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GCSE Edexcel Chemistry > Chemical Changes (1) > Flashcards

Chemical Changes (1) Flashcards

1
Q

What is an

acid?

A
  • anything that forms a solution with a pH of less than 7

the lower the pH, the more acidic the solution

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2
Q

What is an

alkali?

A

anything that forms a solution with a pH of greater than 7
(a base that is soluble in water)

the higher the pH, the more alkaline the substance is

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3
Q

What are

neutral substances?

A

neither acidic nor alkaline substances which have a pH of exactly 7

e.g. pure water

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4
Q

What affects the

pH of a solution?

A

The type of ions that are released by the dissolved substance.

Acids release hydrogen ions when they are aqueous
Alkalis release hydroxide ions when they are aqueous

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5
Q

What is a

base?

A

a substance that reacts with an acid to produce a salt and water

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6
Q

How does

concentration of ions affect pH?

A

The higher the concentration of ions in a solution, the more acidic it is, so the lower the pH will be. So, as concentration of hydrogen ions increases, pH decreases.
In alkaline solutions, the higher the concentration of hydroxide ions, the higher the pH.

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7
Q

What is an

indicator?

A

a dye that changes colour depending on whether it’s above or below a certain pH

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8
Q

What is the colour of

litmus

in acidic, neutral and alkaline solutions?

A

acidic - red
neutral - purple
alkaline - blue

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9
Q

What is the colour of

methyl orange

in acidic, neutral and alkaline solutions?

A

acidic - red
neutral - yellow
alkaline - yellow

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10
Q

What is the colour of

phenolphthalein

in acidic, neutral and alkaline solutions?

A

acidic - colourless
neutral - colourless
alkaline - pink

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11
Q

What is the general equation for a

neutralisation reaction?

(base + acid)

A

Base + Acid -> Water + Salt

BAWS

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12
Q

Describe the core practical

investigating neutralisation reactions.

(involving the reaction of calcium oxide and hydrochloric acid)(5 steps)

A
  1. Measure out 150cm^3 of dilute hydrochloric acid into a conical flask (Use a pipette or a measuring cylinder for this).
  2. Measure out 0.5g of calcium oxide to the hydrochloric acid.
  3. Wait for the base to completely react, then record the pH of the solution, using either a pH probe or universal indicator paper.
  4. Repeat steps 2 to 4 until all the acid has reacted. (You’ll know you’ve reached this point when unreacted calcium oxide starts to collect at the bottom.)
  5. You can then plot a graph to see how pH changes with the mass of base added.
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13
Q

What does

acid strength tell you?

A

the proportion of acid particles that dissociate to produce hydrogen ions in solution

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14
Q

What is a

strong acid?

and give some examples. (3)

A

an acid that ionises almost completely in water

(most of the acid particles dissociate to release hydrogen ions)

e.g. sulfuric, hydrochloric and nitric acid

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15
Q

What is a

weak acid?

and give some examples. (4)

A

an acid that only partially ionises in water

(only some of the acid molecules will ionise and release hydrogen ions)

e.g. carboxylic, citric, carbonic, ethanoic acids

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16
Q

What is the

concentration

of an acid?

A

how much acid there is in 1 dm^3 of water (1L)

(not to be confused with acid strength)

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17
Q

What is the relationship between

acid concentration and pH?

A

The pH of an acid is dependent on the acid’s concentration - increasing the concentration of hydrogen ions leads to a decrease in the pH

If the concentration of hydrogen ions increases by a factor of 10, the pH decreases by 1.

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18
Q

What type of substance are

metal oxides and metal hydroxides?

A

bases

19
Q

What is the general equation for the reaction of

metal oxides or metal hydroxides with acids?

(base + acid)

A

Base + Acid -> Water + Salt

BAWS

20
Q

What is the general equation for the reaction of

a metal with an acid?

A

Metal + Acid -> Salt + Hdrogen

MASH

21
Q

Describe a

test for hydrogen.

(3 steps)

A
  1. Collect the gas in a test tube.
  2. Put a lit splint into the test tube.
  3. If there is a ‘squeaky pop’, hydrogen gas is present.

