Lab Experiences: Lab Experiment n. 1 Observation Data

Tuesday 8th January 2013

Lab Experiment n. 1 Observation Data

Obejtective/Task: Interpret the data on a labelling. Determine the amount of pure substance in a commercial bottle (solution).

How to get the data from the label in the bottles?

Procedure:

1. Get any of the commercial bottle in your lab, look at its main labelling.

2. Make a table to record the data you will obtain. 6 columns: Name of the content, Chemical Representation, Molecular mass, Density, Richness and Purity.

3. Look for the data to fill the table. We would look for them in order, from the top part of the labelling to the bottom part and from the right side to the left side. Most of the labellings follow the standart data organization. Here are some advice to look for the data:

- Name: it is written at the top right side.

- Richness: This can be expressed as Minimum assay/ assay or acidim. It is given in percentages (%) you can look for it either on the front part (pictures 1 and 3, the ones we haven been using) or the back part (pictures 2 and 4) which includes a list with all the important information about the bottle’s content.

- Purity: This characteristic is represented on the labeling with one any of these letters: PS(‘pro sysnthesi’), PR (pure), PRS (extremely pure) or PA (‘pro analysi’). The further to the right you go this series the more expensive the product is.

- Chemical representation: the formula for each compound is written on the left bottom corner of the labeling.

- Molecular mass: it is represented as M or MW (molecular weigh - mol/g). It is on the right bottom corner.

- Density: this magnitude is written at the top part of the list on the labelling at the back (pictures 2 and 4) (mass/volume).

Questions:

Calculate the concentration (M) of the pure substance in the commercial solution.

Examples:

Name of whatever the container has:

From the first picture for example you know that what you have is octanol, as it is written at the top. The same for the other bottle which is the third picture, the name of the content is hydrochloric acid.

Richness:

In the case of (picture 3)HCl bottle the richness is of 37% and in the case of (picture 1)C₈H₁₂O the richness is of 99%.

Purity:

As written on the labellings: HCl is PRS –very pure

C₈H₁₂O is PS – 'pro synthesi'

Chemical representation - formula:

The formula for each compound is written on the left bottom corner of the labelling. As you can see the formula for hydrochloric acid is HCl, and the one for octanol is C₈H₁₂O. The formula is very useful because you can determine if the bottle's content is an element or a compound. In this case, both examples are compounds.

The Molecular mass: it is represented as M or MW (molecular weigh).

HCl: 36.46 g/mol

C₈H₁₂O: 130.23 g/mol

Density: (mass/volume).

HCl : 1L – 1.19 kg 1kg – 0.84L The density of HCl is 1.19 g/mL or 1.19g/cm³.

C₈H₁₂O: 1L – 0.825kg 1kg – 1,212L The density of C₈H₁₂O is 0,825g/mL or 0,825 g/cm³.

Note: All of these data helps you to know a lot about the acid, the containers give a lot of information in some cases the give the ph of a certain quantity of substance, so you have an estimation of its pH without been necessary that you perform the corresponding experiment. However if you carry the corresponding experiment to get the pH of the substance you will get its pH more exactly without giving a set of numbers.

You can see in the following picture that the back part labeling can include on the list the pH of the substance. Look at the second line:

This is KBr (potassium bromide)

With the last three characteristic we have been asked to find we can work out how many moles of each compound we have use the following formula with the data you have.

Formula to calculate the concentration of pure compound in solution:
Volume (try to use 1L to make it easier) · Density (g/L) = mass of the content(g)

Mass of the content(g) · richness (%) = mass of pure substance (g)

Mass of pure substance (g) ÷ molecular mass (g/mol) = moles of pure substance (mol)

Moles of pure substance(mol)÷ litres of solution = concentration of pure substance in solution-> molarity(M)

- Example: Concentration of HCl in solution