Paper 2: 6+7 Flashcards
What group of the periodic table are the alkali metals?
Group 1
List two properties of alkali metals
Relatively low melting points
Soft
Why are group 1 elements called the alkali metals
They react with water form alkaline solutions
How many electrons are in the outer shell of a group 1 element?
One
Why do elements in the same group have similar chemical properties?
They have the same number of electrons in the outer shell.
What are the products of the reaction between lithium and water?
Lithium hydroxide and hydrogen
Write a balanced symbol equation of the reaction of sodium with water
Why should alkali metals be stored in oil
To prevent them reacting with water vapour and oxygen in the air
What would be observed when lithium reacts with water
Slowest reaction of alkali metals
Bubbles of hydrogen are produced
Doesn’t Melt (highest melting point of alkali metals)
What would be observed when sodium react with water?
Faster reaction than lithium
Floats on the surface of water (less dense than water)
Bubbles of hydrogen are produced which cause the sodium to move on the surface of the water
Melts
What would be observed when potassium reacts with water?
More violent reaction than sodium
Bubbles of hydrogen are produced which cause the potassium to move on the surface of the water
Melts into shiny ball
Burns with a lilac flame
Order of reactivity of first 3 alkali metals
Least: Lithium Sodium Potassium Most:
Why does reactivity increase down group 1
The number of electron shells increases down the group so there is more electron shielding. As a result, there is weaker attraction between the positive nucleus and outer shell electron. This means it is easier to remove an outer shell electron to form a positive metal ion
Which group 1 element would you expect to react most violently with water?
Reactivity increases down the group so francium will react most violently with water.
What group are the halogens in? Why?
Group 7 because they have 7 outer shell electrons.
What is the colour and state of chlorine at room temperature
Pale green gas
What is the colour and state of bromine at room temperature?
Red-brown liquid
What is the colour and state of iodine at room temperature?
Black solid
What state would you expect the halogens fluorine and astatine to be at room temperature?
Fluorine is above chlorine so should have a boiling point lower than chlorine. This means it would be a gas at room temperature.
Astatine is below iodine in group 7 so should have a higher melting point than iodine. Therefore you can predict that it would be a solid at room temperature.
Why does melting and boiling increases down group 7
The molecules get bigger down the group so there are more intermolecular forces to overcome during melting / boiling so more energy is required
What is the chemical test for chlorine
Damp blue litmus paper placed into a test tube of gas. If chlorine is present, the litmus paper will turn red then white due to the bleaching effect of chlorine
Halogens are diatomic. What does this mean?
They form molecules consisting of 2 atoms
E.g: Cl2, Br2 …
What charge does a Halide ion carry? Why?
-1
e.g. Cl-, Br-…
They gain one electron to have a stable
electron configuration
What is produced when a halogen reacts with a metal?
Metal Halide salt
Write a balanced symbol equation between bromine and sodium
Predict the product of the reactor between magnesium and fluorine
Magnesium flouride (MgF2)
Describe the trend in reactivity of the halogens. How does this affect the rate of reaction?
Reactivity decreases down group 7.
Rate of reaction decreases down group 7.
What is formed when hydrogen reacts with a halogen?
Hydrogen halides
e.g. HCl, HBr…
Chlorine reacts with hydrogen in the presence of sunlight but bromine required a flame. Why?
Reactivity decreases down the group so bromine requires more energy for the reaction to occur.
What is formed when a hydrogen halide dissolves in water?
An acidic solution. Hydrogen ions dissociate, making the solution acidic.
Write a balanced symbol equation of the reaction between hydrogen and chlorine
H2 + Cl2 → 2HCl
Predict the product of the reaction between hydrogen and fluorine
Hydrogen fluoride (HF)
When does halogen displacement reaction occur?
When a more reactive halogen displaces a less reactive halogen from an aqueous solution of its halide.
Why will halogen A only be displaced by halogen B if B is above A in group 7?
