14. Experimental techniques and chemical analysis

Question 1

Describe a solvent, solute, solution, saturated solution, residue, filtrate

Answer 1

(a) solvent- substance that dissolves a solute

(b) solute- substance that is dissolved in a solvent

(c) solution- mixture of one or more solutes dissolved in a solvent

(d) saturated solution- solution containing the maximum concentration of a solute
dissolved in the solvent at a specified
temperature

(e) residue- substance that remains after evaporation, distillation, filtration or any similar process

(f) filtrate- liquid or solution that has passed through a filter

Question 2

Name appropriate apparatus for the measurement of time, temperature, mass and volume

Answer 2

(a) stopwatches

(b) thermometers

(c) balances

(d) burettes

(e) volumetric pipettes

(f) measuring cylinders

(g) gas syringes

Question 3

acid–base titration

how to identify the end-point of a titration using an indicator

Answer 3

(a) burette- up- to keep adding
(b) volumetric pipette- conical flask
(c) suitable indicator

Question 4

Paper chromatography

Answer 4

used to separate mixtures of soluble colourless substances, using a suitable solvent and a locating agent

R = distance travelled by substance/ distance travelled by solvent

Question 5

Describe and explain methods of separation and purification

Answer 5

(a) a suitable solvent
(b) filtration
(c) crystallisation
(d) simple distillation
(e) fractional distillation

Question 6

gas test and flame test

Answer 6

(a) ammonia, NH3- turns damp red litmus paper

(b) carbon dioxide, CO2- turns limewater milky

(c) chlorine, Cl2- bleaches damp litmus paper
(d) hydrogen, H2- pops with a lighted splint

(e) oxygen, O2- relights a glowing splint

(f) sulfur dioxide, SO2- turns acidified aqueous potassium manganate(VII) from purple to colourless

(a) lithium, Li+- red
(b) sodium, Na+- yellow
(c) potassium, K+- lilac
(d) calcium, Ca2+- orange-red
(e) barium, Ba2+- light green
(f) copper(II), Cu2+- blue-green

Question 7

Test for anions

Answer 7

carbonate, CO32− add dilute acid, then test for carbon dioxide gas- effervescence, carbon dioxide produced

chloride, Cl − [in solution]- acidify with dilute nitric acid, then add aqueous silver nitrate- white ppt

bromide, Br − [in solution]- acidify with dilute nitric acid, then add aqueous silver nitrate- cream ppt

iodide, I− [in solution]- acidify with dilute nitric acid, then add aqueous silver nitrate- yellow ppt

nitrate, NO3– [in solution]- add aqueous sodium hydroxide, then aluminium foil; warm carefully- ammonia produced

sulfate, SO42− [in solution]- acidify with dilute nitric acid, then add aqueous barium nitrate- white ppt

sulfite, SO32− add a small volume of acidified aqueous potassium manganate(VII)- the acidified aqueous
potassium manganate (VII) changes colour from purple to colourless

Question 8

Test for cations-

aqueous sodium hydroxide- aqueous ammonia

Answer 8

aluminium, Al 3+- white ppt., soluble in excess, giving a colourless solution- white ppt., insoluble in excess

ammonium, NH4+- ammonia produced on warming- -

calcium, Ca2+- white ppt., insoluble in excess- no ppt. or very slight white ppt.

chromium(III), Cr3+- green ppt., soluble in excess- green ppt., insoluble in excess

copper(II), Cu2+- light blue ppt., insoluble in excess- light blue ppt., soluble in excess, giving a dark blue solution

iron(II), Fe2+- green ppt., insoluble in excess, ppt. turns brown near surface on standing- same

iron(III), Fe3+- red-brown ppt., insoluble in excess- same

zinc, Zn2+- white ppt., soluble in excess, giving a colourless solution- same

Question 9

measuring cylinder, burette, pipette

Answer 9

burette and pipette more accurate than MC

burette compared to pipette
burettes can measure variable volumes
or volumetric pipettes not available in required volumes / measure fixed volumes

pipette compared to MC
advantage: (more) accurate
disadvantage: slower / takes longer- measuring time taken is less accurate