#### Measurement and Density, Chemistry tutorial

Measurement and Density:

Purpose:

Section 1: Through calculating the density of a recognized substance (water), find out the relative precision and precision of different glassware items.

Section 2: Find out the density of a salt water solution using the most precise and correct piece of glassware concluded in section 1

Equipment / materials:

 Weighing balance Water Unknown metal cube 100 mL beaker Unknown  liquid 100 mL graduated  cylinder Metal  cylinder

Introduction:

The capability to build accurate and featured observations is vital in science. This chapter will focus on quantitative observations, more purposely, measurements. A measurement is described via a number and a scale or unit. The scale utilized is often changed. Due to convenience, the metric system is often utilized in many countries. The universal scale, though, utilized via scientists is the SI unit. In this chapter, we will focus on making accurate and detailed observations in measurements using the metric system while obeying the rules of significant figures.

In calculation to quantities described via a single unit, quantities can as well be described through a combination of units. One such instance is density. Density is simply one way to differentiate a material. Density (d) is described as mass (m) per unit volume (V). Therefore, units of both mass (for example g) and volume (for example mL) are needed in order to find out density.

D = m/V

Instances

1. A cube of copper was originated to contain a mass of 0.630 kg. What are the dimensions of the cube? (The density of copper is 8.94 g/cm3).

Solution:

a)   Find out the volume of the cube (note that kg have been converted to g):

8.94 g/cm3

= 630 g / volume

volume = 70.47 cm3

b)  Each side of a cube is equivalent in length, so take cube root of the volume for length of cube side:

[cube root of] 70.47 cm3

= 4.13 cm

2.  A cube of copper was originated to have a mass of 0.630 kg. What are the dimensions of the cube? (The density of copper is 8.94 g/cm3.)

Solution:

a)   Find out the volume of the cube (note that kg have been converted to g):

8.94 g/cm3 = 630 g / volume

volume = 70.47 cm3

b)   Each side of a cube is equivalent in length, so take cube root of the volume for length of cube side:

[Cube root of] 70.47 cm3 = 4.13 cm.

3. A graduated cylinder is filled to the 40.00 mL mark by mineral oil. The masses of the cylinder previous to and after the computation of mineral oil are 124.966g and 159.446g. In a divide experiment, a metal ball bearing of mass 18.713 g is situated in the cylinder and the cylinder is once more sealed to the 40.00 mL mark by the mineral oil. The joined mass of the ball bearing and mineral oil is 50.952 g. Compute the density of the ball bearing.

Solution:

a)  Determine the density of the mineral oil:

159.446 g minus 124.966 g = 34.480 g

34.480 g / 40.00 mL = 0.8620 g/mL

b)  Determine the volume of the ball bearing:

50.952 g minus 18.713 = 32.239 g (this is the mass of mineral   oil)

32.239 g divided by 0.8620 g/mL = 37.40 mL (this is the volume of mineral oil)

40.00 mL - 37.40 mL = 2.60 mL

c)   The density of the ball bearing is 7.197 g/mL. This came from 18.713 g divided by 2.60 mL.

EXPERIMENT - Measurement and Density

Part A: Density of Liquids

i)  Density of Water:

• Gather about 100 mL of water in a beaker; let it assemble until its temperature is stabilized. Confirmation its temperature.
• Weigh a fresh, dry 10 mL regulated cylinder and verification its mass.
• now add water from the beaker to the cylinder, so that the level is above 5mL, but below 10 mL and record the volume precisely to the accurate significant figures.
• Wipe off any water droplets adhering to the outside in addition to above of the water level inside.
• Record the mass of the cylinder with water.
• Now repeat step 2-4 two more times, each time by a diverse volume, but still between 5-10 mL.
• Now we contain 3 sets of data, compute the average density of water at this temperature. Compute the % error, once we know the true value of density of water from literature.
• % Error = (Experimental value - true value/true value)*100%

ii)  Density of an Unknown Liquid:

Start through another dry graduated cylinder and do again the mass and volume measurements (above steps 1-7) via an unknown liquid (A, B or C assigned by the instructor). Calculate the density of the liquid, identify it (after discussing with the instructor), and compute the % error.

Part B: Density of Solids

i)   Density of an unknown metal cylinder:

• Weigh the metal cylinder and record the mass. As well record the cylinder number.
• Follow via measuring its height and the diameter of the circular base to the accurate important figures, using a ruler. Compute the volume of the cylinder.
• Alternately, we can as well find out the volume of the metal cylinder using volume displacement process as described below:
• Add water from the beaker to a 50 mL graduated cylinder so that the lever is between 25 and 30 mL and confirmation the correct volume (significant figures please).
• Hold the graduated cylinder in an angle and slide the metal cylinder quietly during the side, with no splashing any water or breaking the glass cylinder.

We will see the level of the water inside the graduated cylinder has risen. Evidence the new volume now (important figures once more). The variation in the volume levels provides us the volume of the metal cylinder

Now compute the density of the metal from volume using 2 different techniques.

ii)  Density of an unknown metal cube:

• Weigh the metal cube and record the mass. As well record the cube number. Follow via measuring its height and the width and depth to the accurate important figures using a ruler. Compute the volume of the cube and analyze its density.

DATA and CALCULATIONS:

Part A: Density of liquids

(i)  Density of water:

Temperature of water: _____________

Mass of empty graduated cylinder: _____

 Trial 1 Trial 2 Trial 3 Volume of water (mL) Mass of water + graduated cylinder  (g) Mass of water alone (g) Density of water (g/mL) Density from literature % error

(ii)  Density of unknown liquid:  _____ (A/B/C)

Temperature of liquid: _____________

Mass of empty graduated cylinder: _________

 Trial 1 Trial 2 Trial 3 Volume of  liquid(mL) Mass of  liquid+ graduated cylinder  (g) Mass of liquid alone (g) Density of  liquid (g/mL) Density from literature % error

Part B: Density of solids

Density of unknown metal cylinder #:   ___

Density from diameter and height measurement:

 Mass of metal cylinder (g) Diameter (cm) Height (cm) Volume = _____(cm3) Density of metal (g/cm3) Density from literature (g/cm3) % error

i)  Density from volume displacement:

 Volume of water before dropping metal cylinder (mL) Volume of water after immersing the metal cylinder (mL) Volume of  metal cylinder (mL) Density of metal (g/cm3) % error

ii)   Density of unknown metal cube #:    ___

 Mass of meta l cube (g) Dept h (cm) Heigh t (cm) Widt h (cm) Volume = _____(cm3 ) Density of metal (g/cm3) Density from literature (g/cm3) % Error

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