C3 Titrations, Energy, Chemical Tests. Flashcards
What ion is there when a brown precipitate forms after adding sodium hydroxide?
Brown precipitate means iron 3+ ions.
How so to start the positive metal test for ions?
Add sodium hydroxide (NaOH) to the unknown substance and you will get a coloured or white precipitate.
What ion is there when a green precipitate that turns brown, forms after adding sodium hydroxide?
Iron 2+ ions.
What ion is there when a blue precipitate forms after adding sodium hydroxide?
Copper 2+ ions.
When a white precipitate forms after adding sodium hydroxide, what are the possible ions?
Calcium 2+
Aluminium 3+
Magnesium 2+
When more sodium hydroxide is added to a white precipitate and it dissolves, what is the ion?
Aluminium 3+
If the flame test provides a brick red flame, what is the ion?
Calcium 2+
If the flame test provides no flame colour, what is the ion?
Magnesium 2+
If the flame test provides a crimson flame, what is the ion?
Lithium +
If the flame test provides a lilac flame, what is the ion?
Potassium +
If the flame test provides a green flame, what is the ion?
Barium 2+
If the flame test provides a yellow flame , what is the ion?
Sodium +
How is the flame test carried out?
Dip a nichrome wire in hydraulic acid, heat it and then put it in more acid so to clean it.
Put a small amount of the compound to be tested on the end of the loop.
Put the loop in the blue part of a Brunson burner. (Hottest part)
How can negative ions be rested for?
Looking for carbonates,
Testing for halides,
Testing for sulphates.
How do you test for a carbonate?
Add a carbonate with acid. This will produce salt, water but most importantly CO2.
Put the gas through some lime water, and is it goes cloudy it means CO2 which means a carbonate.
How does one test for halide ions?
Add dilute nitric acid(HNO”3”) (this will remove any carbonate ions present) and then silver nitrate solution (AgNO”3”) The colour of the precipitate will tell you the halide present.
What colour does chloride- produce after the test for halides?
White
What colour does bromide- produce after the test for halides?
Cream
What colour does iodine- produce after the test for halides?
Pale yellow.
Give the ionic equation for testing for chloride.
Ag+ add Cl- = AgCl.
How does one test for sulphates?
Give the ionic equation for this.
First add dilute hydrochloric acid (to remove carbonate ions)
Then add barium chloride solution.
A white precipitate (barium sulphate ) will form if a sulphate is present.
BaCl”2” + MgSO”4” = BaSO”4” + MgCl”2”
Why is a white tile used in titration reactions?
So you can see when the indicator changes colour.
What is the equation to calculate the change in energy
Change = left hand side - right hand side.
