Chemistry required practicals

• Making a pure soluble salt: Method

  1. Use a measuring cylinder, measure 25 cm of X acid.

  2. Pour all the X acid into a beaker and gently warm with a water bath.

  3. Add X base to the acid using a spatula and stir.

  4. Keep adding base until in excess - when no more reacts.

  5. Use a funnel and filter paper to separate the solution and solid into a conical flask.

  6. Pour the solution into an evaporating basin and gently heat with a water bath until crystals form

  7. Wait for the rest of the water to evaporate and then pat dry.
• Why not use an alkali?

  Cant tell when reaction has finished
• Why use a water bath?

  If the solvent is flammable, it's a hazard.

  Also reduces the risk of boiling the acid
• Why not use excess acid?

  can't see when it is in excess
• Why do we not say the base in excess when no more bubbling is seen?

  metal oxides do not produce a gas
• Why do we not use a pure metal?

  Metal oxides and carbonates are more reactive. Pure metals react too slowly
• Titrations: method

  1.Use a graduated pipette to transfer 25 cm' of Alkali into a conical flask on a white tile.

  2. Add 5 drops of phenolphthalein to the alkali.

  3. Fill a burette with Acid to the 0.00 line.

  4. Add the acid whilst swirling. Add the final volume drop by drop until the solution changes clear and colourless.

  5. Read the final volume with the meniscus at eyelevel.

  6. Repeat and calculate mean using only values within 0.1 cm.
• Why we use this equiptment:

  1. Graduated pipette

  2. Burette

  2. White tile

  1. Accurately measures a fixed volume

  2. Accurately measures variable volumes

  3. Allows the colour change to be seen easier
• Why do we do these techniques:

  Measure at bottom of meniscus

  Swirling

  Drop by drop at end

  1. Accurate reading

  2. Mix to find accurate end point

  3. Find accurate volume at end poin
• 2 indicators we can use- Phenolphthalein, Methyl orange

  What are their changes?

  Phenolphthalein= Pink in alkali - clear otherwise

  Methyl orange= Orange in alkali - red in acid
• Electrolysis: Method

  1. Set up the equipment as below:

  2. Turn on the power

  3. Observe changes at positive electrode

  4. Observe changes at negative electrode

  
• how to find these measurement requirements: Volume, Mass

  Volume- Use measuring cylinder not test tubes - they lack graduations

  Mass- Use balance, collect all metal, dry, and subtract mass of cathode
• What happens at the positive electrode (anode)? What is the test for this?

  Bubbling

  Oxygen gas- relight glowing splint

  Chlorine- bleaches damp litmus paper
• What happens at the negative electrode (cathode)? What is the test for this?

  bubbling and a solid forms

  Hydrogen gas- lit splint burns with a squeaky pop

  Solid- not really a test but different colours form lol!
• Energy changes: Method

  1. Use a measuring cylinder to measure 30 cm' of X acid

  2. Pour the X acid into a poly(styrene) cup

  3. Measure the initial temperature of the acid using a thermometer

  4. Use a measuring cylinder to measure 5 cm of X alkali

  5. Pour the alkali into the poly(styrene) cup and swirl to mix and add lid

  6. Measure the maximum temperature reached using a thermometer

  7. Continue adding 5 cm' of alkali until 40 cm' of alkali has been added, measuring the maximum temperature reached each time

  8. Repeat the entire experiment 3 more times

  9. Ignore any anomalous results and calculate means then calculate the change in temperature as max temp - initial temp
• Why use a lid?

  Using a lid and insulator poly(styrene) stops heat being lost and makes the results more accurate.
• Why swirl?

  Swirling helps avoids anomalous results
• Why plot a graph? What would it look like?

  By plotting the maximum temperature (or temperature change against the volume of alkali added and drawing two straight lines of best fit, the intersection shows when the reaction has finished.

  
  

  Volume of acid added X. Max temterature Y