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3 years ago

Pure substance definition in chemistry?

1 answer:

3 0

A pure substance is a sample of matter with both definite and constant composition with distinct chemical properties. To avoid confusion, in chemistry a pure substance is often referred to as a "chemical substance".

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A solution was prepared by dissolving 195.0 g of KCl in 215 g of water. Calculate the mole fraction of KCl. (The formula weight

defon

Answer:

Approximately $0.180$ .

Explanation:

The mole fraction of a compound in a solution is:

$\displaystyle \frac{\text{Number of moles of compound in question}}{\text{Number of moles of all particles in the solution}}$ .

In this question, the mole fraction of $\rm KCl$ in this solution would be:

$\displaystyle X_\mathrm{KCl} = \frac{n(\mathrm{KCl})}{n(\text{All particles in this soluton})}$ .

This solution consist of only $\rm KCl$ and water (i.e., $\rm H_2O$ .) Hence:

$\begin{aligned} X_\mathrm{KCl} &= \frac{n(\mathrm{KCl})}{n(\text{All particles in this soluton})}\\ &= \frac{n(\mathrm{KCl})}{n(\mathrm{KCl}) + n(\mathrm{H_2O})}\end{aligned}$ .

From the question:

Mass of $\rm KCl$ : $m(\mathrm{KCl}) = 195.0\; \rm g$ .
Molar mass of $\rm KCl$ : $M(\mathrm{KCl}) = 74.6\; \rm g \cdot mol^{-1}$ .

Mass of $\rm H_2O$ : $m(\mathrm{H_2O}) = 215\; \rm g$ .
Molar mass of $\rm H_2O$ : $M(\mathrm{H_2O}) = 18.0\; \rm g\cdot mol^{-1}$ .

Apply the formula $\displaystyle n = \frac{m}{M}$ to find the number of moles of $\rm KCl$ and $\rm H_2O$ in this solution.

$\begin{aligned}n(\mathrm{KCl}) &= \frac{m(\mathrm{KCl})}{M(\mathrm{KCl})} \\ &= \frac{195.0\; \rm g}{74.6\; \rm g \cdot mol^{-1}} \approx 2.61\; \em \rm mol\end{aligned}$ .

$\begin{aligned}n(\mathrm{H_2O}) &= \frac{m(\mathrm{H_2O})}{M(\mathrm{H_2O})} \\ &= \frac{215\; \rm g}{18.0\; \rm g \cdot mol^{-1}} \approx 11.9\; \em \rm mol\end{aligned}$ .

The molar fraction of $\rm KCl$ in this solution would be:

$\begin{aligned} X_\mathrm{KCl} &= \frac{n(\mathrm{KCl})}{n(\text{All particles in this soluton})}\\ &= \frac{n(\mathrm{KCl})}{n(\mathrm{KCl}) + n(\mathrm{H_2O})} \\ &\approx \frac{2.61 \; \rm mol}{2.61\; \rm mol + 11.9\; \rm mol} \approx 0.180\end{aligned}$ .

(Rounded to three significant figures.)

8 0

3 years ago

Draw a Lewis structure for SF4 that has minimized formal charges. Include all nonbonding electrons and any nonzero formal charge

gayaneshka [121]

Answer:

See explanation and image attached

Explanation:

The compound SF4 is sulphur tetraflouride. It has a zero formal charge and has a total of 34 valence electrons.

The central atom in the molecule is sulphur in an sp3d hybridization state hence the molecule has a trigonal bipyramidal electron geometry. Since it is a molecule of the sort AX4E; it gives a see-saw molecular shape.

The structure of the molecule is shown in the image attached to this answer.

8 0

3 years ago

Please help me i will give brain list

Strike441 [17]

Answer:

Give me plz plz plz plz plz plz plz plz plz

3 0

3 years ago

Read 2 more answers

True or False: Tsunamis always look like a towering wall of water approaching the beach.

katrin2010 [14]

Answer:

false

Explanation:

6 0

3 years ago

Read 2 more answers

The electronegativity is 2.1 for h and 1.9 for pb. based on these electronegativities pbh4 would be expected to

Sedbober [7]

PbH4 will be formed as a result of a polar covalent bond between the H and the Pb.

Since H is more electronegative than the Pb, it is, thus, expected that the H would be able to pull the electron charge towards itself. This will result in the H being negative.

Based on this:
PbH4 would be expected to have polar covalent bonds with a partial negative charges on the H atoms.

8 0

3 years ago