Can you rescue a mixture?

Gravel, sand and salt are mixed together. Choose a route to recover them, test your plan and use evidence to judge the result.

Starting notebook…

Hands-on · Mix & Flow of Matter

How can we recover gravel, sand and salt from one dry mixture while keeping the collected materials as separate as possible?

A mixture contains substances that keep their own properties. Use differences in grain size and solubility to separate this mixture. Salt dissolves in water; the selected sand and gravel do not. Filter paper can trap sand grains, but dissolved salt passes through with the water. Evaporation can leave salt behind as water enters the air. A clear liquid is not proof of pure or safe water.

Review the related lesson →

Science words you will use

A hypothesis is a possible explanation. A prediction is what you expect to observe. The independent variable is what you change or compare; the dependent variable is what you measure. Controlled variables stay the same in a fair test. Qualitative observations describe what you notice; quantitative observations use numbers and units.

Accuracy means closeness to a trusted value. Precision describes how closely repeated readings agree. Repeating a result does not prove it is accurate. A pattern between two quantities does not, by itself, show that one caused the other.

What good work includes

Justify each separation step using grain size or solubility, and say where every material goes.
Keep model planning separate from real observations and record dry masses without containers.
Judge recovery and contamination together; explain one specific limitation and a justified improvement.

Plan your investigation

My scientific notebook

Plan your investigation

Use your own words. You can return and change your ideas as you collect evidence.

My research questionWhat can you investigate using this equipment or record?My hypothesisGive a possible explanation: I think… because…My predictionIf… then I predict… because…What I change or compareName the independent variable. In an observation study, name what you compare.What I measureName the dependent variable and its units.What stays the sameFor repeats, keep the mixture source, starting mass as close as practical, sieve, filter, water volume, rinsing and drying checks consistent. For a revised route, state the one change and its purpose.My procedure and changesUse repeatable steps. Record changes to the plan and why you made them.Reading my equipmentWhat is the smallest marked division? What units and rounding will you use?

Your apparatus

The Mixture Rescue Challenge

First test your choices on the planning bench. It is a simplified idea model: it produces no measurements and assumes complete dissolving and ideal separation. Then design a teacher-approved practical method using a small dry mixture. Keep every collected material labelled. Real recovery can be incomplete or contaminated.

Planning bench · idea model

Choose a method. Follow every material.

No measurements are generated here. This model assumes the gravel is coarser than the sieve openings, sand and salt grains pass through, salt dissolves fully in enough water, filter paper retains the sand, and the selected materials are non-magnetic. Real equipment needs checking.

Mixture to process

Collected separately

Goal: recover all three solids separately.

Start with a dry mixture of gravel, sand and salt. Choose a method and make a prediction.

Your planning trail

These are model decisions, not measured experimental results. The bench resets when the page reloads. Keep your trail in the notebook before leaving.

Materials & safety

Teacher-prepared dry mixture of clean non-magnetic coarse gravel, washed sand and table salt (about 10 g total)
Sieve chosen by the teacher to retain the gravel while letting sand and salt grains through
Room-temperature water, measuring cylinder, cups, spoon or stirring rod and spill tray
Funnel, filter paper and labelled collecting containers
Shallow evaporation dish, balance and labelled weighing containers
Safety goggles and a place where samples can dry without disturbance

Teacher supervision and goggles are required. Do not taste mixtures or collected materials. Use clean prepared materials, not unknown soil or road salt. Avoid breathing dust; handle gently. Use room-temperature water and leave evaporation dishes in a teacher-approved place. This method uses no student heating, flames or hot plates. Drying may take several days. Wash hands and follow your teacher’s instructions for disposal.

Suggested procedure — adapt and record changes

State what you want to recover. Use the planning bench to test a route, then explain which property each step uses. Record your own plan before beginning.
Ask your teacher to check the sieve, filter and sample. Check that the sieve retains gravel while the finer dry grains pass through. If this equipment does not separate the chosen sizes, change the plan before collecting results.
Measure and record the starting dry mixture mass without its container. Label the run, such as Method A, run 1. Record the balance resolution and how you remove container mass.
Carry out your approved route. Keep gravel, sand and salt solution in separate labelled containers. Add only enough room-temperature water to dissolve the salt fully, stirring gently. Record the water volume, order of steps, observations and any spills.
When using filter paper, collect the liquid as well as the trapped solid. A small measured rinse can carry remaining salt solution from sand into the collected liquid; record it. Rinsing may improve separation but increases the water that must evaporate.
Leave the collected salt solution in a labelled shallow dish to evaporate. Let all collected solids dry. Compare masses at two later checks using the same balance; record both readings. A steady mass is useful evidence of drying, not proof of purity. Do not enter wet masses as finished recovery.
Subtract each empty container mass. Record the gravel, sand and salt masses separately in your observations, then add them. Enter the starting dry mixture mass and the total recovered dry solid mass below. Do not include water, filter paper or containers.
If materials and time allow, repeat with a fresh portion of the same prepared mixture and similar starting mass. Keep the method fixed for repeats. Label a revised route Method B; record what changed. Compare recovery and visible contamination rather than declaring the highest mass the best result.

Collect · check · compare

Your data and graph

Add one row per complete practical run, not one row per substance. Use only measured dry masses, with container mass removed. A measured zero is valid; an unfinished or missing result stays blank. Record the individual gravel, sand and salt masses in the observation or notebook.

Graph titleGraph view

The table keeps your exact readings. On a small screen, scroll inside the table or graph to see the rest. With a keyboard, focus it and use the arrow keys.

Add readings to enable data and graph downloads.

Explain your results and reflect

Think like a scientist

Explain, question and reflect

Patterns in my resultsCalculate apparent recovery for each complete run. Compare the separate collected materials, visible contamination and losses. Explain why a high recovery alone cannot show that your samples are pure.Limits and possible errorsName a specific loss or source of extra mass. Could damp solids, trapped salt solution, filter paper, spills or grains left on equipment affect the result? Explain the likely direction of the effect.My conclusionAnswer your research question. Your result does not have to match your prediction.The evidenceUse measurements, units and trial numbers to support your conclusion.Why the evidence supports my conclusionFor every method, connect the material property to what you observed. Explain where the salt went during filtering. Distinguish planning-bench feedback from real observations.What I would improve or test nextWhat would you change? Why? Revisit your hypothesis and prediction.

A new question to explore

Your new goal is to collect the water as well as the salt. Explain why open evaporation cannot meet that goal. Research how distillation collects and cools water vapour; any apparatus would need a separate teacher-approved plan.

Keep your work

Your lab report

Preview your notes, measurements, calculations and graph. Choose Print / Save as PDF in the report, or download an HTML copy. Submit that PDF in Google Classroom using your teacher’s instructions. This website does not submit your work.

Student name (optional)Class (optional)Investigation date (optional)

Restore notebook backup

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