Section 4: Physical Chemistry Flashcards
an acid has a pH of…
less than 7
an alkali has a pH of…
more than 7
a neutral substance has a pH of…
7
universal indicator turns what colour in the presence of an acid(weak-stronger-strongest)?
yellow-orange-red
universal indicator turns what colour in the presence of an alkali(weak-strong)?
blue-purple
universal indicator turns what colour in the presence of a neutral substance?
green
what colour is litmus paper in an acid?
red
what colour is litmus paper in an alkaline solution?
blue
what colour does litmus paper become in a neutral solution?
purple
what colour is phenolphthalein in an acid?
colourless
what colour is phenolphthalein in an alkali?
pink
what colour is methyl orange in an acid?
red
what colour is methyl orange in an alkali?
yellow
an acid is..
a source of hydrogen ions H+
a base is…
a substance that can neutralise an acid
an alkali is…
a soluble base. A source of hydroxide ions OH-
what is the name for the reaction between an acid and a base/alkali?
a neutralistion reaction
acid + base –>
salt + water
H+ + OH- –>
H2O
is metal oxide an example of a base or an acid?
a base
acid + metal oxide –>
salt + water
hydrochloric acid + metal oxide —>
metal chloride + water
sulfuric acid + metal oxide –>
metal sulfate + water
nitric acid + metal oxide –>
metal nitrate + water
acid + metal carbonate —>
salt + water + carbon dioxide
hydrochloric acid + metal carbonate –>
metal chloride + water + carbon dioxide
sulfuric acid + metal carbonate –>
metal sulphate + water + carbon dioxide
nitric acid + metal carbonate –>
metal nitrate + water + carbon dioxide
are sodium, potassium and ammonium salts soluble or insoluble?
soluble
are nitrates soluble or insoluble?
soluble
are most chlorides soluble or insoluble? what is the exception?
soluble, except for silver chloride
are most sulfates soluble or insoluble? what are the two exceptions?
soluble, except barium sulfate and calcium sulfate
are most carbonates soluble or insoluble? what are the 3 exceptions?
insoluble, except sodium, potassium and ammonium carbonates
what is the method for making soluble salts using acids and insoluble bases?
- Chose an acid and an insoluble base(e.g mostmetal oxides, metal carbonates, metal hydroxide) based on the salt you want to make 2. add the insoluble base to the acid - the solid will disolve in the acid as it reacts. When the acid is neutralised the excess solid will sunk to the bottom. 3. filter off the excess base to get the salt solution - for pure solid salt crystals evaporate off the water
what is the name of the method used to make a soluble salt using an alkali? what does it entail?
titration - you have to add exactly enough alkali to just neutralise the acid, using an indicator to show you when the reaction’s finished
when, in salt making, would you use a precipitation reaction?
to make an insoluble salt
how to use a precipitation reaction to make an insoluble salt?
choose 2 solutions containing the ions you need and mix them. a precipitate of the insoluble salt will form
why is it not good idea to use universal indicator to tell you when the reaction is finished in a titration?
you need an indicator that gives a sudden colour change
concentration =
moles / volume
steps for titration calculations: working out the conc. of alkali/acid needed to neutralise an acid/alkali
- work out the moles of the known sbstance you have using moles = conc. x vol. 2. write down the equation for the reaction 3. use ratios in the balanced equation to find out the moles of the unknown sustance 4. work out the conc. of the unknown substance using conc = moles / volume
what is the unit for concentration
moles per dm3 (or g/dm3)
what 4 things does the rate of a reaction depend on?
- temperature 2. concentration/pressure, depending on liquid/gas 3. catalyst 4. size of particles/surface area
what is the gradient of a very fast reaction look like on a graph??
very steep, flattens out quickly as reactants are use up
rate of reaction =
amount of reactant used/amount of product formed divided by time
how to measure the time it takes for a reaction in which the product is a precipitate which clouds the solution to occur?
put the (initially see-through) solution over a cross drawn with a marker and time how long it takes before the cross becomes invisible due to the cloudiness of the reaction. Quicker the marker disappears, quicker the reaction
how to measure the speed of a reaction that produces a gas?
use a mass balance to weigh the solution as it gives off the gas, taking readings every 10 seconds or so. Quicker the reading drops, the faster the reaction
how to measure the volume of gas given off in a reaction as an indicator of how fast said reaction was?
use a gas syringe to measure vol. of gas given off. The more gas given off during a given time interval, the faster the reaction
what is the reaction used to demonstrate the effect of increased surface area (breaking up the solid into smaller pieces) on the rate of reaction?
reaction of hydrochloric acid and marble chips, using different sizes of marble chips but in the same volume, and measuring the gas evolved for each reaction over time
why does an increase in the surface area mean an increase in the rate of reaction?
more frequent particle collisions
what reaction is used to demonstrate the effect of increased concentration on rate of reaction?
reaction of magnesium metal and dilute HCl - use different concentration of HCl and use a mass balance/gas syringe and a stopwatch to record the gas evolved over time
how do catalysts increase the rate of reaction?
