Chapter 13 - Volumetric Analysis : Acid-Base

Question 1

Solution

Answer 1

A completely perfect mixture of a solute and a solvent. In a solution, the particles of the solute are uniformly distributed throughout the solvent, i.e the mixture is homologous

Question 2

Concentration

Answer 2

The amount of solute that is dissolved in a given volume of the solution

Question 3

What are the three main ways of expressing the concentration of a solution?

Answer 3

% w/w (weight per weight)

% w/v (weight per volume)

% v/v (volume per volume)

Question 4

How many cm³ are there in a litre?

Answer 4

1000cm³

Question 5

How many milligrams are in a gram?

Answer 5

1000mg

Question 6

1 ppm equals…

Answer 6

1 mg

Question 7

Molarity

Answer 7

The number of moles of solute per litre of solution (M or mol/L)

Question 8

1M (one molar) solution

Answer 8

One that contains one mole of the solute dissolved in one litre of solution

Question 9

How do you calculate the number of moles when given the volume and molarity of the solution?

Answer 9

volume (cm³) x molarity

1000

Question 10

Standard solution

Answer 10

A solution of precisely known concentration

Question 11

Primary standard

Answer 11

A substance that can be obtained in a stable, pure and soluble solid form so that it can be weighed out and dissolved in water to give a solution of accurately known concentration

Question 12

Give an example of a primary standard

Answer 12

Anhydrous sodium carbonate (NaCO)

Question 13

Titration

Answer 13

A lab procedure where a measured volume of one solution is added to a known volume of another solution until the reaction is complete

Question 14

What do you rinse a volumetric flask with?

Answer 14

Deionised water only

Question 15

How do you mix the contents of a volumetric flask?

Answer 15

Stopper the flask and invert 20 times to ensure a homogeneous solution

Question 16

What do you rinse a burette with?

Answer 16

First with deionised water (to remove impurities) then with the solution it is to contain (to remove the water which would dilute the solution)

Question 17

What do you rinse a pipette with?

Answer 17

Rinse with deionised water then with the solution it is to contain

Question 18

Why do you not pipette directly from the volumetric flask?

Answer 18

You take the solution from a beaker instead as impurities on the pipette night contaminate the solution in the volumetric flask, or water droplets might dilute it

Question 19

How do you rinse a conical flask?

Answer 19

With deionised water only

Question 20

Why do you not rinse a conical flask with the solution it is to contain?

Answer 20

Remaining drops will mean the total volume of the reagent in the flask will be unknown

Question 21

How do you rinse a graduates cylinder?

Answer 21

With deionised water only

Question 22

Why is the graduates cylinder not very accurate?

Answer 22

The neck is too wide

Question 23

What indicator is used in the titration of a standard sodium carbonate solution and hydrochloric acid solution? What is the colour change?

Answer 23

Methyl orange Yellow to pink

Question 24

How do you calculate the concentration of a solution of unknown concentration from titration data?

Answer 24

Mₐ x Vₐ M_b x V_b

———– = ————

Nₐ N_b

Question 25

Standardised solution

Answer 25

Solution whose concentration was found in a previous experiment/titration

Question 26

What indicator is used in the titration of sodium hydroxide solution and hydrochloric acid solution? What is the colour change?

Answer 26

Methyl orange Yellow to pink

Question 27

Why does the vinegar have to be diluted before use in the titration?

Answer 27

The concentration of the vinegar would be too strong compared with the standardised NaOH so it must be diluted first. If it wasn’t diluted, only a few drops of the vinegar would neutralise the base, so it would not give an accurate titration

Question 28

What is the equation for the titration of a standard solution of sodium carbonate and a hydrochloric acid solution?

Answer 28

Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂

Question 29

What is the equation for the titration of a solution of sodium hydroxide and a hydrochloric acid solution?

Answer 29

HCl + NaOH → NaCl + H₂O

Question 30

What is the equation for the titration of ethanoic acid and sodium hydroxide?

Answer 30

CH₃COOH + NaOH → CH₃COONa + H₂O

Question 31

What is the equation for the titration of hydrated sodium carbonate solution and hydrochloric acid?

Answer 31

Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂

Question 32

What indicator is used in the titration of hydrated sodium carbonate solution and hydrochloric acid? What is the colour change observed?

Answer 32

Methyl orange Yellow to pink

Question 33

How do you calculate the percentage of water crystallisation?

Answer 33

mass of water

———————————– x 100

mass of hydrated crystal

Question 34

What equation do we use to find unknown dilutions/concentrations?

Answer 34

Vol_dil* x M_dil Vol_conc* x M_conc

—————– = ———————

1000 1000

*in cm³

Question 35

How do you find the percentage purity of a chemical?

Answer 35

mass of pure substance

————————————– x 100

mass of impure substance