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Chemistry 🧬 > Chemical Changes > Flashcards

Chemical Changes Flashcards

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1
Q

Do acids contain hydrogen ions or hydroxide ions?

A

Hydrogen

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2
Q

Do alkalis contain hydrogen ions or hydroxide ions?

A

Hydroxide

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3
Q

What colour does litmus turn in acidic solutions?

A

Red

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4
Q

What colour does litmus turn in alkaline solutions?

A

Blue

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5
Q

What colour does phenolphthalein turn in acidic solution?

A

Colourless

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6
Q

What colour does phenolphthalein turn in alkaline solution?

A

Pink

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7
Q

What colour does methyl orange turn in acidic solutions?

A

Red

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8
Q

What colour does methyl orange turn in alkaline solutions?

A

Yellow

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9
Q

Metal + Acid >

A

Salt + Hydrogen

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10
Q

Metal oxide + Acid >

A

Salt + Water

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11
Q

Metal hydroxide + Acid >

A

Salt + Water

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12
Q

Metal carbonate + Acid >

A

Salt + Water + Carbon dioxide

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13
Q

What is a titre?

A

The volume of acid added to exactly neutralise the alkali

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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
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15
Q

What are concordant titres?

A

Titres that are identical to each other, or very close together (usually within 0.1 cm³)

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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
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17
Q

Which ionic compounds are insoluble?

A
  • Silver chloride, lead chloride
  • Lead sulphate, barium sulphate, calcium sulphate
  • Most common hydroxides
  • Most common carbonates
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18
Q

How do you describe a strong acid?

A

If it is fully disassociated into ions in solution

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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
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20
Q

How does the concentration of hydroxide ions affect the pH?

A

The higher the concentration of hydroxide ions, the higher the pH

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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
Q

What is the chemical test for hydrogen?

A

A lit splint ignites hydrogen with a squeaky pop

26
Q

What is the chemical test for carbon dioxide?

A

Turns limewater milky or cloudy white

27
Q

What is neutralisation?

A

A reaction between an acid and a base

28
Q

What happens in an acid-alkali neutralisation?

A

Hydrogen ions (from acid) react with hydroxide ions (from alkali) to form water

29
Q

How do you investigate the change in pH when calcium hydroxide is added to hydrochloric acid?

A
  • 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
Q

How do you investigate the preparation of pure, dry hydrated copper sulphate crystals starting from copper oxide?

A
  • 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
Q

How do you name salts?

A
  • 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
Q

What are the main steps to make a soluble salt from a soluble base?

A
33
Q

Why do you add excess of the solid reactant when making a soluble salt with an insoluble reactant?

A

To ensure all of the acid has reacted

34
Q

Why and how is the excess reactant removed when making a soluble salt with an insoluble reactant?

A
  • By filtration
  • It is removed to leave a pure solution of the salt
35
Q

Why is the remaining solution only salt and water when making a soluble salt with an insoluble reactant?

A

Because all the acid is used up and the insoluble reactant has been removed

36
Q

Why must titration be used when making soluble salts from a soluble reactant?

A

To find the exact volume of the soluble base that reacts with the acid

37
Q

Why are the acid and the soluble reactants mixed in the correct proportions when making soluble salts from a soluble reactant?

A

To obtain a solution containing ONLY salt and water

38
Q

Why is the remaining solution only salt and water when making soluble salts from a soluble reactant?

A

The acid and base have been mixed in correct proportions so the solution so the solution is fully neutralised

39
Q

What ways can help to obtain accurate titre during a titration?

A
  • 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
Q

How can you predict if a precipitate will form when two solutions are mixed ?

A

If at least one product meets the ‘insoluble’ rule a precipitate will form

If not then non will form

41
Q

How do you make insoluble salts?

A
  • 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
Q

What is electrolysis?

A

A process in which electrical energy, from a direct current supply, decomposes an electrolyte

43
Q

What is an electrolyte?

A

An ionic compound in the molten state or dissolved in water

44
Q

What is produced at the cathode?

A
  • Hydrogen
  • Unless the compound contains ions from a metal less reactive than hydrogen, then the metal is produced
  • (Copper, silver, gold)
45
Q

What is produced at the anode?

A
  • Oxygen - from OH- ions
  • Unless the compound contains halide irons (Cl-, Br-, I-)
  • Then chlorides produce chlorine etc
46
Q

What are the steps of electrolysis of copper sulfate using copper electrodes?

A
  • 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
Q

What are anions?

A

Negatively charged ions that move to the positive electrode (anode)

48
Q

What are cations?

A

Positively charged ions that move to the negative electrode (cathode)

49
Q

What are the steps of electrolysis of copper sulphate using inert electrodes?

A
  • 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
Q

How do you use electrolysis to purify copper?

A
  • 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

Chemistry 🧬 (8 decks)

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