Titrations and analysis

Question 1

What is the formula to calculate moles?

Answer 1

Moles = Concentration x volume (dm³)

Volume should be in cubic decimeters (dm³) for this formula.

Question 2

How do you convert volume from dm³ to cm³?

Answer 2

Divide by 1000

Question 3

What is the formula to convert concentration from mol/dm³ to g/dm³?

Answer 3

Multiply by the Mr

Question 4

What is the formula to calculate moles from mass?

Answer 4

Moles = mass / Mr

Question 5

What are the three main steps in concentration calculations?

Answer 5

• Find the moles of the substance
• Look at the ratios in the equation
• Unmole it by dividing by concentration or volume

Question 6

What is a titration used for?

Answer 6

To find out how much acid is needed to neutralise a volume of alkali or vice versa

Question 7

What is required to find the concentration of an unknown acid or alkali in a titration?

Answer 7

You must know the concentration of the other substance

Question 8

What type of reactions do titrations typically involve?

Answer 8

Reactions between strong acids and strong bases

Question 9

What is the first step in the titration method?

Answer 9

Wash out the burette and the pipette with the solutions

Question 10

What should you do after placing acid or alkali in the burette?

Answer 10

Fill the burette until the acid is in line with 0 cm

Question 11

How do you measure a known volume of alkali or acid for titration?

Answer 11

Use a volumetric pipette

Question 12

What indicator is mentioned for use in titrations?

Answer 12

Methyl Orange

Question 13

Why is a white tile used during a titration?

Answer 13

To help see the colour change better

Question 14

What should you do as you approach the end point of a titration?

Answer 14

Add the contents of the burette drop by drop

Question 15

What should you record from the burette during a titration?

Answer 15

Initial and final volume readings

Take all readings from the bottom of the meniscus.

Question 16

What is the purpose of performing a rough titration?

Answer 16

To get an approximate idea of when the end point is.

Question 17

How do you obtain concordant results in titration?

Answer 17

Repeat an accurate titration until you get concordant results.

Question 18

What should you do with your results to determine the final volume needed for neutralization?

Answer 18

Take the mean average of your results, excluding any anomalies.

Question 19

What is the function of a burette in titration?

Answer 19

Dispense a variable amount of acid/alkali and accurately measure how much is dispensed.

Question 20

What is the role of a volumetric pipette in titration?

Answer 20

Measure a fixed portion of alkali or acid added to the conical flask.

Question 21

What is the purpose of the conical flask in a titration?

Answer 21

Hold the solution from the pipette and the indicator.

Question 22

Why is a white tile used during titration?

Answer 22

To allow easy detection of color change.

Question 23

What color does methyl orange turn in alkali?

Answer 23

Yellow.

Question 24

What color does phenolphthalein turn in alkali?

Answer 24

Pink.

Question 25

Why can’t universal indicator be used in titration?

Answer 25

The color change is too gradual/not sharp.

Question 26

What is the uncertainty for a single measurement?

Answer 26

+ or - half the smallest scale of division.

Question 27

How is uncertainty represented for a range of measurements?

Answer 27

+ or - the range.

Question 28

How can uncertainties be represented on graphs?

Answer 28

By plotting vertical lines joining repeat readings for each independent variable value.

Question 29

What happens when you hold a lit splint to hydrogen?

Answer 29

It burns with a squeaky pop.

Question 30

What occurs when you hold a glowing splint in oxygen?

Answer 30

It relights with a glowing splint.

Question 31

What happens when you bubble carbon dioxide through limewater?

Answer 31

A white precipitate forms

This is a test for the presence of carbon dioxide.

Question 32

How can you test for chlorine gas?

Answer 32

Hold damp litmus paper over the sample; it will bleach the litmus paper white

This indicates the presence of chlorine.

Question 33

What is the first step in conducting a flame test?

Answer 33

Clean a nichrome wire in dilute HCl and hold it over a Bunsen burner until it burns without colour

This ensures no contamination affects the test results.

Question 34

What color flame does lithium ions produce in a flame test?

Answer 34

Crimson flame

This is a characteristic color for lithium ions.

Question 35

What color flame does sodium ions produce in a flame test?

Answer 35

Yellow flame

This is a distinctive color for sodium ions.

Question 36

What color flame does potassium ions produce in a flame test?

Answer 36

Lilac flame

This is the specific color associated with potassium ions.

