Acids and alkalis
Some pure acids include the hydroxides of: sodium, potassium and calcium
Acids + Alkali --> salt + water
Hydrochloric acid + metal --> metal chloride + hydrogen
Hydrochloric acid + metal oxide --> metal chloride + water
Hydrochloric acid + metal carbonate --> metal chloride + carbon dioxide + water
Litmus paper, universal indicator and PH meters detect acidity and alkalinity. Universal indicator and PhH meters measure PH.
Acidic compounds produce aqueous hydrogen ions, H+(aq), when they dissolve in water. Alkaline compounds produce aqueous hydroxide ions, OH–(aq), when they dissolve in water. During a neutrilisation reactions these react to create water.
Rates of reaction
Scientists need to research rates of differnt reaction because a reaction occuring too quickly can be hazzardous and areaction occuring too slowly is not practical
Rate of reaction= The quanitity of product produced in a fixed time
How can we measure rate of reaction?
- to collect and measure a gas product the gas should be sent along a tube into a water filled measuring cylinder (in a water bath) and the volume should be recoreded at regular intervals
- you could put cotton wool over the conicle flask so that only gas escapes, place in on measuring sacles and record the mass at regular intervals
- you could mix the solid and solution in the flask and start the timer, stop when you can no longer see the solid
- to a reaction that produces an insoluble solid. Place the conicle flask on an X. Mix the olutions in the flask and start the timer, stop it when you can no longer see the X
It's imporant to control the rate of reaction because a reaction needs to be safe and cost effective
what effects the rate of reaction
Surface area- as surface area increases there are more particles exposed to the solutions so the chances of a collision increases.
Tempersture- as temperature increases the particles gain more energy so they move fastr and the chances of a collision increases
Concentration- if there is a higher concentration of particles there is a higher chance that they will collide
We need chemicals to provide us with: food adictivea, fertilisers, dye, paints, pigments and pharmaceuticles
Pure acidic compunds that are solid include; citric and tartaric, that are liquid include; sulphuric, nitric and ethanoic, that are gases include; hydrogen chloride
When we react acids and alkalis this is called chemical synthesis. The stages that are envolved with this are:
- Choosing the reactant or the series of reactions that make the required product
- Carrying out the rick assessment
- Working out the quantaties of reactants to use
- Carrying out the reaction with suitable appratus in the right conditions (such as temperature, concentration
- Seperating the product from the reactant mixture (such as filtering)
- Purifying the product (such as evaporation, crystallination, drying in an oven or in a desiccator) It is important the product is pure because the smallest impurty could cause harm eg. in a phamaceutical drug. This can be done through titrations
Endothermic and Exothermic reactions
In a reaction bonds are broken releasing energy and bonds are formed absorbing energy.
in a endothermic reaction more energy is envolded to form bonds than to break them so energy is absorbed from the surroundings.
Where as, in an exothermic reaction more energy is needed to break the bonds than to form them so energy is released into the environment (usually as heat energy)
Calculating percentage yeild
Percentage yield = actual yield∕predicted yield × 100
For example, if the predicted yield is 20 g but the actual yield is 15 g:
Percentage yield = 15∕20 × 100 = 75%
Why the percentage yield of a product may be less than 100%:
- Transferring liquids
- Not all reactants react to make product
Industrial processes want a high percentage yeild because it reduces the waste of the reactants and the cost of the process
Measure you acid into a burette using a pipette. Measure your sodium hyrdoxide into a conical flask and add universal indicator. Place the conicle flask on a white tile
Whilst swirling add the acid to the hydroxide faster at the beginning. Stopping when the colour of the indicator changes to record your results.
Repeat your titrations, once you now the rough numbers add your acid drop by drop. These rough numbers can now be discarded.