Blood samples for research or medical tests sometimes have heparin added. Why is this done?

It is essential for accurate results that the correct volume of blood is sampled to achieve a correct concentration (and dilution, if liquid heparin is used), and that blood and anticoagulant are well mixed immediately after sampling.

About 186 g of  NH₄Cl

Explanation:

The translation of the question is:

Specify how many grams of NH₄Cl, ammonium chloride, should be dissolved in 300g of water at 70ºC to obtain a saturated solution.

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Solution

The file attached shows the graph with the solubility curves for a number of solutes in water.

There, I show you the solubility of a solution of NH₄Cl at 70ºC: it is about 62g of NH₄Cl per 100 grams of water.

Then, the amount of  NH₄Cl in 300g of water at that temperature is calculated using proportions:

300 g of water × 62 g of  NH₄Cl / 100 g  of water = 186 g of  NH₄Cl