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Chemistry > Topic 3: chemical changes > Flashcards

Topic 3: chemical changes Flashcards

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1
Q

What do acids produce in aqueous solutions?

A

Acids produce H+ ions in aqueous solutions (hydrogen ions)

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2
Q

What do alkalis produce in aqueous solutions?

A

Alkalis produce OH - ions in aqueous solutions (hydroxide ions)

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3
Q

PH 7

A

NEUTRAL solution

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4
Q

Below ph7

A

acidic solution

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5
Q

Above pH7

A

alkaline solution

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6
Q

effect of acids and alkalis on phenolphthalein

A

Phenolphthalein
○ Alkaline = pink
○ Acidic = colourless

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7
Q

Recall the effect of acids and alkalis on litmus

A

Litmus
○ Litmus solution
■ Alkaline = blue
■ Acidic = red
○ Litmus paper
■ Blue litmus paper goes red in acidic & stays blue in alkaline
■ Red litmus paper goes blue in alkaline & stays red in acidic

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8
Q

Recall the effect of acids and alkalis on methyl orange

A

● Methyl orange
○ Alkaline = yellow
○ Acidic = red

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9
Q

Describe the pH of a acidic solution

A

When an acid is in solution, a higher concentration of H+ ions means that the solution is more acidic, thus having a lower pH

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10
Q

Describe the pH of a alkaline solution

A

When an alkali is in a solution, a higher concentration of OH- ions means that the solution is more alkaline, thus having a higher pH

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11
Q

What happens to the pH of a solution as the hydrogen ion concentration increases by a factor of 10?

A

As the pH decreases by one unit, the H+ concentration of the solution increases by a factor of 10

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12
Q

Core Practical: Investigate the change in pH on adding powdered calcium hydroxide or calcium oxide to a fixed volume of dilute hydrochloric acid
Method

A

● method:
○ add dilute HCl to the beaker and measure pH
○ add weighed mass of calcium hydroxide and stir then record pH
○ keep adding weighed masses of calcium hydroxide until there is no more
change to the pH

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13
Q

Core Practical: Investigate the change in pH on adding powdered calcium hydroxide or calcium oxide to a fixed volume of dilute hydrochloric acid
Analysis

A

● analysis:
○ draw a line graph with mass added on the horizontal axis and with pH on
the vertical axis
○ draw a line of best fit (remember to ignore any anomalies)

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14
Q

Difference between strong/weak and concentrated/dilute

A

Strong and weak is NOT the same as concentrated and dilute – the latter refers to the amount of substance whereas, the former refers the H+ ion conc. in aq.solutions

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15
Q

Concentrated

A

▪ Concentrated = larger amount of substance in a given volume of a solution

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16
Q

Dilute

A

Dilute = lesser amount of substance in a given volume of a solution

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17
Q

Strong acid

A

Strong acid = fully dissociates in aqueous solution (dissociation is where an acid breaks down to release H+ ions in solution)
o e.g. hydrochloric, nitric and sulfuric acids

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18
Q

Weak acid

A

Weak acid = partially dissociates in aqueous solution

o e.g. ethanoic, citric and carbonic acids

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19
Q

Relationship between strength of acids and ions

A

Stronger an acid, greater the dissociation, the more H+ ions released, the lower the pH (for a given conc. of aq. solutions)

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20
Q

What is a base?

A
  • a base is any substance that reacts with an acid to form a salt and water only
  • acid + base → salt + water
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21
Q

What type of base is an alkali?

A

alkalis are soluble bases

● Examples of alkalis are soluble metal hydroxides

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22
Q

general reactions of aqueous solutions of acids with:

metals to produce salts

A

acid + metal → salt + hydrogen gas (H2)

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23
Q

Explain the general reactions of aqueous solutions of acids with:
metals oxides to produce salts

A

acid + metal oxide → salt + water

● Metal oxides are normally bases (because insoluble

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24
Q

Explain the general reactions of aqueous solutions of acids with:
metal hydroxides to produce salts

A

acid + metal hydroxide → salt + water

● Metal hydroxides are bases/alkalis if insoluble/soluble

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25
Q

Explain the general reactions of aqueous solutions of acids with:
metal carbonates to produce salts

A

acid + metal carbonate → salt + water + carbon dioxide (CO2)

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26
Q

How to name the salts?

A 
● To name salts:
○ first part is simply the name of the metal in the oxide/hydroxide/carbonate
○ second part comes from the acid:
■ hydrochloric acid (HCl)- chloride
■ nitric acid (HNO3)- nitrate
■ sulfuric acid (H2SO4)- sulfate
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27
Q

Describe the chemical test for:

hydrogen (using limewater)

A

● Test for hydrogen:
o Use a burning splint held at the open end of a test tube of the gas
▪ Creates a ‘squeaky pop’ sound

28
Q 
Describe the chemical test for:
carbon dioxide (using limewater)
A

Test for carbon dioxide:

o Bubble the gas through the limewater (calcium hydroxide solution) and it will turn milky (cloudy)

29
Q

What is a neutralisation reaction?

