# Tag Info

6

You need to be aware of the dilution formula in order to plot concentration on the x-axis and absorbance on the y-axis: $C_iV_i = C_fV_f$ So your initial concentration is your stock concentration and your initial volume is listed in the table. Your final volume is $\pu{100 mL}$. Can you determine $C_f$? With that you would be able to calculate all 5 ...

5

The density of a substance depends on its molecular density and packing fraction (where you need to be consistent in definiting the molar volume in calculating both attributes). However you are looking for a simpler explanation that gets the general trends right. Just looking at molecular mass is too simple—larger molecules have greater mass, but take up ...

4

Density is a macroscopic measurement so we should look for average properties spread over several molecules. The average density of a liquid is not that much smaller than that of its solid ($\approx 0.9$, there are a v. few exceptions, water/ice, silicon, gallium, germanium, bismuth where it is greater) which means that the distance between molecules is only ...

4

Calcium formate is a white-to-yellow or off-white crystalline powder, has a density of $\pu{2.02 g/ml}$, solubility of $\pu{\sim 17\%}$, decomposes at $\pu{300 ^\circ C}$ . It irritates eyes severely and has a stinging taste, therefore could have an "hard to describe odor" or effect on the nose. One mental conflict I have is that I would expect ...

3

There are ways to quite reliably determine what this solid is. As mentioned above, the counter ion most probably should be $\ce{Ca^2+}$, however there are many organic or inorganic anions that still fit the criteria. The $\ce{AgNO3}$ tests provide insight that its a non-coordinating counter ion. Ways to determine the anion - however this all takes ...

3

Acid (Brønsted–Lowry Acid) is a substance that gives away its $\ce{H+}$, but the environment should be able to accept that $\ce{H+}$. After it accepted it - the acid (which is now its conjugate base) can accept it back. There are 2 extremes: The environment already has plenty of $\ce{H+}$ already. So even if acid gives its $\ce{H+}$ to the environment, it ...

2

I can add some points for the OP which are too long to serve as comments. I have talked to a couple of leading persons who work with a lot a of LODs. The first lesson, which is important, that there is no "the limit of a detection" of an analytical procedure. Second, some analytical chemists also state that it should be abolished because of the ...

1

For a weak acid $\ce{HA}$ with acid constant $K_\mathrm{a}$: $$\ce{HA + H2O <=> H3O+ + A-} \tag1$$ $$K_\mathrm{a} = \frac{[\ce{H3O+}][\ce{A-}]}{[\ce{HA}]} \ \Rightarrow \ [\ce{H3O+}] = K_\mathrm{a} \cdot \frac{[\ce{HA}]}{[\ce{A-}]} \tag2$$ Taking $-\log$ of both side of equation $(2)$: -\log [\ce{H3O+}] = -\log K_\mathrm{a} -\log \frac{[\ce{HA}]}{[\...

1

One idea is to retry the brown ring test with the proper procedure, as the question admits that this had not previously been used (acidified ferrous sulfate was added wrongly). The other evidence is consistent with calcium nitrate, so we need to get that test right. Calcium nitrate also decomposes at 500°C and above, releasing nitrogen dioxide leaving the ...

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