C6 Chemistry out there Flashcards
What is electrolysis?
Electrolysis is the decomposition of liquid by passing electricity through it. (Flow of charge by moving ions and the discharge of ions at the electrodes)
What is the anode?
What is the cathode?
- Positive electrode
- Negative electrode
What are cations?
What are anions?
- Positively charged (Loss of electrons)
- Negatively charged (Gain of electrons)
Describe what the term electrolyte means?
Electrolyte is the liquid which conducts the electricity and is decomposed or broken down during electrolysis
What apparatus is required for electrolysis?
- DC power supply
- Anode
- Cathode
Where are the negative ions and positive ions discharged?
Cathode (Positive ions)
Anode (Negative ions)
Describe the chemical test for oxygen and hydrogen
- When hydrogen burns with a lit splint, it makes a ‘pop’ sound
- Oxygen relights a ‘glowing’ splint
Describe the observations of the electrolysis of Copper(II) Sulfate solution using carbon electrodes
- The cathode gets plated with copper and bubbles are formed at the anode
- The blue colour will slowly disappear
- Oxygen is produced at the anode
What factors affect the amount of substance produced during electrolysis?
- Time
- Current
Name the products made during the electrolysis of NaOH
Oxygen - anode
Hydrogen - cathode
Name the products made during the electrolysis of H2SO4
Hydrogen - Cathode
Oxygen - Anode
Why does the electrolysis of NaOH produce Hydrogen instead of Sodium at the Cathode
Because Na is higher in the reactivity series, hence Hydrogen is discharged as a preference
Explain why an ionic solid can not be electrolysed but the molten liquid can be electrolysed
The ions in the ionic solid can not move as they vibrate in a fixed position, the ions in a molten liquid can move, hence then can be electrolysed
What type of reaction occurs between hydrogen and oxygen?
Exothermic (energy is released into the atmosphere)
Describe what a fuel cell is
A fuel cell is a cell supplied with fuel and oxygen that uses the energy released from the reaction between the fuel and oxygen to produce electrical energy efficiently
What fuel is used in a hydrogen-oxygen fuel cell?
Hydrogen
Why does a hydrogen-oxygen fuel cell not form a polluting waste product?
Unsure
Balanced symbol equation for the reaction between hydrogen and oxygen
2H2 +O2 —-> 2H2O
Energy-level diagram
2H2 + O2 ——–> 2H2O
Energy
Released
Construct the balanced symbol equation for the overall reaction in a hydrogen-oxygen fuel cell
Equation
Advantages of fuel cells
- Provides water for astronauts
- Lightweight
- Compact
- No moving parts
Disadvantages of using fuel cells
- Fuels cells often contain harmful catalysts that have to be disposed at the end of the lifetime of a fuel cell
- Production of the hydrogen and oxygen will involve the use of energy which may have to come from the burning of fossil fuels
Explain why the car industry is developing fuel cells
- No carbon emissions from the car
- Fossil fuels currently used are non-renewable
- Large source of hydrogen is available by decomposing water
What is oxidation and reduction?
- Oxidation is the addition of oxygen
- Reduction is the removal of oxygen
What two conditions are required for rusting of steel and iron?
- Water
- Oxygen
Methods to prevent rusting
- oil and grease
- paint
- galvanising
- sacrificial protection
- alloying
- tin plating
How do these methods prevent rusting?
- they prevent oxygen and water reaching the surface of the metal requiring protection
Order of reactivity (most to least)
Magnesium
Zinc
Iron
Tin
Temperature change during a displacement reaction
Temperature increases because it is an exothermic reaction
Define the terms :
- oxidation and reduction
- oxidising agent and reducing agent
Oxidation is the loss of electrons
Oxidising agent is a substance that can remove electrons from other substances, oxidising them
Reduction is the gain of electrons
Reducing agent is a substance that can give electrons to other substances, reducing them
Why is rusting a redox reaction?
- Iron loses electrons
- Oxygen gains electrons
How does sacrificial protection work and protect the iron underneath it?
