C4 - Predicting And Identifying Reactions And Products Flashcards
What are the group 1 metals?
Lithium, sodium, potassium, rubidium, caesium, francium
They all have one outer electron - thus have similar chemical properties
What are the common physical properties group 1 metals have?
Relative to other metals:
- Low melting points
- Low density
- Very soft
What type of compounds do alkali metals form?
Ionic compounds
How can you test for the presence of group 1 metal ions?
Using a flame test
Why are alkali metals reactive?
The outer electron is more easily lost because it is further from the nucleus, so the nuclear force of attraction is weaker and less energy is required to remove it
What are the Halogens?
Group 7 elements are known as the halogens
It is made up of Fluorine, Chlorine, Bromine, Iodine and Astatine
They all have 7 electrons in their outer shell
They also exist as diatomic molecules e.g. Cl2
Describe the trends going down the group 7 elements
As you go down group 7, the melting points and boiling points of the halogens increase.
Why does reactivity decrease going down group 7?
A halogen atom only needs to gain one electron in order to achieve a stable electronic structure.
As you go down the group, the halogens become less reactive as it gets harder to attract the extra electron due to the weaker nuclear force and the increased electron shielding
How are metal halides formed?
The halogens will react vigorously with alkali metals to form salts called metal halides
e.g. 2Na + Cl2 —> 2NaCl
Desribe a halogen displacement reaction?
A displacement reaction is where a more reactive element ‘pushes out’ (displaces) a less reactive element from a compound.
For example, chlorine is more reactive than bromine. If you add chlorine water to potassium bromide solution, the chlorine will displace the bromine from the salt solution.
e.g. Cl2 + 2KBr –> Br2 + 2KCl
Describe chlorine at room temperature:
Fairly reactive, poisonous, green gas
Describe bromine at room temperature:
Poisonous, red-brown liquid, which gives off an orange vapour
Describe iodine at room temperature:
Dark great crystalline solid which gives off a purple vapour when heated
What are the group 0 elements?
Group 0 elements are called the noble gases.
They include: helium, neon, argon, krypton, xenon, radon
They are all colourless gases at room temp
They have a full outer shell thus are more or less inert (unreactive)
Describe the properties of the transition metals
They have all the typical properties of metals - they are hard, strong and shiny materials that conduct heat and electricity
They have high melting points apart from Mercury
They also have high densities
They make very good catalysts e.g. iron is used in the Haber Process
The compounds of transition elements are also very colourful.
Most of the time, transition metals are much less reactive than Group 1 and 2 metals
What is the reactivity series?
Potassium
Sodium
Calcium
Magnesium
Aluminium
Zinc
Iron
Copper
Silver
What is the reaction between metals and water?
Metal + Water —> Metal Hydroxide + Hydrogen
How to test for oxygen gas?
You test for oxygen by placing a glowing splint near the mouth of the container of gas.
If oxygen is present, the splint should relight.
How to test for carbon dioxide?
You test for carbon duoxide using limewater, a calcium sulfate solution.
If you bubble CO2 through a limewater solution, it should turn cloudy white.
How to test for hydrogen gas?
You test for hydrogen by placing a lighted splint near the mouth of the container of gas.
If hydrogen is present, it should ignite with a squeaky pop.
How to test for chlorine gas?
Use a drop of water to dampen a piece of blue litmus paper.
Hold the paper near to the container that holds the substance
If chlorine is present, the paper turns red then white.
How to detect sulfate ions?
- Add a few drops of dilute hydrochloric acid
- Then a few drops of barium chloride solution
If sulfate ions are present, you get a white precipitate
How do you detect carbonate ions?
- Add a few drops of dilute hydrochloric acid
If carbonate ions are present, bubbles of gas will be produced. Dilute nitric acid can also be used
How to detect halide ions?
- Add a few drops of dilute nitric acid
- Then a few drops of silver nitrate solution
If chloride ions are present - a white precipitate is formed
If bromide ions are present - a cream precipitate is formed
If iodide ions are present - a yellow precipitate is formed
How do you carry out a flame test?
- Dip a clean Nichrome wire loop into the powder or solution
- Use the handle to hold the loop in the edge of a roaring blue flame
- Record the flame colour
What are the different colours produced by different metals from a flame test?
Metal Flame test colour
Lithium Red
Sodium Yellow
Potassium Lilac
Calcium Orange-red
Copper. Green-blue
What are the results from a sodium hydroxide test?
Ion Precipitate colour
Iron (II) Green
Iron (III) Orange-brown
Copper (II) Blue
Calcium White
Zinc White
Why are instrumental methods of analysis better than ‘wet’ tests?
They are more sensitive - can analyse small amounts of substances
They are more accurate
They are much quicker - can be be run constantly
Why does density increase down group 1 metals?
Density increases down group 1 because there are more protons and neutrons which in result increases the atomic mass of the atom
Why does melting point decrease down group 1?
Melting point decreases as you go down group 1 because the strength of the metallic bonds decreases.
There is also a greater distance between the nucleus and electrons therefore less energy is required to break the bonds.
Why does reactivity increase down group 1?
Reactivity increases down group 1 because the atoms get larger making the outer electron further away from the nucleus allowing it to be lost more easily.
Electron shielding also occurs; the other electrons get in the way of the nucleus and the outer electron
Why does melting point increase as you go down group 7?
Melting point increases as you down group 7 because the intermolecular forces get stronger
Why does density increase as you go down group 7?
Density increases because there are more protons and neutrons
Why does reactivity decrease as you go down group 7?
Group 7 halogens are trying to gain an electron.
As you go down, it is harder to gain an electron because the nuclear attraction force is weaker
How do you interpret a gas chromatogram?
Each peak represents a substance present in the mixture
The area under each peak shows the relative amount of each substance in the mixture
The retention time is relatively unique for each substance
What is a mass spectrometer?
A mass spectrometer measures the mass of atoms and molecules.
You can use it to measure the relative mass of different isotopes and also find out information about the structure of a molecule
How do you interpret a mass spectrum?
Each peak represent a fragment of the molecule
The peak on the far right represents the molecular ion
How does mass spectrometry work?
- Ionisation - the molecules are bombarded with electrons of which some will collide with enough force to knock an electron off the molecule - these molecules now have a +1 charge
- Acceleration - the ions are accelerated so they all have the same kinetic energy
- Deflection - the ions are passed through a magnetic field and will deflect in proportion to their mass and charge
- Detection - the beam of ions are detected electronically
How does infra-red spectroscopy work?
- A range of infra-red waves are passed through a sample of an organic compound
- Some are absorbed in varying amounts by different types of bonds
- A detector on the other side can tell which frequencies have been absorbed and by how much
