Chapter 1 Flashcards Preview

Chem 400 > Chapter 1 > Flashcards

Flashcards in Chapter 1 Deck (28):
1

Observation

- first step in scientific method
- observe, describe, and measure some event in nature
- based in measurements called data

example:
A silver tray turns a dull gray color when left uncovered

2

Hypothesis

- possible interpretation of observations
- must be stated in a way that is tested by experiments

example:
Ice cubes has a greater volume than the liquid from which they were formed because the water molecules are farther apart in the ice structure than in the liquid structure.

3

Law

- summary of related observations
-statement that generalizes a body of observations or facts but does not provide an explanation why things happen the way they are

example:
The volume of a gas is directly proportional to its pressure.
Energy may be converted from one form to another, but the total quantity of energy remains constant.

4

Theory

- explanation of observations/ provides underlying reasons for observations
- well-tested, unifying principle explaining body of facts and laws based on them

example:
A gas is composed of small particles in constant motion.

5

Rules for Writing in Scientific Notation

- moving left = positive exponent
example:
93,000,000 = 9.3 × 10^7
- moving right = negative exponent
example:
.00005114 = 5.114 × 10^−5

6

Metric System

-> length: meter (m)
-> volume: liter (L)
-> mass: gram (g)
-> temperature: degree Celsius (°C)
-> time: second

7

System International (SI) Units

-> length: meter (m)
-> volume: cubic meter (m^3)
-> mass: kilogram (kg)
-> temperature: kelvin (K)
-> time: second (s)

8

Metric Conversion Chart

Tm (10^12) -> Gm (10^9) -> Mm (10^6) -> km (10^3) -> m(base unit) -> dm (10^-1) -> cm (10^-2) -> mm (10^-3) -> μm (10^-6) -> nm (10^-9) -> pm (10^-12)

9

Important Conversions/ Formulas

1ml = 1cm^3
D = m ÷ v
°F = 1.8(°C) + 32
°C = (°F -32) ÷ 1.8
K = °C +273
°C = K - 273

10

Mass

- measure of the quantity of material it contains
-measure of the quantity of matter
- independent of acceleration of gravity
-measured on balance "kg"
measured by comparison to a known mass which does not depend on gravitational pull

11

Weight

- has meaning only when an object having a specific mass is placed in an acceleration field like gravitational field of the earth
- depends upon acceleration of gravity
- W = mg "Newton"
- measured on scale
measured by the movement it causes in a spring which depends on the gravitational pull

12

Density

- mass per unit volume (D = m ÷ v)
- larger mass substance relative to volume, denser and heavier the object
- varies according to change in temperature
-physical property of matter
- Describes how its particles are packed together (tighter particles, higher density)
- In general, temperature increases, motion particles increase, volume expansion (since mass constant at all temperatures, density decreases at increasing temperature)
- most substances become denser when colder BUT when water reaches its max density at 4°C, expands and becomes less dense

*Temperature increases, volume expands and becomes larger, causing decrease density
* Temperature drops, volume contracts and becomes smaller, increase density

13

States of Matter

- classified by physical states: solid, liquid, gas
- solid: definite shape, definite volume
- liquid: definite volume, no definite shape
-gas: no definite shape and volume; highly compressible

14

Physical Properties

- observable and measured characteristics without changing composition of substance

examples:
color, state of matter, melting point, boiling point, density, solubility, electric conductivity, heat conductivity, malleability, ductility, viscosity, hardness, odor, taste

15

Chemical Properties

- observable and measured characteristics where one or more substances/ reactants are transformed into one or more different substances/products
- molecular identity no longer remains the same

examples:
flammability, acidity, volatility, corrosiveness, electronegativity

16

Extensive Properties

- properties that depend on the amount of substance present

example:
mass, volume

17

Intensive Properties

- properties that DO NOT depend on the amount of the substance

example:
melting point, density

18

Pure Substance

Pure Element: consists of single type of atom like Au and Pt

OR

Pure compound: consists of two or more different elements that are chemically combined like water and table sugar (C12H22O11)

- because chemically combined, CANNOT be separated from one another by physical process; only chemical processes like electrolysis

19

Mixture

-combination of two or more pure substances that are physically mixed together BUT do not chemically react together to form new substances
-each substance retains its original properties
-NOT chemically combined, so can be separated by physical processes like filtration

20

Homogenous Mixture

- aka solution
- two or more substances mixed together in the same phase
-uniformly dispersed throughout each other even down to the molecular level

examples:
IV saline solution, bronze vase with mixture copper and tin

21

Heterogenous Mixture

- does NOT have uniform composition throughout sample
-uneven texture often detected

examples: blood (consists red blood cells and white blood cells on microscopic level), granite (contains different minerals)

22

Compound vs. Mixture of Elements

- compound = combination of two or more elements held together by chemical bonds
- mixture = two or more elements physically mixed together BUT not chemically combined

compounds have two major differences from mixture of elements:

*distinctly different characteristics from their parent elements + have definite percentage composition by mass of their combining elements

23

Precision

- how close together a group of measurements are to each other
- degree of reproducibility
-determined with multiple measurements
- use AVERAGE DEVIATION, SAMPLE STANDARD DEVIATION, AND STANDARD DEVIATION to calculate precision of data

24

Accuracy

- refers to how close measured value is to the true or accepted value
- degree of veracity
-determined by one measurement
-use PERCENT ERROR and AVERAGE to calculate accuracy of data

25

Percent Error

- measure of accuracy
- how close measured/experimental value is to true/accepted value

EQUATION:
Error = measured value - true value
Percent error = ( I Measured Value - True Value I ÷ True Value ) × 100

26

Average Deviation

- smaller average deviation, more closely clustered data point are (higher precision)

EQUATION:
( Σ I individual value - average value I ) ÷ n

n = total number of data points

27

Q Test

- allows us to examine ONE observation from a small set of replicate observations (typically 3-10) can be "legitimately" rejected or not
-TEST CAN ONLY BE USED ONCE
Steps:
1. N values (set observations) are arranged in ascending order/ least to greatest
2. statistical experimental Q-value (Q exp) is calculated. (Q stands for rejection quotient)
-> Q ratio defined a s difference of suspect outlier value from its nearest neighbor value divided by range of values. Thus, for testing X 1 or X n (like largest or smallest values as possible outliers) use following Q exp valuesL
Q exp = (X 2 - X 1) ÷ (X n - X 1)
Q exp = (X n - X n-1) ÷ (X n - X 1)
* Q = gap ÷ range
3. Obtained Q exp value compared with critical Q value (Q crit) found in tables. Critical value corresponds to confidence level (CL)
4. Q exp > Q crit -> suspect value can be characterized as outlier and it can be REJECTED
Q exp < Q crit -> suspect value must be RETAINED and used in all subsequent calculations

28

Standard Deviation

- indicates how tightly all data points are clustered around the mean in a set of data
- data points bunched together and bell-shaped cure is steep, sd small
-data points spread apart and bell curve is relatively flat, sd large
- data points are all equal, sd = 0
- 1 sd (-1σ -> +1σ) accounts for 68.2% from mean
- 2 sd (-2σ -> +2σ) accounts for 95.4% from mean
- 3 sd (-3σ -> +3σ) accounts for 99.7% from mean

EQUATION:
σ = √[Σ (individual value - mean value)^2] ÷ (n-1)