Section 4: Physical Chemistry Flashcards
what colour is litmus indicator in the presence of acidic, neutral and alkaline solutions?
acidic: red
neutral: purple
alkaline: blue
what colour is methyl orange indicator in the presence of acidic, neutral and alkaline solutions?
acidic: red
neutral: orange
alkaline: yellow
what colour is phenolphtalein indicator in the presence of acidic, neutral and alkaline solutions?
acidic: colourless
neutral: colourless
alkaline: pink
what are acids?
sources of hydrogen ions (H+)
what are alkalis?
sources of hydroxide ions (OH-)
what are the products of the reaction of acids and metals?
salt + hydrogen
what are the products of the reaction of acids and metal oxides?
salt + water
what are the products of the reaction of acids and metal carbonates?
salt + water + carbon dioxide
what are the rules for predicting the solubility of salts?
1) sodium, potassium and ammonium salts are soluble
2) all nitrates are soluble
3) chlorides are soluble except silver chloride
4) sulphates are soluble except those of barium and calcium
5) carbonates are insoluble except those of sodium, potassium and ammonium
how do you prepare soluble salts from acids?
react an acid with an excess of metal/ insoluble base
how do you prepare copper sulphate?
1) add excess copper oxide to sulfuric acid, heating and stirring to speed up the reaction
2) solution turns blue as reaction occurs
3) filter solution to remove excess copper oxide
4) evaporate the water so that crystals of copper sulphate are left behind
how do you prepare insoluble salts?
1) react two soluble salts to form a precipitate
2) filter the solution to get the precipitate
3) wash the salt with pure water to remove traces of the other solution and leave to dry
give an example of an insoluble salt preparation
insoluble silver chloride formed by this reaction:
silver nitrate + sodium chloride –> silver chloride + sodium nitrate
how do you carry out acid-alkali titrations?
1) use burette to add acid to alkali drop by drop, swirling the solution periodically
2) stop adding acid once there is a change in the colour of the indicator
3) take initial and final readings of the acid and subtract to calculate the volume added
4) repeat until obtain concordent results
what is the purpose of titrations?
1) identify the concentration of acids/alkalis
2) make salts with no leftover acid/alkali
what does ΔH represent?
molar enthalpy change (energy transferred from bonds to heat)
how do you calculate heat energy changes in simple calorimetry experiments?
Energy = m x c x ΔT m= mass of water c= SHC of water (4.2J kg °C) T= temperature change of water
for exothermic reactions on a diagram are the products of the reaction below or above the reactants?
Below
for endothermic reactions on a diagram are the products of the reaction below or above the reactants?
Above
is ΔH a negative or positive value for exothermic reactions?
negative
is ΔH a negative or positive value for endothermic reactions?
positive
is the breaking of bonds endothermic or exothermic?
endothermic
is the making of bonds endothermic or exothermic?
exothermic
how does an increase in surface area increase the rate of reaction?
1) more sites for the reaction to take place
2) more frequent collisions
how does an increase in concentration/pressure increase the rate of reaction?
1) more particles in a given volume
2) more frequent collisions
how does an increase in temperature increase the rate of reaction?
Firstly:
1) particles have more kinetic energy
2) more frequent collisions
Secondly:
1) particles have more energy
2) higher proportion of particles have energy equal to or above the activation energy
3) higher proportion of successful collisions
what is the activation energy?
the minimum energy required for a reaction to start
how do catalysts speed up reactions?
they provide an alternative pathway with a lower activation energy
what does ⇌ mean?
the reaction is in equilibrium (reversible)
what is the affect of increasing the temperature on the equilibrium reaction of ammonia chloride to hydrogen chloride and ammonia?
shift towards the endothermic reaction (more hydrogen chloride and ammonia)
what kind of reaction is the dehydration of hydrated copper sulphate?
reversible reaction
what is true of something in dynamic equilibrium?
1) the rate of the forward reaction is equal to the rate of the backward reaction
2) the concentrations of the products and reactions are constant (but no necessarily equal)
3) forwards and backwards reactions occur at the same time
what is the affect of increasing the temperature on the equilibrium position in reversible reactions?
shifts in the endothermic direction
what is the affect of increasing the pressure on the equilibrium position in reversible reactions?
shifts to the side with the fewest gaseous moles
What name is given to a reaction that involves both reduction and oxidation?
Redox
What kind of reaction is metal reacting with acid to form a salt?
Neutralisation
Why is universal indicator not a good choice for titration experiments?
colour change is gradual/not defined
Explain why increases in pressure increases the rate of reaction in terms of particle collision theory
1) particles closer together
2) particles collide more frequently
Explain in terms of making and breaking bonds why reactions are exothermic
1) breaking bonds is endothermic
2) making bonds is exothermic
3) more heat energy given out than taken in
How could a dry gas be collected?
Using a gas syringe
Describe two observations made when magnesium burns in air
1) white solid produced
2) bright white flame
In the excess metal/salt method why is excess added?
To neutralise the acid
How do you calculate molar enthalpy change from heat energy change?
ΔH = q ÷ m q = heat energy m = moles
How do you use average bond energies to calculate molar enthalpy change?
1) draw out molecules showing bonds
2) calculate reactants energy
3) calculate products energy
4) energy change = bonds broken - bonds made
Why are acids heated before the base or metal is added?
To increase the rate of reaction
How do you know when a salt or base is in excess?
It stops disappearing and forms as a solid at the bottom of the beaker
How do you know when the crystallisation point is reached?
A drop of solution forms crystals when removed and cooled
Why are noble gases inert?
1) atoms do not readily lose or gain electrons
2) as contains 8 electrons in outer shell
explain why potassium is more reactive than sodium
1) outer electron lost in K further from the nucleus
2) less attracted by nucleus
suggest why copper strips would dry more quickly when washed with ethanol rather than water
ethanol is more volatile