The most reactive halogen (B) will displace the less reactive halogen (A) to become part of the ionic compound. Reactivity increases as you go up the group so B must be higher in group 7 to be more reactive than A.
Which halogens can chlorine displace from an aqueous ionic solution?
Chlorine can displace any halogens below it in group 7. It will displace iodine and bromine.
Which halogens can’t be displaced from an aqueous ionic solution by bromine?
Bromine can’t displace any halogens above it in group 7. These are chlorine and fluorine.
Write the balanced symbol equation for the reaction that takes place between bromine and potassium iodide
Br2 + 2KI → I2 + 2KBr
Which halogens would you expect astatine to be able to displace?
None of them. It is at the bottom of group 7 so has the lowest reactivity
Why does reactivity decrease down group 7?
As you go down group 7, the outer shell is further from the nucleus and electron shielding increases.
Attraction between the nucleus and outer electrons decreases so it is harder for the atom to gain an electron meaning reactivity decreases.
What colours are solutions of chlorine, bromine and iodine?
Chlorine water - colourless
Bromine water - orange
Iodine solution - brown
What would you observe when chlorine is added to potassium bromide?
Cl2 + 2KBr → Br2 + 2KCl
Solution will turn (orange/red) from colourless
What is a redox reaction?
A reaction where oxidation and reduction take place at the same time
Are halogen displacement reactions redox reactions? Explain your answer
Yes because the halide ion is oxidised (loses an electron) to form a halogen atom and the halogen is reduced (gains an electron) to form a halide ion.
Write the two half equations for the reaction between chlorine and potassium bromide, stating which is reduction and which is oxidation
Overall equation: Cl2 + 2KBr → Br2 + 2KCl
Reduction: Cl2 + 2e- → 2Cl-
Oxidation: 2Br- → Br2 + 2e-
Bromine reacts with potassium iodide. What is reduced and what is oxidised?
Bromine is reduced to bromide ions. Iodide ions are oxidised to iodine.
What name is used to describe the elements in group 0 of the periodic table?
Noble gases
What name is used to describe the elements in group 0 of the periodic table?
Noble gases
How many electrons do the Noble gases have in their outer shell
0
They have no incomplete shells of electrons
Why are noble gases chemically inert?
They have full outer electron shells. This is a very stable electron configuration and means the elements are very unreactive.
Why is argon used to fill electric light bulbs?
It is very chemically inert so will not react when the light bulb gets hot. It is non-flammable.
Why is argon used for welding?
It provides an inert welding atmosphere. Argon is more dense than air so keeps air away from the metal.
What is the trend in boiling points down group 0?
Boiling point increases down group 0 because the relative atomic mass increases so there are more intermolecular forces between atoms.
What is the trend in density down group 0?
Density increases down the group. Helium is the least dense and radon is the most dense.
What is the equation for rate of reaction?
Rate of reaction =
Amount of reactant used or product formed/
Time (s)
What units could be used for rate of reaction?
g/s
cm3/s
mol/s
How can you measure the rate of reaction when a gas is given off?
- Measure time and collect gas in an upside down measuring cylinder in a trough of water
or in a gas syringe to measure the volume of gas produced.
- Measure time and the change in mass.
How can you measure the rate of reaction when a precipitate is formed?
Put a black cross below a beaker containing one reactant. Time how long it takes for the cross to disappear after the second reactant is added
Why is using the precipitation method to investigate rate of a reaction not very accurate?
It’s subjective so people are likely to disagree over the exact point at which the cross is no longer visible.
How can you measure rate of reaction using a digital balance?
When a gas is produced as this will cause mass to decrease. The experiment can be carried out on a digital balance and the rate of reaction can be calculated by recording the mass at regular time intervals.
What does the term ‘activation energy’ mean?
The minimum amount of energy required for a reaction to occur between two reacting particles.
What must happen for a reaction to occur?