(This noise comes from the hydrogen burning quickly with the oxygen in the air to form water.)

22
Q

What is the general equation for the reaction of

metal carbonates and acids?

A

metal Carbonates + Acid -> Water + Carbon dioxide + Salt

CAWCS

23
Q

Describe a

test for carbon dioxide.

A

Bubble the gas through limewater (aqueous calcium hydroxide).
If the solution turns cloudy then there is carbon dioxide present.

(The cloudiness is caused by the formation of calcium carbonate.)

24
Q

What ions suggest that the

salt is soluble in water?

A

If the salt contains any of the ions then it is soluble in water.
- Sodium
- Nitrates
- Ammonium
- Potassium
- Ethanoate

If it contains chlorine then it is soluble except for silver chloride and lead chloride.
If it contains sulfate then it is soluble except for lead, barium and calcium sulfate.

25
Q

What ions suggest that the

salt isn’t soluble in water?

A

If the salt contains carbonate or hydroxide then it is insoluble in water. Except for sodium, potassium and ammonium ones.

(this abides by the SNAPE rule, always check that first)

26
Q

How would you make an

insoluble salt?

A

A precipitation reaction.

This involves the reaction of two soluble salts to form an insoluble salt (precipitate).

27
Q

Describe a

precipitation reaction to make lead chloride.

(8 steps)

A
  1. Dissolve one spatula of lead nitrate in some deionised water in a test tube. Shake the test tube thoroughly to ensure that all the lead nitrate has dissolved.
  2. Repeat step 1 in a different test tube, using on spatula of sodium chloride instead.
  3. Tip the solutions into a small beaker and stir thoroughly to make sure the solutions are fully mixed. The lead chloride should precipitate out.
  4. Fold a piece of filter paper and place it into a filter funnel. Place the funnel into the top of a conical flask.
  5. Pour the contents of the beaker into the middle of the filter paper. Make sure that the solution doesn’t go above the top of the filter paper - otherwise some of the solid lead chloride could end up in the filtrate.
  6. Swill out the beaker with more deionised water, and tip this into the filter paper (in order to ensure that all of the precipitate is taken from the beaker).
  7. Rinse the contents of the filter paper with deionisied water to make sure that all the sodium nitrate has been washed away.
  8. Leave the lead chloride to dry.
28
Q

What are the

two methods of making a soluble salt?

A
  1. Reacting an acid with a metal or insoluble base.
  2. Reacting an acid with an alkali.

insoluble bases include metal oxide, metal hydroxide and metal carbonate

29
Q

Describe how you would make

copper sulfate.

(by reacting an acid with an insoluble salt) (6 steps)

A
  1. Put some sulfuric acid into a beaker. Gently warm this dilute acid by placing the beaker in a water bath (this will speed up the reaction). Carry out this step in a fume cupboard to avoid releasing acid fumes into the room.
  2. Keep adding copper oxide and stirring until it is in excess (the oxide will sink to the bottom and won’t react).
  3. Filter out the excess copper oxide to separate it from the copper sulfate solution using filter paper and a filter funnel.
  4. At the end of the filtration, you’ll be left with a solution of copper sulfate salt dissolved in water. This can be converted into pure, solid crystals of copper sulfate using crystallisation.
  5. To do this, heat the salt solution using a bunsen burner and an evaporating dish in order to concentrate the solution.
  6. When you have reached the point of crystallisation, stop heating and leave the solution to cool. Blue crystals of hydrated copper sulfate should form, which can be filtered out of the solution and then dried.
30
Q

Describe an

acid-alkali titration reaction.

(6 steps)

A
  1. Measure out the set amount of acid into a concal flask using a pipette. Add a few drops of indicator, then place the flask on a white tile.
  2. Fill a burette with alkali and record the volume.
  3. Slowly add the alkali to the acid, gently swirling the flask between additions, until the indicator changes colour (indicating that the acid has been neutralised).
  4. Read the final volume of alkali left in the burette and calculate the amount of alkali that was needed to neutralise the acid.
  5. Carry out the reaction using exactly the same volumes of alkali and acid (but no indicator so that the salt is not contaminated).
  6. The solution that remains when the reaction is complete contains only salt and water. Crystallisation can be carried out to obtain a pure, dry salt.
31
Q

Define

electrolyte.

