Acids and Bases Flashcards
Why do some substances dissolve?
Before solute is added to solvent: attraction exists between solute and solute. Solvent and solvent
When solvent is added to solute: attraction between particles is overcome.
Once solute has dissolved: attraction exists between solvent and solute particles
Ionic compounds
When ionic compounds dissolve in water the process is called dissociation.
What happens when ionic compounds dissolve in water?
- ionic bonds in the solid lattice are overcome
- hydrogen bonds between water molecules are overcome
- ion dipole attraction between ions and polar water molecules are formed
What happens in an ionisation reaction?
Ionisation= reaction of molecule with water to form ions. Polar 🔹HCl molecules attracts water molecules and polar covalent bond between HCL molecules overcome to produce H+ and Cl-. 🔹Covalent bond forms between H+ and h2O forming H3O+.
🔹Ion dipole attraction between H3O+ and Cl-.
Why are some ionic compounds not soluble?
For insoluble ionic substances, the energy required to separate the ions from the lattice is much greater than the energy produced when ions are hydrated. The ions therefore tend to stay in the lattice.
Why is the hydrogen ion H+ represented as H3O+?
In an aqueous solution, a proton will be surrounded by many water molecules. The H+ bonds to the H2O forming H3O+ which can be called a hydrated proton or hydronium ion.
Strong acid
A strong acid ionises completely in water, the H3o+ producing process is complete in aqueous solution, proton (H+) transfer to H2O is essentially complete
Little or no back reaction
Weak acid
H3O+ producing process is incomplete in aqueous solution or proton transfer (H+) to water is incomplete. Back reaction is significant
What happens to strength property as you increase the concentration of the solution?
The concentration (amount of substance present in a set volume) may increase but strength stays the same.
Why is ethanoic acid a monoprotic acid despite having 4 hydrogens?
Only the hydrogen that is part of the highly polar O-H bond is donated. This is called the acidic proton
Explain why a 0.1M solution of HCl has a pH of 1, whereas a 0.1M solution of CH3COOH has a pH of 2.9
HCl is a strong acid, completely ionises in H2O so the [HCl] can be consider to equal [H3O+] = 10^-1 so pH = 1. CH3COOH is a weak acid and only partially ionises in H2O so the [H30+] is not equal to [CH3CooH] and is less than 0.1M so pH will be higher
Why is the accuracy of pH calculation limited for Ch3COOH?
The calculation assumes that the ethanoic acid fully ionises in water. However, as a weak acid this is not alway the case. Therefore this is not an accurate determination of the pH of this solution
Why is pH affected by dilution?
Dilution changes the concentration of hydronium ions. Since pH is a function of hydronium concentration, decrease in the concentration causes the pH to increase