A

neutralisation reaction is a reaction between an acid and a base

30
Q

What is an acid-alkali neutralisation reaction?

A

-acid-alkali neutralisation is a reaction in which hydrogen
ions (H+) from the acid react with hydroxide ions (OH-) from the alkali to form water
● for any neutralisation reaction with an acid and an alkali the ionic equation is:
H+ (aq) + OH- (aq) -> H2O(l)

31
Q

Explain why, if soluble salts are prepared from an acid and an insoluble reactant: excess of the reactant is added

A

▪ Excess of the reactant is added

o this is to ensure your volume of acid reacts completely

32
Q

Explain why, if soluble salts are prepared from an acid and an insoluble reactant:
the excess reactant is removed,

A

excess reactant is removed

o this is done by filtration of the insoluble reactant and is done so that you are left with just a salt and water

33
Q

Explain why, if soluble salts are prepared from an acid and an insoluble reactant:
the solution remaining is only salt and water

A

▪ the remaining solution is only salt and water
o this is because all of your acid has fully reacted and you have filtered off your other reactant, and that the only products of your reaction are a salt and water
o if you have used a carbonate you would still only have a salt and water remaining as carbon dioxide gas would have been given off into the atmosphere

34
Q

Explain why, if soluble salts are prepared from an acid and a soluble reactant:
titration must be used

A

● Titration must be used:
○ both reactants are liquids/soluble, so if you have an excess of one you would not be able to easily remove it from your mixture of products, this means you need to measure the exact amount of volumes that react, which is easily done using a titration.

35
Q

Explain why, if soluble salts are prepared from an acid and a soluble reactant:
the acid and the soluble reactant are then mixed in the correct proportions, and the solution remaining, after reaction,
is only salt and water

A

● The exact amount of acid has thus been added to the soluble reactant, meaning that the leftover solution is only salt and water, no acid or alkali, because they have been completely neutralised

36
Q

Core practical: Investigate the preparation of pure, dry hydrated copper sulfate crystals starting from copper oxide including the use of a water bath
● method:

A

method:
○ add an excess of copper oxide (insoluble) to your acid (sulfuric acid H2SO4- as you are making copper SULFATE)
○ use a filter and filter paper to filter off any copper oxide that hasn’t
reacted (your solution should be blue as copper sulfate solution has been formed)
○ evaporate off the water by placing your final solution in a water bath

37
Q

Describe how to carry out an acid-alkali titration

A

How to carry out a titration:
1. Wash burette using the acid and then water
2. Fill burette to 100cm3 with acid with the meniscus’ base on the 100cm3 line
3. Use 25cm3 pipette to add 25cm3 of alkali into a conical flask, drawing alkali into the pipette using a pipette filler
4. Add a few drops of a suitable indicator to the conical flask (eg:
phenolphthalein which is pink when alkaline and colourless when acidic)
5. Add acid from burette to alkali until end-point is reached (as shown by indicator)
6. The titre (volume of acid needed to exactly neutralise the acid) is the
difference between the first (100cm3) and second readings on the burette)
7. Repeat the experiment to gain more precise results
8. To prepare a pure, dry salt – you warm the salt solution to evaporate the
water
9. Crystals form

38
Q

Is sodium soluble in water?

A

Yes ALL sodium is soluble in water

39
Q

Is potassium soluble in water?

A

Yes ALL potassium is soluble in water

40
Q

Is ammonium soluble in water?

A

Yes ALL ammonium is soluble in water

41
Q

Are nitrates soluble in water?

A

Yes ALL nitrates are soluble in water

42
Q

Are chlorides soluble in water?

A

Yes ALL chlorides are soluble in water EXCEPT FOR silver and lead

43
Q

Are sulfates soluble in water?

A

Yes ALL sulfates are soluble in water EXCEPT FOR lead,barium and calcium

44
Q

Are carbonates soluble in water?

A

NO ALL carbonates are insoluble EXCEPT FOR sodium, potassium,
ammonium

45
Q

Are hydroxides soluble in water?

A

NO ALL hydroxides are insoluble EXCEPT FOR sodium, potassium,
ammonium

46
Q

How would you know whether or not a precipitate will be formed when named solutions are mixed together?

A

● first, work out what the products of your reaction will be
● then, determine if any salts formed are soluble/insoluble
● any INSOLUBLE salts will form as a precipitate (as any soluble salts will remain in solution)

47
Q

Describe the method used to prepare a pure, dry sample of an insoluble
salt

A
  1. mix the two solutions needed to form the salt
  2. filter the mixture using filter paper, which the insoluble salt will be left on
  3. wash the salt using distilled water
  4. leave the salt to dry on filter paper (water will evaporate, speed this process up by drying it in an oven)
48
Q

What are electrolytes?

