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topic 3 - chemical changes (equations (acid + base = salt + water --------…
topic 3 - chemical changes
Acids produce H+ ions in aqueous solutions Alkalis produce OH- ions in aqueous solutions
indicators
Phenolphthalein
Alkaline = pink ○ Acidic = colourless
Methyl orange
Alkaline = yellow ○ Acidic = red
Litmus solution
Alkaline = blue ○ Acidic = red
Litmus paper
Blue litmus paper goes red in acidic & stays blue in alkaline Red litmus paper goes blue in alkaline & stays red in acidic
more hydrogen ions means more acidic
more hydroxide ions means more alkilin
minus 1 pH is plus factor 10 of hydrogen ions
core practical
method
add dilute HCl to the beaker and measure pH
add weighed mass of calcium hydroxide and stir
then record pH
keep adding weighed masses of calcium hydroxide until there is no more change to the pH
analysis
draw a line graph with mass added on the horizontal axis and with pH on the vertical axis
draw a line of best fit (remember to ignore any anomalies)
stong and weak solutions are referring to the amount of h+ ions within the solution
concentrate and dilute is referring to their being a larger or lesser amount of substances in a given volume of a solution
equations
acid + base = salt + water ----------- > neutralisation
acid + metal → salt + hydrogen gas (H2)
acid = metal oxide = salt + water
acid + metal hydroxide = salt + water
acid + metal carbonate = salt + water + co2
H+(aq) + OH-(aq) -> H2O(l)
hydrochloric acid (HCl) - chloride
nitric acid (HNO3) - nitrate
sulfuric acid (H2SO4) - sulfate
neutralisation is when the H+ ions from the acid react with OH- ions in the alkali to form water H2O
core practical
method
○ add an excess of copper oxide (insoluble) to your acid (sulfuric acid- H2SO4- as you are making copper SULFATE)
○ use a filter and filter paper to filter off any copper oxide that hasn’t reacted (your solution should be blue as copper sulfate solution has been formed)
○ evaporate off the water by placing your final solution in a water bath
Titration must be used:
both reactants are liquids/soluble, so if you have an excess of one you would not be able to easily remove it from your mixture of products
You can then mix the exact proportions of the two reactants
The exact amount of acid has thus been added to the soluble reactant, meaning that the leftover solution is only salt and water, no acid or alkali, because they have been completely neutralised
How to carry out a titration:
Wash burette using the acid and then water
Fill burette to 100cm3 with acid with the meniscus’ base on the 100cm3 line
Use 25cm3 pipette to add 25cm3 of alkali into a conical flask, drawing alkali into the pipette using a pipette filler
Add a few drops of a suitable indicator to the conical flask (eg: phenolphthalein which is pink when alkaline and colourless when acidic)
Add acid from burette to alkali until end-point is reached (as shown by indicator)
The titre (volume of acid needed to exactly neutralise the acid) is the difference between the first (100cm3) and second readings on the burette)
Repeat the experiment to gain more precise results
To prepare a pure, dry salt – you warm the salt solution to evaporate the water
Crystals form
types of salt that are soluble
chlorides all except... silver, lead
potassium all
ammonium all
nitrates all
sodium all
sulfates all except... lead, barium, calcium
types of salt that are insoluble
carbonates sodium, all except ….potassium, ammonium
hydroxides sodium, all except ….potassium, ammonium
mix
filter
wash
dry