Particles must collide at the correct orientation with sufficient energy to react
In terms of particles, what 2 things could happen when the rate of reaction increases?
More frequent collisions.
- Energy of collisions increases.
How can the rate of a reaction be increased?
Increase the temperature.
- Increase the concentration.
- Increase surface area to volume ratio. - Add a catalyst.
- Increase the pressure (for gases)
How does temperature affect the rate of reaction
Increasing temperature increases the rate of reaction. This is because the reactants have more energy so more particles have energy above the activation energy meaning more collisions will be successful.
Collisions also occur more frequently because the particles have more kinetic energy.
How does surface area affect the rate of reaction?
Increasing the surface area of reactants increases the rate of reaction. This is because a greater surface area means there are more exposed particles so more frequent successful collisions
How does a catalyst affect the rate of reaction?
A catalyst increases the rate of reaction. This is because it provides an alternate reaction pathway with a lower activation energy. More particles will have sufficient energy to overcome the activation energy and react so more
successful collisions occur in the same time
How does concentration affect the rate of reaction?
Increasing concentration increases the rate of reaction. This is because there are more reacting particles in the same volume so there are more frequent successful collisions.
How does pressure affect the rate of a gaseous reaction?
Increasing the pressure of a gaseous reaction increases the rate of reaction. This is because there are more reacting particles in the same volume of gas (or the same number of particles in a smaller volume) so more frequent successful collisions occur.
Marble chips react with hydrochloric acid to produce calcium chloride, water and carbon dioxide. How could you measure the rate of reaction?
Since gaseous carbon dioxide is released, the rate can be measured by using a digital balance to measure the change in mass
over a period of time.
After completing an experiment, how can you find the rate of reaction using a graph?
● X axis: time
● Y axis: amount of reactant used or product formed
Draw a tangent to a point on the graph and find the gradient of this line to find the rate of reaction at that time.
Marble chips react with hydrochloric acid to produce calcium chloride, water and carbon dioxide. How could the rate of this reaction be increased?
Increase the surface area of the marble chips by turning them into a powder.
- Increase concentration of acid.
- Increase temperature.
What is a catalyst?
A substance which speeds up the rate of a reaction without being chemically changed at the end.
How does a catalyst speed up the rate of a reaction?
It provides an alternate reaction pathway with a lower activation energy.
What are enzymes?
Enzymes act as biological catalysts that increase the rate of reactions in living cells.
Which enzyme is used to produce ethanol from glucose?
Yeast
What do the terms exothermic and endothermic mean?
Endothermic - a reaction that takes in heat energy from the surroundings.
Exothermic - a reaction that gives out energy to the surroundings.
Are neutralisation reactions endothermic or exothermic?
Exothermic
Are displacement reactions endothermic or exothermic?
Either exothermic or endothermic.
Is salt dissolving in water endothermic or endothermic
Either exothermic or endothermic
Are precipitation reactions endothermic or exothermic
Exothermic
How could you measure the temperature change of a neutralisation reaction
- Measure initial temperature of the solutions.
- Mix both reactants in a polystyrene cup.
- Record the highest temperature reached.
- Calculate the temperature chan
When measuring the temperature change of a reaction, heat loss means that measurements may be inaccurate.
How could heat loss be minimised during an experiment?
- Use polystyrene cup.
- Place reaction cup in a beaker full with cotton
wool for extra insulation. - Lid on the reaction cup.
Is bond breaking exothermic or endothermic?
Endothermic
Is bond making exothermic or endothermic?
Bond making is exothermic
How can the energy change of a reaction be calculated from bond energies?
Energy change (kJ mol-1) = Total energy of bonds broken - total energy of bonds made.
If the energy change of a reaction is negative, is the reaction exothermic or endothermic?
Exothermic, energy has been lost to the surroundings.
Draw a reaction profile for an endothermic reactions
Draw a reaction profile for an exothermic reaction
