Chem pracx Flashcards
Indicators
Screened Methyl Orange
red, grey, green (3-5)
Thymol Blue
red, green blue (8-10)
Which only reacts with concentrated base
Silicon dioxide
Metal oxides are
Basic
Amphoteric (Zinc, Aluminium, Lead)
Non-metal oxides are
Acidic
Neutral (Water, Carbon monoxide, Nitrogen monoxide)
Solubility table
Sulfate: BP CA (sparing)
Halides: Silver, Lead (II)
Oxides: CaO (sparing)
Hydroxides: Calcium and Barium both sparingly
How to prepare insoluble salt
Precipitation
1. Mix the solutions to produce a precipitate
2. Filter the mixture to obtain a residue
3. Wash the residue with a small amount of distilled water to remove any impurities
4. Dry the precipitate between a few sheets of filter paper
Why cannot use precipitation for soluble salt
Difficult to determine endpoint and will produce an impure salt
Insoluble salt prep option 1
Insoluble solid-Acid reaction
- Add solid in excess (metal, carbonate base)
- Add ____ a little at a time to hot ____ while stirring
- Filter the mixture to obtain the filtrate
- Heat the filtrate gently till saturation
- Allow the solution to cool for crystal to form
- Filter the mixture to remove excess water
- Wash the crystals with a small amount of distilled water to remove impurities
- Dry the crystals between sheets of filter paper
Why need to add solid in excess for solid-acid reaction
To ensure the reaction is complete and all the soluble reactant is used up (to prevent contamination)
Titration to obtain what salts
SPA salts
(can use alkali or carbonate)
Titration steps
- Fill up a 50cm3 burette with _______ of unknown concentration
- Pipette 25cm3 of ________ into a 250cm3 conical flask and add 2 drops of ______ indicator
- Titrate _____ against ________
- Record the volume of _______ used when the indicator first turns ______ in a single drop
- Repeat the titration till consistent results are obtained
- Calculate the average volume of _____ used from the 2 best readings
- Repeat the titration with the calculated volume of _____ without the indicator
- Heat the solution till saturation
- Allow the solution to cool for crystals to form
- Filter the mixture to remove excess _____
- Wash the crystals with a small amount of distilled water
- Dry the crystals between a few sheets of filter paper
Base + Ammonium salt
Ammonia + Salt + Water
Strongest oxidising agent
Fluorine (Group 7)
Strongest reducing agent
Lithium (Group 1)
Test for reducing agent
Acidified potassium manganate VII (purple to colourless)
Iodine (brown to colourless)
Test for oxidising agent
Potassium iodide (colourless to brown)
More reactive metal stronger or weaker ____ agent
Stronger reducing agent
Carbon vs Hydrogen _____ agent
Carbon stronger reducing agent
Reactivity table
Please Stop Calling Me A Careless Zebra, (HYDROGEN) Instead Try Learning How Copper Saves Gold Platinum
Methods to prevent rusting
- Protective layer
- Galvanising
- Sacrificial protection
- Alloys
Rusting formula
Iron + Oxygen + Water –> Hydrated iron III oxide
4Fe + 3O2 + 2xH2O –> 2Fe2O3.xH2O
Acid-Alkali reaction (pH)
Use pH meter to measure rate of change in pH
Colour change
Use a colorimeter to measure the change in intensity of colour
Production of ppt
- Conductivity meter to measure the change in concentration of mobile ions over time (electrical conductivity)
- Mark a thick big cross in pencil on a piece of white paper
- Stand a 100cm3 beaker over the cross on the paper
- (do the experiment)
- Observe the cross by looking vertically down through the solution from above the beaker. Record the time taken to the nearest seconds when the cross just disappears completely
- Work out the reciprocal of the time for the cross to disappear. This is proportional to the average rate of reaction during that interval of time
cannot determine instantaneous