solid catalysts provide the reacting particles with a surface to stick to. They provide an alternative pathway for the reaction. This increases the number of successful collisions and lowers the activation energy
what is the activation energy?
the initial energy needed to break the initial bonds, eg. 100degreesC is needed to first heat up water to boiling point and break the bonds
what does the collision theory state?
that the rate of reaction depends on how often and how hard reacting particles collide with each other. Particles must collide with enough energy and hard enough to react to react
what must be supplied in order to break bonds?
energy
what happens in an exothermic reaction? compare energy needed to break bonds and energy released when new bonds are formed…
energy is given out- the energy released in bond formation is greater than the energy used in breaking bonds. The reaction GIVES OUT ENERGY to the surroundings as heat- shown by rise in temperature
what happens in an endothermic reaction? compare energy needed to break bonds and energy released when new bonds are formed…
Energy is taken in: the energy requires to break old bonds is greater than the energy released when new bonds form. the reaction TAKES IN energy from the surroundingsin the form of heat - shown by drop in temp.
what must be released when new bonds are formed?
energy
what is the overall change in energy in a reaction called?
enthalpy change
what is the symbol for enthalpy change?
/_\H (delta H - a triangle followed by an H)
what are the units for enthalpy change?
kJ/mol (amount of energy in kilojoules per mole of reactant)
if the reaction is exothermic, will the enthalpy change have a negative or positive value?
negative- because the reaction is giving out energy
if the reaction is endothermic, will the enthalpy change have a negative or positive value?
positive, because the reaction takes in energy
Energy level diagrams: in an exothermic reactions, are the products at a higher or lower energy than the reactants?
lower
Energy Level Diagrams: in an exothermic reaction, what does the difference in height between the reactants and products represent?
the energy given out during the reaction
Energy Level Diagrams: what does the initial rise in the line represent?
the activation energy
Energy level diagrams: in an endothermic reaction, are the products at a higher or lower energy than the reactants?
higher
Energy Level Diagrams: in an endothermic reaction, what does the difference in height between the reactants and products represent?
the energy taken in during the reaction
what effect do catalysts on activation energy? how to they produce this effect?
they lower the activation energy needed by providing an alternative reaction pathway with a lower activation energy
when a catalyst is involved in an exo/endothermic reaction, what happens to the overall energy change for the reaction, delta H?
it stays the same
how do you calculate the enthalpy change for a reaction?
add up the average energies of the bonds that are broken and and subtract the energy of the bonds that are made
what is the effect of a higher temperature on the rate of reaction?
particles have more energy and therefore move quicker, thus colliding more frequently
what does the collision theory state?
that the rate of reaction depends on how often and how hard the reacting particles collide with each other
what is the effect of a higher concentration/pressure on the the rate of reaction?
Concentration: more concentrated means moe particles of reactant are knocking about between the water molecules- making the collision between the important particles more likely Pressure: increased pressure means that the particles are more squashed up thus more successful collisions will occur
what is the effect of a catalyst on the rate of reaction?
a solid catalyst works by providing the reacting particles with a surface to stick to. This increases the number of successful collisions by lowering the activation energy.
there is only one factor that, when increased, caused FASTER collisions. What is this factor?
temperature
what is needed to break bonds?
energy
What is activation energy?
the energy needed to brake the initial bonds… energy needed to start the reaction- eg water needs activation energy of 100degreesC until boiling occurs and bonds break
how to measure the enthalpy change of dissolving, displacement, and neutralisation reaction? what are 2 precautions you could take to minimise energy loss and why are they effective?
mix the reactants in a polystyrene cup, making sure minimum energy is lost to surroundings by placing cup in a beaker of cotton wool for more insulation, and putting a lid on the cup to reduce energy loss by evaporation
what is a reversible reaction?
a reaction where the products of the reaction can react with each other and convert back to the original reactants
a state of what will be reached if a reversible reaction takes place in a closed system?
equilibrium
what is meant by the term equilibrium?
the relative % qualities of reactants and product will reach a certain balance and remain there
what does it mean when a dynamic equilibrium is reached?
the reactions are still taking place in both directions, but the overall effect is nil because the forward and reverse reactions cancel each other out. The reactions are taking place at exactly the same rate in both directions.
in a reversible reaction, what does the position of equilibrium depend on?
temperature and pressure
how can you alter the position of equilibrium?
by altering the temp. and pressure of the reaction
all reactions are exothermic in one direction and……. in the other
endothermic
what will happen if you raise the temperature of a reversible reaction?
the endothermic reaction will increase in order to use up the extra heat
what will happen if you lower the temperature of a reversible reaction?
the exothermic reaction will increase to give out more het
what will happen if you raise the pressure of a reversible reaction?
it will encourage the reaction (either forwards or back) that produces less volume (fewer MOLES
)
what will happen if you lower the pressure of a reversible reaction?
it will encourage the reaction which produces more volume
