C6
- Created by: emchown
- Created on: 10-03-15 17:12
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- C6
- The pH Scale
- Acids have a pH of less than 7
- Alkalis have a pH greater than 7
- Bases are the oxides and hydroxides of metals, soluble ones are called Alkalis
- Bases are the oxides and hydroxides of metals, soluble ones are called Alkalis
- Acidic Compounds produce Hydrogen Ions when dissolved in water
- Alkalis produce Hydroxide Ions when dissolved in water.
- Acidic Compounds produce Hydrogen Ions when dissolved in water
- Neutralisation
- Acid and Base mixed in correct amounts = cancel eachother out (Neutralisation)
- Acid + Base = Neutral Salt Solution + Water
- H+ + OH- = H2O
- Hydrochloric Acid = Chloride salts
- Sulfuric Acid = Sulfate salts
- Nitric Acid = Nitrate salts
- Acid and Base mixed in correct amounts = cancel eachother out (Neutralisation)
- Energy Changes
- When reactions occur, energy is tranferred to or from the surroundings.
- Many chemical reactions are accompanied by a temp. change
- When reactions occur, energy is tranferred to or from the surroundings.
- Exothermic Reactions
- They are a RISE in temp.
- They transfer heat energy to surroundings
- 'Exo' = Exit?
- Examples
- Combustion of Carbon
- C + O2 = CO2
- Neutralising Alkalis with Acids
- Oxidation reactions
- Combustion of Carbon
- Products have LESS energy than reactants
- Endothermic Reactions
- They have a FALL in temp.
- They take in heat from surroundings
- Examples
- Reaction betwwn Citric Acid + Sodium Hydrogencarbonate
- Dissolving Ammonium Nitrate crystals in water
- Thermal Decomposition
- Products have MORE energy than reactants
- Very important these changes are managed during Chem Synth. eg nasty accident if too much energy given out
- Chemical Synthesis
- Starting minerals react to produce new substances.
- Greater amount of reactants = greater amount of product
- Percentage Yeild calculated by comparing actual amount of product with the amount you'd expect to get.
- 1) Find out reactions needed for product
- 2) Risk assessment
- 3) Calculate amount of reactants to use
- 4) Do reaction under suitable conditions
- 5) Seperate product from reaction mixture
- 6) Purify product
- 7) Measure yeild
- 8) Check purituy (titration)
- Titration
- Calculates concentration of acid - how much alkali needed to neutralise
- 1) Fill burette with alkali solution and take reading of volume
- 2) Use pipette to measure 25cm3 of acid and put in conical flask
- 3) Add a few drops of indicator and put flask under burette
- 4) Add alkali to acid drop by drop - swirl flask to mix well
- 5) Keep adding and swirling until acid has been neutralised
- 6) Record final burette reading.
- Titration
- Measuring the Rates of Reaction
- Chemical reactions only occur when the reacting particles collide with one another with sufficient energy
- Chemical reactions can happen at different speeds.
- Weighing reaction mixture
- Product is gas - mass of mixture will decrease
- Volume of gas produced
- Gas syringe to measure volume of gas produced at timed intervals
- Observing formation of precipitate
- Watching a cross under flask - see when disappears (time)
- Colour change using Light Sensor - accurate and reliable results, more data collected.
- Analysing Rate of Reaction
- Graphs plotted to show progress
- Steeper line = faster reaction
- Reactant used up = reaction stops (flat line)
- Same amount of product made from same amount of reactant - no matter how fast reaction is
- Why one reaction is faster than another
- Surface area of solid reactants is greater
- Temperature is greater
- Concentration greater
- Catalyst used
- Changing Rate of Reaction
- 1) Temperature of Reactants
- Cold reaction mixture = particles move slowly (less kinetic energy)
- Collide less often, less energy = fwer collisions
- Hot reaction mixture = paritcles move more quickly (more kinetic energy)
- Collide more often, greater energy = more successful collisions
- 2) Concentration of Dissolved Reactants
- Low concentration = particles spread out so collide successfully less often
- High concentration = particles close together so collide successfullt more often.
- 3) Surface Area of Solid Reactants
- Large particles = small surface area
- Fewer particles exposed to collisions
- Collide succeessfully less often - slow rate of reaction
- Small particles = big surface area
- More particles exposed to collisions
- Collide successfully more often - fast rate of reaction
- 4) Using a Catalyst
- Substance that increases rate of chemical reaction
- Hydrogen Peroxide = Water + Oxygen
- Measure rate of reaction by measuring amount of oxygengiven off at one min. intervals
- This reaction happens slowly unless catalyst of manganese oxide
- With a catalyst, plenty of fizzing seen as oxygen id given off
- 1) Temperature of Reactants
- Collision Theory
- Results in more energetic collisions happening more frequently
- Increasing temp. = increase of kinetic energy of particles
- Chemical reactions only occur when particles collide with each other with sufficient energy
- Minimum energy required for a reaction will be achieved more often resulting in a greater rate of reation
- An increase in concentration of surface area results in more frequent collisions and more collisions that are sufficiently ebergetic for a reaction to occur
- Controlling a Chemical Reaction
- Rate of manufacture must be high enough to produce a sufficient daily yeild of product
- Percentage yield must be high enough to produce sufficient daily yield of product
- Low percentage yield accepted as long as reaction can be repeated many times with recycled starting materials
- Optimum conditions should be used that give the lowest cost - rather than fastest reaction or highest % yield
- Care taken if reactants or products could harm environment
- Avoid putting any harmful by-products into environment
- Risk assessment must be carried out and necessary precautions taken
- The pH Scale
- Collision Theory
- Results in more energetic collisions happening more frequently
- Increasing temp. = increase of kinetic energy of particles
- Chemical reactions only occur when particles collide with each other with sufficient energy
- Minimum energy required for a reaction will be achieved more often resulting in a greater rate of reation
- An increase in concentration of surface area results in more frequent collisions and more collisions that are sufficiently ebergetic for a reaction to occur
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