication and division, the final answer is written so that it has the same number of significant figures as the measurement with the fewest significant figures.
Adding Significant Zeros: If the calculator reveals a whole number, but you used measurements that have three significant figures, you can add two significant digits to give 4.00 as the correct answer.
Addition and Subtraction with Measured Numbers:
In addition and subtraction, the final answer is written so that it has the same number of decimal places as the measurement with the fewest decimal places.
2.3b Significant Figures in Calculations
When determining the number of Significant figures used in an answer, round the number down if the digit to be dropped is four or less, and round the number up if the digit to be dropped is five or greater
When Multiplying and Diving measured numbers write the final answer so that it has the same number of significant figures as the measurement with the fewest significant figures
When adding or subtracting measured numbers, write the final answer so that it has the same number of decimal places as the measurement having the fewest decimal places
2.4 Prefixes & Equalities
A prefix can be placed in front of a measurement to increase or decrease its size.
To remember the order:
King - Kilo
ex. (.001 km = 1m) (1000 m = 1 km)
Henry - Hecto
ex. (.01 hm = 1 m) (100 m = 1 hm)
Died - Deka
ex. (.1 dam = 1 m) (10 m = 1 dam)
By - Base
ex. (1 m)
Drinking - Deci
ex. (10 dm = 1 m) (.1 m = 1 dm)
Chocolate - Centi
ex. (100 cm = 1 m) (.01 m = 1 cm)
Milk - Milli
ex. (1000 mm = 1 m) (.001 m = 1 mm)
When going down, move the decimal to the right one time per level
when going up, move the decimal to the left one time per level
An equality is a relationship between 2 units that measure the same quantity
Ex. 100 cm = 1 m
2.5a Writing Conversion Factors
Summary:
An equality expresses the equivalence between two different units
Ex: 1 L = 1000 mL
A conversion factor is a ratio in which the numerator and denominator are quantities or given relationship.
Ex: 100 cm/1 m and 1m/100cm
When converting two numbers between two metric units or two U.S system units, the numbers are exact.
Ex: 1 m to cm; 1 m = 100 cm; 100 cm is exact
When converting two numbers that are from different systems, the numbers are measured and count towards significant figures
Ex: 1 inch to cm; 1 inch = 2.54 cm; 2.54 cm is measured
You can write a percent as a conversion factor by writing the percent number in relation to 100 units
Ex: 18% body fat ---> 18 mass units of body fat in every 100 mass units
Remember to square and cube the number and the units when finding area and volume
Ex: (100cm)^2
2.5b Writing Conversion Factors
Any equality can be written as fractions called conversion factors. This is when one of the quantities is in the numerator and the other quantity is in the denominator.
Example:
When writing conversion factors, the word per means "divide". This means that the numerator is dividing into the denominator. Because they are equivalent, they can be written inversed and are the same.
The numbers in any definition between two metric units or between two U.S. units are exact
For Example: 1g = 1000mg - is a definition where both numbers are exact
When an equality consists of a metric unit and a U.S. unit, one of the numbers in the equality is obtained by measurement and counts toward the significant figures in the answer.
For example, the equality of is obtained by measuring the grams in exactly 1 lb. In this equality, the measured quantity 453.6 g has four significant figures, whereas the 1 is exact.
An equality may be stated within a problem that applies only to that problem.
1 onion = $1.24
A percent (%) is written as a conversion factor by choosing a unit and expressing the numerical relationship of the parts of this unit to 100 parts of the whole.
2.6a Problem Solving Using Unit Conversion
2.6b Problem Solving Using Unit Conversion
The process of problem solving in Chemistry often requires one or more conversion factors to change a given unit to the unit needed
The unit you want in your final answer is the one that remains after all of the units have been canceled out
Given unit x one or more conversion factors = needed unit
Steps to Convert factors:
State the given and needed quantities
Write a plan to convert the given unit to the needed unit
State the equalities and conversion factors
Set up the problem to cancel units and calculate the answer
Examples using one conversion factor:
Greg’s doctor has ordered a PET scan of his heart. In radiological imaging, dosages of pharmaceuticals are based on body mass. If Greg weighs 164 lb, what is his body mass in kilograms?
2.7a Density
Density: The relationship of the mass of an object to its volume expressed as grams per cubic. (g/cm^2)
Use volume displacement to measure a solids volume.
If an object is less dense than a liquid, the object floats when placed in the liquid.
Density can be used as a conversion factor.
Specific gravity is a relationship between the density of a substance and the density of water.
Specific gravity is one of the few unitless values you will encounter in chemistry.
Density practice questions:
Determine the density (g/mL) for each of the following:
A 20.0-mL sample of a salt solution has a mass of 24.0 g.
A cube of butter weighs 0.250 lb and has a volume of 130.3 mL.
A lightweight head on a golf club is made of titanium. The volume of a sample of titanium is 114 cm3 and the mass is 514.1 g.
A 4.000-mL urine sample from a person suffering from diabetes mellitus has a mass of 4.004 g.
A block of aluminum metal has a volume of 3.15 L and a mass of 8.51 kg.
3.1 Classification of Matter
Matter: anything that has mass and occupies space; everything around us
Pure Substance: Matter that is only one type of atom or molecule
Element: simplest type of pure substance
Compound: pure substance that consist of two or more elements
Mixtures: two or more different substances that are physically mixed; proportions are not consistent
Homogeneous Mixture: the composition is uniform throughout the solution; cannot see the individual components
Heterogeneous Mixture: the composition is not uniform throughout the sample; the components appear in separate regions
3.2 States & Properties of Matter
States of Matter: the three physical forms that you can find Earth's matter in
The states of matter are solid, liquid, and gas.
Solid: the state of matter where the matter has a definite shape and volume
Example: apple, chair, window
Liquid: the state of matter where the matter has no definite shape but a definite volume
Example: water, soda, coffee
Gas: the state of matter where the matter has no definite shape or volume
Example: air, smoke, oxygen
Physical Property: a property that can be measured without having to change the substance into another substance
Example: length, mass, color
Physical Change: some part of the matter will change, but the matter itself still has the same composition
Example: cutting, melting, breaking
Chemical Property: a property that can only be measured when a substance changes into a new substance
Example: combustibility, acidity, reactivity
Chemical Change: one or more original substances are converted into one or more new substances
Example: cooking, burning, water + baking soda