Atmosphere and acids - 3.4 Flashcards
what is an indicator?
an indicator is a substance that changes colour to tell you about the pH of a soluti9on
what colours do methyl orange and phenolphthalein go when in different solutions?
methyl orange
- acidic colour = red
- neutral colour = yellow
- alkaline colour = yellow
phenolphthalein
- acid colour = colourless
- neutral colour = colourless
- alkaline colour = pink
what colours do red and blue litmus paper go when in different solutions?
red litmus
- acidic colour = red
- neutral colour = red
- alkaline colour = blue
blue litmus
- acidic colour = red
- neutral colour = blue
- alkaline colour = blue
what are the four gases air is mostly composed of?
nitrogen - 78%
oxygen - 21%
argon - 0.96%
carbon dioxide - 0.04%
what is element combustion?
when an element reacts with oxygen to produce an oxide
what are the three important combustions?
1 - Magnesium
magnesium + oxygen –> magnesium oxide
2 - Sulphur
sulphur + oxygen –> sulphur dioxide
3 - Hydrogen
hydrogen + oxygen –> hydrogen oxide (water)
what is iron(II)?
Fe 2+
what is silver?
Ag +
what is iron(III)?
Fe 3+
what is zinc?
Zn 2+
what is copper?
Cu 2+
what is lead?
Pb 2+
what is the chemical test for oxygen?
glowing splint –> relights
This is because the oxygen allows the wood in the splint to combust more efficiently
What happens if they dissolve in water?
oxides tend to form a acid or alkaline solution depending on whether the original element was metal or non-metal
metal –> alkaline solution
non-metal –> acid solution
how can you determine if an unknown element was metal or non-metal?
- combust it in oxygen
- dissolve the oxide formed
- check the pH of the solution with an indicator
What is an acid?
H+ donor
What is a base?
H+ acceptor
What is an alkali?
OH- donor
What is the formula for Hydrochloric acid?
HCl
What is the formula for Nitric acid?
HNO3
What is the formula for Sulphuric acid?
H2SO4
What is the formula for Phosphoric acid?
H3PO4
What is the formula for Carbonic acid?
H2CO3
What is the formula for Sodium hydroxide?
NaOH
What is the formula for Potassium hydroxide?
KOH
What is the formula for Ammonium hydroxide?
NH4OH
What is the formula for Ammonia?
NH3
What are polyatomic ions?
A polyatomic ion is an ion that contains more than one atom
What happens when bases react with metals?
They form a salt and water
What is an important observation that is made when an acid and base reacts?
The base disappears because it is used up in the reaction.
Making Salt Crystals:
- add excess base to hot acid - this makes the salt solution quickly and ensures all the acid is used up
- filter out excess base - the salt solution is the filtrate and is collected in an evaporating basin
- heat the salt solution until crystals start to form around the edges - this saturates the solution so that crystals form most efficiently
- leave the salt solution to crystallise - evaporation of water allows crystals to form
Making pure, dry crystals of a soluble salt:
- First, you make the salt solution
a. The insoluble base method
b. The titration method - Second, you crystallise the salt
- This is done in the same way, regardless of the method you use to make the salt solution
The insoluble base method:
- Heat the acid
- hot acid has more energy so it reacts faster with the base - While stirring, add base until no more will dissolve
- This guarantees the base is in excess so that we know all the acid has been used up - Filter out the excess base
The titration method
- Perform a titration to measure the volumes of acid and alkali that neutralise each other
- Repeat the titration, but this time:
a. don’t put the indicator in
b. use the burette to add exactly the right volume for neutralisation
Now the salt solution is made you perform crystallisation to get pure, dry salt crystals
What happens when carbonates react with metals?
They from a salt, water and carbon dioxide
What are the two important observations in an acid and carbonate reaction?
- The carbonate disappears
This is because it is used up in the reaction - There is fizzing
This is because a gas(carbon dioxide) is produced
What is the chemical test for carbon dioxide?
Bubble into limewater –> goes cloudy
This is because CO2 reacts with the limewater to make an insoluble white solid
What is precipitates
A precipitate(ppt) is an insoluble solid that forms inside a solution.
How can you tell if precipitate will form by mixing ions up and seeing if either of the resulting compounds are insoluble?
If an insoluble compound is formed, it will appear as a precipitate.
Making salts by precipitation:
mix solutions together
filter out the solid precipitate
wash - by rinsing under water
method of drying - pat dry with filter paper