- Use of metal such as zinc or magnesium
- Use of metal which is more reactive than iron
- Sacrificial metal will lose electrons in preference to the underlying iron
Explain the disadvantage of using tin plating to protect the iron
- Tin acts as a barrier stopping water or oxygen reaching the surface of the iron
- When the tin layer is scratched, the iron will lose electrons in preference to the tin as it is more reactive than tin and so the iron rust even more quicker than on its own
Rusting word equation
Oxygen + Water + Iron —-> Hydrated iron (III) Oxide
Explain how galvanising protects iron from rusting
- Galvanised iron is coated with zinc
- Layer of zinc stops water and oxygen from reaching the surface of the iron
- Zinc also acts as a sacrificial metal
Explain displacement reactions in terms of oxidation and reduction
- Metal ion is reduced by gaining electrons
- Metal atom is oxidised by losing electrons
Explain why alcohols aren’t hydrocarbons
Because they contain atoms other than hydrogen and carbon
What are the required conditions for fermentation?
- 25 to 50 degrees Celsius
- Presence of water
- Yeast
What are the main uses of ethanol?
- Alcoholic beverages
- Solvent ( industrial methylated spirits)
- Fuel for care
Word equation for fermentation
Glucose —-> Carbon dioxide + Ethanol
Word equation for Hydration of ethene
Ethene + Water —-> Ethanol
Describe how ethanol can be made from fermentation
- Glucose solution
- Reaction catalysed by enzymes in yeast
- Absence of oxygen
- Fractional distillation to obtain ethanol
Conditions during fermentation
- Temperature too low, enzymes are inactive
- Temperature too high, enzymes become denatured
- Absence of oxygen, to prevent ethanoic acid being made
Explain why fermentation is a renewable process
It’s raw material is sugars from plants
Explain why hydration is a non-renewable resource
It uses ethene from crude oil as its raw material
Evaluate the merits at which the two processes are judged by
Conditions used Raw materials used Sustainability Batch verses continuous Purification Atom Economy Percentage yield
Ethanol is produced for industrial use, how?
- Passing ethene and steam over a heated phosphoric acid catalyst
Chlorofluorocarbon is an organic molecule containing carbon, fluorine and chlorine atoms
True
Give some uses of CFCs
Refrigerators
Aerosols propellants
Air conditioning systems
Ozone is a form of oxygen p, what is the formula?
O3
Describe some properties of CFCs
- Chemically inert
- Insoluble in water
- Low boiling point
Describe the problems increased Ultraviolet light can caus
- Eye cataracts
- Accelerated ageing of skin
- Skin cancer
- Increased chances of sunburn
Alternatives to CFCs
HFCs
Hydrofluorocarbon
Hydrocarbons provide a safer alternative
Alkanes
Explain why the use of CFCs has been banned in the UK
Society agrees with scientists’ views that CFCs deplete the ozone layer
Describe and explain how scientists’ attitudes towards CFCs have changed
- initial enthusiasm for the use of CFCs based upon their inertness
- later discovery of ozone depletion and link to CFCs being used
- acceptance by scientists and the rest of the world community that use of CFCs should be banned
Describe how CFCs deplete the ozone layer
- CFCs molecules are broken down in the stratosphere by UV light to give highly reactive chlorine atoms
- chlorine atoms react with ozone molecules
- chlorine atoms are regenerated so they can react with more ozone molecules, causing a chain reaction
Explain in terms of electrons how a carbon-chlorine bond can break to form highly reactive chlorine atoms
Unsure
Explain why only a small number of chlorine atoms will destroy a large number of ozone molecules
Unsure
Explain why CFCs will continue to deplete ozone a long time after their use has been banned
Unsure
What atom is a chlorine radical
Chlorine atom
Explain why CFCs are only removed slowly fro the stratosphere
Unsure
Describe how the depletion of the ozone layer allows more UV light to reach the earth
Unsure
Explain how ozone absorbs UV light in the stratosphere
Unsure
Does hard water lather well with soap?
No, but soft water does
Both hard and soft water lather well with soap less detergents
True
What ions cause water hardness?
Magnesium and Calcium ions
What method is used to remove temporary hardness, but can’t be used to remove permanent hardness?
Boiling
Describe how hardness in water can be removed?
