Viscosity Investigation

In this worksheet, students will answer questions about how to test the viscosity of liquids.

Key stage:  KS 3

Curriculum topic:   Chemistry: The Particulate Nature of Matter

Curriculum subtopic:   Properties of Solids, Liquids and Gases

Difficulty level:

QUESTION 1 of 10

Viscosity is a measure of how 'gloopy' or sticky a liquid is. Liquids have different properties and viscosity is one of them.

We use oil to reduce the friction between surfaces, but it must be thick, or sticky, enough to stay on these surfaces.

If liquid soap was as runny as water, it would run off our hands before we had time to wash them.

The thicker a liquid, the more viscous it is.  Let's have a closer look.

Finish this sentence:

Viscosity is a measure of a liquid's......

speed

temperature

thickness

Laura is investigating viscosity:

She collects four test-tubes and four marbles. She also collects:

• water
• washing up liquid
• cooking oil
• salt solution

To make the test fair, the test tubes and marbles are the same size.

Which TWO 'liquid' factors must she keep the same?

the temperature of the liquids

the volume of the liquids

the colour of the liquids

the time of the test

Laura leaves 2cm of air at the top of each test tube when she has added the liquids. She puts the test tubes in a test tube holder to keep them steady and upright.

To collect a set of results, one at a time, Laura places a marble on top of the liquid in the test-tube, lets go and.......

counts out loud how long it takes to reach the bottom

measures the length of the tube

measures the time it takes for the marble to drop

turns the test tube upside down

watches the marble drop

What is the name of the force that pulls the marble through the liquid?

friction

gravity

magnetism

So, which force is SLOWING the marble down?

friction

gravity

air resistance

Can you help Laura to fill in the missing word in her prediction?

The more VISCOUS the liquid, the __________ the marble travels to the bottom of the tube.

slower

faster

bigger

Laura's results show that:

The more VISCOUS the liquid, the SLOWER the marble travels.

This is because in VISCOUS liquids, the particles are.......

slimy

loosely packed

densely packed

Laura's results show that the marble took longer to travel through the salt solution than the water.

What do you think is the best explanation for this?

Laura's results are wrong

dissolved salt particles make the solution more viscous

the salt changed the temperature of the liquidpw

Laura wants to check that dissolved solids in water DO change the viscosity.

Which THREE of these could she do to investigate further?

repeat her original test

make a sugar solution to test

nothing

ask another student to repeat her test

change the temperature of the liquids

Once Laura had recorded the time for each marble, she filled in her results in a table:

 Water Washing-up liquid Cooking oil Salt solution Time to fall/s 0.5 1.2 1.8 0.7

Place the liquids in order of their viscosity from MOST VISCOUS to LEAST VISCOUS on the basis of Laura's results.

Column B

Most Viscous
Salt solution
2nd
Cooking oil
3rd
Water
Least Viscous
Washing-up liquid
• Question 1

Finish this sentence:

Viscosity is a measure of a liquid's......

thickness
EDDIE SAYS
As we'll discover, how viscous a liquid is is a measure of how runny or how thick it is. Treacle is viscous. Water is not. We'll find out what's going on further down the line.
• Question 2

Laura is investigating viscosity:

She collects four test-tubes and four marbles. She also collects:

• water
• washing up liquid
• cooking oil
• salt solution

To make the test fair, the test tubes and marbles are the same size.

Which TWO 'liquid' factors must she keep the same?

the temperature of the liquids
the volume of the liquids
EDDIE SAYS
The temperature has an enormous effect upon how viscous a liquid is - you may have noticed that your bottle of syrup is much runnier on a warm summer's day than a cold winter's day. Similarly, the volume of liquid used in each test must be controlled. The colour and the time of the test doesn't affect the way the liquids behave.
• Question 3

Laura leaves 2cm of air at the top of each test tube when she has added the liquids. She puts the test tubes in a test tube holder to keep them steady and upright.

To collect a set of results, one at a time, Laura places a marble on top of the liquid in the test-tube, lets go and.......

measures the time it takes for the marble to drop
EDDIE SAYS
To give her an accurate set of results, Laura measures the time it takes for the marble to fall to the bottom of the tube.
• Question 4

What is the name of the force that pulls the marble through the liquid?

gravity
EDDIE SAYS
Gravity PULLS all objects down towards the centre of the Earth.
• Question 5

So, which force is SLOWING the marble down?

friction
EDDIE SAYS
The force between two surfaces is called FRICTION. So, the upthrust of the liquid as the marbles try to push the liquid particles out of the way in order to fall to the bottom is causing a slowing force to its fall.
• Question 6

Can you help Laura to fill in the missing word in her prediction?

The more VISCOUS the liquid, the __________ the marble travels to the bottom of the tube.

slower
EDDIE SAYS
Can you see the relationship between the viscosity of the liquid and the speed of fall? The more viscous a liquid, the slower it's going to fall because the particles are harder to move out of the way as the liquid is more dense.
• Question 7

Laura's results show that:

The more VISCOUS the liquid, the SLOWER the marble travels.

This is because in VISCOUS liquids, the particles are.......

densely packed
EDDIE SAYS
If you were able to look at these liquids with a microscope that enabled you to see the particles it is made of, not only would you notice that they were different sizes but also the distance between them would be different. Those with molecules closer together are denser and these will be more viscous.
• Question 8

Laura's results show that the marble took longer to travel through the salt solution than the water.

What do you think is the best explanation for this?

dissolved salt particles make the solution more viscous
EDDIE SAYS
Dissolved solids in water make it denser, and so more viscous. Think about it: the water molecules are already there, but now they've got salt molecules in between them too - more for the marble to shift out of the way, so denser and a little more viscous.
• Question 9

Laura wants to check that dissolved solids in water DO change the viscosity.

Which THREE of these could she do to investigate further?

repeat her original test
make a sugar solution to test
ask another student to repeat her test
EDDIE SAYS
It's very important that ideas are tested MORE THAN ONCE - they are REPEATED. Using a different solution, made with other dissolved solids would give Laura MORE EVIDENCE to back-up her ideas too! Bear in mind that she only carried out each test ONCE only - how many things could go wrong in that one test??
• Question 10

Once Laura had recorded the time for each marble, she filled in her results in a table:

 Water Washing-up liquid Cooking oil Salt solution Time to fall/s 0.5 1.2 1.8 0.7

Place the liquids in order of their viscosity from MOST VISCOUS to LEAST VISCOUS on the basis of Laura's results.

Column B

Most Viscous
Cooking oil
2nd
Washing-up liquid
3rd
Salt solution
Least Viscous
Water
EDDIE SAYS
If viscosity is a measure of how thick or how runny a liquid is, then the most viscous is the goo-iest liquid. That's the one that the marble is going to find it hardest to move through and so the one that takes the longest time to fall to the bottom. It took the marble 1.8 seconds to fall through the cooking oil, so that must be the most viscous. On the other hand, the fastest fall was through the water - only half a second.
---- OR ----

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