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3 years ago

I really need help, I don’t know what to do on this

Chemistry

1 answer:

Shtirlitz [24]3 years ago

7 0

Answer:

A: dependent variable

B: experimental group

C: independent variable

D: control variables

E: control group

Explanation:

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Antimony has two naturally occuring isotopes, 121 Sb and 123 Sb . 121 Sb has an atomic mass of 120.9038 u , and 123 Sb has an at

valina [46]

Answer:

Percentage abundance of 121 Sb is = 57.2 %

Percentage abundance of 123 Sb is = 42.8 %

Explanation:

The formula for the calculation of the average atomic mass is:

$Average\ atomic\ mass=(\frac {\%\ of\ the\ first\ isotope}{100}\times {Mass\ of\ the\ first\ isotope})+(\frac {\%\ of\ the\ second\ isotope}{100}\times {Mass\ of\ the\ second\ isotope})$

Given that:

Since the element has only 2 isotopes, so the let the percentage of first be x and the second is 100 -x.

For first isotope, 121 Sb :

% = x %

Mass = 120.9038 u

For second isotope, 123 Sb:

% = 100 - x

Mass = 122.9042 u

Given, Average Mass = 121.7601 u

Thus,

$121.7601=\frac{x}{100}\times 120.9038+\frac{100-x}{100}\times 122.9042$

$120.9038x+122.9042\left(100-x\right)=12176.01$

Solving for x, we get that:

x = 57.2 %

<u>Thus, percentage abundance of 121 Sb is = 57.2 % </u>

<u>percentage abundance of 123 Sb is = 100 - 57.2 % = 42.8 %</u>

6 0

3 years ago

How many moles are in 7.00E24 atoms of Ca?

iris [78.8K]

Explanation:

In chemistry, a mole is the base unit of the amount of substance in a system containing elementary entities (atoms, molecules, ions, electrons), and one mole of substance corresponds to the Avogadro's constant or $6.023 \ \times \ 10^{23}$ entities. The stoichiometry equation that relates the amount of substance into the measurement in moles is

$n \ = \ \displaystyle\frac{\alpha}{N_{A}}$ ,

where $n$ is the number of moles, $\alpha$ is the amount of substance and $N_{A}$ is the Avogadro's constant.

Therefore,

$n \ = \ \displaystyle\frac{7.00 \ \times \ 10^{24} \ \text{atoms}}{6.023 \ \times \ 10^{23} \ \text{atoms mol}^{-1}} \\ \\ n \ = \ 11.624 \ \text{mol}$ .

3 0

2 years ago

Experiments show that each of the following redox reactions is second-order overall: (1) NO2(g) + CO(g) → NO(g) + CO2(g) (2) NO(

MatroZZZ [7]

Answer:

a) rate law1 = k[NO2]²

b) rate law2 = k[NO][O3]

Explanation:

NO2(g) + CO(g) → NO(g) + CO2(g)

NO(g) + O3(g) → NO2(g) + O2(g)

When [NO2] in reaction 1 is doubled, the reaction quadruples

Rxn is second order.

rate law1= [NO2]^a [CO]^b

rate law1= [NO2]² [CO]^0

rate law1 = k[NO2]²

When [NO] in reaction 2 is doubled, the rate doubles.

Rxn is first order

The ratio is 1:1

this makes the rate law2 = k[NO][O3]

6 0

3 years ago

What’s the correct answer

butalik [34]

He ^ 2+

Helium has two electrons the 2+ means that it has lost its two electrons leaving it with none.

3 0

3 years ago

Use the amount (mol) of solute and amount (mol) of solvent to calculate the mole fraction. An aqueous solution of ethanol, CH3CH

Blizzard [7]

Answer:

%m/m = 0.9975%

Xₐ = 0.0039

Explanation:

In order to do this, we need various data. First to all, we need tje molecular mass of the ethanol. this can be obtained in handbooks, or simply taking the atomic weights of carbon (12 g/mol), Hydrogen (1 g/mol) and oxygen (16 g/mol) and summing those values:

MM C₂H₆O = (2*12) + (6*1) + (16*1) = 46 g/mol

Now, there is an expression that is commonly used to determine the molarity of a solution given the mass percent and density, and assuming of course, 1 liter of solution:

M = d * %m/m * 1000 / MM * 100 (1)

From here, we can solve for %m/m:

%m/m = M * MM * 100 / d * 1000

As the problem is not saying the volume of solution, we can easily assume we have 1 liter of solution. Therefore, the %m/m replacing the given data is:

%m/m = 0.216 *46 * 100 / 0.996 * 1000

To get the mole fraction, we first need to get the volume of solvent. From the density, we can get the mass of solution:

m = V * d

m = 1000 * 0.996 = 996 g of solution.

The mass of solute is:

m = 0.216 mol/L * 46 g/mol

m = 9.936 g/L, or simply we have 9.936 g of ethanol in 1 L of solution.

The mass of solvent:

solvent = 996 - 9.936 = 986.064 g

The molecular mass of water, so we can get the moles is 18 g/mol so:

moles water = 986.064 / 18 = 54.78

Finally the mole fraction:

Xₐ = 0.216 / (0.216 + 54.78)

Hope this helps

4 0

2 years ago