C6 Flashcards
What do acids from in water?
H+ ions
What do alkalis form in water?
OH- ions
What pHs are considered acids?
0-6 pH
What pH is considered neutral?
7
What pHs are considered alkalis?
8-14 pH
What is the relationship between pH and concentration of H+ ions?
They are inversely proportionate, meaning as concentration of H+ ions increases, pH decreases
What is universal indicator?
A combination of dyes which when added to a solution, changes colour according to the pH
What happens if H+ concentration increases by a scale factor of 10?
The pH decreases by 1
Example question:
A solution with a H+ concentration of 0.001 mol/dm has a pH of 3. Predict the new pH if the H+ concentration is increased to 0.01 mol/dm.
The H+ concentration has increase by a scale of 10, therefore the pH decreases by 1. 3 - 1 = 2
Answer: 2
How can you estimate the pH of a solution from the concentration of H+ ions when in the unit mol/dm?
The pH will roughly be equal to the amount of 0s behind the first non zero number- for example the pH of 0.001 mol/dm will be 3, as there are 3 zeros before the 1
Example question:
Estimate the pH of a solution with a H+ concentration of 0.00023
There is 4 zeros before the 2, therefore the pH is 4.
Answer: 4
What is the difference between stronger and weaker acids?
In stronger acids, a higher proportion of acid molecules dissociate to release H+ ions.
In weaker acids, a lower proportion of acid molecules dissociate to release H+ ions.
What is the difference between an acids strength, and an acids concentration?
Strength is the proportion of how many acid molecules dissociate to make H+
Concentration is the amount of dissolved acid molecules in a set volume
In what reaction are salts formed?
Neutralization reactions
Are salts ionic compounds?
Yes
Acid + Metal Hydroxide –>
Salt + Water
Acid + Metal –>
Salt + Hydrogen
Acid + Metal Carbonate –>
Salt + Water + Carbon Dioxide
What are soluble salts?
Salts that can’t dissolve in water
What is a soluble salt?
A salt that can be dissolved in water
Describe the process of making a soluble salt using neutralization
1) You must measure the exact amount of alkali needed to neutralize the acid (or vise versa) by carrying out a titration
2) Next, carry out the reaction with the exact right proportions
3) The solution that remains after the reaction is over contains only salt and water
4) Slowly evaporate some of the water off and then leave the solution to crystallize
5) Filter off the solid
6) Finally, dry the salt
What is an insoluble salt?
A salt that cannot be dissolved in water
Describe the process of making a soluble salt using an acid and an insoluble reactant
1) Add the insoluble substance to the acid- they will react to produce the soluble salt
2) When the excess solid has sank to the bottom of the flask, the reaction has finished
3) Filter out the excess solid so only the salt and water is left
4) Evaporate some of the water off, then leave the salt to crystallize
5) Filter off the solid
6) Finally, dry the salt
How do you make a insoluble salt?
If you react 2 soluble salts, a insoluble salt (precipitate) will be made
How does higher surface area to volume ratio increase rate of reaction?
If the surface area increases, it means there is more area exposed for reaction, therefore frequency of collisions increases, increase rate of reaction
What is a catalyst?
A substance that speeds up reactions but isn’t used up
How do catalysts increase rate of reaction?
They provide an alternative reaction pathway with a lower activation energy, increasing the frequency of successful collisions
State 3 ways you can measure the rate of reaction
1) Precipitation / Colour change
2) Mass change (usually given off as gas)
3) Volume of gas given off
What is the formula for rate of reaction?
Rate of reaction = Amount of reactants used up/products made / Time
What instrument can be used to decide whether a colour has changed?
A colorimeter
What is a reversible reaction?
A reaction is which the products can react with each other to produce the original reactants
What 3 things can affect the position of equilibrium?
1) Temperature
2) Pressure (only gases)
3) Concentration
What happens to the equilibrium if you increase the temperature?
It will move in the endothermic direction to absorb the extra heat
What happens to the equilibrium if you decrease the temperature?
It will move in the exothermic direction to produce more heat
What happens to the equilibrium if you increase the pressure?
It will move to the side with fewer moles of gas to reduce pressure
What happens to the equilibrium if you decrease the pressure?
It will move to the side with more moles of gas to increase pressure
What happens to the equilibrium if you increase the concentration of reactants?
It will move to the products side to make more products
What happens to the equilibrium if you increase the concentration of products?
It will move to the reactants side to make more reactants
What is the formula atom economy?
Atom economy = (Relative mass of desired products / Relative mass of all reactants)*100
What is sustainable development?
An approach to development that considers present needs while avoiding long term environmental impacts
What are the reactants in the Haber process?
Nitrogen and Hydrogen
What is the formula for ammonia?
N2 + 3H2 2NH3
How is hydrogen for the Haber process obtained?
Natural gas -> Methane -> Hydrogen + Carbon dioxide
How is nitrogen for the Haber process obtained?
From the air
What are the conditions of the Haber process?
High temperature (450C) and high pressure (250 Atmospheres)
What catalyst is used?
An iron catalyst
What reaction is the Haber process in the forward direction?
Exothermic
What are the 3 essential elements in fertiliser?
Nitrogen, Phosphorus and Potassium
What is eutrophication?
When fertiliser runs off into rivers and streams, meaning the levels of nitrates and phosphates rise in the water. Due to this, algae and weeds grow rapidly and form an algae bloom which blocks light for river plants below, likely killing them. Aerobic bacteria then feed of the dead plants meaning they multiply rapidly, causing all the oxygen in the water to be used up, which kills almost everything
What is the role of a fertiliser?
They provide plants with the neccersary nutrients for growth, allowing them to grow faster
How are fertilisers made using ammonia?
Ammonia can be neutralised with acids to produce fertilisers
Where are elements necessary for plant growth sometimes lost?
During crop growth and harvesting
What are the benefits of continuous reactions (bulk)?
- High quantity
- Economic advantages
- Process doesn’t stop
What are the negatives of continuous reactions (bulk)?
- Little monitoring
- Little quality assurance
What are the benefits of batch reactions (fine)?
- Large amount of monitoring
- Good quality assurance
What are the negatives of batch reactions (fine)?
- Expensive
- Lower quantity
