Chemistry Flashcards
Why does a chemical cell eventually stop producing a voltage?
Eventually, one of the reactants is used up so the reaction stops and a voltage is no longer produced.
Describe the main features of a hydrogen-oxygen fuel cell
A hydrogen-oxygen fuel cell contains two platinum electrodes which catalyse the formation of hydrogen ions and electrons from hydrogen gas.
There is also a membrane, which lets the hydrogen ions pass but not the electrons.
The electrons flow through the external circuit, connected to an electric motor.
At the right hand electrode, hydrogen gains electrons and reacts with the oxygen coming in. Water is a waste product.
What is electroplating?
This is when electricity is used to coat one metal with a thin layer of another
Give some examples of electroplating
- Producing jewelry that has gold/silver electroplated onto cheaper ‘‘base metals’’.
- To improve a metal’s ability to resist corrosion e.g electroplating with chromium, which resists corrosion.
How is electroplating carried out?
Electrolysis set up:
- anode, made from the plating metal
- cathode - metal object itself
- electrolyte - containing ions of the plating metal
What is an isotope?
Atoms of the same element with the same number of protons but different mass numbers due to different numbers of neutrons.
What does group number tell us about electronic configuration?
It tells us the amount of electrons in the outer shell
What does the period tell us about electronic configuration?
It tells us how many electron shells there are
What substances are generally soluble in water?
- All nitrates
- All sodium, potassium and ammonium salts
- Most chlorides
- Most sulfates
What substances are insoluble in water?
- Most hydroxides
- Most carbonates
- Silver, lead chloride
- Calcium, barium, lead sulfates
How can we predict whether a precipitate is formed in a reaction?
We can view the products, if one product is insoluble then a precipitate is formed
Describe the movement of ions during electrolysis
Positive ions (cations) will be attracted to the negative electrode (cathode)
Negative ions (anions) will be attracted to the positive electrode (anode)
What is meant by theoretical yield?
The maximum mass of product that can be formed from a given amount of reactants
What is actual yield?
The actual amount of product produced when an experiment is carried out
How do you calculate percentage yield?
Actual / Theoretical X 100
Explain 3 reasons why actual yield is lower than theoretical yield
1) Some product may be lost - for example when transferring containers, some liquid may be left behind
2) The reaction may be incomplete - not all the reactants have reacted yet
3) There may be side reactions occurring - which competes with the main reaction, producing different products
How do you calculate atom economy?
(Sum of Mr of useful products / Sum of Mr of reactants) X 100
How do we use atom economy and yield to determine reaction pathway?
We want a reaction pathway that produces a higher yield as this will allow for higher profit since more product is being made in a given time.
Atom economy means the process is more efficient, so there will be less wasted molecules.
When should we use fractional distillation when separating a mixture?
If there is a small difference in the boiling points of the liquids
Describe some physical properties of transition metals
- Malleable
- Ductile
- Good conductors of electricity
- Shiny when polished
Describe some chemical properties of transition metals
- Form coloured compounds
- Can act as catalyst
Describe the two biological methods of extraction
Bioleaching - This is where bacteria are grown on a low grade ore. This produces a solution containing copper ions, called a leachate. Copper can be extracted from the leachate by displacement, then purified by electrolysis
Phytoextraction - this is where plants that absorb metal compounds are grown. Then, they are burnt to form ash from which we extract the metal.
Describe how to carry out fractional distillation
A column is fixed above the distillation flask.
We heat the solution, then hot vapour rises up the column. At first, the vapour condenses when it hits the glass and drips back down into the flask.
As the column heats up gradually, a temperature gradient is created, warmer at the bottom, cooler as you go up.
The fraction with the lowest boiling point will reach the top of the column first, it will then pass through the condenser and the distillate is collected in a flask.
What happens in a reversible reactions?
The products react to reform the reactants