Question 37

What color flame does calcium ions produce in a flame test?

Answer 37

Orange-red flame

This is the unique flame color for calcium ions.

Question 38

What color flame does copper ions produce in a flame test?

Answer 38

Green flame

This indicates the presence of copper ions.

Question 39

What can affect the visibility of flame test colors?

Answer 39

Mixture of ions

Some flame colors may be hidden by others if multiple ions are present.

Question 40

What is the procedure when sodium hydroxide (NaOH) is added to a solution containing unknown ions?

Answer 40

Add a few drops of NaOH and record the color of the precipitate

This helps identify the positive ions present in the solution.

Question 41

What color precipitate do iron (II) ions form when treated with NaOH?

Answer 41

Green precipitate

This indicates the presence of iron (II) ions.

Question 42

What color precipitate do iron (III) ions form when treated with NaOH?

Answer 42

Brown precipitate

This is a characteristic result for iron (III) ions.

Question 43

What color precipitate do copper (II) ions form when treated with NaOH?

Answer 43

Blue precipitate

This indicates the presence of copper (II) ions.

Question 44

What happens to the precipitate formed by aluminum ions when excess NaOH is added?

Answer 44

White precipitate dissolves to form a colorless solution

This behavior helps differentiate aluminum ions from others.

Question 45

What color precipitate do calcium ions form when treated with NaOH?

Answer 45

White precipitate which persists in excess NaOH

This indicates the presence of calcium ions.

Question 46

What color precipitate do magnesium ions form when treated with NaOH?

Answer 46

White precipitate which persists in excess NaOH

This helps confirm the presence of magnesium ions.

Question 47

What is the method to test for carbonates?

Answer 47

Add dilute acid (e.g., HCl) to the sample and bubble the products into limewater

This test indicates the presence of carbonates if a white precipitate forms in limewater.

Question 48

What occurs when carbonate ions (CO3^2-) are treated with dilute acid?

Answer 48

Effervescence occurs and a white precipitate forms when bubbled through limewater.

This is due to the release of carbon dioxide gas.

Question 49

What is the chemical reaction for sodium carbonate reacting with hydrochloric acid?

Answer 49

Sodium Carbonate + Hydrochloric acid → sodium chloride + Water + Carbon Dioxide

This reaction illustrates the formation of products from carbonate ions.

Question 50

How can sulfate ions (SO4^2-) be detected?

Answer 50

By adding HCl or nitric acid followed by barium chloride solution, resulting in a white precipitate.

A positive result confirms the presence of sulfate ions.

Question 51

What is the procedure to test for halides?

Answer 51

Add dilute nitric acid followed by silver nitrate solution.

This helps to identify chloride, bromide, and iodide ions based on the color of the precipitate.

Question 52

What color precipitate forms for chloride ions in the halide test?

Answer 52

White precipitate forms.

This indicates the presence of chloride ions.

Question 53

What color precipitate indicates the presence of bromide ions?

Answer 53

Cream precipitate forms.

This is a specific indicator for bromide ions.

Question 54

What color precipitate indicates the presence of iodide ions?

Answer 54

Yellow precipitate forms.

This is a specific indicator for iodide ions.

Question 55

Why is an acid added before testing for halides?

Answer 55

To remove impurities such as carbonates by reacting with them.

This ensures accurate test results.

Question 56

What is a critical consideration when selecting an acid for halide tests?

Answer 56

The acid used should not contain chloride ions, as it would interfere with the results.

Using hydrochloric acid would cause a false positive for chloride ions.

Question 57

What must be remembered when forming ionic equations?

Answer 57

Ions can only be split up if they are aqueous.

This is important for correctly representing the reactions in ionic form.

Question 58

What are the pros of using instrumental methods for detection?

Answer 58

Very accurate, sensitive, and rapid.

These advantages make instrumental methods favorable for analysis.

Question 59

What are the cons of using instrumental methods?

Answer 59

Expensive, can only compare to known substances, requires specialised training.

These limitations can restrict the use of instrumental methods.

Question 60

What is an example of an instrumental method used for analysis?

Answer 60

Flame emission spectroscopy.

This method analyzes metal ions in solutions using a flame photometer.

Question 61

How does flame emission spectroscopy work?

Answer 61

The sample is put into a flame, and the light emitted is passed through a spectroscope to produce a line spectrum diagram.

This spectrum can be compared to known diagrams for element identification.