C5 - Precipitation and Testing For Ions Flashcards
What is a precipitation reaction?
When two different solutions react together to form an insoluble substance.
Give an example of a precipitation reaction?
Lead nitrate + potassium iodide -> lead iodide + potassium nitrate
Why are precipitation reactions fast?
The collision frequency between ions in solution is very large. There is a high chance that different ions will collide with each other and cause a reaction, so precipitation reactions are extremely fast. Precipitates form as soon as two suitable solutions are mixed together.
What are state symbols?
They show the state of each substance: (s) means solid, (l) means liquid, (g) means gas, and (aq) means aqueous solution or dissolved in water.
What are the three main stages in making an insoluble compound?
- A suitable combination of solutions is mixed together to form a precipitate of the required insoluble compound.
- The mixture is ltered to separate the precipitate from the other reactants and product.
- The precipitate is washed with water while it is on the filter paper. It is then dried, for example, in a warm oven.
Give an exemple of a medical precipitate and how it works.
Barium sulfate. X-rays pass through it with difficulty, making it useful for medical investigations. A patient who needs an X-ray image of their digestive system is given a ‘barium meal’, a drink containing barium sulfate. The outline of the digestive system shows up in the X-ray image, giving doctors the information they need.
How is barium sulfate made?
Barium chloride + sodium sulfate -> barium sulfate + sodium chloride
BaCl2(aq) + Na2SO4(aq) → Na2SO4(aq) + BaSO4(s)
Ionic equation : Ba2+(aq) + SO^2– (4)(aq) → BaSO4 (s)
How do you test for sulfate ions?
A sample of the test solution is placed in a test tube, then acidi ed with a few drops of hydrochloric acid. A few drops of barium chloride solution are added. If sulfate ions are present, a white precipitate of barium sulfate forms.
How do you test for halide ions?
Halide ions are ions produced by the halogens. The presence of these ions can be detected using lead nitrate solution:
• Chloride ions give a white precipitate
• Bromide ions give a cream precipitate
• Iodide ions give a yellow precipitate.
A sample of the test solution is placed in a test tube, then acidified with a few drops of nitric acid. A few drops of lead nitrate solution are added. If a precipitate forms, its colour lets you identify the halide ion present.
What are spectator ions?
They don’t take part in the reaction
