ib chem paper 3

he heats the solution to convert it to a suspension of copper oxide. describe how to optain pure dry solid produdct (2)

• filter paper to separate

• then rinse with water for purity and let dry

use the combustion equation to suggest why x acts as a high explosive

• lots of gases are released produced in the reaction

state 3 ways of monitoring conc changes in a reaction

• Measuring mass changes (open system)

• Monitoring color changes (colorimeter)

• chang in volume of gas

mathematical realtionship between wavenumber and wavelength

inverse relationship

state two reasons for using analytical chemistry technique

1. To determine the structure of substances.

2. To identify chemical compounds and their concentrations.

A student wished to determine the concentration of a solution of sodium hydroxide by titrating it against a 0.100moldm−3 aqueous solution of hydrochloric acid. 4.00g of sodium hydroxide pellets were used to make 1.00dm3 aqueous solution.

(a) Outline, giving your reasons, how you would carefully prepare the 1.00dm3 aqueous solution from the 4.00g sodium hydroxide pellets (3)

• use volumetric flask and mix the solution

• mix pellets in beaker with distilled water

• safety: let the solution cool because NaOH reacts with water exothermically

The student added the acid too quickly. Outline, giving your reason, how this could have affected the calculated concentration. (2)

• equivalence point been exceeded

• thus the concentration increases

Suggest why, despite preparing the solution and performing the titrations very carefully, widely different results were obtained

• usually impurities work unless the question says its pure

• temperature changes during experiment

• incorrect method of calculation

what is a concordant titre

Two or more final burette readings (titre = vol delivered from burette) that are within ±0.10 cm³ of each other. for more precision, only include concordants in the average / repeat until u get 2 concords

how to tell if a compound is aqueous in water adn will dissociate

• Is it ionic (metal + nonmetal or polyatomic ion)?

  • Yes → go to 2

  • No → likely molecular → doesn’t dissociate fully

• Does it contain Group 1 metal, NH₄⁺, NO₃⁻, or CH₃COO⁻?

  • Yes → soluble → dissociates

  • No → check solubility rules

Delayed or inconsistent mixing of the solution after adding NaOH. how to improve

USE MAGNETIC STIRRER to ensure consistent

improve a titration

• use a pH meter

• calibrate equipment before use IWTH 2 BUFFER solutions

systematic error in titration (3)

• Using wrong concentration of standard solution

• Miscalibrated equipment

• not rinsing the pipette with solution

empirical formula apparatus and method

app:

• crucible with lid

• mg ribbon (if MgO)

• clay triange + bunsen burner

• balance

Method:

• weigh empty crucible and lid before rewighing after adding the mg ribbon

• strongly heat with lid open

• cool and then weigh crucible lid and final product

why is the lid left open in the crucible

prevent vapor/ssmoke from escaping and affecting mass, sometimes to let O2 in

suggest a modification to ensure complete crucible empirical formula reuslt / how can u check all of it reacted

heat crucible until mass becomes constant (check by reheating)

butane molar mass lighter experiment method

• Weigh the lighter before release

• Collect butane gas by displacing water into an inverted measuring cylinder

• Weigh the lighter again → mass of butane lost

• Record volume of butane collected

• Measure atmospheric pressure and room temperature

butane gass lighter - suggest why molar mass calc is lower than expected

Some gas escaped during transfer, or volume measured was too high due to trapped air.

modification to butane gas lighter

use gas syringe instead of water displacement to avoid confounding water vapor error

why temp and presure be recorded in butane gas lighter

pv = nrt

suggest why water displacement itroduces error in butane lighter

Butane is slightly soluble in water; volume collected may be less than actual.

suggest a reason for vairbaility in stopwatch with iodine clock exp/rate

human reaction time

suggest a way to improve the accuracy of rate measurement.

• use light sensor or colorimeter instead of visual detection

• KEEP ALL VARIABLES CONSTANT (req)

suggest modification to investigate effect of another variable

Keep og constant, react under changing new vairbale

suggest a way to improve the gas mass experiment with a beaker

use a sealed conical flask with a tube connected to a gas syringe instead of open beaker

voltaic cell apparatus

• Two beakers (for two half-cells)

• Metal strips (e.g., Zn and Cu electrodes)

• Solutions of each metal’s ions (e.g., ZnSO₄ and CuSO₄ same conc)

• Salt bridge (e.g., filter paper soaked in KNO₃ or NaNO₃)

• Voltmeter with wires & crocodile clips

suggest reason the voltage is lower than expected in a voltaic cell

Solutions not equal concentration, or the salt bridge ions were not mobile enough. it must touch both solutions

why can but-2-ene show cistrans isomerism but not butane

the double bond restricts rotation, and each carbon of the C=C has two different groups attached.
Butane cannot, because single bonds allow rotation, so there’s no fixed geometry to create cis–trans isomers.

why are universal indicators not suitable for titrations

gradual color change over a wide pH range, hard to tell equivalence point