Will the ball float on liquid mercury?Will the ball float on liquid mercury?

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The ball floats on liquid mercury!The ball floats on liquid mercury!

Why did it happen????

• Mercury density = 13600kg/m3

• The ball’s density = 11340kg/m3

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SI Units

Density

Density

Must (Pass)

Should (Merit)

Could (Distinction)

• Be able to calculate density from given values.

• Be able to suggest the order of liquids in a density ladder.

• Be able to explain a density ladder.

• Be able to calculate the density of regular objects by experimental means.

• Be able to manipulate and use the density triangle.

• Be able to calculate the density of irregular objects by experimental means.

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Density

Density compares the mass of an object to its volume

D = mass = g or g

volume mL cm3

Note: 1 mL = 1 cm3

What is Density?

Density is the Mass per unit VolumeDensity is the Mass per unit Volume

Wood Water Iron

1 cm3

1 cm3

1 cm3

If you take the same volume of different substances, then they will weigh different amounts.

0.50 g 1.00 g 8.00 g

Q) Which has the greatest mass and therefore the most dense?

IRON

Density = Mass

Volume

g or kg

cm3 or kg3gcm-3 or kgm-3

= m

V

Density Equation:

m

V

Example:

Q) Liquid water has a density of 1000kgm-

3, while ice has density of 920kgm-3.

Calculate the volume occupied by 0.25kg of each.

Density Equation:

V = m = 0.25 = 0.000250m3

1000

V = m = 0.25 = 0.000272m3

920

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Learning Check D1

Osmium is a very dense metal. What is its

density in g/cm3 if 50.00 g of the metal occupies

a volume of 2.22cm3?

1) 2.25 g/cm3

2) 22.5 g/cm3

3) 111 g/cm3

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Solution

2) Placing the mass and volume of the osmium metal into the density setup, we obtain

D = mass = 50.00 g = volume 2.22 cm3

= 22.522522 g/cm3 = 22.5 g/cm3

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Volume Displacement

A solid displaces a matching volume of water when the solid is placed in water.

33 mL

25 mL

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Learning Check

What is the density (g/cm3) of 48 g of a metal if the metal raises the level of water in a graduated cylinder from 25 mL to 33 mL?

1) 0.2 g/ cm3 2) 6 g/m3 3) 252 g/cm3

33 mL

25 mL

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Solution

2) 6 g/cm3

Volume (mL) of water displaced = 33 mL - 25 mL = 8 mL

Volume of metal (cm3) = 8 mL x 1 cm3 = 8 cm3

1 mLDensity of metal =

mass = 48 g = 6 g/cm3

volume 8 cm3

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Learning Check3

Which diagram represents the liquid layers in the cylinder?

(K) Karo syrup (1.4 g/mL), (V) vegetable oil (0.91 g/mL,) (W) water (1.0 g/mL)

1) 2) 3)

K

K

W

W

W

V

V

V

K

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Solution

(K) Karo syrup (1.4 g/mL), (V) vegetable oil (0.91 g/mL,) (W) water (1.0 g/mL)

1)

K

W

V

DENSITY OF A REGULAR SOLID

• Find the Mass of the solid on a balance.

• Measure the three lengths and calculate the Volume.

(ie V = l x w x h )• Calculate the

Density.4.0 cm

2.0 cm

3.0 cm

= m = 240 =10.0 g/cm3

V 24

m = 240 g

DENSITY OF AN IRREGULAR SOLID

Find the Mass of the solid on a balance.Fill the Measuring Cylinder with Water to a known Volume. Add the Object. Work out the Volume of Water that is displaced. Calculate the Density.

50 cm3

80 cm3

m = 360 g = m = 360 =12.0 g/cm3

V 30

DENSITY OF AN IRREGULAR SOLID

• OR use a Eureka Can to find the Volume. Find the mass of the solid on a balance.Add water until just overflowing. Place a Measuring Cylinder under the spout. Add the Object. Collect the Water and read off the Volume.Calculate Density

m = 440 g

40.0 cm3

= m = 440 =11.0 g/cm3 V 40

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Learning Check

You have 3 metal samples. Which one will displace the greatest volume of water?

1 2 3

Discuss your choice with another student.

25 g Al2.70 g/mL

45 g of gold19.3 g/mL

75 g of Lead11.3 g/mL

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Solution

1) 25 g Al x 1 mL = 9.2 mL 2.70 g

25 g Al2.70 g/mL

Pre-Lab• How do you correctly read a graduated cylinder?• What techniques can you use to measure the volume of

an irregularly shaped object? What tips should you remember?

• How do you take the slope of a line?• How is percentage error defined?• Name the two general types of mathematical

relationships between variables to be investigated in this lab

• What safety precautions must be taken for this lab

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Materials

• Rock sample

• Balance

• Graduated cylinder(s)

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Procedure• Choose equipment to make and record all

measurements as accurately and precisely as possible. Be sure to record the correct number of digits for your data.

1.Obtain 2 rock samples

2.Make sure the samples are dry and clean. Obtain their masses. Remember the uncertainty

3.Measure the volume of the rock using the volume displacement method

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4. Repeat method 2 and 3 and obtain an average

5. Calculate the volume of the rock.

6.Repeat for the second sample.

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Results

Data table and calculations

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Initial Vol (ml)

Final Vol(ml)

Calculated volume (ml)

Mass (g)

Sample 1

Trial 1

Trial 2

Average

Sample 2

Trail 1

Trail 2

Average

• More Calculations

1.Make a single table using mass and volume, density for all samples. Display the formula and show all working. Ensure all units are correctly displayed.

2.Obtain the class data for each group for each sort of rock sample and make another table, showing mass, volume, as well as the computation of mass x volume and mass/volume. Use the appropriate units.

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3. Your graph will show a scatter of points, draw a line of best fit.

4. Look at the data/calculations table, which is constant; mass x volume OR mass/vol ?

5. What type of relationship was found in this lab? Hint: If A/B is constant, then there is a direct relationship. If AxB is constant then there is an inverse relationship.

6. Using the above data, explain what the gradient of the line represents?

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7. Calculate the gradient of the line. You can choose any two points on a line to calculate slope, but it is best to choose them far apart.

8. Accurately calculate your gradient. Write your final slope as a decimal, to two decimal places. Don’t forget units!!

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Discussion: Answer the following questions.

1. Compare your calculated gradient from the class results to your calculated density from your own results. What is the error margin?

2.Should a density graph go through the point (0,0)? Why or why not?

3.Would you get the same values of slope if you just counted the number of grid lines in the rise and run (ignoring the scales on your graph)? Give one example.

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4. Why must the samples be clean and dry to start?

5. If I randomly picked two pure solid substances in the room, is it likely that they would have the same density? If I could take any size piece of either, could I make them have the same density? Comment on your answers.

6. If you were given another rock sample, would you rather know its mass or its density if you wanted to find out what kind of rock it is. Explain.

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7. Would the presence of an air bubble stuck on the submerged rock tend to make the density too high or too low? Explain.

8. Discuss any experimental errors that could of lead to the inaccuracies in this lab.

9. What improvements could you put in place to increase the accuracy of your results.

Conclusion:

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Lab Report Due:

• When you hand in your full lab report, make sure the pre-lab is on the top. For this lab make sure your graph is the last page of the report.

• Due Date: Wednesday Sept 19th.

• All questions will be on the PowerPoint on teacherweb.

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