A

Electrolytes are ionic compounds in the molten state or
dissolved in water
● When an ionic substance is melted or dissolved, the ions are free to move about within the liquid or solution. This is called an electrolyte

49
Q

What is electrolysis?

A

● Electrolysis = process in which electrical energy, from a direct current supply decomposes electrolytes
● Passing a current through substances that are molten or solution means that the solution can be broken down into elements. This is electrolysis, and the substance being broken down is the electrolyte.

50
Q

Explain the movement of ions during electrolysis

A

● During electrolysis, positively charged ions (cations) move to the negative
electrode (cathode), and negatively charged ions (anions) move to the positive
electrode (anode).
● Ions are discharged at the electrodes producing elements

51
Q

Explain the formation of the products in the electrolysis

A

● When you have a ionic solution (NOT a molten ionic compound), your solution will contain: the ions that make up the ionic compound, and the ions in water (OH- and H+)

52
Q

● at the anode (+):

A

● at the anode (+):
○ oxygen (from OHin water) will be produced UNLESS the ionic compound contains halide ions (Cl,Br,I-)○ if there are halide ions, the halogen will be produced instead(e.g.Cl2)

53
Q

Electrolysis of:

○ Copper chloride solution

A

Copper chloride solution
■ Cu+ ions go to cathode, Cu (s) is produced (Cu is less reactive than hydrogen)
■ Cl ions go to anode, Cl2(g) is produced (Cl- are halide ions)

54
Q

Electrolysis of:

Sodium chloride solution

A

Sodium chloride solution
■ H+ions go to cathode, H2(g) is produced (Na is more reactive than
hydrogen)
■ Cl ions go to anode, Cl2(g) is produced (Cl- are halide ions)

55
Q

Electrolysis of:

Sodium sulfate solution

A

Sodium sulfate solution
■ H+ ions go to cathode, H2 (g) is produced (Na is more reactive than hydrogen)
■ OH ions go to anode, O2(g) is produced (SO4 2- ions are not halide ions)

56
Q

Electrolysis of:

Water acidified with sulfuric acid

A

Water acidified with sulfuric acid
■ H+ to cathode, H2(g) is produced (these are the other ions present in sulfuric acid H2SO4)
■ OH to anode, O2(g) is produced (SO42- ions are not halide ions)

57
Q

Electrolysis of:

Molten lead bromide

A

Molten lead bromide
■ Pb2+ to cathode, Pb (s) is produced (not in solution so these are
the only + ions present)
■ Br toanode, Br2(l) is produced (not in solution so these are theonly - ions present)

58
Q

Predict the products of electrolysis of other binary, ionic compounds in the molten state

A

if ionic compounds are molten it is much more simple to predict the products of electrolysis as there are no ions present except those in the ionic compound:
● identify which ions there are within the ionic compound
● the + ions will go to the cathode
● the - ions will go to the anode

59
Q

Oxidation

A

Oxidation Is Loss (of electrons)

60
Q

Reduction

A

Reduction Is Gain (of electrons)

61
Q

Where does oxidation occur?

A

ANODE – loss of electrons, oxidation of anions (-) (they would have to lose
electrons to have a neutral charge)

62
Q

Where does reduction occur?

A

CATHODE – gain of electrons, reduction of cations (+) (they would have to gain
electrons to get a neutral charge)

63
Q

Explain the formation of the products in the electrolysis of copper sulfate solution, using copper electrodes, and how this electrolysis can be used to purify copper:
Set up

A

set up:
○ anode is made of impure copper (that you are purifying)
○ cathode is made of pure copper
○ the solution is copper sulfate

64
Q

Explain the formation of the products in the electrolysis of copper sulfate solution, using copper electrodes, and how this electrolysis can be used to purify copper:
What happens

A

what happens:
○ Cu2+ ions from the anode move to the cathode, where they gain electrons
and are discharged as pure copper
○ impurities form as sludge below the anode
● the cathode will increase in mass as it gains pure copper, whilst the anode will
lose mass as copper ions are lost (they replace the ones from the CuSO4 solution
that go to the cathode) and so are impurities

65
Q

Core practical: Investigate the electrolysis of copper sulfate solution with inert electrodes

A

with inert electrodes:
● at the cathode Cu (s) is produced (Cu is less reactive than hydrogen)
● at the anode O2 is produced (SO42- ions are not halide ions)
● this leaves H+ and SO42- ions in the solution, which will react to form H2SO4- sulfuric acid

66
Q

Core practical: Investigate the electrolysis of copper sulfate solution with copper electrodes

A

with copper electrodes:
● same as experiment in 3.30, where the Cu2+ ions deposited as Cu at the cathode from the solution are replaced by Cu2+ ions from the anode, meaning the
concentration of Cu2+ ions in the solution remains constant

Chemistry (10 decks)

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