Unit 1 AOS 1 Chapter 4.4 Precipitation reactions Flashcards
What are the 4 rules of soluability of ions when dissolved in water?
Rule 1) Group 1 ions , Ammonium NH4+ , Hydrogen H+ , Nitrate (NO3-) , Nitride (NO2-) they are always soluable and thus will never form a precipitate.
Rule 2) All of group 17 are soluble expect when paired with Silver Ag+ , Mercury Hg2+ , Lead Pb2+ ions they are insoluble and will form precipitates.
Rule 3) All sulfates SO4-2 are soluable expect when paired with Silver Ag+ , Mercury Hg2+ , Lead Pb2+ , Strontium Sr+2 , Barium Ba+2 ,and Calcium Ca+2 ions.
Rule 4)All of CHOPS; carbonate CO3-2 , Hydroxide OH- , Oxide O2-1 , Phosphate PO4-3 , Sulfide S2 - will be insoluble expect when paired with Rule number one ions.
What is a precipitation reaction?
A precipitation reaction is a reaction where two solutions are mixed and a solid is formed.
What visible signs indicate a precipitation reaction when two solutions are mixed?
- Bubbling in the test tube
- Solid settling out in the test tube
- A hazy or cloudy appearance ( happens when solid particles are very small and may settle very slowly, or even remain in the bulk of the liquid as a suspension)
- A color change
- Some cases a gelatinous precipitate These form when water molecules get trapped in the precipitate as it forms, leading to a ‘jelly-like’ appearance in the precipitate.
Describe how the structure of a water molecule makes it a good solvent for ionic and polar molecular compounds.
Water molecules have a polar arrangement of the oxygen and hydrogen atoms. One side (hydrogen) has a positive electrical charge and the other side (oxygen) has a negative charge. This allows water molecules to become attracted to many other types of molecules. Water can become so heavily attracted to another molecule that it can disrupt attractive forces; for example, with NaCl, where water can disrupt the attractive forces that hold the sodium and chloride together and thus dissolve it.
In order to dissolve the salt lithium bromide, LiBr, in water, what types of bonds need to be broken and what interactions are formed?
LiBr is an ionic compound. The ionic bonds between the Li+ and Br− ions must be broken, and the hydrogen bonds between the water molecules must be broken. New ion–dipole interactions are formed between the ions and water.
Define the term ‘dissociation’.
Dissociation the process by which ions separate when an ionic substance dissolves
What are ion-dipole bonds?
ion–dipole bonds are the bonds between an ion and a polar molecule
Why is silver chloride AgCl insoluble in water?
For some substances, the energy required to break the bonds in the ionic lattice is too great and dissociation does not occur. Such substances are insoluble. In silver chloride, AgCl, not enough energy is released when the ion–dipole interactions are formed to provide the energy needed to break the bonds between the ions.
What is ionisation?
Ionisation is the reaction of a molecular substance with water to produce ions.
Describe the process by which potassium chloride dissolves in water and give an equation for this process.
Potassium chloride is an ionic compound because it consists of a metal and non-metal.
Potassium ions and chloride ions are dissociated by the polar water molecules.
The positive potassium ions are attracted to the negative ends of the water molecules by ion–dipole interactions.
The negative chloride ions are attracted to the positive ends of the water molecules by ion–dipole interactions.
The ions are separated and hydrated.
KCl(s) H20 ON TOP OF ARROW −→ K+(aq)+Cl−(aq)
Explain why hydrochloric acid can conduct electricity. Use the appropriate terms ionisation and ions in ur explanation.
When hydrochloric acid is added to water it is ionised into H3O+(aq) and Cl−(aq) ions: i.e. HCl(aq)+H2O(l)→H3O+(aq)+Cl−(aq)
Such solutions are good conductors of electricity because the ions are free to move.
Suppose that the precipitate is filtered and the remaining liquid (the filtrate) is then heated to evaporate the remaining water. Describe what happens, naming any new substances that might be formed.
As the water is evaporated, the solution will form solid crystals of the precipitate.
