Introductory Chemistry Midterm Study Guide >

The scientific method involves observing/collecting data, forming hypotheses, experimenting, and then forming theories backed up by the data.

**(1)Observation** is describing and using your senses to gather information. This can be __quantitative__, meaning numerical data, or __qualitative__, which is descriptive data. The scientist then uses the gathered data to form a **(2)hypothesis**, which is a testable statement. Using the hypothesis, people can then begin **(3)testing** through experimentation, to obtain the data needed to support or refute the claim. **(4)Theorizing** can then begin, this process typically involves the use of models to help demonstrate or explain the phenomena, and find any correlations. From this, scientists can form theories or broad generalizations that give an explanation.

**Accuracy** is the closeness of a measurement to the actual or true value of something, while **precision** is defined as the closeness of the measurements to one another.

**Really large or small numbers** can be difficult to keep track of for scientists, so they use scientific notation to express numbers through the product of a coefficient and the number 10 raised to a power. When using this method, the coefficient must be greater than or equal to 1, but less than 10. So for example, if you had the number 56,000 your coefficient would be 5.6, and it would be multiplied by 10^4, so 5.6 x 10^4. If you had the number 0.000056, your coefficient would be 5.6, and it would be multiplied by 10^-5, (negative due to the fact that you are moving to the right) so 5.6 x 10^-5.

**Significant figures are used** for the precision of a number because if we express a number that has more digits than the actual measured value, it can be seen as less accurate.

5 basic rules for identifying significant numbers

All nonzero digits are significant

The zeroes in between nonzero digits are significant

Zeroes to the left of the first nonzero digits are insignificant

All zeroes to the right of a decimal point and a number are significant

Zeroes to the end of the number but not to the right of a decimal point are not significant

When **multiplying and dividing** with significant numbers, you count the number of significant figures in each number and choose the least amount. Then, you multiply or divide normally and the product should be rounded to that minimum number of significant digits.

When **adding or subtracting** with significant figures, you see which number has the least digits. After adding/subtracting the two numbers, you then round your final answer to the number of decimal places that you counted earlier.

Giga (G) | 1,000,000,000 |
---|---|

Mega (M) | 1,000,000 |

Kilo (k) | 1,000 |

Hecto (h) | 100 |

Deka (da) | 10 |

Base (Meter, Liter, Gram) | 1 |

Deci (d) | 0.1 |

Centi (c) | 0.01 |

Milli (m) | 0.001 |

Micro (µm) | 0.000001 |

Nano (n) | 0.000000001 |

1ft = 30.48 cm

1 inch = 2.54 cm

1 calorie = 4.184 joules

Specific heat of water = 4.184

1 Calorie = 1000 calories

1 Kilowatt-hour = 3.60 x 10^6 Joules

D (density) = m (mass) / v (volume)

**Practice Question:**

Calculate the percent error if the density of alcohol (ethanol) is found to be 0.802 g/mL but the true value is 0.798 g/mL

Answer:

Physical vs. Chemical Change

**Physical**

-Change of shape/size

-Change in state

**Chemical Change**

-Difficult to revert (Cooking an egg is a chemical change because it is difficult to change back to uncooked)

-Usually a state change

-Color change

-Odor

-Temperature change

-Precipitate

-Bubbles

-Light emission

☆Centrifugation

Using a centrifuge to separate particles in a liquid, or molecules with different densities, by spinning them at a high speed. Examples: extracting fat from milk, separating heterogeneous mixtures

-solids from liquids, liquids from liquids

☆Chromatography

The process of using chemical properties to separate substances, this can show you what makes up a solution because the substances all move at different speeds up the medium used.

-liquids from liquids

☆Decanting

When you pour the top of a mixture

-liquids in liquid, solids in liquids

☆Distillation

Using evaporation or condensation through heating

-separating liquids from liquids, solids from liquids

☆Filtration

Using a filter, or a material with minuscule holes to separate liquids and solids

☆Evaporation/boiling

Using heat to change a liquid to a gas, in order for it to leave behind the solute dissolved in it.

Thermal Energy Formula:

Practice Problem: A car with magnesium wheels is parked in the sun. If the temperature rises from 22C to 35C how much MJ of heat does each 6.8 kg wheel absorb? (C= 1.02 J/gC)

The atomic theory states that all matter is composed of small particles called atoms, and states: all matter is made up of invisible and indestructible particles called atoms, compounds are made up of 2 or more kinds of atoms, and that the atoms of an element are identical in size, mass, and other properties.

an __ion__ is an atom or molecule with a charge, while an __isotope__ is a form of an element with a different number of neutrons, therefore having a different mass number as well.

can be found displayed on the periodic table, and describes the average mass of naturally occurring atoms of that element.