A

the liquid that conducts electricity in electrolysis

this contains free ions - either because it is molten or a dissolved ionic compound

32
Q

Define

electrolysis.

A

the process of breaking down a substance using electricity

33
Q

Define

electrode.

A

a solid that conducts electricity and is submerged in the electrolyte

34
Q

What type of reaction is

electrolysis?

and why?

A

Electrolysis is a redox reaction because both reduction and oxidation occurs. Reduction is occuring at the cathode as the cations are gaining electrons and oxidation is occuring at the anode as anions are losing electrons.

35
Q

What are

binary compounds?

A

ionic compounds containing two elements which are ions

(a positive metal ion and a negative non-metal ion)

36
Q

What are the

products of electrolysis of molten binary compounds?

A

the neutral metal and non-metal elements

the metal ions move to the cathode and gain electrons to become neutral
the non-metal ions move to the anode and lose electrons to become neutral

37
Q
A

Please - Potassium
Stop - Sodium
Lazily - Lithium
Calling - Calcium
Me - Magnesium
A - Aluminium
Careless - (Carbon)
Zebra - Zinc
Instead - Iron
Now - Nickel
Try - Tin
Learning - Lead
How - (Hydrogen)
Copper - Copper
May - Mercury
Save - Silver
Gold - Gold
Perfectly - Platinum

38
Q

What occurs at the

cathode during the electrolysis of aqueous solutions?

A

Both the metal ions and hydrogen ions are attracted.

If the metal is more reactive than hydrogen, the metal ions will stay in solution and hydrogen gas will be produced.

If the metal is less reactive than hydrogen, a solid layer of pure metal will be produced instead.

This is because the more reactive an element, the more likely it is to stay as ions.

39
Q

What occurs at the

anode during the electrolysis of aqueous solutions?

A

Both the non-metal ions and hydroxide ions are attracted.

If halide ions are present then the respective metals will be formed.

If no halide is present, then the hydroxide ions are discharged and oxygen gas and water will be formed.

halides:
Cl- > Cl2
Br- > Br2
I- > I2

40
Q

How would you set up the

electrolysis of an aqueous solution?

A
  1. Get two inert electrodes (e.g. platinum or carbon) and clean their surfaces using a piece of emery paper (or sandpaper). Be careful not to touch the surfaces of the metals with your hands as you could transfer grease back onto the electrodes.
  2. Place both electrodes into a beaker filled with electrolyte and place them so they are inside inerted test tubes containing the aqueous solution.
  3. Connect the electrodes to a power supply using crocodile clips and wires.

As the reaction progresses, gases may form and collect inside the test tubes.

41
Q

Why is the result different when electrolysing

copper sulfate using non-inert (copper) electrodes?

A

As the reaction continues, the mass of the anode will decrease and the mass of the cathode will increase. This is because the copper is transferred from the anode to the cathode

The electrical supply removes electrons from copper atoms at the anode and donates electrons at the cathode to nearby copper ions (making copper atoms).

This reaction is quite slow but if you increase the current, you will increase the rate of electrolysis.

42
Q

How can electrolysis be used to

purify copper?

(intro + 3 steps)

A

When copper is purified using electrolysis, the anode starts off as a big lump of impure copper and the cathode starts off as a thin piece of pure copper. The electrolyste is copper sulfate solution.
1. Copper in the impure copper anode forms copper ions which dissolve into the electrolyte.
2. The copper ions move to the pure copper cathode and react to form a layer of pure copper.
3. Any impurities from the impure copper anode sink to the bottom of the cell, forming a sludge.

43
Q

Describe how you would perform

electrolysis of a molten ionic substance.

(4 steps)

A
  1. Put your solid ionic substance in a crucible.
  2. In a fume cupboard, heat the crucible with a bunsen burner until the solid melts.
  3. Once the solid is molten, put two clean, inert electrodes into the electrolyte.
  4. Then, connect the electrodes to a power supply using wires and clips.

Step 2 should be done in a fume cupboard to avoid releasing toxic fumes.

GCSE Edexcel Chemistry (19 decks)

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