Chemistry Experiments and Formulas

Empirical Formula using Combustion

1. Use a crucible and heat until it is hot → this is for cleaning and to remove traces of oil or water from previous experiments

2. Leave crucible to cool, then weigh with lid on

3. Add magnesium ribbon and reweigh with the lid and ribbon. The mass of magnesium using is this reading minus the reading for just the crucible and lid

4. Heat crucible with lid on but leave a small gap for oxygen → Lid prevents any bits of solid escaping so no mass is lost

5. Heat for 10 mins or when ribbon turns white, cool it down

6. Reweigh crucible with the lid and contents, the mass of magnesium oxide is this reading subtract the initial reading for the mass of the crucible and lid

Empirical formula calculation

1. List all elements in the compound

2. Then under, write their masses from the experiment

3. Find the number of moles of each element

4. Turn numbers into a simple ratio by dividing them by the smallest number of moles

5. Get the ratio to the simplest whole number form

Moles, mass, Mr

Mr x Moles = Mass

Empirical Formula using Reduction

1. Place a rubber bung (beaker lid with a hole in the middle and a tub) into a test tube with a hole in the end and weigh them together

2. Take the bung off and place copper (II) oxide in the middle of the tube

3. Place the bung back and weigh the tube again

4. Clamp the tube horizontally and heat up a bunsen burner below the middle of the tube

5. Expel air in the tube by gently turning on the gas, after 5 seconds, light the gas by holding a burning splint next to the tube’s hole in the end of the tube.

6. Turn off the bunsen burner and leave the test tube to cool

7. Once cooled, turn off the gas and weight the test tube with the bung and contents

Proportion of Oxygen in the Air

1. Soak some iron wool in acetic acid (acid will catalyse reaction), then push the wool into a measuring cylinder

2. Flip it over and place it in the beaker of water

3. Record starting position of water using the scale on the measuring cylinder

4. Over time, the level of water in the measuring cylinder will rise → because iron reacts with oxygen in air to make iron oxide, and water rises to fill the space oxygen took up in the cylinder

5. Leave experiment for a week or until water level stops rising

6. Record finishing position of water → this is the final volume of air

Oxygen in the Atmosphere with Phosphorus

1. Place phosphorus in a tube and attach a glass syringe at both ends

2. One syringe should be empty and the other filled with air

3. Heat the phosphorus and use syringes to pass the air over it, phosphorus will react with oxygen in the air to make phosphorus oxide

4. While it reacts, the amount of air in the syringes decreases

5. Measure the starting and final volumes of air using the scale on one of the syringes → push all air into one syringe to measure final volume

6. Then calculate the % of oxygen in the air

% of Oxygen

(start volume - final volume)/start volume x 100

Reactions of Metals

1. Some metals react with acids to form a salt and hydrogen gas

2. Using reactions of different metals with dilute acids, we can work out how reactive they are → the more reactive a metal, the faster the reaction, very reactive metals explode

3. Set up three boiling tubes and fill them with equal volumes of dilute HCL or Sulphuric acid

4. Then place magnesium, zinc and iron pieces in separate test tubes

5. Speed of reaction is indicated by the rate of bubbles of hydrogen is released

6. Hydrogen is confirmed by the burning splint test, magnesium should give the loudest squeaky pop as it has the most vigorous reaction producing the most hydrogen

Making Soluble Salts

1. Heat the acid in a water bath inside a fume cupboard to avoid releasing acid fumes in the room → this speeds up the reaction

2. Add the base to the acid → they will form a soluble salt + water

3. The base will be in excess and all acid has been neutralised because the excess solid will sink to the bottom of the flask

4. Mix gently and place inside the filter, which will filter out the soluble salt and water

5. Heat the filtered solution gently to slowly evaporate off the water

6. Leave solution to cool and allow salt to crystallise

7. Filter off the solid salt and leave it to dry

Enthalpy changes with Dissolving, Displacement and Neutralisation