This can be calculated by adding the product of each isotope’s percent abundance and atomic mass.

Radioactive decay occurs when an unstable nucleus gives off radiation/energy to reach a more stable state. To show this, we use nuclear equations which must be balanced, to demonstrate the law of conservation of mass properly.

Particles and their symbols:

and

Below is a nuclear equation, it represents the reactants and products in radioactive decay.

Practice Problem:

Answers:

A

B

C

Half-life is the time it takes for a quantity of a radioactive sample reduce to half.

Example:

**λ (lambda) = wavelength**

A wavelength is the distance between where a wave’s shape repeats. In other words, it is the distance from crest to crest (Top to top) or trough to trough (bottom to bottom). An example is included in the diagram below.

**ν (nu) = frequency**

The frequency is the number of waves repeated over a certain unit of time, waves with high frequency have shorter wavelengths, and this is the opposite for low-frequency waves.

**C= speed of light**

The speed at which light propagates through certain materials. In the air, the speed of light is:

*3 × 10^8 m / s*

E= energy

h= Planck’s constant

*Planck’s constant is a fundamental foundational constant in quantum mechanics-*

__6.626 x 10^-34__

**C = λ x ν**

*Speed of light = wavelength x frequency*

**E = h x ν**

*Energy = Planck’s constant x frequency*

**E = h c/λ**

Energy = (Planck’s constant x Speed of light ) / wavelength

https://knowt.io/note/8fd6753b-4120-44eb-99ac-1bfbec78d869/Unit-5-The-Periodic-Table

Exothermic is when a reaction releases energy, it typically gets hotter, while endothermic does the opposite and absorbs energy, getting colder. Anabolic reactions are endothermic, while catabolic reactions are exothermic.

The Bohr model is a system that consists of a nucleus surrounded by orbiting electrons. It explains how electrons move through orbits when they gain energy and return back to their ground state with the emission of light, and loss of energy.

Different elements have varying line spectrums, which is observed when these pure samples are heated. As an example, if you heat a sample of hydrogen gas at low pressure, it emits a red light. This color is one of the few lines shown on the line spectrum diagram, depicting the range of wavelength of light that can be emitted or absorbed.

The scientific method involves observing/collecting data, forming hypotheses, experimenting, and then forming theories backed up by the data.

**(1)Observation** is describing and using your senses to gather information. This can be __quantitative__, meaning numerical data, or __qualitative__, which is descriptive data. The scientist then uses the gathered data to form a **(2)hypothesis**, which is a testable statement. Using the hypothesis, people can then begin **(3)testing** through experimentation, to obtain the data needed to support or refute the claim. **(4)Theorizing** can then begin, this process typically involves the use of models to help demonstrate or explain the phenomena, and find any correlations. From this, scientists can form theories or broad generalizations that give an explanation.

**Accuracy** is the closeness of a measurement to the actual or true value of something, while **precision** is defined as the closeness of the measurements to one another.

**Really large or small numbers** can be difficult to keep track of for scientists, so they use scientific notation to express numbers through the product of a coefficient and the number 10 raised to a power. When using this method, the coefficient must be greater than or equal to 1, but less than 10. So for example, if you had the number 56,000 your coefficient would be 5.6, and it would be multiplied by 10^4, so 5.6 x 10^4. If you had the number 0.000056, your coefficient would be 5.6, and it would be multiplied by 10^-5, (negative due to the fact that you are moving to the right) so 5.6 x 10^-5.

**Significant figures are used** for the precision of a number because if we express a number that has more digits than the actual measured value, it can be seen as less accurate.

5 basic rules for identifying significant numbers

All nonzero digits are significant

The zeroes in between nonzero digits are significant

Zeroes to the left of the first nonzero digits are insignificant

All zeroes to the right of a decimal point and a number are significant

Zeroes to the end of the number but not to the right of a decimal point are not significant

When **multiplying and dividing** with significant numbers, you count the number of significant figures in each number and choose the least amount. Then, you multiply or divide normally and the product should be rounded to that minimum number of significant digits.

When **adding or subtracting** with significant figures, you see which number has the least digits. After adding/subtracting the two numbers, you then round your final answer to the number of decimal places that you counted earlier.

