Scientific Method

1. Recognize a quetions/problem

2. Make a hypothesis: testable prediction

3. Predict consequences that can be observed if hypothesis is correct

4. Experiment & make observations to see if PC are correct

5. Evaluate results a draw conclusions

• What the invetigator measures, and is what the investigator thinks will change during the experiment.
• The dependent variable is the y axis on a graph.

*Example*:

• What the investigator deliberately varies during the experiment.
• The independent variable is the x axis on a graph.

*Example*:

• AKA the constants-- are the factors that are kept constant throughout the experiment.
• Helps compare changes that occured in dependent variable and changes made in independent variable.

*Example*:

• How close a series of measurements are to each other
• Reproducibility
• Check by repeating measurements
• Poor precison from poor technique
• Small errors are more likely than large when dealing with precison

*Example*: 3.62345 -- very precise number

• How close the measurement is to the "accpeted" value
• Correctness or closeness to actual value.
• Check by using different instruments
• Poor accuracy is a consequence of procedural or equip. flaws.

*Example*: 4-- accepted value = 3.9 --> very accurate

Measurement

• Counted numbers such as 0,1,2,3,4,5... are exact. COunted numbers are numbers that you don't measure during an experiment, but are already present.
• Measured numbers that you measure during an experiment are inexact. Because of this, the Sig. Fig. rule applies to them.

  1.  All digits besides 0 are Sig. Figs.

          -3.245--> 4 SF

  2.  All 0's btwn Sig. Figs. are significant.

          -8.002--> 4 SF 

  3.  0's at beginnig of # - non sig.

          -0.00000024--> 2 SF

  4.  0's to right of last non zero digit w/ decimal = significant

          -9.000--> 4 SF

  5.  0's to right of last non zero digit w/out decimal - non SF

          -9000--> 1 SF

• Round to decimal point with number that has least amount of SF.

            5.5 * 6.50 = 35.75 --> 35.8

            55/10 = 5.5 --> 6

• Round to the measured number that is least precise.

                6.551 + 10 = 16.551 --> 17

                100.0 - 25.567 = 74.433 --> 74.4

• Anything that has mass, volume, weight, and is made up of small particles.

• Amount of matter in an object
• Kg/g --> use balance
• Inertia is consequece of mass only

• Effect of gravity on a given mass
• Newtons
• weight on earth remains measurably constant

• Amount of space occupied by a substance.
• L/ml/cm^3
• graduated cylinder, metric rule, water displacement

• Mass per unit volume
• m/v = d
• g/cm^3, kg/m^3

Physical Changes

• generally reversible
• occurs at molecular level
• rearrangement is in only in terms of molecular structure
• Expected change in color

• Involves change in chemical composition
• Irreversible
• Occurs at molecular level
• rearrangement of atoms causing new chem. bonds to form
• change in temperature
• production: heat, light, sound
• unexpected change in color
• Fizzing/bubbling

• Measure of the average kinetic energy of molecules

• mass is a measure of the quantity of matter in an object.
• weight is the force with which gravity pulls on a quantity of matter.
  

• Inertia is the resistance an object has to a change in its    state of motion
• The greater the mass in an object, the greater the inertia. For example, a heavy wagon will be hard to push because of its large inertia, but will be hard to stop once it gets going because of its great inertia (vise versus)

   

• The buoyancy of an object equals the wight of the fluid the object displaces.

• The force that pushes upwards in a fluid
• Formula: Fb = true weight - apparent weight

Charles Law

• Describes the effect of temperature on volume. A sample of gas at a fixed pressure, the volume is directly proportional to temperature (kelvin).
• Formula- V1/T1 = V2/T2

• For a given mass of gas at a constant temperature, the volume varies inversely with the pressure. It describes the relationship between pressure and volume occupied by a gas.
• Formula: P1*V1 = P2*V2 

• Describes the effect of temperature of a gas on pressure. For a given mass of gas at a constant volume, the pressure of the gas is directly proportional to temperature (kelvin).
• Formula: P1/T1 = P2/T2

• Force per unit given (F/A = P)

• The higher the temperature there is, the higher the pressure will be, if the volume remains constant.
• More collisons will occur as the temperature has increased. Since there is more collisons, there is more force. When the force becomes greater and the area remains the same, the pressure will increase.

• more than one substance mixed together
• can be seperated by physical means

• Another name for a homogenous mixture.
• Particles are constant and uniformly mixed.
• Mostly exists in liquids but can be in solid--> alloy or   gas--> air.

• two or more elements chemically combined in definite proportions.
• seperated by chemical means

• simplest kind of substance that can exist. 
• An element cannot be changed into simpler substances

• Homogenous - mixture that is uniform, or the same throughout any sample
• Particles in homogenous mixture are very small
• Heterogenous - mixture that doesn't appear to be the same throughout
• Sometimes referred to as mechanical mixtures.

Colloid

• Heterogenous mixture that never settles
• Occurs with two or more homogenous mixtures
• Appears homogenous, but isn't

Example: Milk, blood, shaving cream

• An unstable dispersion of one substance in another (heterogenous)
• Particles much larger than colloid--> may be visible to naked eye
• Contains a liquid w/ visible particles settled.
• Seperated by filtration                            *Example*: muddy water, opaque

  - Solutions are seperated by physical means, while pure substances are seperated by chemical means.

  - Solutions are made of 2 or more mixtures, while a pure substance is made of only 1 substance.

  *Both homogenous, constant composition, particles dont settle out, & exist in 3 forms of matter.

  Examples: solution = soda, pure substance = water (H2O)

• Metal solution in which solids dissolve in solids
• Example: brass - copper + zinc         gold jewls - silver and gold

Compare/Contrast Elements & Compounds

  - Element has one molecule, while a compound has 2 or more molecules chemically combined.

  *Both homogenous, chemically combined, & definate

Examples: element - O = oxygen, compound H2O - water

• Matter absorbs heat during phase change
• Occurs with Melting & Boiling

• Matter releases heat during phase change
• Occurs with Freezing & Condensation