How to test for the presence of calcium and magnesium ions in an unknown solution??? 20

Of course, it's replaced with something more lively than these two things.。。 For example, what kind of sodium? As soon as those lively metals are put on and replaced, it means that there is.

If not, it means that there is ... There seems to be a song recipe that talks about the top metal.

At the same time, the one downstairs, do you read the question? How to test for the presence of calcium and magnesium ions in an unknown solution??? If there are these two ions, then replace them with a metal that is more reactive than him, and if there are none, they cannot be replaced.

Of course na doesn't work... He's too lively. Hehe, I mean to ask this friend who asked the question to read the next book.

I haven't seen that in more than a decade, and I gave it back to the teacher. And what is it talking about downstairs? How do you tell the difference between two solutions?

Then I ask you, what if it is magnesium sulfate and calcium sulfate? Can it be useful for you to use sodium hydroxide? If it's an exam and you only get 0 points, hehe, although you are very smart, maybe you know a lot.

But see what the question is. You know?

Upstairs misunderstood. CaCo3 and MgCo3 are white precipitates that cannot be distinguished.

Therefore, a sufficient amount of NaOH dilute solution should be added, note that it is diluted, and avoid Ca(OH)2 suspension.

White precipitate Mg(OH)2 can be obtained

In the introduction of CO2 turbidity, CaCO3 is obtained

How to detect if it contains calcium and magnesium ions?

There are several ways to determine the presence of calcium ions in acidic solutions:

1.Use of calcium and copper reagent: A small amount of calcium and copper reagent is added to the acidic solution to be tested, if a white or blue precipitate is produced, it means that the solution contains calcium ions. Because calcium ions are able to react with copper ions in the calcium and copper reagent to form insoluble white or blue precipitates.

2.Use barium sulfurium sulfate reagent: add a small amount of barium sulfate reagent to the acidic solution to be tested, if there is a white precipitate, it means that the solution contains calcium ions.

Because the calcium ions are able to react with the sulfate ions (SO42-) in the barium sulfate reagent to form an insoluble white precipitate.

3.EDTA titration: the EDTA solution is added to the acidic solution to be tested, the titration process of EDTA and calcium ions is monitored by using an indicator, and the titration is stopped when the color of the indicator changes, and the content of calcium ions is calculated according to the volume of EDTA added.

It should be noted that the above methods need to understand the properties of the samples and the required operation steps before the experiment to ensure the reliability of the experimental results.

Example 1: To check whether a cup of unknown solution contains sulfate ions, you can add a barium chloride solution to the solution, if so, barium sulfate will be generated, and the phenomenon is that there is a white precipitate.

Supplement: The exchange of ions can only occur in the solution, barium chloride is soluble in water [containing chloride ions, such as sodium chloride, calcium chloride, etc., most of them are soluble in water], and barium sulfate is a white precipitate.

Example 2: To check whether a cup of unknown solution contains chloride ions, you can add a silver nitrate solution to the solution, which will form silver chloride, which is a white precipitate.

Supplement: Silver nitrate is soluble in water, with the exception of silver chloride, which is a rare compound with chloride ions but insoluble in water, and is a white precipitate generated.

Generally, it is identified by precipitation method. What are your calcium ions associated with? The following methods are for different compounds:

1。Add H2SO4 to the solution, there is precipitation indicating that there is Ca+ (the introduction of CO2 can also identify calcium ions, but the solution has Cl-, and there is no reaction when introducing CO2, so it is not feasible to introduce CO2, first add NaOH Mg ions with precipitation, then add sulfuric acid with precipitation BA ions, and calcium sulfate is slightly soluble so it does not react, and finally it is CA).

2。Plus naohBA(NO3)2 can be identified, and the addition of sulfuric acid can distinguish conjectures 1 and 2. Calcium sulfate is a precipitate, magnesium sulfate is not.

3。Magnesium ions will be precipitated by ammonia detection, calcium sulfate is soluble in acid, and barium sulfate is insoluble. Therefore, use this principle to distinguish calcium ions and barium ions, add excess sulfuric acid to see which one disappears.

Uses: It is yellow in acidic solution, red or purple in alkaline solution, it reacts with magnesium ions to form sky blue precipitate, which can detect the presence of magnesium ions.

Chemical description: Reddish-brown powder. The melting point is about 200. soluble in dilute alkali, reddish-purple, slightly soluble in boiling alcohol; Acetone; Acetic acid and toluene are yellow and insoluble in water.

Magnesium Reagent II Molecular Formula: C16H11N3O3

Relative molecular weight:

Melting Point: 270

Chinese name: magnesium reagent ii; 4-[(4-nitrophenyl)azo]-1-naphthol; p-nitrobenzoazo-1-naphthol; Try Magalin II

Magnesium reagent is an organic dye that is yellow in acidic solutions and red or purple in alkaline solutions, but is azure blue after being adsorbed by Mg(OH)2 precipitation, so it can be used to test the presence of Mg2+. With sodium hydroxide, I think it's not appropriate, and hydroxide will form a precipitate is not only magnesium ions, how to conclude that it is, it's hard to say, but some interfering ions can be eliminated by other reagents and then tested with hydroxide, because there are not many common substances that can precipitate with sodium hydroxide, but it depends on what specific interfering ions are in the solution to decide how to identify.

Magnesium reagent is an organic dye, it is yellow in acidic solution, red or purple in alkaline solution, but after adsorption by magnesium hydroxide precipitation, it is sky blue, so it can be used to test the presence of magnesium ions. The detection of magnesium ions with magnesium reagents is a general method for qualitative analysis of magnesium ions in laboratories.

The method of identifying magnesium liter vertical ions is also the sodium hydroxide method, but the method of identifying magnesium ions with sodium hydroxide is more cumbersome. Because it is not only magnesium ions that form precipitation with hydroxide, it is necessary to eliminate the interfering ions by other reagents before hydroxide can be tested.

The presence of calcium ions and magnesium ions in the water means that it is hard water, which can be detected with soapy water.

Method: Put a part of the water in the container, put a little soapy water and stir, after a period of time, if there is a white flocculent object, it means that it is hard water, that is, it contains calcium ions and magnesium ions.

If not, it means soft water, that is, it does not contain calcium ions and magnesium ions.

The first grasp base first removes magnesium ions with hydroxide white precipitate, removes iron ions with potassium hydroxide to turn red, removes calcium ions with potassium carbonate to produce white precipitate, and sulfate uses barium ions to precipitate white.

Try not to introduce new impurities when removing impurities.

The addition of reagent should be slightly excessive to ensure that the impurities are completely removed.

So excess barium ions can be removed with carbonic acid**, and potassium hydroxide and barium nitrate can be interchanged.