Chapter 1: Basic Concepts
The careful, systematic approach to investigation
Data can be qualitative or quantitative.
Qualitative
This ice is cold!
This professor talks loudly.
Class lasts forever!
Quantitative
The ice is –4.8 °C.
This professor is outputting 78 db on average.
Class is 50 minutes long.
Source: openStax
What takes up more space?
Source: Wikimedia
\[\underbrace{\mathrm{H_2O}(l)}_{\mathrm{chemical~formula}}\]
Source: openStax
blend of two or more substances that preserve their identities
Homogeneous
uniform composition
Heterogeneous
not uniform
Element
Compound
Law of Definite Proportions – a chemical compound always contains exactly the same proportion of elements by mass, regardless of the amount or source of the compound; also known as the Law of Constant Composition
Example: water (H2O) is always made up of 2 hydrogen atoms and 1 oxygen atom, and the ratio by mass is always approximately 11% hydrogen and 89% oxygen, no matter where the water comes from or how much water you have.
Law of Multiple Proportions - whenever the same two elements form more than one compound, the different masses of one element that combine with the same mass of the other element are in the ratio of small whole numbers.
Example: Carbon and oxygen form in a 1:1 ratio in carbon monoxide whereas carbon and oxygen form in a 2:1 ratio in carbon dioxide. They do not form in a weird ratio such as 1.346:1.
Filtration
Separate sand from water using a filter
Source: Wikimedia
Distillation
Separate salt from water by distillation
Source: Wikimedia
Chromatography
Separate the components of a mixture (purple) by passing the mixture through a medium where different substances (red and blue) move at different speeds.
Source: Wikimedia
Most elements involve a collection of single atoms, e.g. Fe(s)
Some are diatomic containing a covalent bond between pairs of atoms.
Extensive
does depend on the amount of matter present
Intensive
does not depend on the amount of matter present
Physical
can be measured or observed without changing the chemical nature of matter
Chemical
describes the ability of a substance to undergo chemical change
Property | Using the Property to Distinguish Substances |
---|---|
Color |
Is the substance colored or colorless? What is the color, and what is its intensity? |
State of matter |
Is it a solid, liquid, or gas? If it is a solid, what is the shape of the particles? |
Melting point |
At what temperature does a solid melt? |
Normal boiling point |
At what temperature does a liquid boil (at 1 atm pressure)? |
Density |
What is the substance’s density (mass per unit volume)? |
Solubility |
What mass of substance can dissolve in a given volume of water or other solvent? |
Electric conductivity |
Does the substance conduct electricity? |
Malleability |
How easily can a solid be deformed? |
Ductility |
How easily can a solid be drawn into a wire? |
Viscosity |
How easily will a liquid flow? |
Ratio of the mass of an object to its volume
\[\begin{align*} \mathrm{density} &= \dfrac{\mathrm{mass}}{\mathrm{volume}}\\[4ex] d &= \dfrac{m}{V} \end{align*}\]
What has a higher density, ice or water?
Temperature (°C) |
Density (g cm–3) |
---|---|
0 (ice) |
0.917 |
0 (liq water) |
0.99984 |
2 |
0.99994 |
4 |
0.99997 |
10 |
0.9997 |
25 |
0.99707 |
100 |
0.95836 |
Ice floats in water.
A 236.3 g sample of water completely fills a 237 mL (8 fl oz) bottle of water.
\[\begin{align*} d &= \dfrac{m}{V} \\[1.5ex] &= \dfrac{236.3~\mathrm{g}}{237~\mathrm{mL}} \\[1.5ex] &= 0.997~\mathrm{g~mL^{-1}} \end{align*}\]
The density of water at 25 °C is 0.997 g mL–1.
Press q
for answer.
A pot of boiling water (at 100 °C) contains 1000 mL of water with a density of 0.95805 g mL–1.
\[\begin{align*} d &= \dfrac{m}{V} \longrightarrow \\[1.5ex] m &= dV \\[1.5ex] &= (0.95805~\mathrm{g~mL^{-1}})(1000~\mathrm{mL}) \\[1.5ex] &= 958.05~\mathrm{g} \end{align*}\]
Press q
for answer.
\[\begin{align*} \overbrace{\mathrm{H_2O}(l)}^{\mathrm{reactants}} &\longrightarrow \overbrace{\mathrm{H_2O}(g)}^{\mathrm{products}} \\[1.5ex] 1.0~\mathrm{g} ~~ &\longrightarrow ~~ 1.0~\mathrm{g} \end{align*}\]
Law of Conservation of Mass - mass is neither created nor destroyed; it is conserved
\[\begin{align*} \overbrace{2\mathrm{H_2}(g) + \mathrm{O_2}(g)}^{\mathrm{reactants}} &\longrightarrow \overbrace{\mathrm{2H_2O}(g)}^{\mathrm{products}}\\[1.5ex] 4.04~\mathrm{g} ~ + ~ 32~\mathrm{g} ~~ &\longrightarrow ~ 36.04~\mathrm{g} \end{align*}\]
Mass is conserved.
Energy is the capacity to do work
Law of Conservation of Energy - energy is neither created nor destroyed, only transformed; the energy of the universe is constant
Source: Wikimedia
Source: Wikimedia