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3 years ago

What’s molar mass? For chemistry

1 answer:

3 0

In chemistry, the molar mass of a chemical compound is defined as the mass of a sample of that compound divided by the amount of substance in that sample, measured in moles.

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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

If the crucible is contaminated with the volatile impurities. While heating, the impurity is then burned off and removed. Descri

Art [367]

Answer:

The presence of the contaminant increases the total mass.

And on continuous heating to remove the volatile impurities, the hydrated salt gets overheated and the anhydrous salt gets thermally decomposed thereby producing a gas.

The heating leads to the formation or release of a gas which leads to loss of a higher percentage of mass from the compound making the mass percent of water in the hydrated salt too high and the mass of the anhydrous salt remaining in the crucible too low.

Hydrated Salt ⇒ Anhydrous salt + Water hydration

$(C_{u}SO_{4} . 5H_{2}O)_{(s)}$ $(C_{u}SO_{4})_{(s)}$ $(5H_{2}O)_{(g)}$

6 0

3 years ago

Electrcity cannot pass through a/an

evablogger [386]

Electricity can't pass through an insulator.

Hope this helps!

4 0

3 years ago

What is the net ionic equation for this reaction?

Elenna [48]

The ionic equation represents the element in cation and anionic form. The equation is given as OH⁻ + 2H⁺ → 2H₂O. Thus, option A is correct.

<h3>What is the ionic equation?</h3>

The ionic reaction equation is the representation of the chemicals dissociated as the ions in an aqueous solution. The ionic reaction is given as the cations and anions dissociated from the respective molecule or compound.

The ionic equation between potassium hydroxide and sulfuric acid is shown as,

2K⁺ + OH⁻ + 2H⁺ + SO₄²⁻ → 2H₂O + 2K⁺ + SO₄²⁻

It can also be written as,

Net ionic equation: OH⁻ + 2H⁺ → 2H₂O

Here, others are eliminated as they are spectator ions.

Therefore, option A. OH⁻ + 2H⁺ → 2H₂O is the net ionic equation.

Learn more about ionic equation here:

brainly.com/question/27980783

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8 0

1 year ago

Potassium forms ions with a charge of +1 (K+). Iodine forms ions with a charge of -1. Selenium forms ions with a charge of -2 (S

Taya2010 [7]

It is given that the charge on potassium is +1 i.e. Potassium is a cation, K⁺

The charge on selenium is given as -2, i.e. selenium is an anion, Se²⁻

The two ions are shown to combine to form a molecule: KXSeY where X and Y correspond to the proportions in which the two atoms combine.

Since the molecule is neutral, the positive and negative charges need to be balanced. This is possible only if 2 units of K⁺ combines with 1 unit of Se²⁻.

Therefore, the formula would be K₂Se

X = 2 and Y = 1

3 0

3 years ago