Question

Observing chemical reactions. Bolded reactions indicate the solution made in previous step

For the reactions listed below, provide the following:

-product formed from the reaction

-evidence that a chemical change occurred

-eg. Color change, temperature increase or decrease, evolution of gas, sight of a precipitate, or appearance of odor.

CoCl2 + 95% ethyl alcohol

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H2O + [CoCl2(6H2O)+95%ethyl alcohol]

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0.5M NaHCO3 + [H2O + CoCl2(6H2O)+95%ethyl alcohol]

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Mg + 1M HCl

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Steel Wool + CaSO4

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0.5M NaHCO + 0.1M CuSO4

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1M NH3 + [0.5M NaHCO + 0.1M CuSO4]

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NaHCO3 + 1M HCl

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NH4SCN + BaOH2(8 H2O)

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Answer 1

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CoCl₂ + 95% ethyl alcohol

In CoCl₂ cobalt is in oxidation state +2. Aqueous solutions of ion Co²⁺ [Co²⁺(aq)] are pink. Other compounds of cobalt(II), that are anhydrous or in anhydrous solutions are commonly blue. In this case the solutions is almost anhydrous because is 95% ethyl alcohol. Nevertheless there is still 5% of water so the solution could take a purple color.

H₂O + [CoCl₂(6H₂O)+95%ethyl alcohol]

When you add water to the previous solution cobalt(II) immediately gets hydrated so it turns pink:

0.5M NaHCO₃ + [H₂O + CoCl₂(6H₂O)+95%ethyl alcohol]

In this reaction we are adding a basic solution, high concentration of ion OH^-. Cobalt hydroxide [Co(OH)₂] is formed. It is also insoluble in water so a precipitate should be formed here, which is evidence of the reaction.

Mg + 1M HCl

Magnesium dissolves in HCl forming magnesium chloride:

The evidence of this reaction happening is a bubbling from the solution because there is evolution of a gas (hydrogen) and also the disappearance of solid magnesium, which dissolves in the acid.

Steel Wool + CaSO₄

Steel wool is a bundle of very fine and flexible sharp-edged steel filaments. It is made from low-carbon steel, which is iron and carbon. The addition of carbon to steel retards the oxidation of iron making the metallic surface more resistant to corrosion. But if there is some corrosion on the steel wool the reaction between calcium sulfate particles and metal substrates produces iron sulfide, which is black. So an evidence of the reaction would be the blackening of the wool.

0.5M NaHCO + 0.1M CuSO₄

Is there something missing in this reaction? The first solution seems to be a solution of sodium bicarbonate and the formula should be NaHCO₃. If this is the case, as in an earlier reaction we are adding an alkaline solution to the aqueous copper sulfate. The reaction produces Cu(OH)₂

The evidence of this reaction occurring is the formation of a precipitate

1M NH₃ + [0.5M NaHCO + 0.1M CuSO₄]

Ammonia forms complex compounds with copper. If you add ammonia solution to an already precipitated [Cu(OH)₂], it will probably dissolve back again into solution

Complex is deep blue in color so the evidence of the reaction is the dissolving of the precipitate and the deep blue color.

NaHCO₃ + 1M HCl

Hydrochloric acid is an acid and sodium bicarbonate is a base. The reaction is:

Carbonic acid, which is formed as hydrochloric acid neutralizes sodium bicarbonate is an unstable substance that rapidly decomposes in the aqueous media to produce CO₂ and water. Since carbon dioxide is a gas, the evidence that the reaction is occurring is the evolution of a gas, in this case carbon dioxide.

NH₄SCN + Ba(OH)₂(8H2O)

Again in this reaction seems to be something missing. If the reaction occurs with barium hydroxide like it seems to be, this is a typical example of an endothermic reaction. The evidence to see that the reaction happens is a cooling of the solution that in general is very intense. Reaction:

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