Section 4 - Physical Chemistry Flashcards
What colour is phenolphalein in acid and alkali?
Acid - colourless
Alkali - bright pink
What colour is methyl orange in acid and alkali?
Acid - bright red
Alkali - bright orange or yellow
What contains hydrogen ions?
Acids
What is a base?
A substance that can neutralises an acid.
Acid and base =
Salt and water
Acid and metal oxide =
Salt and water
Acid and metal carbonate =
Salt and water and carbon dioxide
What salts are soluble?
Sodium Potassium Ammonium Nitrates Most chlorides, sulfates
Which chlorides and sulfates are insoluble?
Silver chloride
Barium sulfates and calcium sulfates
What colour does red litmus paper go in acidic and alkaline solutions?
Acid - no change (red)
Alkali - blue
How do you make soluble salts using acids and insoluble bases?
Add insoluble base (metal carbonate, oxide or hydroxide) to the acid
Base will dissolve in the acid and then excess will sink to bottom
Filter out the excess to get a salt solution
Evaporate water to get crystals of the salt
How do you make soluble salts using an alkali?
Alkalis are soluble bases so can’t be filtered
So have to add exactly right amount of alkali to neutralise acid
Use an indicator to show when reactions finished
Best way: doing a titration
Repeat without indicator
How do you make insoluble salts?
Precipitation reaction
Just mix two solutions that contain the ions you need
Explain how to do a titration?
Use a puppeteer and filler to add alkali to a flask wit indicator
Fill a burette with the acid below eye level
Using the burette add the acid a bit at a time
When the indicator changes colour the alkali has been neutralised
What is the equation for concentration?
Concentration = number of moles / volume
What does the rate of reaction depend on?
Temperature
Concentration
Catalyst
Size of particles
What is the equation for enthalpy change using bond energies?
Total energy absorbed to break bonds - total energy release in making bonds
How do you work out the molar enthalpy change?
- Calculate the amount of energy transferred
- Find out how many moles of fuel produced this heat
- Work out the heat produced by one mole
What colour does blue litmus paper go in acidic and alkaline solutions?
Acid: pink or red
Alkaline: no change (blue)
What does universal indicator do?
Gives you an approximate pH value of a solution.
Acid are sources of ….. ions and Alkalis are sources of ….. ions.
Acids- hydrogen, H+
Alkalis- hydroxide, OH-
What is the difference between hydrogen chloride gas and hydrochloric acid?
Hydrogen chloride is a gas and hydrochloric acid is formed when hydrogen chloride gas is dissolved in water.
When is hydrogen chloride acidic and why?
In water but not in methyl benzene as when it is dissolved in water it dissociates (splits up) and forms H+ ions making the solution acidic. Hydrogen doesn’t dissociate in methyl benzene.
What is the equation linking the number of moles (n), concentration (c), and volume (v)?
Number of moles = concentration x volume
What are the four methods for soluble salts?
- Metal + acid ➡️ salt + hydrogen
- Alkalis + acid ➡️ salt + water
- Base + acid ➡️ salt + water
- Metal carbonate + acid ➡️ salt + water + carbon dioxide
Which salts are soluble?
Salts with nitrates or group 1 elements are soluble.
Describe an energy level diagram that is exothermic and an energy level diagram that is endothermic.
EXOTHERMIC REACTION:
- reactants line (first) higher than products line (second)
- 🔺H (difference between two lines) is positive
- energy on x axis
- progress of reactants on y axis.
- Ea = between reactants line and top of curve.
ENDOTHERMIC REACTION:
- reactants line (first) lower than products line (second)
- 🔺H (difference between two lines) is negative
- energy on x axis
- progress of reactants on y axis.
- Ea = between reactants line and top of curve.
What is an alkali?
Alkalis are soluble bases, and sources of hydroxide ions.
In exothermic reactions…..
In endothermic reactions…..
Heat energy is given off
Heat energy is taken in
How do you calculate enthalpy changes from calorimetry experiments?
Using dissolving, displacement, and neutralisation reactions
OR
Using combustion.
What is the equation for Heat energy change?
Q = mass x temp change x 4.2
What happens to the equilibrium position in reversible reactions if you increase the temperature and increase the pressure?
Increased temperature: endothermic reaction will increase, uses up more heat
Increased pressure: produces less volume
What happens to the equilibrium position in reversible reactions if you decrease the temperature and decrease the pressure?
Decreased temp: exothermic reaction will increase, gives out more heat.
Decreased pressure: produces more volume.
