A chemistry worksheet to help students i) understand the design of nappies and ii) design a fair test

This activity could be easily adapted by students to use as a science project.

See also Nappy Dissection

The Design of Nappies

 

Disposable nappy manufacturers had to design a nappy.

It had to be soft on the baby's skin, keep skin dry, have a high water absorbency and a waterproof external surface.

They produced the following design.

Nappy

 

(a) Draw and label a diagram to show a side view (a cross-section diagram) of the nappy layers between A and B.

 

Outline box

 

(b) The most important overall property of any nappy is to absorb high volumes of water.

Some students tested the water absorbency of several materials that could be used for nappy padding. 

They dripped water slowly onto each material until water started to drip through.

Nappy experiment

 

For this to be a fair test, name TWO things that should have been kept the same for each material tested.

 

(i) .........................................................................................................................................

 

(ii) ......................................................................................................................................... 

 

(c) The table below lists the properties of some materials that could be used to make disposable nappies.

Material

Price

Bio-
degradable?†

Water-
proof?

Water
absorbency‡

Strength

Softness

Water
permeability*

Superabsorbent
polymer

high

yes,
but slowly

no

very high

weak

soft

low

Fluffed cellulose
pulp (made from
wood)

low

yes

no

high

weak

soft

high

Tissue paper

low

yes

no

medium

weak

soft

low

Woven cotton cloth

high

yes

no

medium

strong

soft

medium

rayon fabric

low

yes

no

low

strong

soft

high

Non-woven
poly-propylene fabric

low

no

no

nil

strong

soft

high

 

medium

no

yes

nil

strong

hard

nil

Clear polythene
sheeting

low

no

yes

nil

strong

soft

nil

Whitened polythene
sheeting

low

no

yes

nil

strong

soft

nil

* permeability          = how easily it lets water through
 †biodegradable       = whether it will readily break down in the environment
‡ absorbency          = how much water it holds

 

(d) From this table, which material would be most suitable for a nappy lining that meets the manufacturer's requirements?

 

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(e) How are the properties of a good padding different from the properties of a good lining?

 

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Molar Mass