# Chemistry. Accuracy and Precision

Chemistry/ Semester 1

Procedure

* Access the virtual lab and complete the experiments.

Data

* Below is the table that you will complete for the virtual lab. Either type your results into this table or print the table from the virtual lab (it must be submitted to receive full credit for this assignment.)

* To print from the virtual lab.

1. Be sure the data table is viewable.

2. Right-click (PC) or Command-Click (Mac) on the table and select print.

Part I: Density of Unknown Liquid |

| Trial 1 | Trial 2 | Trial 3 |

Mass of Empty 10 mL graduated cylinder (grams) | 2.56g | 2.55g | 2.60g |

Volume of liquid (milliliters) | 8.50mL | 8.80mL | 8.90mL |

Mass of graduated cylinder and liquid (grams) | 36.10g/mL | 36.60g/mL | 36.90g/mL |

Part II: Density of Irregular-Shaped Solid |

Mass of solid

(grams) | 41.000g | 38.890g | 42.960g |

Volume of water (milliliters) | 50mL | 55.5mL | 53.1mL |

Volume of water and solid (milliliters) | 54.9g/mL | 60g/mL | 58.1g/mL |

Part III: Density of Regular-Shaped Solid |

Mass of solid (grams) | 28.00g | 27.70g | 28.10g |

Length of solid (centimeters) | 5.20cm | 5.00cm | 4.50cm |

Width of solid (centimeters) | 3.00cm | 4.00cm | 3.50cm |

Height of solid (centimeters) | 2.50cm | 3.00cm | 2.00cm |

Calculations

Show all of your work for each of the following calculations and be careful to follow significant figure rules in each calculation.

Part I: Density of Unknown Liquid

1. Calculate the mass of the liquid for each trial. (Subtract the mass of the empty graduated cylinder from the mass of the graduated cylinder with liquid.)

* Trial 1

36.10-2.56= 33.54g

* Trial 2

36.60-2.55= 34.05g

* Trial 36.90-2.60= 34.30g

2. Calculate the density of the unknown liquid for each trial. (Divide the mass of the liquid calculated above by the volume of the liquid.)

* Trial 1:

33.54/8.50=3.95g/mL

* Trial 2:

34.05/8.80=3.87g/mL

* Trial 3:

34.30/8.90=3.85g/mL

Part II: Density of Irregular-Shaped Solid

3. Calculate the volume of the irregular-shaped solid for each trial. (Subtract the volume of the water from the total volume of the water and solid.)

* Trial 1:

54.9-50=4.9mL

* Trial 2:

60-55.5=4.5mL

* Trial 3:

58.1-53.1=5mL

4. Calculate the density of the irregular-shaped solid for each trial. (Divide the mass of the solid by the volume of the solid calculated above.)

* Trial 1:

41.000/4.9=8.4g/mL

* Trial 2:

38.890/4.5=8.6g/mL

* Trial 3:

42.96042/5=8.6g/mL

Part III: Density of Regular-Shaped Solid

5. Calculate the volume of the regular shaped solid for each trial.

(Multiply the length × width × height for each trial to get the volume in the unit cm3.)

* Trial 1:

5.20x3.00x2.50=39cm3

* Trial 2:

5.00x4.00x3.00=60cm3

* Trial 3:

4.50x3.50x2.00=31.5cm3

6. Calculate the density of the regular-shaped solid for each trial. (Divide the mass of the solid by the volume calculated above.)

* Trial 1:

28.00/39=0.72g/mL

* Trial 2:

27.70/60=0.50g/mL

* Trial 3:

28.10/31.5=0.90g/mL

Questions and Conclusions:

1. How would you determine the proper number of significant figures of a liquid using a graduated cylinder? (See practice interactive in "Activity" tab of lesson.)

You estimate one decimal place past the smallest division on the cylinder. If the smallest division is to the ones place, then estimate the tenths place. Smallest is in tenths, then estimate to the hundredths place.

2. Can just one measurement be considered precise? Can just one measurement be considered accurate? Explain your answers completely.

It can never be precise because precise determines by how many close groups of measurements are to each other. It can be accurate because it can match an accepted value.

3. In parts II and III of the lab you used different sized objects in each trial. Compare the density values that you calculated for these items, how do the three trials compare?

Well they compare even with using different techniques because the calculations are still precise and the answer will still need to be divided into the mass and volume. Since, the objects are irregular shaped then you find the volume by subtracting the initial volume with the new volume once the shaped was put inside the graduated cylinder. While the regular shape you can easily find it with the centimeters of length x width x height.