Chemistry IA · Structure 1 · Models of the particulate nature of matter · topic 1 of 25

Ethanol and water: do the volumes really add up? · IB Chemistry IA idea: guide, sample graph and step-by-step plan

simple kit, surprising result. nice

Mix 50 mL and 50 mL and you don't get 100 mL. Measure the shortfall, then explain it.

Difficulty●○○ Gentle
KitBasic: volumetric flask or density bottle, balance, thermometer
TimeAbout 10 hours
FitsSL and HL
  • ✓ you like a result that surprises people
  • ✓ you can be careful with a balance
  • ✓ you enjoy explaining with intermolecular forces

The big idea

← this is your RQ hook!

If liquids simply added, the volume of a mixture would equal the two volumes put together. Ethanol and water don't: hydrogen bonding between the two kinds of molecule lets them pack more closely, so the mixture is denser than the 'ideal' value. Measure density across the composition range, work out the contraction at each point, and find where it is biggest. Make the contraction itself your dependent variable, with its uncertainty, because it is a small effect and a measuring cylinder is far too coarse to see it.

Make it yours: pick one twist

Copying a classic won't show your choices. Pick one of these (or invent your own) and your IA becomes yours.

Swipe for more twists →

Use mole fraction

Plot the contraction against the mole fraction of ethanol instead of volume per cent.

→ Needs molar masses and the pure-liquid densities. The peak moves, and the explanation links to the ratio of molecules.
Change the temperature

Repeat one or two compositions at 10, 20 and 30 °C in a water bath.

→ You now vary a variable that was a control. Compare how the contraction changes with temperature.
Try another pair of liquids

Replace ethanol with propan-1-ol, or pair ethanol with a non-polar liquid. Check the hazards with your teacher first.

→ Tests whether hydrogen bonding is the cause: a mixture with no hydrogen bonding is a useful contrast.
Convert to excess volume per mole

Turn each contraction into cm³ per mole of mixture.

→ An extra processing step. You can compare with published excess molar volumes.
Compare two density methods

Measure density with a volumetric flask, then with a density bottle.

→ The evaluation compares methods using the same mixtures.
Give it a purpose

Frame it around alcoholic strength in drinks or hand sanitiser, where volume per cent and mass per cent differ.

→ A real reason for the introduction. You must link the strength scale to density.

Your Chemistry IA research question: run the check

Write your own question first. Then make sure it ticks every box:

  • Names the independent variable (ethanol content, by volume, mass or mole), its range, its step and how many values.
  • Names the dependent variable, contraction, and says which formula turns density into contraction.
  • Says which instrument measures volume and why not a measuring cylinder.
  • Says how temperature is controlled and checked, and how evaporation and water absorption are limited.
  • Says what you compare with, such as published density tables, and gives the temperature they apply to.

Get your RQ checked · S$29

The set-up

One way to set it up. Draw your own version, with your real apparatus and resolutions, for the Method section.

0.001 gethanolwater20 °Cfill exactly to the markkeep the stopper in:ethanol evaporatesthermometer: read itmass ÷ fixed volume= density

How your Chemistry IA could be laid out

The usual order for a topic like this, what each part needs to show, and roughly how much of your 3,000 words it takes. The words are all yours.

Research question and context~250
Your question; where mixing volumes matters (drinks, sanitiser, fuels); what you predict about the shape of the contraction.
Background chemistry~400
Intermolecular forces in ethanol and water; what ideal mixing would mean; how contraction is defined; a prediction of the shape of your graph.
Variablestable
Independent, dependent and controlled variables, each with how you set, measure or keep it constant, and why it matters.
Method~450
How each mixture is made (by mass or volume, and why); the flask or bottle used; how mass is read; temperature control; sources of the pure-liquid densities; repeats.
Safety, ethics, environment~70
Ethanol is highly flammable: no flames or hot plates, bottles closed, ventilation. Goggles. Use laboratory ethanol, not methylated spirit, unless your teacher agrees. Wipe up spills; dispose of dilute waste as your school directs.
Raw datatable
One clear table: composition, masses, temperature and flask volume, with units and instrument resolution.
Processing~300
Density, ideal density for each mixture, contraction and its uncertainty; one worked example for each calculation type.
Graphs and analysis~350
Contraction against composition with error bars; where it peaks; whether the ideal-mixing line is within your uncertainty anywhere.
Conclusion~350
Answer with numbers: how the contraction changes with composition, where it is largest and by how much, compared with a published density table (cite it).
Evaluation~600, the biggest part!
Weaknesses ranked by effect on the contraction (use numbers), limits of the range, and improvements linked to each.
Referencesnot counted
Every source for the pure-liquid densities and the comparison table.

