SURVEY OF CHEMISTRY LABORATORY I

CHEM 1151L

DETERMINATION OF THE DENSITY OF WATER

CAUTION!!!CAUTION!!!BE SURE TO WEAR SAFETY GLASSES AT

ALLTIMES IN THE LABORATORY

NO EXCEPTIONS TO THIS RULE!

This experiment is designed for students to

- familiarize themselves with common measuring devices in the laboratory

- demonstrate an understanding of mathematical and computer skills (graphing, linear equations, slopes and intercepts)

Measuring Devices to be Used

- Thermometer

- Mass balance

- Graduated cylinder

- Buret

DETERMINATION OF THE DENSITY OF WATER

DENSITY

- The amount of mass in a unit volume of a substance

Density =

UnitsSolids: grams per cubic centimeter (g/cm3)

Liquids: grams per milliliter (g/mL)Gases: grams per liter (g/L)

- Density of 1.00 g/mL implies 1.00 grams per 1 mL

- Density usually changes with change in temperature

volume

mass

MASS MEASUREMENT

- Mass is the amount of matter in an object

- SI unit is the gram (g)

- The mass balance is used to measure the mass of samples in the

laboratory

- The mass rather than the weight of a sample is measured

Volume is the amount of space that the matter takes up

Unit: milliliter (mL)

Measuring Devices

- Buret

- Graduated Cylinder

VOLUME MEASUREMENT

MASS AN OBJECT

- Mass any object on you

(watch, ring, coin, necklace, etc.)

- Record all digits shown on the mass balance

(DO NOT ROUND-OFF)

ROOM TEMPERATURE

- Measure the room temperature using a thermometer

- Hold thermometer upright

(do not touch the bulb)

- Take the reading to the nearest 0.1 oC

This reads 23.0 oC

Obtain

- a 125 mL Erlenmeyer flask

- a 50 mL graduated cylinder

- Record all volumes to one decimal place

GRADUATED CYLINDER

- Fill the graduated cylinder with distilled H20

- Fill to the 50.0 mL mark

- Read and record the initial volume (one decimal place) of water in the

graduated cylinder

- Read at eye level and at the bottom of the meniscus (the concave “crescent”

shaped surface of the liquid)

GRADUATED CYLINDER

- Tare (zero) the mass balance

- Do this by pressing ‘TARE’

GRADUATED CYLINDER

- Mass the empty flask (should be dry)

GRADUATED CYLINDER

- Pour 10-15 mL of H20 from the cylinder into the flask

GRADUATED CYLINDER

- Read and record the volume of H20 remaining in the graduated

cylinder

- This is the final volume for trial 1

GRADUATED CYLINDER

- Measure and record the mass of flask and H20

GRADUATED CYLINDER

- Do not empty flask

- Final volume of trial 1 is the initial volume of trial 2

- Pour another 10-15 mL of H20 from the cylinder into the flask

- Record the final volume for trial 2

GRADUATED CYLINDER

- Measure and record the mass of flask and H20

GRADUATED CYLINDER

- Repeat steps for the remaining trials without emptying the flask

- Refill the graduated cylinder if necessary

(read and record new initial volume in such cases)

GRADUATED CYLINDER

GRADUATED CYLINDER

SAMPLE TABLE OF VALUES

Initial Reading (mL)

Final Reading (mL)

Volume of H2O delivered (mL)

Total volume of H2O (mL)

Mass of the flask and H2O (g)

Trial 1

50.0

39.5

10.5

10.5

109.032

Trial 2

39.5

28.5

11.0

21.5

122.147

Trial 3

28.5

18.5

10.0

31.5

1132.014

Obtain

- a 125 mL Erlenmeyer flask

- a 50 mL buret

- Record all volumes to two decimal places

BURET

- Wash and rinse buret with faucet water and with distilled water

- Allow water to drain through the tip to rinse the tip

- Buret tip is closed when in horizontal position and opened

when in vertical position

BURET

- Obtain a stand and a buret clamp

- Put buret in place as shown

BURET

- Use a small beaker to fill the buret with distilled H20

- Do not use a funnel

- Fill past the 0.00 mL mark

- Open the tip in order to fill the tip and eliminate bubbles

BURET

- Read and record the initial volume (two decimal places)

- Place a white card behind buret for easy reading

BURET

- Read at eye level and at the bottom of the meniscus (the concave “crescent”

shaped surface of the liquid)

- Note that buret reading is the opposite of that of the graduated cylinder

- For instance, the initial buret reading would be 0.00 mL but not 50.00 mL

BURET

- Each small graduation is 0.10 mL

- 10 graduations per 1.00 mL

BURET

- Mass the empty flask (should be dry)

BURET

- Allow 10-15 mL of H20 to drain into the flask

BURET

- Read and record the final buret reading

- This is the final volume for trial 1

BURET

- Measure and record the mass of flask and H20

BURET

- Do not empty flask

- Final volume of trial 1 is the initial volume of trial 2

- Drain another 10-15 mL of H20 from the buret into the flask

- Record the final volume for trial 2

BURET

- Measure and record the mass of flask and H20

BURET

- Repeat steps for the remaining trials without emptying the flask

- Refill the buret if necessary

(read and record new initial volume in such cases)

- Note that you cannot go beyond the 50.00 mL mark

STOP and refill the buret

BURET

GRADUATED CYLINDER

SAMPLE TABLE OF VALUES

Final Reading (mL)

Initial Reading (mL)

Volume of H2O delivered (mL)

Total volume of H2O (mL)

Mass of the flask and H2O (g)

Trial 1

10.50

0.00

10.50

10.50

109.032

Trial 2

21.50

10.50

11.00

21.50

122.147

Trial 3

31.50

21.50

10.00

31.50

1132.014

DATA ANALYSIS

- Construct two graphs using Microsoft Excel’s Chart Wizard

- Graph 1 – Graduated cylinter

- Graph 2 – Buret

- Draw a trendline (the best straight line) for each- Horintal axis is the Volume axis

- Vertical axis is the Mass

- Label all axes (with correct units) and give titles

- Include equations of the trendlines

- Answer all questions that follow