Acids Flashcards
Give the formula of the 7 weak acids you need to know
- Hydrochloric acid = HCl
- Sulfuric acid = H2SO4
- Nitric acid = HNO3
- Phosphoric acid = H3PO4
- Methanoic acid = HCOOH
- Ethanoic acid = CH3COOH
- Propanoic acid = CH3CH2COOH
Give the definition of an acid
(Proton doner)
- Release H+ ions in aqueous solutions
Give the definition of a strong acid
(one way reaction)
- Completely dissociate when dissolved in water.
Give the definition of a weak acid
(reversible reaction)
- Only slight dissociate when dissolved in water, giving an equilibrium mixture
What is formed when an acid dissociates in water?
A proton (H+ ion) and a negative anion.
Are carbonates, hydroxides and oxides bases? Could they also be alkalis?
Yes, anything that reacts with an acid is a base, however to be an alkali it must react or dissolve in water to form OH- ions and react with acids.
Give the definition of a base
A substance which neutralises an acid (proton acceptor)
Give the definition of an alkali
A soluble substance that releases OH- ions in aqueous solutions
State whether soluble metal oxides, soluble hydroxides and ammonia reacts or dissolves in water and if so what does it form?
- Soluble metal oxides react with water as the oxide ions react with water to form OH- ions e.g. Na2O + H2O –> 2Na+ + 2OH-
- Soluble hydroxides just dissociate in water to form OH- ions e.g. NaOH —> Na+ + OH-
- Ammonia reacts with water to form ammonium ions and OH- ions e.g. NH3 + H2O —> NH4+ + OH-
Give the definition of a salt
- A chemical compound formed from the reaction of an acid and a base, with all or part of the hydrogen of the acid is replaced by a metal or other cation e.g. NH4+
Give the reaction of when an acid reacts with a base, when an acid reacts with an alkali, when an acid reacts with a carbonate and when an acid reacts with ammonia
- acid + base —> salt + water
- acid + alkali —> salt + water
- acid + carbonate —> salt + carbon dioxide + water
- acid + ammonia —> ammonium salt
Does salt dissolve in water; if so what does it form?
- Yes
- It will dissolve to form aqueous ions e.g. NaCl —> Na+ + Cl-
What is an ionic equation and give all the steps to creating an ionic equation
- An ionic equation will only show the ions or species that change state in a reaction, and they omit (leave out) those ions that are not involved in the reaction
- assign correct state symbols
- separate anything aqueous into its ions
- cancel out anything that appears on the side of the equation (anything that stays the same)
- write the ionic equation
Give the 7 steps for making a standard solution
- Weigh out an accurate mass of solid in a clean and dry beaker
- Add enough deionised water to dissolve the solid, stirring with a glass rod
- Transfer the solution to a volumetric flask using a funnel
- Rinse the beaker, stirring rod and funnel with deionised water and transfer washings to to volumetric flask
- Add deionised water to volumetric flask to make up to the graduation mark. Use a dripping pipette when close to the mark. Going beyond the mark will result in an unknown concentration, make sure the bottom of the meniscus is on the mark
- Stopper the flask and invert to mix thoroughly to ensure a homegenous solution
- Use concentration=mass/volume to work out concentration
How do I do a titration reaction in 7 steps?
- Rinse burette with deionised solution, then rinse with standard solution, then fill the burette including the jet with standard solution. Take initial reading and record to two d.p. ending in 5 or 0
- Rinse pipette with deionised water, then rinse with unknown concentration solution, and then transfer 25cm^3 of the solution from the beaker into conical flask using pipette
- Add 3-4 drops of Phenolphthalein in (the end result will be very pale pink) and place under the burette
- Remove filter funnel and add the solution from the burette, with constant swirling of the conical flask, until the solution is a very pale pink (indicates neutralisation), add deionised water to sides of conical flask to ensure all of solution has reacted
- Write down burette reading to 2 d.p. ending in 0 or 5 to calculate titre value
- Empty the conical flask and wash thoroughly with deionised water
- Refill your burette if necessary . Repeat steps 2-7
Why can you not add any more than 3-4 drops of indicator in a titration?
Indicators are weak acids so too much will affect the titre value
How would you make sure the jet of a burette is always full in a titration reaction? What would happen if a student did not do this?
Let some of the solution out of burette into a waste beaker
Titre volume too high
Why do you rinse the pipette with the unknown concentration solution after rinsing it with deionised water?
Removes any drops of deionised water that would lower the concentration of the solutions and therefore to prevent affecting the titre value
What calculations should you do after doing a titration to work out concentration of the unknown concentration solution? 4 steps
- Have a balanced equation
- Work out moles for the substance that has the most info
- Determine moles in other species
- Use moles=concentration x volume to work out concentration of unknown concentration solution
Should the rough titre be used as a concordant result?
No
What is the equation for apparatus error
apparatus error = margin of error / quantity measured x 100
What is the margin of error for a 3 d.p. balance, a pipette, a volumetric flask and a burette?
3 d.p. balance = 0.00050g
Pipette = 0.060cm^3
Volumetric flask = 0.15cm^3
Burette = 0.05cm^3
What should you do when you are calculating apparatus error when you have measured something twice e.g. titre?
Times the margin of error by two
