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Dafna11 [192]
3 years ago
13

How many molecules of Ca are found in a sample with 0.2 mols?

Chemistry
1 answer:
DochEvi [55]3 years ago
6 0

Answer:

\boxed{1.2 \times 10^{23}\text{ atoms}}

Explanation:

6.023 × 10²³ atoms of Ca are in 1 mol of Ca

\text{No. of atoms} = \text{0.2 mol} \times \dfrac{6.023 \times 10^{23}\text{atoms }}{\text{1 mol }} = \mathbf{1.2 \times 10^{23}} \textbf{ atoms}}\\\\\text{There are }\boxed{\mathbf{1.2 \times 10^{23}} \textbf{ atoms}} \text{ atoms in 0.20 mol of Ca}

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How many 20 mL extractions of organic solvent are needed to extract at least 99.5% of 50.0 g Compound A from 100 mL of water if
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Answer:

5 extractions to extract at least 99.5% of 50.0 g Compound A from 100 mL of water

Explanation:

<em>If K=10...</em>

<em />

Partition coefficient is defined as the ratio of concentrations of a compound A in two inmiscibles solvents:

K = 10 = Conc. Organic solvent / Conc. Water

<em>Usually organic phase over aqueous phase.</em>

<em />

In the first 20mL extraction, the organic solvent will extract:

10 = X / 20mL / (50.0g - X) / 100mL

10 = 100X / (1000-20X)

10000 - 200X = 100X

10000 = 300X

X = 33.3g of compound A are extracted in the first extraction

<em>Remember you want to extract 99.5%, that is 50.0g*99.5% = 49.75g</em>

<em />

In the aqueous phase remain: 50-33.3g = 16.7g:

<em>Second extraction:</em>

10 = X / 20mL / (16.7g - X) / 100mL

10 = 100X / (334-20X)

3340 - 200X = 100X

3340 = 300X

11.1g are extracted and will remain: 16.7g - 11.1g = 5.6g

<em>Third extraction:</em>

10 = X / 20mL / (5.6g - X) / 100mL

10 = 100X / (112-20X)

1120 - 200X = 100X

1120 = 300X

3.8g are extracted and will remain: 5.6g - 3.8g = 1.8g

<em>Fourth extraction:</em>

10 = X / 20mL / (1.8g - X) / 100mL

10 = 100X / (36-20X)

360 - 200X = 100X

360 = 300X

1.2g are extracted and will remain: 1.8g -1.2g =  0.6g

<em>Fifth extraction:</em>

10 = X / 20mL / (0.6g - X) / 100mL

10 = 100X / (12-20X)

120 - 200X = 100X

120 = 300X

0.4g are extracted. The total extractions gives:

33.3g + 11.1g + 3.8g + 1.2g + 0.4g = 49.8g

That means, you need to do:

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