Giga (G) | 1,000,000,000 |
---|---|

Mega (M) | 1,000,000 |

Kilo (k) | 1,000 |

Hecto (h) | 100 |

Deka (da) | 10 |

Base (Meter, Liter, Gram) | 1 |

Deci (d) | 0.1 |

Centi (c) | 0.01 |

Milli (m) | 0.001 |

Micro (µm) | 0.000001 |

Nano (n) | 0.000000001 |

1ft = 30.48 cm

1 inch = 2.54 cm

1 calorie = 4.184 joules

Specific heat of water = 4.184

1 Calorie = 1000 calories

1 Kilowatt-hour = 3.60 x 10^6 Joules

D (density) = m (mass) / v (volume)

**Practice Question:**

Calculate the percent error if the density of alcohol (ethanol) is found to be 0.802 g/mL but the true value is 0.798 g/mL

Answer:

Physical vs. Chemical Change

**Physical**

-Change of shape/size

-Change in state

**Chemical Change**

-Difficult to revert (Cooking an egg is a chemical change because it is difficult to change back to uncooked)

-Usually a state change

-Color change

-Odor

-Temperature change

-Precipitate

-Bubbles

-Light emission

☆Centrifugation

Using a centrifuge to separate particles in a liquid, or molecules with different densities, by spinning them at a high speed. Examples: extracting fat from milk, separating heterogeneous mixtures

-solids from liquids, liquids from liquids

☆Chromatography

The process of using chemical properties to separate substances, this can show you what makes up a solution because the substances all move at different speeds up the medium used.

-liquids from liquids

☆Decanting

When you pour the top of a mixture

-liquids in liquid, solids in liquids

☆Distillation

Using evaporation or condensation through heating

-separating liquids from liquids, solids from liquids

☆Filtration

Using a filter, or a material with minuscule holes to separate liquids and solids

☆Evaporation/boiling

Using heat to change a liquid to a gas, in order for it to leave behind the solute dissolved in it.

Thermal Energy Formula:

Practice Problem: A car with magnesium wheels is parked in the sun. If the temperature rises from 22C to 35C how much MJ of heat does each 6.8 kg wheel absorb? (C= 1.02 J/gC)

The atomic theory states that all matter is composed of small particles called atoms, and states: all matter is made up of invisible and indestructible particles called atoms, compounds are made up of 2 or more kinds of atoms, and that the atoms of an element are identical in size, mass, and other properties.

an __ion__ is an atom or molecule with a charge, while an __isotope__ is a form of an element with a different number of neutrons, therefore having a different mass number as well.

can be found displayed on the periodic table, and describes the average mass of naturally occurring atoms of that element.

This can be calculated by adding the product of each isotope’s percent abundance and atomic mass.

Radioactive decay occurs when an unstable nucleus gives off radiation/energy to reach a more stable state. To show this, we use nuclear equations which must be balanced, to demonstrate the law of conservation of mass properly.

Particles and their symbols:

and

Below is a nuclear equation, it represents the reactants and products in radioactive decay.

Practice Problem:

Answers:

A

B

C

Half-life is the time it takes for a quantity of a radioactive sample reduce to half.

Example:

**λ (lambda) = wavelength**

A wavelength is the distance between where a wave’s shape repeats. In other words, it is the distance from crest to crest (Top to top) or trough to trough (bottom to bottom). An example is included in the diagram below.

**ν (nu) = frequency**

The frequency is the number of waves repeated over a certain unit of time, waves with high frequency have shorter wavelengths, and this is the opposite for low-frequency waves.

**C= speed of light**

The speed at which light propagates through certain materials. In the air, the speed of light is:

*3 × 10^8 m / s*

E= energy

h= Planck’s constant

*Planck’s constant is a fundamental foundational constant in quantum mechanics-*

__6.626 x 10^-34__

**C = λ x ν**

*Speed of light = wavelength x frequency*

**E = h x ν**

*Energy = Planck’s constant x frequency*

**E = h c/λ**

Energy = (Planck’s constant x Speed of light ) / wavelength

https://knowt.io/note/8fd6753b-4120-44eb-99ac-1bfbec78d869/Unit-5-The-Periodic-Table

Exothermic is when a reaction releases energy, it typically gets hotter, while endothermic does the opposite and absorbs energy, getting colder. Anabolic reactions are endothermic, while catabolic reactions are exothermic.

The Bohr model is a system that consists of a nucleus surrounded by orbiting electrons. It explains how electrons move through orbits when they gain energy and return back to their ground state with the emission of light, and loss of energy.

Different elements have varying line spectrums, which is observed when these pure samples are heated. As an example, if you heat a sample of hydrogen gas at low pressure, it emits a red light. This color is one of the few lines shown on the line spectrum diagram, depicting the range of wavelength of light that can be emitted or absorbed.