Separating sand and salt
In this experiment students separate a mixture of sand and salt, illustrating the fundamental means of separating a mixture of an insoluble material from one which is soluble.
This is a very straightforward experiment. It can be carried out individually or in groups of two. Pupils must stand up during heating activities and beware of hot salt spitting when evaporation is almost complete.
Mixture of sand and sodium chloride (salt), about 6 or 7 g per group of students (Note 1)
Refer to Health & Safety and Technical notes section below for additional information.
Beaker (250 cm3)
Glass stirring rod
Conical flask (250 cm3)
Heat resistant mat
Health & Safety and Technical notes
Wear eye protection throughout this experiment.
Sodium chloride (e.g. table salt), NaCl(l) - see CLEAPSS Hazcard.
1 A suitable sand-salt mixture should contain approximately 20% salt by mass.
a Pour the sand-salt mixture into the beaker so that it just covers the base.
b Add about 50 cm3 of water, or add water until the beaker is about one-fifth full.
c Stir the mixture gently for a few minutes.
d Filter the mixture into a conical flask.
e Pour the filtrate into an evaporating basin.
f Heat the salt solution gently until it starts to decrepitate (“spit”). CARE: Keep eye protection on and do not get too close.
g Turn off the Bunsen burner and let the damp salt dry in the dish.
If desired, the experiment can be extended to isolate dry samples of sand and salt. To do this, the damp sand in the filter paper can be transferred to another sheet of dry filter paper, and, by folding and dabbing, the sample can be dried. If necessary, another piece of filter paper can be used.
Students often like to present their specimens in small bottles for approval, so a spatula could be used to accomplish this. Whilst the first student of a pair is transferring the sand, the other can be scraping the dried salt from the evaporating dish and transferring it to another specimen bottle.
If this extension is carried out, the students should be encouraged to label the bottles. They should be told that all samples prepared in this way need to be labelled, even if in this case, it should be obvious which substance is which.
Here are some questions for students.
a Why can sand and salt be separated using this experiment?
b Why is the salt, sand and water mixture stirred in step c?
c Why is the salt solution heated in step f?
d How might the final traces of water be removed from your samples to ensure that they’re totally dry.
e Give two reasons why the sand you have obtained might still be contaminated with salt.
f How could you adapt your experiment to obtain a purer sample of sand?
g Give two reasons why the salt you have obtained might still be contaminated with sand.
h How could you adapt your experiment to obtain a purer sample of salt?
Health & Safety checked April 2008
Page last updated on 16 December 2011