- Passing water through an ion-exchange column
- Adding washing soda (sodium carbonate)
Describe the origin of temporary hardness in water. Give the word equation
Calcium carbonate in rocks reacts with dissolved carbon dioxide and water to form soluble calcium hydrogen-carbonate
Calcium Carbonate + Water + Carbon Dioxide —->Calcium Hydrogen-carbonate
What is temporary hardness caused by?
What is permanent hardness caused by?
- Calcium hydrogen carbonate
- Calcium Sulfate
Describe how boiling removes temporary hardness
- Decomposition of calcium hydrogen carbonate to give insoluble calcium carbonate(limescale), water and carbon dioxide
- Soluble Calcium ions are changed in to insoluble compounds
Explain how an ion exchange resin can soften water
- tiny beads are packed in to a plastic column, the water softens as it passes through the column
- the ions from the resin swap with the ions in the water
- as the water passes through, the magnesium and calcium ions are attached to the resin and sodium ions leave the resin
- the water softens because the Mg and Ca ions are gone
- the resin is regenerated by flushing the resin with sodium chloride solution. The sodium ions are swapped back in to the resin. The other ions are pushed out washed in to waste water
What can vegetable oil be used to make, which is an alternative to diesel from crude oil?
Bio-diesel
At room temperature:
- oils are_______
- fats are _______
- liquids
- solids
Describe an emulsion
In an emulsion, tiny droplets of one of the liquids are dispersed throughout the other liquid. The two liquids in an emulsion will eventually settle out in to separate layers agin.
Give an example of a oil-in-water emulsion
Milk
Give a water-in-oil emulsion
Butter
Vegetable oil + Sodium Hydroxide —->___________
Soap
Animals fats, vegetable fats and oils are ____________
Esters
Explain why unsaturated fats are healthier as a part of balanced diet
Reduce the risk of heart disease
…
Describe how margarine is manufactured from vegetable oils
Unsaturated vegetable oil is turned in to saturated vegetable oils by reacting them with hydrogen. A nickel catalyst may be used
Describe how immiscible liquids can form an emulsion
If the two liquids have different densities, they will not dissolve in one another. However if they are shaken vigorously, they form an emulsion.
Describe an oil-in-water (milk)
It contains tiny droplets of oil dispersed in water
Describe a water-in-milk emulsion (butter)
Consist of tiny droplets of water dispersed in oil
Describe how natural fats and oil can be split up by hot sodium hydroxide solution. (Saponification)
During saponification, the hydroxide ions from sodium hydroxide solution breakdown the oil or fat molecule. This causes the bonds between fatty acids and glycerol to break.
Fat+Sodium Hydroxide —-> Soap + Glycerol
What type of a reaction is saponification?
Hydrolysis
Ingredients of a washing powder and it’s purpose
- Active detergent: does the cleaning
- Water softener: to soften hard water
- Bleaches: to remove coloured stains
- Optical brighteners: to give a whiter than white appearance
- Enzymes: used in low temperature washes to remove food stains
Describe the term solvent
The liquid that does the dissolving
Describe the term solute
The dissolved substance
Describe the term solution
If the substance dissolves in the liquid, it forms a solution
Ingredients in a washing up liquid and it’s purpose
- Active detergent does the cleaning
- Water: to thin out detergent so it can be dispensed easily
- Colouring agent and fragrance: to improve attractiveness to the product
- Rinse agent: to help drain the water out of the crockery
Advantages of washing clothes at low temperature
- Saving energy costs
- A greater range of clothing can be washed
Describe the term detergent
Detergents are ingredients of washing-up liquid and washing powders. They are substances that can surround fat or oil molecules in stains and remove them from clothing or plates. They have a hydrophobic tail and hydrophilic head.
Explain how detergents remove fat or stains
- Hydrophilic end of detergent molecule forms strong intermolecular forces with water molecules
- Hydrophobic rails of detergent molecule forms strong intermolecular forces with fat or oil molecules
Describe dry cleaning
Solvent does not involve water
Stain will not dissolve in water
Explain in terms of intermolecular forces how dry cleaning works
- There are weak intermolecular forces between grease molecules
- There are weak intermolecular forces between solvent molecules
- Solvent molecules form intermolecular forces with molecules of grease and so solvent molecules can surround molecules of grease
