Topic 3- Chemical Changes Flashcards Preview

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Flashcards in Topic 3- Chemical Changes Deck (33):
1

Acids form... in water

H+ ions

2

Alkalis form...in water

OH- ions

3

Litmus indicates...
In acidic solutions?
In neutral solutions?
In alkaline solutions?

Acid- red
Neutral- purple
Alkaline- blue

4

Methyl orange indicates...
In acidic solutions?
In neutral solutions?
In alkaline solutions?

Acid- red
Neutral- yellow
Alkaline- pink

5

Phenolphthalein indicates...
In acidic solutions?
In neutral solutions?
In alkaline solutions?

Acid- colourless
Neutral- colourless
Alkaline- pink

6

Acid + base

Neutralisation
Produces salt and water

7

Calcium oxide and dilute hydrochloric acid neutralisation reaction:
Method?
Graph shape?

1. Measure out the base intervals and acid out correctly
2. Add the base into the acid
3. Wait for the base to react completely and test the pH
4. Repeat steps 1-3 until all the acid has reacted (when there is unreacted calcium oxide at the bottom of the flask)

Graph- not much change in pH but then the is a sudden change as you approach the point where the solution is neutral and then it levels off again (like a S shape)

8

All acids can .../... in solution which means that...

Ionise/dissociate which means splitting up to produce a hydrogen ion, H+ and another ion

9

Strong acid ionise...
Example of strong acids

Ionise completely in water i.e. a large proportion of the acid molecules dissociate to release H+ ions. They tend to have lower pHs (pH 0-2)
Eg. Sulfuric, hydrochloric and nitric acids

10

Weak acid ionise...
Example of weak acids

Do not fully ionise in solution i.e. only a small proportion of the acid molecules dissociate to release H+ ions. There pHs tend to be around pH 2-6
Eg. Ethanoic, citric and carbonic acids

11

Acid strength (strong or weak) tells you...

What proportion of the acid molecules ionise in water

12

Concentration measures...

How much acid there is in a litre of water
( how watered down an acid is )

13

An acid with a large number of acid molecules compared to the volume of water is said to be...
Whereas an acid with a small number of acid molecules compared to the volume of water is said to be...

1. Concentrated - the more grams or moles of acid per dm (3) the more concentrated an acid
2. Dilute

14

Concentration describes the total number of...

Dissolved acid molecules
NOT the number of molecules that produce hydrogen ions

15

If the concentration of H+ ions increases by a factor of 10, the pH...
Therefore if the concentration increases by a factor of 100 the pH...

1. The pH will decrease by 1

2. The pH will decrease by 2

16

If the concentration of H+ ions decreases by a factor of 10, the pH...
Therefore if the concentration decreases by a factor of 100 the pH...

1. The pH will increase by 1

2. The pH will increase by 2

17

Acid + metal oxide
Produce what?

Acid + Metal Oxide = Salt + Water

18

Acid + Metal Hydroxide
Produce what?

Acid + Metal Hydroxide = Salt + Water

19

Acid + Metal
Produce what?

Acid + Metal = Salt + Hydrogen

20

Acid + Metal Carbonate
Produce what?

Acid + Metal Carbonate = Salt + Water + Carbon Dioxide

21

Test for Hydrogen

You test for hydrogen using a lighted splint
If there is hydrogen it will make a squeaky pop
Because the hydrogen is burning with the oxygen in the air to form water

22

Test for Carbon Dioxide

To test to see whether a gas is carbon dioxide, you bubble it through limewater
If the gas is carbon dioxide, the limewater will turn cloudy

23

Common salts of sodium, potassium and ammonium
Soluble or insoluble?

Soluble

24

Nitrates
Soluble or insoluble?

Soluble

25

Common chlorides
Soluble or insoluble?

Soluble
EXCEPT... silver chloride and lead chloride

26

Common sulfates
Soluble or insoluble?

Soluble
EXCEPT... lead, barium and calcium sulfate

27

Common carbonates and hydroxides
Soluble or insoluble?

Insoluble
EXCEPT... sodium, potassium and ammonium ones

28

Making in soluble salts- precipitation reactions
What reacts?
Example?

Two soluble salts react together

Eg. Lead Nitrate + Sodium Chloride = Lead Chloride + Sodium Nitrate
(Lead Chloride is an insoluble salt)

29

Precipitation method for getting Lead Chloride
(4 steps)

1. Dissolve a spatula of Lead Nitrate in deionised water, in a test tube and do the same for Sodium Chloride in a separate test tube
2. Tip the two solutions into a beaker and stir to mix it together- the Lead Chloride should precipitate out
3. Filter the contents through a filter funnel and paper, the residue left behind is the precipitate
4. Then leave the Lead Chloride to dry in an oven or desiccator

30

Making soluble salts using ...
Example?

An acid and insoluble base

Eg. Copper oxide + Sulfuric acid = Copper sulfate + Water

31

Method for making soluble salts
(5 steps)

1. Heat the acid in a water bath
2. Add the base to the acid, this will produce a soluble salt and water
(You know the acid has been neutralised when excess solid sinks to the bottom of the flask)
3. Filter the excess solid, so the solution is just salt and water
4. Heat the solution to evaporate the water, then leave the solution to cool and dry so the salts crystallise
5. Then filter off the solid salt and leave it to dry

32

Soluble salts can also be made from...

Acid and Alkali reactions

33

Titration method (acid and alkali = soluble salt)
(5 steps)

1. Measure out a set amount of acid into a chronically flask using a pipette and add a few drops of indicator
2. Slowly add alkali to the acid, until you reach an end point where the acid has been completely neutralised and the indicator changes colour
3. Then carry the experiment out again using the exact same volumes of acid and alkaline but with no indicator
4. The solution that remains after this only contains salt and water, therefore you evaporate off some of the water and then leave to crystallise
5. Filter of the solid and dry it