Physical Chemistry Flashcards
Describe the pH levels
- pH 1-4: strongly acidic
- pH 4 - 6: weakly acidic
- pH 7: neutral
- pH 8-9: weakly acidic
- pH 10-14: strongly alkaline
How do you determine the pH of a solution?
- universal indicators
- litmus paper: red in acidic solutions, purple in natural and blue in alkaline solutions
- phenolphthalein: colourless in acidic solutions and in weak alkaline, it is pink and in strong alkaline, it is pink/purple
- methyl orange: changes from red in acidic solution to orange-yellow in weak acid, to yellow in alkaline
What is an acid?
- a source of hydrogen ions (H+)
- pH less than 7
What is a base?
- a substance that can neutralise and acid
- alkalis are soluble bases
What is an alkali?
- a source of hydroxide ions (OH-)
- pH greater than 7
What is the reaction between an acid and base called?
- a neutralisation reaction
- acid + base = salt + water
- H+(aq) + OH-(aq) = H2O
acid + metal oxide =
- acid + metal oxide = salt + water
acid + metal =
-acid + metal = salt + hydrogen
acid + metal carbonate =
acid + metal carbonate = salt + water + carbon dioxide
acid + metal hydroxide =
acid + metal hydroxide = salt + water
What are the solubility rules?
- all common sodium, potassium and ammonium salts are soluble
- all nitrates are soluble
- all chlorides are soluble except for silver chloride
- all sulphates are soluble except for barium and calcium sulphate
- all carbonates are insoluble except for sodium, potassium and ammonium carbonates
How to make and purify a soluble salt (a pure dry sample)?
- e.g. sulphuric acid + copper oxide = water + copper sulphate
- warm the acid to about 50 degrees
- spoon copper oxide and dissolve it
- make it dissolve in excess
- warm to about 70 degrees, add more copper oxide, if cannot dissolve, all acid has been reacted
- filter through filter paper into an evaporating basin
- gently boil until a third is left, not all because there may be thermal decomposition
- leave to crystallise. leave it in a warm place or desiccator
How do you make an insoluble salt?
- a precipitation reaction
- mix the two solutions
- separate with a funnel and filter paper
- it is not pure if you dry immediately because some of the filtrate will be left in the residue as impurities. rinse with dilute water
- dry in desiccator or evaporate slowly
How do you do titration?
- using a pipette, add some alkali (about 25cm^3) to a conical flask, along with two or three drops of indicator
- fill a burette with the acid, below eye level
- using the burette, add the acid to the alkali a bit at a time, given the conical flask a swirl
- indicator changes colour when all the alkali has been neutralised
- record the volume of the acid
- repeat for more reliable results
What four things do the rate of reaction depend?
- pressure/concentration
- temperature
- catalyst
- surface area
What is the equation for rate of reaction?
- rate of reaction = amount of reactant used or amount of product formed / time
How can you measure the rate of reaction?
- precipitation: observe a marker through the solution and measure how long it takes to disappear.
- change in mass: most accurate method. cotton wool used to prevent spitting of the HCl, so that mass does not reduce
- volume of gas: using a gas syringe to measure the volume of gas given off
Describe different rate of reaction experiments
- hydrochloric acid and marble chips: for surface area.
measure volume of gas at regular herbals - magnesium with HCl: for concentration
- sodium thiosulfate and HCl: for temperatures. colourless to react to form yellow precipitate of sulphur.
- decomposition of hydrogen peroxide: for catalyst
How does higher temperature increase rate of reaction?
- particles have more kinetic energy
- so more frequent collisions
- and a higher proportion of collisions have activation energy,
- so more successfully collisions
How does higher concentration or pressure increases rate of reaction?
- there are a greater amount of particles in a the same space
- therefore, more frequent collisions
How does larger surface area increase rate of reaction?
- particles will have more area to work on, more sites for potential collision to occur
- more frequent useful collisions
How do catalysts increase rate of reaction?
- increase the rate of reaction by providing an alternative route of reaction with lower activation energy. a greater proportion of collisions will have sufficient energy to result in reaction