What your Chemistry IA graph could look like

ideal line drawn too ✓

Made-up data, to show you the form of a strong graph, not the answer. Yours will look different. example only

0102030405060708090100012345Ethanol content / % by volume (± 0.2 %)Volume contraction / % (± 0.2)a smooth fit through the dataideal mixing: no contractionyour mixtures, with error barswhere is YOUR peak?bigger than the bars?ILLUSTRATIVE · MADE-UP DATA
  • Both axes carry units and the uncertainty of what you set or measured.
  • The ideal-mixing line is drawn too: the gap above it is the whole point.
  • Error bars on every point. Check whether the ideal line passes through any of them.
  • A fit through the middle is fine, but do not use it to claim a peak position more precisely than your spacing allows.
  • Another graph to consider: density against composition, with the ideal straight line. The contraction is the gap between them.

Which uncertainty matters most?

rank them: don't just list them

Rank by the effect on your result, the contraction (a few per cent), not on raw readings. Here is a made-up 50 % mixture. Work out yours.

Flask volume (±0.16 mL of 100 mL)4.2%Temperature (±1 °C)1.5%Ethanol evaporating (about 0.05 g)1.4%Composition (±0.1 mL on 50 mL)1.2%Balance (±0.002 g)0.1%biggest effect: discuss this first!% uncertainty in the contraction at 50 % ethanol (about 3.7 %)ILLUSTRATIVE · MADE-UP NUMBERS

Your game plan

weigh the same flask 3 times first

Tick steps off as you go. We'll remember on this device.

0 of 11 done

  1. Read and predictRead about hydrogen bonding in ethanol and water, and about excess volume. Predict the shape of the contraction against composition, and why it should be zero at both ends.
  2. Trial run (1 lesson)Make one 50 % mixture and weigh a flask of it. Repeat the weighing three times. How steady is it? Does the mass fall as ethanol evaporates?
  3. Decide composition, method and repeatsChoose at least 8 compositions, decide whether to mix by mass or volume, and how many repeats. Write the reason for each choice.
  4. Control temperatureDecide how you will hold the liquids and the flask at one temperature, and how you will read it each time.
  5. CollectRecord masses straight into your table with the balance resolution. Note anything odd, such as bubbles or drifting readings.
  6. ProcessWork out density, the ideal density from the pure liquids, and the contraction, with uncertainty. Decide how the flask volume tolerance enters.
  7. Graph and fitPlot the contraction against composition with error bars, and add the ideal-mixing line. Decide whether a fit helps.
  8. Compare with published dataFind a cited density table for ethanol and water at your temperature. How far apart are you, compared with your uncertainty?
  9. EvaluateRank the weaknesses with numbers. Which one dominates at the composition where the contraction is largest?
  10. Write, then cutWrite in the order of the layout above, within 3,000 words. Tables, calculations and graphs are not counted.
  11. Check before your teacher's draftRun the checklist, then get your RQ or draft checked. Your teacher reads one draft only.

Chemistry you'll need

Traps to avoid in this Chemistry IA

  • Using a measuring cylinder to find volumes. It cannot resolve a contraction of a few per cent.
  • Ethanol evaporating while you pour or weigh: the mass drifts down and the composition changes. Keep the flask stoppered.
  • Not controlling temperature. Density changes with it, and the effect you want is only a few per cent.
  • Assuming the stated purity of ethanol. Concentrated ethanol takes up water from the air.
  • Mixing up volume per cent, mass per cent and mole fraction when you plot or compare.
  • Taking pure-liquid densities from a table at a different temperature to your lab.
  • Reporting 'the volume decreased' with no comparison against an ideal-mixing value.

More Chemistry IA ideas like this

Make sure it's yours

This guide shows how a topic like this is usually approached. It is not an IA. Your question, choices, data, analysis and words must be your own: change something, tell your teacher where the idea came from, and follow your school's rules on outside help.

Get your RQ checked · S$29