22 votes
Accepted

Why is it that every snowflake is unique?

It turns out that 2 identical snowflakes have been observed, but... Two Identical Snowflakes Although when we think "snowflake" we usually picture an object with 6-fold radial symmetry, snowflakes ...
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14 votes
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Reaction of silver nitrate and hydrochloric acid

One of the most difficult parts of chemistry is learning to recognize a type of reaction based solely on its reactants. This has to be done before you can apply a reaction pattern to the problem, and ...
  • 10.1k
14 votes
Accepted

Why exactly does precipitation occur?

Short story Maybe it will help to think first about a ridiculous case. Say you have a large hydrophilic solid, and a small drop of water is added on top. We would not expect the entire solid to ...
14 votes
Accepted

Are precipitations exothermic and/or endothermic?

No, absolutely not. Precipitation reactions can be either endothermic and exothermic. Table 1. Thermodynamic data of precipitation for some salts \begin{array}{cccccc} \hline \text{Salt} & \Delta ...
13 votes
Accepted

In the wet medium of an ocean, how does a hard shell form?

Carbon dioxide from the atmosphere (or from decaying matter in the ocean) reacts with water to form carbonic acid: $$ \ce{ CO2 + H2O -> H_2CO_3 }$$ and this reacts with calcium ions to form ...
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11 votes

What is the simplest way to create a precipitation reaction at home?

Here's one easy way : Make a solution of salt ($\ce{NaCl}$) in water, and another solution of Silver Nitrate ($\ce{AgNO_3}$), which you can buy easily) in water. Upon mixing the two, $\ce{AgCl}$ (...
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10 votes
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How do Precipitation Reactions behave in the Absence of Gravity?

In gravityless environment, all directions are equivalent save the very vicinity of the surface(*), where just few water molecules are toward the surface. Therefore, in the bulk volume, the ...
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9 votes
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Difference between precipitation and crystallisation

The two words are often used interchangeably (perhaps incorrectly), though there is a slight nuance. IUPAC defines the following: Crystallisation: The formation of a crystalline solid from a solution,...
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8 votes

Why exactly does precipitation occur?

Although you ask specifically about forming precipitates your question is also about the solubility of one substance in another. The simplest answer as to why precipitates form is because the free ...
  • 27.6k
7 votes

Mathematical explanation of blank titration in Mohr method for argentometry

$\ce{AgCl}$ ppts before $\ce{Ag2CrO4}$. But in order to visually detect the $\ce{Ag2CrO4}$ you must add a slight excess of $\ce{Ag^+}$. Hence you use a "blank" with no $\ce{Cl^-}$ to account for the ...
  • 21.6k
7 votes
Accepted

Why is only the carbonate anion used to precipitate Barium?

Actually, the textbook should remove this question. You should discuss this with your teacher. It will be a service to future students. The heavier elements of group II elements form insoluble ...
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6 votes
Accepted

Do all double displacement reactions lead to precipitates?

No, recall the definition of a precipitate "insoluble ionic compound". Take this reaction into consideration $$\ce{ NaOH~(s) + HCl~(l) <=> H2O~(l) + NaCl~(aq)}$$ none of the products are ...
6 votes

Obtain precipitated iron?

Is it possible to obtain pure, precipitated iron with no oxidation by some chemical process? Very pure iron can be obtained by pyrolysis of iron pentacarbonyl. Iron metal obtained in this manner is ...
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6 votes

Why are transition metal hydroxides insoluble?

The rule of thumb for hydroxide salts is actually that all hydroxides are insoluble save those of the alkali metals and the heavier alkaline earth metals (namely $\ce{Ca^{2+}}$, $\ce{Sr}^{2+}$, and $\...
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6 votes
Accepted

What reactions occur when mixing copper sulfate and sodium hydroxide?

As noted in your question and in one of the comments, copper forms many different complexes having a variety of colors from red to green to blue to black and probably more. Of course the situation ...
  • 16.9k
6 votes

Finding sulfate contamination in crystallized silver nitrate

Barium nitrate has a water solubility of $\pu{10.5g/100mL}$ at $\pu{25^oC}$. It isn't specified in the question what concentration of sulfate you suspect might be present, but given that you are ...
  • 16.9k
6 votes
Accepted

Finding sulfate contamination in crystallized silver nitrate

Your choices are restrained as the precipitation of $\ce{SO4^{2-}}$ in $\ce{BaSO4}$ is the classical way to quantify the former and an electrochemical determination (in aqueous solution) is not ...
  • 23.8k
6 votes
Accepted

Precipitation of CaCl2 and FeCl3 in Na2CO3

This must have been a very good question for a geochemist. They'd give you a complete answer with details of why $\ce{Fe2(CO3)3}$ does not but $\ce{Fe2O3}$ exist in our surrounding. Yet, I would like ...
6 votes

Can precipitation occur in states of matter other than liquids?

As stated in my previous answer on precipitation, formation of precipitates in supercritical is a common issue. Ask those who do sub/supercritical fluid chromatography. Sometimes you inject a methanol ...
  • 33.6k
6 votes
Accepted

How do I separate an Indium-Gallium alloy into Indium and Gallium?

The Gallium-Indium binary system is assessed by Bridget C. Rugg and Tim G. Chart in Calphad 14(2) 115-123 (1990). It is a very simple system, exhibiting essentially no solubility of In in Ga, and ...
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6 votes
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Magnesium vs calcium vs barium ions from these 3 tests

The unfortunate thing is that salts of these ions are white and can't be differentiated by just looking. But you can take solubility to your advantage. The solubility of the sulfates of alkaline earth ...
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5 votes

Reaction of citric acid and calcium chloride

This procedure is done in our laboratory class, but first you have to add sodium hydroxide until the lemon juice is somewhat alkaline. Then add the calcium chloride (use $1~\mathrm{ml}$ for every $2~\...
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5 votes

Constructing an equation for the precipitation of a salt

Precipitation is usually a single or double displacement reaction, and refers to the formation of an insoluble, solid salt from soluble ions. For instance, silver bromide, $\ce{AgBr}$, is insoluble in ...
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5 votes
Accepted

Why does precipitate always form so naturally?

The ions combine while in solution, and since the resulting compound is not soluble, it precipitates. This happens so quickly because as the precipitate forms, it takes those individual ions out of ...
  • 3,818
5 votes

Difference between precipitation and crystallisation

Both are physical changes. In neither does the substance crystallising/precipitating truely change, in both it is more or less the same after as before. (Technically, ions in solution are something ...
  • 64.8k
5 votes

What is the chemical composition of Turnbull's blue?

Though your textbook is right, Wikipedia isn't completely wrong as in aqueous solution, $\left(\ce{Fe3[Fe(CN)6]2} \right)$ gets converted and is in equilibrium with $\left(\ce{Fe4[Fe(CN)6]3} \right)$ (...
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5 votes

How to remove sulfuric acid from sample

Sulfuric acid is an excellent dessicant and is also very non-volatile itself (it boils at 337 °C). In other words it would likely still have been there in yet another month. Your instructor ...
  • 16.9k
5 votes
Accepted

Aluminium sulphate solubility as function of the pH

The lack of continuity for the curve indicates that the concentration of $\ce{Al2(SO4)3}$ was below the detection limit of the analytical technique being used to measure the concentration of $\ce{Al2(...
  • 21.6k
5 votes
Accepted

Are precipitation and crystallization both analogous between Chemistry and Meteorology?

In chemistry, on Earth in gravity, if a material from solution conformally, over all surfaces vertical and horizontal (e.g. the sides as well as the bottom of a container) is that still sometimes ...
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