Chemical Changes Flashcards
1
Q
Do acids contain hydrogen ions or hydroxide ions?
A
Hydrogen
2
Q
Do alkalis contain hydrogen ions or hydroxide ions?
A
Hydroxide
3
Q
What colour does litmus turn in acidic solutions?
A
Red
4
Q
What colour does litmus turn in alkaline solutions?
A
Blue
5
Q
What colour does phenolphthalein turn in acidic solution?
A
Colourless
6
Q
What colour does phenolphthalein turn in alkaline solution?
A
Pink
7
Q
What colour does methyl orange turn in acidic solutions?
A
Red
8
Q
What colour does methyl orange turn in alkaline solutions?
A
Yellow
9
Q
Metal + Acid >
A
Salt + Hydrogen
10
Q
Metal oxide + Acid >
A
Salt + Water
11
Q
Metal hydroxide + Acid >
A
Salt + Water
12
Q
Metal carbonate + Acid >
A
Salt + Water + Carbon dioxide
13
Q
What is a titre?
A
The volume of acid added to exactly neutralise the alkali
14
Q
What are the steps of a titration?
A
- Fill the burette with acid
- Use a pipette to put a known volume of alkali into a conical flask on a white tile
- Put a few drops of a suitable indicator solution, such as phenolphthalein or methyl orange, into the alkali
- Record the burette start reading
- Add acid to the alkali, swirl to mix, until the colour changes, the endpoint
- Record the burette end reading
- Repeat steps until you get concordant titres
- To get the salt on its own, warm the salt solution to evaporate the water
15
Q
What are concordant titres?
A
Titres that are identical to each other, or very close together (usually within 0.1 cm³)
16
Q
Which ionic compounds are soluble?
A
- All common sodium, potassium and ammonium salts
- All nitrates
- Most common chlorides
- Most common sulfates
- Sodium hydroxide, potassium hydroxide, ammonium hydroxide
- Sodium carbonate, potassium carbonate, ammonium carbonate
17
Q
Which ionic compounds are insoluble?
A
- Silver chloride, lead chloride
- Lead sulphate, barium sulphate, calcium sulphate
- Most common hydroxides
- Most common carbonates
18
Q
How do you describe a strong acid?
A
If it is fully disassociated into ions in solution
19
Q
How does the concentration of hydrogen ions affect the pH?
A
- The higher the concentration of hydrogen ions, the lower the pH
- As hydrogen ion concentration increases by a factor of 10, the pH decreases by 1
20
Q
How does the concentration of hydroxide ions affect the pH?
A
The higher the concentration of hydroxide ions, the higher the pH
21
Q
How do you describe a weak acid?
A
It is only partially disassociated into ions in solution
22
Q
What are alkalis?
A
Soluble bases
23
Q
What is a base?
A
Any substance that reacts with an acid to form a salt and water only
24
Q
What is the difference between a concentrated and dilute solution?
A
Concentrated solution has a greater amount of dissolved solute particles than a dilute solution
25
What is the chemical test for hydrogen?
A lit splint ignites hydrogen with a squeaky pop
26
What is the chemical test for carbon dioxide?
Turns limewater milky or cloudy white
27
What is neutralisation?
A reaction between an acid and a base
28
What happens in an acid-alkali neutralisation?
Hydrogen ions (from acid) react with hydroxide ions (from alkali) to form water
29
How do you investigate the change in pH when calcium hydroxide is added to hydrochloric acid?
- Add dilute hydrochloric acid to beaker
- Transfer a drop of liquid to universal indicator paper
- Match the colour to a pH chart, record the estimated pH
- Add a level spatula of calcium hydroxide powder to the beaker
- Stir thoroughly then estimate and record the pH of the mixture
- Repeat until there are no more changes in pH
- Plot a titration curve on a graph with mass on the horizontal axis and pH on the vertical axis
30
How do you investigate the preparation of pure, dry hydrated copper sulphate crystals starting from copper oxide?
- Place sulfuric acid in a conical flask and warm in a water bath
- Add a spatula of copper oxide powder and stir
- Continue adding copper oxide powder until it is in excess

- Filter the mixture to remove the excess copper oxide
- Heat the copper sulphate solution to evaporate half the water
- Leave to allow all of the water to evaporate
31
How do you name salts?
- The first part comes from the metal, metal oxide or metal carbonate
- The second comes from the acid:
Hydrochloric acid – chloride salts
Nitric acid – nitrate salts
Sulphuric acid – sulphate salts
32
What are the main steps to make a soluble salt from a soluble base?
33
Why do you add excess of the solid reactant when making a soluble salt with an insoluble reactant?
To ensure all of the acid has reacted
34
Why and how is the excess reactant removed when making a soluble salt with an insoluble reactant?
- By filtration
- It is removed to leave a pure solution of the salt
35
Why is the remaining solution only salt and water when making a soluble salt with an insoluble reactant?
Because all the acid is used up and the insoluble reactant has been removed
36
Why must titration be used when making soluble salts from a soluble reactant?
To find the exact volume of the soluble base that reacts with the acid
37
Why are the acid and the soluble reactants mixed in the correct proportions when making soluble salts from a soluble reactant?
To obtain a solution containing ONLY salt and water
38
Why is the remaining solution only salt and water when making soluble salts from a soluble reactant?
The acid and base have been mixed in correct proportions so the solution so the solution is fully neutralised
39
What ways can help to obtain accurate titre during a titration?
- Swell the flask continuously to mix thoroughly
- Near the end-point, add the acid drop by drop, pausing between each addition
- Rinse the inside of the flask to make sure all the acid mixes with the alkali
40
How can you predict if a precipitate will form when two solutions are mixed ?
If at least one product meets the ‘insoluble’ rule a precipitate will form
If not then non will form
41
How do you make insoluble salts?
- Mix solutions of two suitable substances 
- Filter the mixture, the salt will be left as a residue in the filter paper
- Wash the salt with distilled water
- Leave to dry
42
What is electrolysis?
A process in which electrical energy, from a direct current supply, decomposes an electrolyte
43
What is an electrolyte?
An ionic compound in the molten state or dissolved in water
44
What is produced at the cathode?
- Hydrogen
- Unless the compound contains ions from a metal less reactive than hydrogen, then the metal is produced
- (Copper, silver, gold)
45
What is produced at the anode?
- Oxygen - from OH- ions
- Unless the compound contains halide irons (Cl-, Br-, I-)
- Then chlorides produce chlorine etc
46
What are the steps of electrolysis of copper sulfate using copper electrodes?
- Pour copper sulphate solution into a beaker
- Measure and record the mass of each copper electrode and attach them to the negative and positive terminals
- Ensure they do not touch then turn on the power supply and allow to run
- Remove and gently wash with distilled water
- Measure and record the masses again
- Calculate the change in mass of each electrode, the gain of one should equal the loss of the other
47
What are anions?
Negatively charged ions that move to the positive electrode (anode)
48
What are cations?
Positively charged ions that move to the negative electrode (cathode)
49
What are the steps of electrolysis of copper sulphate using inert electrodes?
- Pour copper sulphate solution into a beaker
- Place two graphite rods into the solution, attaching one to the negative terminal and one to the positive
- Completely fill two small test tubes with the solution and place each test tube over an electrode
- Turn on the power supply and allow to run
- Test any gas produced with a glowing splint and burning splint
- Record the observations
50
How do you use electrolysis to purify copper?
- Pure and impure copper rods are dipped into copper sulphate solution
- The pure copper rod is connected to the negative terminal and the impure rod is connected to the positive
- The pure copper rod increases in size and the impure deteriorates, leaving a pool of anode sludge
