C2T2 - Barium meals and flame tests

C2T2 - Barium meals and flame tests

1. Barium sulfate is an example of an insoluble salt.

   • Exam question : Describe how you would make a pure dry sample of barium sulphate (BaSO4), an insoluble salt. You can use any of the following : Barium iodide, barium nitrate , potassium chloride, potassium sulfate.
     • Answer : 1)Mix solutions of barium nitrate and potassium sulfate 2) Filter out the precipitate of barium sulphate 3) Wash it with distilled water 4) Dry it on filter paper
     • Check : So you want a soluble salt of barium 'something' and a soluble salt of 'something' sulfate. Barium nitrate is soluble and potassium sulphate is soluble. OK so far.
       • The question asks you for a pure dry sample, so you need to wash impurities off the precipitate and then dry it.

2. Barium sulphate can be used for X rays .

   • Normally only bones show up when you have a x ray.
     • However barium sulphate is opaque to x rays. When drunk it shows up the gut so that any problems (e.g. blockages) can be seen.
       • Barium salts are toxic, but barium sulfate can be safely drunk because its insoluble. This means it isn't absorbed into the bloodstream - it just passes through the body.
         • When a patient drinks barium sulphate before an x-ray, this is known as a barium meal.

3. Flame tests.

   • Metals give a flame with a characteristic colour , as you see in fireworks.
     • Sodium ions (Na+) give a yellow/orange flame.
       • Potassium ions (K+) give a lilac flame
         • Calcium ions (Ca2+) give a brick red flame.
           • Copper ions (Cu2+) give a blue-green flame.
     • To flame test a compound in the lab, first make sure the wire loop is really clean by dipping it into hydrochloric acid, and rinsing it with distilled water, so there are no access ions left on it.
       • Then dip the clean wire loop into the sample of compound and put the wire loop in the clear blue part of the Bunsen Flame (the hottest bit.
         • You can use this method to test for sodium, potassium , calcium or copper ions in a solid or a solution.If you're using a powdered solid, you can dip the wire in the hydrochloric acid again to moisten it before dipping it in the solid , so that some of the solid sticks to the wire.
   • Flame tests don't just work when you've got a sample of pure element - they also work with a compound that contains that element. So if you stick a sample of copper sulphate in a bunsen flame, you'll also see and blue-green flame because of the (Cu2+) ions present.