CHEMISTRY Exam 2023

chromatography

a method of separating mixtures and analysis of a mixture of a soluble chemical substance

what is the stationary phase

paper

what is the mobile phases

solvent (liquid → usually water but not always)

do substances that are more attracted to the mobile move farther up the paper?

YES

chromatography method

1. draw baseline in pencil, 1 cm from the bottom of paper
2. draw samples/dots onto base line
3. add chromatography paper to beaker so solvent paper but below the baseline
4. wait until solvent has traveled up to almost the top of paper, draw a new line in where it reached in pencil (solvent front)
5. calculate Rf of substances

how to calculate the Rf value

distance traveled by substance (colour) DIVIDED BY distance traveled by solvent (liquid or solvent front)

what does do simple distillation?

separates 2 liquids

the mixture is heated enough so one liquid boils, the vapour moves up and into the condenser where it is cooled and turned back into a liquid.

fractional distillation

used to separate 3 or more liquids/gases into individual fractions

filtration

used to remove an insoluble solid from a liquid

crystallisation

used to remove water from an insoluble salt solution (evaporation)

atomic structure

protons and neutrons in the nucleus and electrons in the outer shells

electron relative mass and relative charge

relative mass - 1/2000

relative charge - -1

neutron relative mass and relative charge

relative mass - 1

relative charge - 0

proton relative mass and relative charge

relative mass - 1

relative charge - +1

history of the atom

John Dalton in 1803 thought that all matter was made of particles called **atoms**

Nearly 100 years later, J J Thomson carried out experiments and discovered the **electron**. This led him to suggest the **plum pudding model** of the atom.

In 1909 Ernest Rutherford designed an experiment to test the plum pudding model. In the experiment, positively charged **alpha particles** were fired at thin gold foil. Most alpha particles went straight through the foil. But a few were scattered in different directions.

Niels Bohr adapted Ernest Rutherford's nuclear model to suggest that electrons orbit the nucleus in shells. The shells are at certain distances from the nucleus.

Further experiments led to the idea that the nucleus contained small particles, called **protons**. Each proton has a small amount of positive charge.

In 1932 James Chadwick found evidence for the existence of particles in the nucleus with mass but no charge. These particles are called **neutrons**. This led to another development of the atomic model, which is still used today.

relative atomic mass calculations

* To calculate the relative atomic mass: 
* Multiply the % amount of each isotope by its mass 
* Add these numbers together 
* Divide by the total abundance (which when using % abundance, will be 100%) 
* Here it is as an equation: 

group 1

as you go farther down group 1 the metals get more reactive as the electron needed to be removed is farther away from the nucleus so lower attraction.

nicknamed Alkali Metals

group 7

Nicknamed the halogens

the closer the outer shells to the nucleus the greater ability to react

group 0

nicknamed the noble gases

they have full outer shells so do not need to react

Earth's atmosphere

made up of multiple layers

Early atmosphere

* lots of water vapour (over 100 degrees)
* high levels of CO2
* high levels of sulfur dioxide
* very hot
* lots of volcanoes and eruptions
* some ammonium
* no free oxygen

Changes in the earth’s atmosphere - H2O

the earth cooled to below 100.C and water vapour condensed and fell onto the surface

Changes in the earth’s atmosphere - CO2

levels were decreased - absorbed into oceans - used by sea creatures to make shells - locked up in fossil fuels & limestone

Changes in the earth’s atmosphere - O2

organisms evolved to photosynthesis - plants, algae and bacteria

Exothermic

gives out energy to the surroundings

endothermic

takes in energy from surroundings

exothermic profile diagrams

endothermic profile diagrams

bond energy calculations

1. calculate the energy for each reaction
2. the LEFT HAND SIDE - RIGHT HAND SIDE = ANSWER
3. if answer is positive it is endothermic and if answer is negative it is exothermic