| Table of contents |
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2 Concentrations 3 Help! It won't dissolve 4 Reagents used for testing foodstuffs 5 Iodine Solution 6 Buffer Solutions |
Dilution of concentrated acid should always be done in a fume cupboard.
It is important only to pour acid into water, not the other way around, especially with concentrated acids. Acids may quickly absorb water, creating a lot of heat in the process. When acid is poured into water, the heat can quickly become evenly distributed in the water. If water is poured into acid, the water may quickly boil, spraying acid everywhere.
Hydrochloric acid can be purchased as either 36% or 32% solution so carefully check the bottle first.
To make a 1 molar solution (1M):
Add 84mL of 36% hydrochloric acid to about 600mL of distilled water in a 1 litre measuring cylinder in a fume cupboard. Make up to 1L, mix well and pour into a labelled bottle.
As above, except use 97mL of hydrochloric acid.
Concentrated hydrochloric acid is highly corrosive and very irritating to the lungs, wear a face shield and use a fume cupboard.
Assuming the concentrated nitric acid is 70%w/v, then to make a 1M solution:
Add 62mL of concentrated nitric acid to about 700mL of water then dilute to 1L.
Concentrated sulphuric acid is highly CORROSIVE and a dehydrating agent. It causes severe burns. It should only be handled under close supervision by an experienced person. Wear gloves and protect the eyes with safety goggles or even better, a face shield.
In a fume cupboard, add 54mL of concentrated sulphuric acid to about 700mL of iced water and dilute to 1 litre. This is a 1M solution.
Known also as acetic acid. The concentrated acid is called Glacial acetic acid as it freezes at 17°C. Glacial acetic acid is CORROSIVE and the vapour is an extreme IRRITANT. Wear gloves and protect the eyes with safety goggles or even better a face shield. Work in a fume cupboard.
To make a 1M (mole/litre) solution, add 29mL of the concentrate to about 600mL of distilled water and dilute to 1 litre.
Biuret reagent
This is used to test for the presence of protein. There are two recipes the first consists of two reagents Biuret A and Biuret B.
Benedict's reagent is used to test for reducing sugars. It has two recipes. Benedict's qualitative and Benedict's quantitative.
The reagent is made up by first dissolving 173g of Sodium citrate and 100g ofanhydrous Sodium Carbonate in about 600ml of distilled water. Then 17.3g copper sulphate5H2O is dissolved in about 100ml of distilled water. The two solutions are then mixed together and when cool are made up to 1L with distilled water.
In about 600ml of hot water dissolve
Diluting Concentrated Acids
Hydrochloric acid
36%
32%
Safety Notes
Nitric Acid
Sulphuric acid
Ethanoic acid
Concentrations
Help! It won't dissolve
Some substances do not dissolve very readily in water and require special methods.
Most iron III salts do not form stable aqueous solutions. In order to get them to dissolve you need to add a small amount of acid. Add hydrochloric acid to the chloride etc...Reagents used for testing foodstuffs
For the second (Quantitative) recipe, in about 600mL of distilled water, dissolve in order 3g of copper sulphate. 5H2O, 5g of potassium iodide, 9g of potassium sodium tartrate.4H2O, and 8g of sodium hydroxide. Make the dissolved solids to 1 litre. Label the solution IRRITANTBenedict's Qualitative Reagent
Benedict's Quantitative Reagent
In about 100ml of water dissolve
When the solutions have cooled mix them together stirring constantly.Add
Iodine Solution
Recipes vary but 1g of iodine plus 1g of potassium iodide in 100mL water is suitable. Dissolve the iodide then the iodine.
| pH | 0.2M Na2HPO4 /ml | 0.1M Citric Acid /ml |
|---|---|---|
| 3.0 | 20.55 | 79.45 |
| 4.0 | 38.55 | 61.45 |
| 5.0 | 51.50 | 48.50 |
| 6.0 | 63.15 | 36.85 |
| 7.0 | 82.35 | 17.65 |
| 8.0 | 97.25 | 2.75 |