Chemistry Lab Reports

Determination of the Molar Mass of Magnesium

Introduction

The aim of this investigation is to find the molar mass of magnesium by making magnesium and hydrochloric acid react and then apply the ideal gas equation.

The independent variable of this experiment is the amount used of each substance. However, these were not not be varied. The dependent variable is the amount of hydrogen gas which is formed. The controlled variables are the pressure and temperature in the room, and the width (and thereby weight) of the magnesium ribbon.

Materials and Methods

Materials used:

• Magnesium (Mg) ribbon
• Hydrochloric acid (HCl), 35% concentrated
• Copper (Cu) wire
• Eudiometer
• Thermometer
• Barometer
• Measuring cylinder (2000 cm³)

Method:

• 50 mm of the Mg ribbon was weighed.
• 10 cm³ of HCl was poured into the eudiometer.
• The rest of the eudiometer was filled with water.
• The Mg ribbon was wrapped around the Cu wire and hung in the eudiometer cork.
• The measuring cylinder was filled with water.
• The eudiometer was put upside-down in the measuring cylinder.
• After the reaction between HCl and Mg was complete, the eudiometer was allowed to cool down to reach room temperature.
• The eudiometer was arranged so that the gas inside had the same pressure as the air pressure outside the room.
• The molar mass of magnesium was calculated using

In order to ensure that the investigation resulted in valid results, the experiment was conducted four times.

Results

These were the measured values:

The mean volume is then 64.75 ml.

The ideal gas equation will be used to calculate the number of moles:

n = (PV)/(RT)
n = (9.81 * 64.75) / (8.31 * 293 ) = 2.61

Thus, we have 2.61 moles of H₂. The reaction carried out should be:

Mg + 2HCl => MgCl₂ + H₂

For every mole of Mg, we will have one mole of H₂. Therefore, we know that we will also have 2.61 moles of Mg. This is the formula for molar mass:

M = m/n = 64.75 / 2.61 = 24.8

The molar mass of magnesium must then be 24.8 g.

Conclusion

From this, we can conclude that the average magnesium atom has 24.8 protons. According to Wikipedia, the molar mass of magnesium is 24.3 g, which is close to our result.

Evaluation

This investigation could have been performed better in an environment where we could control the pressure more accurately, such as in a pressure chamber.

Determination of the Empirical Formula of Copper Sulfide

Introduction

The aim of this experiment is to determine the empirical formula of copper sulfide, which is formed when copper and sulfur are heated together. The independent variables are the amount of copper and sulfur, but they will not be varied. The dependent variable is the amount of copper sulfide formed. The controlled variables were among other the size of the beaker and the temperature that the experiment was conducted in.

Materials and Methods

Materials used:

• Copper (Cu)
• Sulfur (S)
• Bunsen burner
• Clay triangle
• Crucible
• Crucible tong
• Scale
• Spoon

First, the copper was weighed on the scale. The copper was then heated together with the sulfur over the Bunsen burner, after which the newly formed copper sulfide was weighed.

Results

First, the Cu was weighed on the scale. Its weight can be found in Table 1: Measured Values.

The weight of the substance was measured after the reaction had occurred. The substance, which probably was copper sulfide, weighed 62 g. Because there was initially 49 g of Cu, there must be 13 g of S.

We will use the following formula to calculate the amounts of the mentioned substances in moles:

n = m / M

Where n is the amount of substance in moles, m is the mass of the substance, and M is the molar mass of it. The values of molar mass are according the elements’ respective Wikipedia articles.

Conclusion

The amount of copper, 0.0077 mol, is approximately double the amount of sulfur, 0.0041 mol. From this, we can conclude that the amount of copper in copper sulfide is twice as large as the amount of sulfur. This means that the empirical formula of copper sulfide is
Cu₂S.

Since the amount of sulfur was not exactly half the amount of copper, we had an error somewhere. Probably, not all sulfur reacted with the copper and left some pure sulfur.

Evaluation

The method for making the copper and sulfur react is flawed, because it is not given that all sulfur will react. This is difficult to improve in a standard lab, though.

Another flaw is that the experiment was only conducted once, which means that errors are difficult to spot. We should have performed it at least thrice.

Flame Colours of Different Molecules

Introduction

The aim of this experiment is to investigate what colours different substances will emanate when they are burnt. The independent variable to be changed is the substance that is tested. The dependent variable will be the colour of the flames. There are many controlled variables, such as the heat of the flame.

Materials and Methods

The substances used were: Sodium chloride (NaCl), barium chloride (BaCl₂), lithium chloride (LiCl), strontium chloride (SrCl₂), potassium chloride (Kcl) and calcium chloride (CaCl₂). Also, a Bunsen burner was used for heating and a platinum hook for holding the substances.

One substance was burnt at a time by placing a small part of it on the platinum hook and holding it over the Bunsen burner. The independent variable was varied by changing the substance on the platinum hook. The dependent variable, the colour of the flame, was observed and noted. The controlled variables were maintained constant by not changing anything, e.g. letting the Bunsen burner be.

The platinum hook was cleaned thoroughly between every experiment with a new substance, which means that the results were trustworthy.

Results

Most flames’ colours were easily distinguishable, except potassium chloride’s, which might have been more pink or purple.

Conclusion

We can conclude that different substances emanate different colours when they are burnt. I compared my results with Wikipedia’s information on those subjects:

Only two shades were marginally wrong, which suggests that the results are trustworthy.

These different colours are seen because the electrons in the molecules are excited and “jump” between different orbitals. The electrons jump different distances in various molecules, and when they do, they release waves at a certain wavelength. This wavelength decides where on the visible spectrum the colour is.erotic movie freeporn celeb free moviesextreme movies sapphicnude movies celebrityadult movie rentalmovie post teenmovies bukkakemovies lesbain free Map